A Practical Approach to Cardiac Anesthesia (Practical Approach Series) 5th Ed.

13 Alternative Approaches to Cardiac Surgery with and without Cardiopulmonary Bypass

James Y. Kim, James G. Ramsay, Michael G. Licina, and Anand R. Mehta

KEY POINTS

 1. Off-pump coronary artery bypass grafting (OPCAB) challenges the anesthesiologist and surgeon to maintain hemodynamic stability while delicate coronary arterial anastomoses are performed on a beating heart.

 2. OPCAB has not produced the expected reductions in neurologic and renal complications, although it has consistently reduced perioperative blood loss and transfusion.

 3. Adept positioning of the heart during OPCAB minimizes hemodynamic disturbances from reduced venous return, especially while performing coronary anastomoses within the right coronary and left circumflex arterial distributions. Maintaining adequate intravascular volume is essential.

 4. Adjuncts such as intracoronary shunts, ischemic and/or anesthetic preconditioning, and intra-aortic balloon pumps may help to minimize ischemia during OPCAB. Circulatory support with vasoconstrictors and/or inotropic drugs is often required.

 5. Robotic-assisted minimally invasive techniques can be used for coronary artery bypass grafting (CABG) performed either on- or off-cardiopulmonary bypass (CPB).

 6. Transesophageal echocardiography (TEE) monitoring during OPCAB can promptly identify acute ischemia, although transgastric views are often compromised by the cardiac positioning required for distal coronary anastomoses.

 7. Anesthetic techniques compatible with fast-tracking are most often used for OPCAB, which typically involves a “balanced” technique utilizing a combination of inhalational anesthetic, modest amounts of opioid, and intermediate-duration muscle relaxation. Excessive use of benzodiazepines and long-acting medications is avoided.

 8. Minimally invasive cardiac valve surgery most often requires CPB, but the incisions are smaller and sometimes off the midline, and cannulation for CPB often utilizes port-access technology. Robotic-assisted techniques can be used for minimally invasive mitral valve replacement or repair.

 9. TEE is critical during minimally invasive valve surgery (MIVS) for CPB cannulation and assessment of valve structure and function.

10. Percutaneous approaches to mitral regurgitation (Mitraclip), mitral stenosis (balloon mitral valvuloplasty), and aortic stenosis (transcatheter aortic valve implantation [TAVI]) are rapidly growing in popularity. Each approach presents unique challenges to the anesthesiologist; these procedures can be performed either with sedation or general anesthesia, each with its own benefits and risks.

11. Percutaneous valve procedures often involve transient profound hypotension from obstruction (e.g., balloon mitral valvuloplasty and predilation for TAVI) and either incidental or intentional dysrhythmias (e.g., rapid ventricular pacing for TAVI).

12. Hybrid operating rooms allow for interventional cardiology or radiology procedures to be performed in conjunction with open cardiac surgery including the use of CPB.

13. Transmyocardial laser revascularization (TMLR) may provide relief from ischemia through neovascularization and sympathetic denervation, although the exact mechanism remains unclear.

14. Patients undergoing TMLR typically have severe coronary artery disease, poor left ventricular (LV) function, and multiple coexisting diseases, making intraoperative anesthetic management challenging.

15. Intraoperative TMLR complications include gas embolization, major hemorrhage, acute decrease in ventricular function, injury to the mitral valve apparatus or conduction system, and atrial and ventricular arrhythmias.

THE PAST TWO DECADES HAVE witnessed a major evolution in cardiac surgery in parallel with “minimally invasive” and laparoscopic developments in other surgical fields [1]. Two major objectives have been a reduction in the use of CPB for revascularization and a reduction in the invasiveness of the surgical approach. The overall goals are to preserve and enhance the quality of the procedure(s) while providing faster recovery, reduced procedural costs, and reduced morbidity and mortality. The contribution of the anesthesia care team is to facilitate cost-effective early recovery while providing safe, excellent operating conditions both for the patient and the surgeon. Anesthetic techniques and monitoring modalities have needed to evolve with changes in surgical practice. Anesthesiologists have learned more about how to support the circulation during cardiac manipulation and periods of coronary occlusion. We have been charged with monitoring and support while the surgeon operates with minimal exposure while at the same time facilitating early recovery and discharge. The surgical techniques and their anesthetic considerations discussed in this chapter include the following: CABG without the use of CPB (off-pump CABG [OPCAB] and minimally invasive direct coronary artery bypass [MIDCAB]); MIVS, including TAVI; computer-enhanced, endoscopic robotic-controlled CABG; and TMLR, as an alternative revascularization technique. Although not mentioned subsequently, we recommend the routine use of intra-arterial blood pressure monitoring for all of these procedures because of the rapidity and frequency of significant hemodynamic disturbances and the need for frequent assessment of labs (e.g., arterial blood gases, activated clotting times, coagulation studies, etc.).

I. Off-pump coronary artery bypass (OPCAB) and minimally invasive direct coronary artery bypass

   A. Historical perspective

     1. Early revascularization surgery

        a. Early attempts at coronary artery surgery without the use of CPB included the Vineberg procedure in Canada (tunneling the internal mammary artery [IMA] into the ischemic myocardium) in the 1950s, and internal mammary to coronary anastomosis in the 1960s by Kolessov in Russia.

        b. Sabiston from the United States and Favolaro from South America reported the use of the saphenous vein for aorta-to-coronary artery bypass grafts, performed without CPB, in the same period.

        c. The introduction of CABG in the late 1960s expanded the indications for CPB, which had enabled congenital heart repairs and heart valve surgery since the 1950s. CPB with the use of cardioplegia became the standard of care in the 1970s, providing a motionless field and myocardial “protection” with asystole and hypothermia.

     2. Reports in the early 1990s

        a. South American surgeons with limited resources continued to develop techniques for surgery without CPB, publishing in North American journals in the 1980s and early 1990s. In 1991, Benetti et al. [2] reported on 700 CABG procedures without CPB performed over a 12-yr period with very low morbidity and mortality.

        b. North American and European interest grew in the 1990s, fueled by a desire to make surgery more appealing (vs. angioplasty) as well as the need to reduce cost and length of stay. Alterative incisions were explored, and techniques and devices to facilitate surgery on the beating heart were developed. The terms “OPCAB” and “MIDCAB” were coined.

     3. Port-access (or “Heartport”)

        a. Simultaneous with attempts to perform CABG without CPB, a group from Stanford University introduced a technique permitting surgery to be done with endoscopic instrumentation through small (1 to 2 cm) ports and a small thoracotomy incision. This was termed port-access surgery or by the trade name of Heartport (Johnson and Johnson, Inc., New Brunswick, NJ, USA). A motionless surgical field was required, necessitating CPB. Extensive use of TEE is required to assist in the placement of and to monitor the position of the various cannulae and the endoaortic balloon (see below).

        b. Port-access cardiac surgery contributed new knowledge in two major areas: Percutaneous, endovascular instrumentation for CPB and instrumentation for performing surgery through a small thoracotomy incision. The latter techniques continue to be developed and modified to permit “minimally invasive” valve surgery through partial sternotomy or thoracotomy incisions.

     4. MIDCAB. A number of alternative incisions to midline sternotomy have facilitated access to specific coronary artery distributions to allow CABG without CPB. The most popular alternative approach is the left anterior thoracotomy, which allows IMA harvest and grafting to the left anterior descending (LAD) artery territory. This is the procedure usually referred to as MIDCAB.

     5. North American/European experience after 1998

        a. Initially viewed by most as experimental, off-pump techniques are now established as an acceptable alternative to CABG with CPB. The reported use of OPCAB has been reported to be as high as 33% [3], but the range in practice is wide. Some surgeons perform virtually all revascularizations as OPCAB, which typically refers to a multivessel CABG performed through a median sternotomy without CPB. Most large cardiac surgery practices have at least one surgeon who performs a significant number of OPCAB procedures. The physiology and anesthetic management for OPCAB has been recently reviewed by Chassot et al. [4].

        b. MIDCAB procedures are more technically demanding than OPCAB because they require specialized instrumentation and operating through a small incision. These procedures are done in a smaller number of institutions than OPCAB. Some surgeons harvest the IMA endoscopically before making the small incision to do the coronary anastomosis.

   B. Rationale for avoiding sternotomy and cardiopulmonary bypass for coronary artery surgery

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     1. Reduction in complications

        a. Sewing coronary vessels on the beating heart is technically challenging and not necessarily appropriate for all surgeons [5]. Whether or not there is a benefit of performing on-pump versus OPCAB is a topic of heated debate. Several published randomized trials [610] confirm reductions in enzyme release, bleeding, time to extubation, and length of stay. While there are long-term follow-up studies suggesting similar rates of survival and graft patency between the two groups [11,12], other studies suggest that graft patency is lower in off-pump procedures [9,13], with one large randomized controlled trial finding a higher 1-yr mortality rate in the off-pump group [13]. Of note, the latter studies came from surgeons less experienced in the off-pump technique. Intraoperative conversion from off-pump to on-pump has been associated with an increase in mortality [14,15]. Although reduction in stroke has been one of the proposed benefits of the technique (due to avoidance of aortic cannulation and cross-clamping), studies do not demonstrate this benefit. Similarly, reduction in renal dysfunction has been proposed but not proved in these studies and in one additional recent publication [16]. In August 2004, an updated guideline for CABG surgery was published by the American College of Cardiology and American Heart Association; this guideline recognizes the potential benefits for avoiding CPB but the need for further data with the lack of proved benefit in randomized controlled trials [17].

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        b. Avoidance of aortic manipulation and cannulation might reduce embolic complications such as stroke, yet a partial or side-biting aortic clamp may be necessary to perform proximal venous anastomoses in multivessel OPCAB. This can be avoided by using the IMA as the only proximal vessel with its origin intact or with the use of devices designed to avoid the use of a cross-clamp (e.g., the “Heartstring”).

        c. The whole body “inflammatory response” induced by extracorporeal circulation is avoided with MIDCAB and OPCAB. This approach should result in lower fluid requirements and less coagulopathy and is consistent with lesser volumes of blood loss and transfusion demonstrated in several comparisons of OPCAB to CABG with CPB.

     2. Competition with angioplasty. Refinements in interventional cardiology and reductions in postprocedure restenosis have allowed an ever-increasing population of patients to have coronary lesions treated in the catheterization laboratory, although long-term outcomes in multivessel coronary disease are slightly better with CABG than with stents. However, patients will often choose the less invasive interventional cardiology approach over surgery if those results are nearly equivalent. Evolution of surgical techniques to provide excellent results with less physiologic trespass may be necessary for coronary artery surgery to survive.

     3. Progress toward truly “minimally invasive” surgery

        a. Avoidance of CPB is more physiologically important than avoidance of sternotomy, but postoperative recovery from sternotomy is foremost in patients’ minds. The smaller the surgical scar, the better. The MIDCAB addresses this issue, but this approach can only access the LAD and its diagonal branches.

        b. Cardiac surgeons have been slow to embrace endoscopic approaches partly because, until recently, existing technology did not provide the range of motion and control required for coronary artery anastomoses.

        c. The port-access approach introduced endoscopic techniques to cardiac surgery; surgeons are now working with computer-assisted instruments to perform surgery on the beating heart (see later). Techniques developed for off-pump surgery are likely to contribute to the ability to perform such procedures endoscopically.

   C. Refinement of surgical approach

     1. Development of modern epicardial stabilizers

        a. In early reports, compressive devices (e.g., metal extensions rigidly attached to the sternal retractor) were used to reduce the motion of the coronary vessel during the cardiac and respiratory cycles. These devices often interfered with cardiac function and were impossible to use for left circumflex coronary artery lesions.

        b. Modern devices typically apply gentle pressure or epicardial suction, reducing the effect on myocardial function while providing better fixation of the area immediately surrounding the coronary artery anastomotic site. These devices also allow greater access to arteries on the inferior and posterior surfaces of the heart (Fig. 13.1).

Figure 13.1 The Octopus 2 tissue stabilizer (Medtronic Inc., Minneapolis, MN, U.S.A.). Through gentle suction the device elevates and pulls the tissue taut, thereby immobilizing the target area. (Courtesy of Medtronic Inc.)

     2. Techniques to position the heart (through midline sternotomy)

        a. Surgery on the anterior wall of the heart (LAD and diagonal branches) usually requires only mild repositioning, such as a laparotomy pad under the cardiac apex. This is associated with minimal effects on cardiac function.

        b. Surgery on the right coronary artery (RCA) or the circumflex artery and its marginal branches requires turning or twisting of the heart. To do this manually (i.e., by an assistant) is cumbersome and is associated with hemodynamic compromise.

        c. Use of posterior pericardial traction stitches and a gentle retracting “sock” (web roll wrapped around the apex in a “sling” to pull the heart to either side) greatly improves the hemodynamic tolerance of these abnormal positions.

        d. For circumflex vessel distribution surgery, dissection of the right pericardium to prevent the right ventricle (RV) from being compressed as it is being turned allows preservation of hemodynamic function.

     3. Surgical adjuncts to reduce ischemia

        a. Performing CABG surgery on the beating heart requires a mandatory period of coronary occlusion for each distal coronary artery anastomosis.

        b. Intracoronary shunts can maintain coronary flow at the possible cost of trauma to the endothelium.

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        c. “Ischemic preconditioning” involves a brief (e.g., one to four 5-min periods) occlusion and then the same period of reperfusion before performing the anastomosis. In animal models of myocardial infarction, this technique reduces the area of necrosis. A nearly equivalent physiologic effect can be provided by 1 MAC end-tidal isoflurane [18] or other inhaled agents, which is termed anesthetic or pharmacologic preconditioning. Ischemic preconditioning for 7- to 10-min occlusions, such as those required for OPCAB and MIDCAB, probably does not provide the same benefit as one might see with longer periods of occlusion, but this technique is employed by some surgeons.

        d. The proximal anastomosis of a vein graft can be performed first in order to allow immediate perfusion once the distal anastomosis is completed.

        e. Regional hypothermia techniques have been described for use during coronary occlusion.

        f. Preoperative insertion of an intra-aortic balloon pump (IABP) has been used for patients with reduced ventricular function requiring multivessel OPCAB.

   D. Patient selection: High risk versus low risk

      1. Early reports of OPCAB often described single-vessel or double-vessel bypass performed on low-risk patients. This was promoted as permitting early recovery and discharge.

     2. OPCAB is now promoted for multivessel bypass in patients with risk factors for adverse outcomes. Elderly patients at risk for stroke, patients with severe lung disease, or patients with severe vascular disease and/or renal dysfunction are often selected. As mentioned earlier, scientific studies have not yet demonstrated reduced adverse outcomes with OPCAB in these populations.

      3. Zenati et al. [19] and others have described combining MIDCAB (i.e., IMA to LAD) with angioplasty/stent to other vessels in high-risk patients.

      4. As mentioned earlier, a small number of surgeons attempt to perform virtually all CABG procedures as OPCAB regardless of preoperative risk status.

   E. Anesthetic management

     1. Preoperative assessment

        a. The cardiac catheterization report should be reviewed and the procedure discussed with the surgeon, including the planned sequence of bypass grafts and the potential use of specific adjuncts (e.g., shunts or perfusion-assisted direct coronary artery bypass grafting, or PADCAB). This allows the anesthesiologist to predict the effect of each coronary occlusion, which requires knowledge of the coronary anatomy and its usual nomenclature (Fig. 13.2).

Figure 13.2 Coronary anatomy. The main branches from the circumflex artery (CX) are named “marginal” or “obtuse marginal” vessels. D1, first diagonal; D2, second diagonal; LAD, left anterior descending artery; LM, left main; PDA, posterior descending artery; RCA, right coronary artery; LVBr, LV branch; Ra, Ramus intermedius (<40% of individuals).

        b. The vessel, location, and degree of stenosis determine the functional response to intraoperative coronary occlusion. Even with a proximal stenosis, an important vessel (e.g., LAD) may supply adequate resting flow to a large area of myocardium. Acute loss of flow to this large area (with surgical occlusion) may cause ventricular failure. A stenosis further down the vessel may be less important for overall ventricular performance.

        c. High-grade stenosis (e.g., 90%) is likely to be associated with some collateral blood flow from adjacent regions, as flow through the stenosis may be inadequate even at rest. A 10-min occlusion of such a vessel may have surprisingly little effect on regional function and hemodynamics because of the collateral flow. A lesser degree of stenosis (e.g., 75% to 80%) may not affect resting flow, hence there may be little or no collateral blood flow. Occlusion of such a vessel may cause severe myocardial dysfunction in the distribution of the vessel.

        d. If incisions other than sternotomy are to be employed to access specific coronary regions, positioning of the arms and the body, the potential need for one lung anesthesia, and sites for vascular access need to be discuss. Some surgeons prefer one-lung anesthesia even for a median sternotomy approach to OPCAB.

     2. Measures to avoid hypothermia

        a. Unlike on-pump CABG, it is difficult to restore heat to a hypothermic OPCAB patient. In order to maintain hemostasis and facilitate early recovery, prevention of heat loss needs to be planned before the patient enters the room.

        b. While in the preoperative area, the patient should be kept warm with blankets.

        c. The operating room should be warmed to the greatest degree tolerated by the operating team (e.g., 75°F or higher). The temperature can be reduced once warming devices have been placed and the patient is fully draped.

        d. The period and degree to which the patient remains uncovered for preoperative procedures (e.g., urinary catheter placement) and surgical skin preparation and draping should be minimized. This requires vigilance on the part of the anesthesiology team and frequent reminders to the surgical team.

        e. Various adjuncts to preserve heat include heated mattress cover or insert; forced-air warming blankets, including sterile “lower body” blankets placed after vein harvesting; and circumferential heating tubes. A more expensive and possibly more effective option is the use of disposable surface-gel heating devices [20].

        f. Fluid warmers should be used at least for the principal intravenous volume infusion “line,” if not for all intravenous lines other than those used for intravenous drug infusions.

        g. Low fresh-gas flows and circle/CO2 reabsorption circuits will help prevent heat loss.

     3. Monitoring (Table 13.1)

Table 13.1 Monitoring approaches for OPCAB and MIDCAB

        a. Preoperative assessment of ventricular function

           (1) Preoperative LV function is a major determinant of the need for extensive monitoring. Patients with normal or near-normal LV function are less likely to need diagnosis and therapy guided by invasive monitoring.

           (2) A patient with an elevated LV end-diastolic pressure (at cardiac catheterization) may have a “stiff” ventricle, or diastolic dysfunction. This commonly results from hypertrophy or ischemia. Filling pressures obtained intraoperatively must be interpreted in this context (i.e., the filling pressure may overestimate LV preload). Volumetric assessment of preload (by TEE) can be valuable in this situation.

           (3) Patients with poor ventricular function may tolerate coronary occlusions poorly. Appropriate responses may be best guided by monitors of cardiac output (CO) and filling pressures, or TEE [21,22].

           (4) Repeated occlusions in multiple regions of the myocardium (i.e., for multivessel OPCAB) are likely to result in a cumulative detrimental effect on hemodynamics. There may be a period of myocardial dysfunction requiring inotropic support even in patients with good underlying LV function. The combination of reduced ventricular function and the need for multiple bypass grafts is likely to result in a need for inotropic and/or vasopressor infusions guided by monitoring with a pulmonary artery catheter (PAC) and/or TEE.

           (5) Preoperative placement of a PAC introducer, but with an obturator of some kind or a single- or double-lumen central venous catheter placed through it rather than a PAC may be a reasonable first approach in most patients. This avoids the use of the PAC in uncomplicated patients while allowing for rapid PAC placement should this be desired any time in the perioperative period.

        b. Specific monitors

           (1) Lead V5 of the electrocardiogram (ECG) detects 75% of the ischemia found on all 12 leads. This lead should be monitored in all patients undergoing OPCAB or MIDCAB, as permitted by the surgical incision. Lead II gives clear P waves, but adds little to the sensitivity of ischemia detection.

           (2) The PAC is variably useful during OPCAB. For single- or double-vessel bypass in patients with preserved LV function, there can be little justification for this monitor [23]. The worse the ventricular function and the greater the number of planned bypass grafts, the more likely it is that information from the PAC will be useful.

           (3) Continuous CO from the PAC or other devices and continuous mixed venous oximetry may provide incremental benefit in assessing the adequacy of cardiac function. Use of these devices is often institution-specific or even surgeon/ anesthesiologist-specific.

           (4) Monitoring with TEE can provide detailed information about the effects of coronary occlusion and recovery, and it provides the earliest, most specific information during acute deterioration and interventions. Acute ventricular dilatation and mitral regurgitation may occur when a large region of the myocardium becomes ischemic, and this is detected immediately with TEE. In addition, distortion of the mitral annulus due to abnormal positioning may cause mitral regurgitation [24]. Obtaining adequate images may be distracting to clinical care. With the heart in an unusual position, images may be difficult or impossible to obtain. A reversible wall-motion abnormality that resolves with restoration of flow is reassuring; however, this does not guarantee a good quality graft or anastomosis.

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           (5) Normal carbon dioxide (CO2) elimination requires adequate CO. If ventilation is constant, an acute decline in CO will cause an acute decrease in end-tidal CO2 concentration.

        c. Monitoring for specific procedures

           (1) For MIDCAB or other reduced-access procedures, provision must be made for transcutaneous defibrillation and pacing. An important consideration is the requirement to reinflate the lungs for defibrillation during closed-chest surgery to provide tissue (rather than air) for the current to traverse [25].

           (2) For port-access surgery (Heartport or related procedures), TEE is required to guide and monitor cannula placement and function.

     4. Anesthetic technique

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        a. Early recovery is usually desired. Extubation immediately or shortly after surgery should be the goal.

        b. A vapor-based anesthetic technique facilitates early recovery. Keys to prevention of delayed awakening are as follows: Minimizing the dose of benzodiazepine; use of modest doses of opioids; and avoiding residual paralysis at the end of surgery. Some clinicians use very short-acting opioids such as remifentanil to facilitate early extubation, but this approach requires awareness of the need for effective longer-lasting analgesia at the time of extubation and thereafter. Use of bispectral index (BIS) monitoring can help guide administration of hypnotic agents.

        c. Transfer of the intubated yet awakening patient to the intensive care unit (ICU), and early ICU care are facilitated by use of short-acting sedative drugs such as propofol or dexmedetomidine.

        d. Thoracic epidural or lumbar spinal anesthetic and analgesic techniques have been promoted by some as suitable adjuncts to off-pump approaches. There are reports of OPCAB procedures done without general anesthesia. Most centers are reluctant to risk major neuraxial techniques immediately before full heparinization for CPB. Use of such techniques is unlikely to shorten postoperative length of stay and has not been shown to provide a measurable benefit.

        e. For MIDCAB (thoracotomy), postoperative epidural analgesia [26], paravertebral block, or intercostal blockade may be useful for pain control.

     5. Anticipation and management of ischemia

        a. Knowledge of the coronary anatomy and surgical plan is essential. This allows appropriate timing of pharmacologic and other interventions before ischemia is induced. Use of isoflurane (or other volatile inhalational agent) anesthesia can provide pharmacologic “preconditioning,” as mentioned earlier. Avoidance of hemodynamic alterations associated with ischemia such as tachycardia (especially in the presence of hypotension) must be avoided. Intravenous β-adrenergic blockade may be beneficial; however, this must be balanced with the possibility of impaired myocardial performance during coronary occlusion.

        b. Maintenance of adequate coronary artery perfusion pressure is of great importance in allowing collateral blood flow to ischemic regions. Volume loading and appropriate positioning (see following), alteration of the depth of anesthesia, and/or use of α-adrenergic agonists may all be indicated.

        c. Prophylactic nitrate infusions may interfere with preload (see later).

        d. Early experience without modern stabilizers suggested that bradycardia (to reduce motion) would aid the surgeon. This is no longer an issue. Grafting to the RCA territory (supplying the sinus and AV nodes) can be associated with bradycardia. Thus, although β-adrenergic blockade may be useful to prevent or treat tachycardia, epicardial pacing may be required for ischemia-induced bradycardia.

        e. Anecdotally, patients with compromised ventricular function undergoing multivessel procedures may benefit from “prophylactic” administration of an inotropic medication.

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     6. Intravascular volume loading

        a. Positioning of the heart may kink or partially obstruct venous return and/or compress the RV. Intravascular volume loading and head-down (Trendelenburg) position can help reduce this effect (Fig. 13.3) [27]. Close observation of the heart, filling pressures, and blood pressure to provide feedback to the surgeon is essential.

Figure 13.3 Relative changes in hemodynamic parameters during vertical displacement of the beating porcine heart by the Medtronic Octopus tissue stabilizer and the effect of head-down tilt. BASE, pericardial control position; Cx, circumflex coronary artery; DIS, displacement of the heart by the Octopus; DIS + TREND, Trendelenburg maneuver (20-degree head-down tilt while the heart remains retracted 90 degrees); LAD, left anterior descending artery; RCA, right coronary artery; x = mean arterial pressure. Statistical comparison with control values: *p < 0.05; **p < 0.01; #p < 0.001; ^p =0.046 versus combined relative value of LAD and RCA flows. (From Grundeman PF, Borst C, van Herwaarden JA, et al. Vertical displacement of the beating heart by the Octopus tissue stabilizer: Influence on coronary flow. Ann Thorac Surg. 1998;65:1348–1352, with permission.)

        b. Intravenous vasodilators (e.g., nitrates) can exacerbate reductions in cardiac filling. More commonly, intravenous vasoconstrictors (phenylephrine, norepinephrine) will be required during abnormal cardiac positions.

     7. Surgery-anesthesiology interaction. With all the above considerations, it should be clear that there must be excellent communication between the surgeon and the anesthesiologist for OPCAB or MIDCAB. Anticipation and planning for problems allow the anesthesiologist to intervene in a timely manner. The surgeon must say in advance what he is planning to do. Similarly, changes in cardiac performance and the need for intervention must be continuously communicated to the surgeon. The anesthesiologist must observe the surgical field, watching the procedure as well as the position, size, and function of the heart. An observant, communicative team with basic monitoring (ECG, blood pressure, and central venous pressure) is likely to produce better results than a team that communicates poorly, but uses extensive monitoring.

   F. Anticoagulation

     1. Heparin management

        a. Heparin anticoagulation protocols are institution-specific. Similar to on-pump surgery, there are few data to recommend targeting specific activated clotting time (ACT) values.

        b. Some surgeons request full heparinization similar to on-pump procedures (i.e., ACT target >400 s); others request lower doses of heparin such as would be used for noncardiac vascular procedures (ACT target typically >200 s), or something in between. Outcomes appear to be equivalent using either approach, which suggests that ACT targets as high as those used for CPB are unnecessary.

     2. Protamine reversal

        a. Extracorporeal circulation induces a postoperative multifactorial defect in coagulation that may reduce early graft thrombosis. When coagulation is reversed after OPCAB or MIDCAB, no such hypocoagulable state exists; indeed, there is evidence that the coagulation system is activated by the stress of surgery, similar to what has been showed for other major procedures [28].

        b. In order to gradually return the coagulation to normal leaving perhaps a little residual heparin effect, reversal may be achieved with incremental doses of protamine. If “full” heparinization has been employed, administration of 50 mg of protamine may bring the ACT down to near 200 s, after which small increments (10 to 25 mg) can be given to achieve an ACT that is about 25% to 50% above control (i.e., 150 to 180 s).

        c. If the patient is clinically bleeding with an elevated ACT, then heparin should be reversed completely. Even in the absence of clinical bleeding, some cardiac surgeons prefer complete reversal immediately after completion of the grafts.

        d. Prolonged OPCAB procedures may be associated with extensive blood loss and therefore facilitated by the use of cell-saver devices (i.e., washing of salvaged blood so it is free of coagulation proteins and platelets). Over time, this may induce a dilutional coagulopathy similar to what is often seen after CPB.

     3. Antiplatelet therapy

        a. Thrombosis at the site of vascular anastomoses is initiated by platelet aggregation and adhesion. Similar to strategies that are used in angioplasty/stent procedures, antiplatelet therapy may help reduce early graft thrombosis in CABG, whether done with or without CPB.

        b. A common practice is to administer a dose of aspirin preoperatively. This can be achieved with a suppository if the patient is already anesthetized.

        c. In on-pump CABG, administration of aspirin within 4 h after the procedure reduces graft thrombosis. This strategy should also be applied to OPCAB and MIDCAB.

        d. There are no published data about the use of newer antiplatelet drugs in this setting. As with all such therapies (including aspirin), the concern for bleeding must be balanced with the desire to prevent graft thrombosis.

     4. Antifibrinolytic therapy. Use of lysine analogs to inhibit fibrinolysis has become common practice with on-pump CABG, as they have been shown to reduce perioperative blood loss. Recent investigations now support the use of these agents during OPCAB as well [29].

   G. Recovery

     1. Extubation in the operating room

        a. For uncomplicated procedures, recovery from OPCAB or MIDCAB can be rapid without the requirement for postoperative ventilation or sedation.

        b. Normothermia, hemostasis, and hemodynamic stability must be assured.

        c. Residual anesthesia and paralysis from long-acting agents (e.g., pancuronium, large doses of morphine) must be avoided.

        d. Extra time spent in the operating room to achieve extubation may be more costly than a few hours of postoperative ventilation and sedation.

     2. ICU management

        a. For most patients, early postoperative management can employ the “fast track” technique where mechanical ventilation is withdrawn within a few hours of surgery, and patients are extubated and possibly mobilized at the bedside late in the day or during the evening of surgery.

        b. ICU stay is driven by institutional practice, but for patients having straightforward, uncomplicated procedures, there may be no need for more than a few hours in a high-intensity nursing area (i.e., postanesthetic care unit or ICU).

        c. If length of stay is reduced, cost will almost certainly be reduced. If there is no significant reduction in stay, the cost of specialized retractor systems may exceed the cost of the disposables required for CPB.

        d. Some surgeons passionately believe that OPCAB is better for their patients; perhaps with time and additional randomized trials, the hoped-for reductions in neurologic events, renal dysfunction, and other adverse outcomes will become apparent.

II. Minimally invasive valve surgery (MIVS)

   A. Introduction

     The Society of Thoracic Surgeons National Database defines minimally invasive surgery as “any procedure that has not been performed with a full sternotomy and cardiopulmonary bypass support. All other procedures, on- or off-pump with a small incision or off-pump with a full sternotomy are also considered minimally invasive” [30]. Similar to MIDCAB, the premise of MIVS is that “smaller is better” for valve surgery as well. A partial sternotomy or small thoracotomy with port incisions may achieve some benefits when compared to standard median sternotomy. Similar to OPCAB, alternative approaches were explored in the late 1990s, with the first publication in 1998. Proposed [31,32] but unproved advantages to these approaches include the following:

      1. Reduced hospital length of stay and costs

      2. Quicker return to full activity

      3. Less atrial fibrillation (26% vs. 38% in one report [33])

      4. Less blood transfusion

      5. Same results (mortality, valve function)

      6. Less pain

      7. Earlier ambulation

          In addition, the surgical opinion is that reoperation should be easier after MIVS, as the pericardium is not opened over the RV outflow tract. These proposed benefits may be observed with specific surgeons in specific centers; however, there have been no rigorous or randomized studies. The limited data that exist suggest that acute postoperative pulmonary function impairment is not improved by the use of the limited incision. Minimally invasive reoperative aortic valve surgery is a new and successful technique, especially in patients who have had previous cardiac operations using a full sternotomy (e.g., prior CABG). This surgical approach does not disturb the vein grafts or the patent IMAs [34].

   B. Surgical approaches (Fig. 13.4)

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      1. Port-access (Heartport): This approach involves direct surgical visualization and operation through small openings (ports) and a small right horizontal thoracotomy incision for access to the mitral valve or atrial septum. In order to avoid sternotomy, the port-access system uses alternative access sites and cannulae. The aorta is cannulated through a long femoral arterial catheter or a shorter transthoracic aortic catheter. These devices are advanced to the ascending aorta and include an “endo-aortic clamp” or inflatable balloon to achieve aortic occlusion (“cross-clamp”) from within. They include a cardioplegia administration port. Venous cannulation is achieved with a long femoral venous catheter, supplemented as needed with a pulmonary artery vent. A coronary sinus catheter is used to administer cardioplegia. Placement of these catheters can be time-consuming and requires imaging with fluoroscopy and/or TEE. A limited number of institutions still use this approach to MIVS. Some reports have raised concerns about device-related aortic dissections as well as endoaortic balloon rupture and dislocation [35].

      2. Video-assisted port-assisted (using the port-access cannulae and small incisions with video equipment to visualize and perform valve surgery). This is currently performed in a small number of institutions worldwide.

      3. Robotic (see below). This is an evolving technique, particularly for mitral valve repair, with excellent results being reported.

      4. Direct-access (small incision—many types: Anterolateral mini-thoracotomy, partial upper or lower sternotomy, right parasternal incision, and others). The right parasternal approach is preferred by some surgeons (especially for aortic valve access) because there is no sternal disruption and it is cosmetically pleasing. The avoidance of sternotomy bleeding into the pericardial sac with associated fibrinogen depletion may result in less perioperative bleeding and less pain that is easier to control, although the need to divide two or more costochondral cartilages with the parasternal approach does induce considerable postoperative pain. As mentioned earlier, avoidance of opening the pericardium over the RV outflow tract may make future cardiac reoperation easier and safer. One problem with this approach is the sacrifice of the right IMA.

      5. The current standard approach for aortic valve surgery using a minimally invasive approach is an “inverse L” shaped partial sternotomy extending to the third or fourth right intercostal space. In order to bring the entire heart more anteriorly, three to four retention stitches are passed through the pericardial rim and fixed to the skin incision. This may be associated with compression of the right atrium and a decrease in the venous return to the heart. The arterial cannula for CPB is placed in the ascending aorta. Venous return is established by direct cannulation of the right atrial appendage or by percutaneous femoral vein cannulation of the right atrium. With the latter cannulation technique, often a two-stage cannula is used with the distal tip placed at the junction of the SVC and RA as confirmed by TEE (bicaval view) [36].

      6. Minimally invasive mitral valve surgery can use a right anterolateral minithoracotomy for which the patient is positioned supine with slight elevation of the right chest (often using a folded blanket) and extension of the right arm. Optimal visualization the heart requires deflation of the right lung, which is achieved most often by using a double-lumen endobronchial tube. CPB is established via the femoral vessels. The superior vena cava may also be cannulated percutaneously via the right internal jugular vein (IJV). A percutaneous transthoracic aortic cross-clamp is placed through a separate stab incision in the right posterior axillary line [35], and the mitral valve is accessed through the left atrium. Another approach is a right parasternal incision with mitral valve exposure via the right atrium and interatrial septum.

      7. Reduced-size skin/soft tissue incision compared with full median sternotomy can give a more cosmetically pleasing result.

Figure 13.4 Incisions for MIVS. The most common approach is the “mini” sternotomy, which extends from the sternal notch part way to the xiphisternum but is diverted to the right at the level of the third or fourth interspace (for the aortic valve), leaving the lower sternum intact. The mitral valve can be accessed through the small right thoracotomy. (From Clements F, Glower DD. Minimally invasive valve surgery. In: Clements F, Shanewise J, eds. Minimally Invasive Cardiac and Vascular Surgical Techniques. Society of Cardiovascular Anesthesiologists monograph. Philadelphia, PA: Lippincott Williams & Wilkins; 2001:30.)

   C. Preoperative assessment. In addition to understanding the valvular and associated cardiac disease, the anesthesiologist must have a good appreciation for the surgical plan. Nonsternotomy and port-access approaches require specific positioning, including having the arms extended or cephalad either suspended in a sling or resting on an “airplane” type of armrest, and will have implications for peripheral venous, central venous, and arterial catheter placement. Port-access procedures will require planning for fluoroscopic and TEE assistance to guide and monitor placement of catheters.

   D. Monitoring

      1. Central venous catheter versus PAC. Because of pericardial traction and/or compression of the right atrium, pulmonary artery, or RV outflow tract, the relationship between pressures recorded from central venous or PACs and chamber volumes may be changed. In addition, due to limited ability to palpate around the heart, there may be an increased risk of inadvertently including the PAC in surgical sutures. These considerations must be balanced with the potential need to guide fluid and inotropic therapy perioperatively.

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      2. TEE. There can be little doubt that TEE monitoring is an integral part of MIVS [36]. With such limited access, the surgeon cannot rely on visual cues about cardiac distension or volume status. Thus, TEE is used in the following ways:

        a. Pre-CPB to determine:

           (1) Valve dysfunction

           (2) Cardiac volume and function

           (3) Arterial cannulation site

           (4) Specialized cannula placement, especially for port access

        b. During CPB for port-access and robotic surgery, TEE is used to monitor appropriate placement of the endoaortic “clamp” and to detect intracardiac air, which can be extensive in MIVS cases.

        c. After CPB, TEE is used in the usual manner to assist with identification and management of new-onset ventricular dysfunction, which may occur in as much as 20% of MIVS patients. This is more frequent in patients with significant intracardiac air. TEE is also used to assess valve function and to look for aortic dissection.

   E. Specific anesthesiology concerns. Regardless of the type of surgical access to MIVS, there are several common problems that require enhanced awareness:

      1. Long surgical learning curve: Be prepared for anything during this period.

      2. Limited surgical access (small incision)

        a. Urgent cardiac pacing and direct current cardioversion may need to be done transthoracically. Appropriate skin electrodes or patches must be placed before surgery is started.

        b. Big fingers, sponges, or instruments can compress vascular structures, causing large swings in hemodynamics.

        c. “Blind” suture placement can lead to bleeding from posterior sites which can be very difficult to control. Full median sternotomy is occasionally required to control the bleeding.

        d. Inadequate valve repair or replacement: Paravalvular leaks or valve dysfunction secondary to suture-induced valve leaflet sticking can occur.

        e. Errant suture placement may cause coronary artery compromise leading to myocardial ischemia, or may affect the conduction system leading to heart block or dysrhythmias.

        f. De-airing is very difficult, even when guided by TEE. Residual air may embolize to the coronary arteries resulting in acute cardiac decompensation. CO2 gas is very commonly administered into the operating field to minimize this complication, with varying success.

        g. Tamponade: After chest closure, even a small amount of bleeding can lead to tamponade physiology in the mini-incision area.

   F. Postoperative management. The goal is early recovery and extubation. As in MIDCAB and OPCAB, this is governed by a number of factors, including patient stability and temperature, duration of the procedure, and the use of short-acting agents. Extubation in the operating room is possible but uncommon. Certain incisions (i.e., thoracotomy) may lend themselves to the use of paravertebral or intercostal nerve blocks for postoperative pain relief.

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   G. Percutaneous valve repair/replacement. Percutaneous approaches to mitral regurgitation, mitral stenosis, and aortic stenosis are rapidly growing in popularity. Each approach presents unique challenges to the anesthesiologist.

     1. MitraClip [37,38]. A clip has been developed for mitral regurgitation which captures the free edges of both mitral valve leaflets, creating a double orifice valve similar to the Alfieri surgical repair. Under general anesthesia, the femoral vein is accessed, and with fluoroscopic and TEE guidance the device is advanced over a guidewire through the interatrial septum and through the regurgitant portion of the mitral valve, where it is deployed. Multiple clips may be used if necessary. Early studies suggest that though the procedure is safe, it may be most beneficial to high-risk surgical candidates with functional MR, as conventional surgical methods are more effective in reducing the severity of MR. Potential complications include hemopericardium leading to tamponade, damage to the mitral valve, device failure requiring surgical repair, device embolization, creation of mitral stenosis, and persistent interatrial shunt from the septal puncture. This procedure continues to be investigated.

     2. Percutaneous Balloon Mitral Valvuloplasty [39]. Certain patients with symptomatic or severe mitral stenosis may be candidates for percutaneous balloon mitral valvuloplasty as an effective alternative to open surgical mitral commissurotomy. Prior to the procedure, TEE is performed to interrogate the left atrium and left atrial appendage for thrombus which may dislodge during the dilation and lead to systemic embolization. The procedure can be performed using local anesthesia with sedation or general anesthesia. Under fluoroscopic guidance, a guidewire is advanced through the femoral vein into the right atrium then through the interatrial septum. The balloon catheter is advanced along the guidewire and positioned in the mitral valve. Once properly positioned, the balloon is inflated, thereby dilating the valve. Repeated dilations are performed until there is an improvement of the pressure gradient between the left atrium and left ventricle, significant mitral regurgitation occurs, or echocardiographic assessment reveals adequate fracture of the commissures. Complications include damage to cardiac structures, hemopericardium leading to tamponade, emboli release, worsening or creation of mitral regurgitation, damage to the subvalvular apparatus, and persistent interatrial shunt. Acute success rates and long-term restenosis rates are comparable to those for open surgical mitral commisurotomy.

     3. TAVI. Although surgical replacement of the aortic valve is the treatment of choice for patients with severe aortic stenosis, some patients are at very high risk for mortality or major morbidity with surgery. TAVI is a less invasive alternative performed without CPB in which a bioprosthetic valve is implanted within the native aortic valve via a catheter introduced through a major artery or the apex of the left ventricle [40].

        a. There are two valves currently available:

           (1) Edwards SAPIEN valve (Edwards Lifesciences, Irvine, CA): Transfemoral or transapical deployment. This valve requires rapid ventricular pacing during deployment and is expanded with a balloon. Thus, the CO is zero during deployment.

           (2) CoreValve ReValving system (Medtronic, Minneapolis, MN): Transfemoral deployment. This valve is self-expanding and does not require rapid ventricular pacing to deploy. The left ventricle continues to eject during deployment.

            Both are available for use in Europe [41]. In the United States, only the SAPIEN valve is approved for nonsurgical candidates.

        b. Contraindications. Contraindications used in clinical trials to date include acute myocardial infarction within 1 month, congenital unicuspid or bicuspid valve, mixed aortic valve disease (stenosis and regurgitation), hypertrophic cardiomyopathy, LV ejection fraction below 20%, native aortic annulus size outside of the manufacturer’s recommended range, severe vascular disease precluding safe placement of the introducer sheath (for the transfemoral approach), cerebrovascular event within 6 months, and need for emergency surgery.

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        c. Hybrid operating room [42,43]. Cardiovascular hybrid surgery, which includes TAVI, is a rapidly evolving field where less invasive surgical approaches are combined with interventional cardiology techniques in the same setting. Such procedures require a combination of high-quality imaging modalities found in a cardiac catheterization suite (fluoroscopy, navigation systems, post-processing capabilities, high-resolution invasive monitoring, intracardiac and intravascular ultrasound, echocardiography, etc.) in addition to the ability to perform open surgery under general anesthesia, including the use of CPB. These procedures require close collaboration and communication among multidisciplinary teams including interventional cardiologists, surgeons, anesthesiologists, perfusionists, technicians, and nursing staff, some of whom may be distant from the operating field. Thus, the presence of multiple monitor panels in areas visible to all and advanced communication systems are critical. Large amounts of space and careful planning of room layout are crucial for all of the equipment to be readily accessible and to allow unobstructed access to the patient. In addition, both the radiation safety requirements of the cardiac catheterization suite and the hygienic standards of the operating room must be met. These many demands have led to the creation of specialized hybrid operating rooms (Fig. 13.5).

Figure 13.5 An example of a setup for a hybrid operating room; ARKS, anesthesia information system.

        d. Surgical approaches (Fig. 13.6) [4446]

Figure 13.6 Approaches to TAVI.

           (1) Retrograde or transfemoral approach

             (a) The right femoral artery is accessed for device deployment. The left femoral artery and vein are accessed to provide for hemodynamic monitoring, transvenous pacing, contrast administration, and preparation for emergent CPB.

             (b) Heparin (100 to 150 units/kg) is given intravenously, titrating therapy to an ACT of about 300 s.

             (c) A guidewire is advanced across the aortic valve, and the balloon angioplasty catheter is advanced over the wire.

             (d) Ventricular pacing at about 200 beats/min (bpm) creates a low CO state (Fig. 13.7). In combination with apnea, a motionless field is obtained during inflation of the balloon, after which ventilation is resumed and pacing is terminated.

Figure 13.7 Hemodynamics during rapid ventricular pacing. The bottom waveform is taken from the arterial catheter.

             (e) The valve catheter is positioned using fluoroscopy and TEE. Rapid ventricular pacing and apnea are used during valve deployment.

             (f) Fluoroscopy and TEE are used to assess valve position and function and to check for leak.

           (2) Anterograde transapical approach

             (a) This more invasive approach is reserved for patients with peripheral arterial disease which would not accommodate the introducer and valve deployment systems.

             (b) The left femoral artery and vein are accessed as mentioned earlier.

             (c) The LV apex is exposed via left anterolateral thoracotomy. TEE may facilitate identification of the apex.

             (d) Heparin is given with the same ACT targets described earlier.

             (e) A needle is inserted through the LV apex, through which a guidewire is passed through the aortic valve under fluoroscopic and TEE guidance.

             (f) A balloon valvuloplasty catheter is introduced over the guidewire and positioned in the aortic valve. Similar to the retrograde approach, rapid ventricular pacing and apnea are initiated to create a motionless field during inflation.

             (g) The valvuloplasty sheath is then replaced by the device introducer sheath through which the prosthetic valve is deployed in a similar fashion.

           (3) Other approaches

             (a) Transsubclavian approach has been described as an alternative for patients with severe iliofemoral arterial disease [47]. Preoperative CT imaging is obtained to ensure that the vasculature is suitable for this approach. Access is obtained via surgical cutdown, and the valve is deployed similar to the retrograde (transfemoral) approach.

             (b) Transaortic approach via ministernotomy has also been reported.

             (c) Recently, a transcarotid approach has been used in patients not candidates for the other approaches.

        e. Anesthetic considerations

           (1) In addition to standard monitors, large-bore venous access and invasive blood pressure monitoring are essential. For the ongoing clinical trials, a PAC is usually placed; however, the catheter is withdrawn during the procedure itself as it interferes with the fluoroscopic image. TEE is helpful as a monitor and guide for valve placement, but transthoracic imaging or fluoroscopy alone may be used in patients having the procedure done via the retrograde transfemoral approach, using local anesthesia and sedation.

           (2) Blood should be readily available, as massive hemorrhage from arterial injury can occur acutely.

           (3) Radiolucent defibrillation pads should be placed prior to draping the patient in case the need arises for cardioversion or defibrillation.

           (4) With the transapical approach, general anesthesia is necessary. Lung isolation may be helpful for surgical exposure, but it is not absolutely needed. For the retrograde approach, local or regional anesthesia with MAC may be adequate, but each patient should be assessed on an individual basis. The advantages of using local/regional anesthesia with sedation include the ability to assess neurologic status, avoidance of airway manipulation, and a more rapid early recovery. However, general anesthesia may be more comfortable for the patient, provide immobility during valve deployment, and provide a secure airway in the event of complications and the need for emergent CPB [4850]. General anesthesia is especially helpful when TEE is used, and some clinicians see this as the “tipping point” for its selection. With either method of anesthesia, the goal is for the patient to recover rapidly. Shorter-acting anesthetic agents along with other adjuncts, such as intercostal nerve blocks performed under direct vision by the surgical team (transapical approach), will help accomplish this goal.

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           (5) During the procedure, there may be periods of acute hemodynamic instability as a result of the device occluding the already narrow valve, the creation of acute aortic regurgitation during valvuloplasty, massive bleeding from dissection of major vasculature, damage to the left ventricle or mitral valve, or acute occlusion of a coronary ostium. Arrhythmias are common during insertion of guidewires and catheters into the left ventricle. Clear communication with the surgical team is of utmost importance in order to treat appropriately and to avoid “overshooting” with vasopressors. Sometimes the solution is as simple as repositioning the catheter.

           (6) Normothermia should be actively maintained with the use of forced air warming blankets and fluid warmers as needed.

           (7) TEE is used to assess global cardiac function, measure the aortic root for sizing of valve, screen for aortic disease, facilitate proper valve positioning, and identify complications of the procedure such as paravalvular leak, tamponade, or coronary occlusion [41,51].

        f. Complications [52,53]. Major complications of TAVI include stroke, vascular damage including dissection, rupture of the aortic root, occlusion of coronary ostia, cardiac conduction abnormalities, damage to other cardiac structures such as the mitral valve, embolization of the prosthesis requiring emergent surgical retrieval, and massive blood loss from vascular damage or rupture of the LV. Paravalvular leak is more common after TAVI than open surgery, probably because diseased, calcified tissue that may hinder optimal valve deployment is not removed. Paravalvular leaks may be treated with balloon reinflation to better appose the stented prosthesis to the aortic annulus.

        g. Outcomes [40,54]. For nonsurgical candidates, TAVI has been associated with an improvement of symptoms and mortality at 1 yr as compared to medical management. In high-risk surgical candidates, TAVI and open surgery have similar 1-yr mortality rates. However, there appears to be a higher incidence of stroke and major vascular complications with TAVI. We look forward to more long-term outcome data as the procedure becomes more common.

III. Robotically enhanced cardiac surgery

   A. Historical perspective

      1. Use of robotics in surgery was initially considered for facilitation of surgical expertise at a site remote from the surgeon (e.g., battlefield, developing country).

      2. Robotic enhancement of dexterity has been applied to endoscopic instruments, allowing on-site performance of complex tasks that were impossible using the endoscopic approach.

      3. Computer-assisted, robotic cardiac surgery in patients was first reported by Loulmet et al. [55] and Reichenspurner et al. [56] in 1999.

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      4. Since then, a variety of procedures ranging from multivessel totally endoscopic coronary artery bypass grafting (TECAB), both on-pump and off-pump, to hybrid procedures involving robotic revascularization and PCI have evolved with promising results.

   B. Overview

      1. Taylor et al. [57] described the complementary capabilities of surgeon and machine.

        a. Surgeons are dextrous, adaptive, fast, and can execute motions over a large geometric scale; they develop judgment and experience. Limiting factors include geometric inaccuracy and inexact exertion of directional force. Performance is compromised by confined spaces or bad exposure. Surgeons get tired, and with age can lose skills and vision.

        b. Machines are precise and untiring. Computer-controlled instruments can be moved through an exactly defined trajectory with controlled forces, facilitating work in confined spaces.

      2. Endoscopic surgery, by avoiding stress, pain, and cosmetic insult of open procedures, improves some outcomes and increases patient satisfaction. Laparoscopic cholecystectomy illustrates rapid adaptation of surgical practice to endoscopic techniques. In 1999, 85% of gall bladder surgeries (approximately 1,100,000 surgeries) were performed via this minimally invasive approach [58].

      3. Many excisional or ablative procedures lend themselves to current endoscopic instrumentation. Reconstructive procedures (e.g., vascular anastomoses) are more difficult due to the requirement for multiple planes of fine motor activity.

      4. Robotic enhancement of dexterity potentially allows the use of endoscopic techniques for complex surgery. For coronary artery bypass surgery, the goal is to avoid both sternotomy and CPB. Robotic devices permit construction of coronary artery grafts through endoscopic portals on the beating heart. This potentially allows surgical coronary bypass with a degree of invasiveness more comparable to angioplasty than to sternotomy [59].

   C. Technologic advances permitting endoscopic surgery

      1. Development of the charge-coupling device (CCD) allows high-resolution video images to be transmitted through optical scopes to the surgeon.

      2. High-intensity xenon and halogen light sources improve visualization of the surgical field.

      3. Improved hand instrumentation permit procedures that previously could only be performed through an open incision to be executed by less invasive methods [60].

      4. The surgeon can now view digitally enhanced images that provide better visualization than direct viewing, due to magnification and illumination.

      5. The major limitations of endoscopic instruments are the control of fine motor activity, surgery in a confined space, and a somewhat reduced sensory feedback of tissue resistance or firmness.

      6. Placement of a microprocessor between the surgeon’s hand and the tip of the surgical instrument dramatically enhances control and fine movement. Table 13.2 lists the ways in which computerized dexterity enhancement addresses limitations of conventional endoscopy.

Table 13.2 Endoscopic versus computer-enhanced instrumentation systems

   D. Endoscopic robotic-assisted systems

      1. Robotic systems consist of three principal components (Fig. 13.8):

Figure 13.8 Schematic illustration of setup for endoscopic beating heart CABG using two consoles and five manipulator arms. The surgeon at the primary console manipulates two instruments and navigates the endoscope. The assisting surgeon directs the stabilizer and an assisting tool from a second console. A, left tool (primary surgeon); B, right tool (primary surgeon); C, stabilizer (left-hand assisting surgeon); D, assisting tool (right-hand assisting surgeon). (Adapted from Falk V, Fann JI, Grunenfelder J, et al. Endoscopic computer-enhanced beating heart coronary artery bypass surgery. Ann Thorac Surg. 2000;70:2029–2033, with permission.)

        a. A surgeon console. The surgeon sits at the console and grasps specially designed instrument handles. The surgeon’s motions are relayed to a computer processor, which digitizes hand motions.

        b. A computer control system. The digitized information from the computer control system is related in real time to robotic manipulators, which are attached to the operating room table.

        c. Robotic manipulators. These manipulators hold the endoscopic instrument tips, which are inserted into the patient through small ports.

      2. Currently, only one robotic system is commercially available: the da Vinci system (Intuitive Surgical, Mountain View, CA, USA).

      3. A number of enhancements are required to move robotic systems toward more widespread acceptance.

        a. Development of endoscopic Doppler ultrasonography may aid in internal thoracic (mammary) artery harvesting, especially when the vessel is covered by fat or muscle.

        b. Although providing articulation, the endoscopic stabilizers need refinement to permit easier placement.

        c. Multimodal three-dimensional image visualization and manipulation systems may allow modeling of the range of motion of the robotic arms to individual patient data sets (computerized tomographic scan, ECG-gated magnetic resonance imaging). This may help optimize port placement and minimize the risk of collisions in the future.

        d. “Virtual” cardiac surgical planning platforms will allow the surgeon to examine the topology of a patient thorax for planning the port placement and the endoscopic procedure.

   E. Anesthetic considerations related to robotic surgery. Robotic surgery requires the anesthesiologist to prospectively interact with the surgeon and machine to maintain ideal operating conditions, as well as stable hemodynamics and cardiac rhythm in an environment that may change rapidly from regional ischemia and cardiac manipulation. When the patient is fully instrumented and the robotic surgery is under way, direct access to the operative field is very limited and likely to be delayed. Anticipation and excellent communication are especially important where rapid surgical interventions are all but impossible.

      1. Preoperative preparation

        a. Similar to OPCAB or MIDCAB, the anesthesiologist must discuss the procedure with the surgeon to understand the coronary anatomy, what is planned, and what special considerations might be involved (see above).

        b. Specific to robotic surgery are considerations that may be applicable to the robot (e.g., site of ports, location of manipulators, electrical interference).

      2. Monitoring must take into account the patient’s pathology (i.e., underlying ventricular function), the surgeon’s familiarity with the robotic technique, anticipated problems, and duration of the procedure. As robotic procedures are still in the early stage of development, increased intensity of monitoring is probably warranted in most patients (i.e., use of PA catheters and/or TEE).

      3. Induction and maintenance of anesthesia

        a. Specific anesthetic techniques are similar to other cardiac surgery where rapid emergence from anesthesia is desired (“fast track”).

        b. Position is critical for appropriate location of ports and access for robotic manipulators. Typically this consists of the left arm stabilized beside the body, right arm up (i.e., suspended in a sling).

        c. Deflation of the left lung is required for visualization in robotic CABG surgery. This can be accomplished with a double-lumen endobronchial tube or bronchial blocker.

        d. Endoscopic robotic mitral valve surgery requires deflation of the right lung to facilitate access through the right fourth or fifth intercostal space.

        e. During robotic CABG surgery, CO2 is insufflated into the left hemithorax during one-lung anesthesia. The insufflation pressure should be 6 to 8 mm Hg. This sustained positive intrathoracic pressure may mechanically decrease myocardial contractility and/or impair cardiac filling, which is rapidly reversible after the release of CO2 from the chest cavity [61]. There may be sufficient absorption of CO2 to induce respiratory acidosis and its attendant potential for tachycardia, dysrhythmias, and pulmonary hypertension.

        f. External defibrillator/pacing pads should be attached to the patient as surgical access to the heart for either of these functions is very limited and delayed.

        g. Similar to OPCAB and MIDCAB, a multimodal approach should be taken to prevent heat loss. Although robotic procedures often reduce the extent of exposed intrathoracic surfaces as compared to OPCAB or CABG using CPB, the procedures can be lengthy, so the risk for hypothermia remains significant.

      4. Anticoagulation and reversal. See discussion under “OPCAB and MIDCAB” in Section II. F.

      5. Avoiding hemodynamic compromise. As in OPCAB, the heart may be positioned within the chest in a manner that compromises venous return or ventricular function.

        a. Keep preload high. Consider intravascular volume loading and the head-down (Trendelenburg) position.

        b. Tilt the operating table to the right or left as needed to facilitate surgical exposure.

        c. Maintain coronary perfusion pressure with α-adrenergic agonists if needed.

        d. Use epicardial pacing if bradycardia occurs.

        e. Closely watch insufflation pressure and monitor end-tidal CO2 concentration as well as periodic arterial blood gases.

      6. TEE. If the surgery is to be done on CPB, TEE guidance may be necessary to facilitate the placement of cannulas and endoaortic occlusion device, as described earlier (see MIVS section above).

      7. Postoperative management

        a. Extubation in the operating room may be possible (see above for OPCAB and MIDCAB).

        b. If postoperative ventilation is anticipated, plan to change the double-lumen endobronchial tube to a single-lumen endotracheal tube.

        c. Postoperative pain management will depend on the size and number of port incisions. If a thoracotomy incision was made, intercostal, paravertebral, or epidural analgesia can be considered.

   F. Summary. The field of robotically enhanced cardiac surgery will present a wide range of anesthetic challenges as it continues to develop. Anesthesiologists and surgeons alike must adapt to rapidly changing techniques in our continuing efforts to improve clinical outcomes.

IV. Transmyocardial laser revascularization

   A. Historical perspective

      1. TMLR is a procedure for the treatment of refractory angina pectoris that utilizes laser energy to create numerous channels in ischemic myocardium (Fig. 13.9).

Figure 13.9 Illustration of transmyocardial laser and epicardial position of the laser device for creating channels. The device can be placed through a left thoracotomy incision (isolated procedure) or through a standard sternotomy (supplement to CABG). Full-thickness penetration is confirmed by transesophageal echocardiographic visualization of microbubbles in the LV cavity.

      2. TMLR was approved by the Food and Drug Administration (FDA) in 1998.

      3. The concept dates back to 1933 when Wearn et al. [62] demonstrated direct vascular communication between the coronary arteries and the chambers of the heart via a sinusoidal network within the ventricular muscle. Beck’s mobilization of omentum onto the heart in 1935 [63] and Vineberg’s implantation of the IMA directly into the myocardium in 1954 [64] were attempts at indirect myocardial perfusion based on Wearn’s description.

      4. In 1965, Sen et al. [65] utilized acupuncture needles to create transmural channels through ischemic myocardium to direct blood into the myocardium from the ventricle. This concept was based on the reptile heart in which the LV is directly perfused via channels radiating from the LV.

      5. In the 1980s, Mirhoseini et al. [66] utilized CO2 laser energy to create transmyocardial channels.

      6. Reports of prospective randomized clinical trials [67,68] led to the approval of CO2 and holmium lasers for the treatment of refractory angina pectoris. In addition, the safety and efficacy of these lasers utilized as an adjunct to CABG has been evaluated [69].

   B. Laser mechanism of injury

      1. Three types of lasers are utilized for TMLR: CO2, holmium:yttrium-aluminum-garnet (Ho:YAG), and XeCl excimer. CO2 and holmium lasers operate in the infrared region, whereas excimer laser is in the ultraviolet region.

      2. To create a channel through myocardium, tissue is ablated (chemical bonds between atoms are broken). The infrared lasers achieve ablation by vaporization of myocardium, which is followed by intense collagen deposition and scarring.

      3. The ventricle should be filled with blood to act as beam stop and prevent perforation of the posterior ventricular wall or damage to the chordae tendineae of the mitral valve.

      4. Infrared lasers tend to induce more thermal damage to the myocardium surrounding the channels than do ultraviolet lasers.

      5. In addition to thermal injury, mechanical injury occurs through the production of vapor bubbles and the presence of shock waves [70,71].

      6. Free radical molecules also form, which induce cellular injury.

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   C. Mechanisms responsible for clinical benefit

     1. The exact mechanism contributing to improved clinical outcome from TMLR remains controversial.

      2. Endothelialization of the channels has been proposed. However, histopathologic studies have failed to confirm this hypothesis.

      3. Neovascularization in response to laser-induced tissue injury has also been proposed as a mechanism. TMLR may induce the production of vascular angiogenic growth factor–like molecules to result in neovascularization with improved regional collateral blood flow.

      4. A placebo effect has been postulated, but is unlikely to account for the sustained relief of angina demonstrated in some studies.

      5. Sympathetic afferent denervation has been postulated, especially to explain the immediate relief of angina experienced by some patients [72].

      6. Although more studies are necessary, neovascularization and sympathetic denervation are the most likely mechanisms of benefit, and these may occur concurrently.

   D. Patient selection

      1. The largest use of TMLR is as an adjunct to conventional CABG, especially in reoperative CABG patients. TMLR is then used in anatomic regions where complete coronary artery revascularization is infeasible.

      2. TMLR is also indicated in a select group of patients with severe diffuse coronary artery disease who are poor candidates for conventional angioplasty or coronary revascularization. These patients experience anginal symptoms that are either refractory to oral medical therapy or that cannot be weaned from intravenous antianginal medications. These patients must demonstrate reversible ischemia determined by myocardial perfusion scanning and possess an LV ejection fraction greater than 25%.

      3. Additional candidates may include heart transplant recipients who develop severe coronary artery disease as a result of allograft rejection.

      4. Contraindications to TMLR include severely depressed LV ejection fraction, ischemic mitral regurgitation, pre-existing ventricular arrhythmias, ventricular mural thrombus, long-term anticoagulant therapy, and severe chronic obstructive pulmonary disease.

   E. Preoperative evaluation

      1. Preoperative assessment of patients who present for TMLR is similar to that of patients who present for CABG.

      2. Electrocardiography, exercise stress testing, and transthoracic echocardiography (with or without dobutamine stress) are performed to assess arrhythmias, valvular and ventricular function, or the presence of ventricular thrombus in low CO states. Multiple-gated scintigraphic angiography scanning may be utilized to assess ventricular function.

      3. Coronary angiography is performed to determine if the vessels can be grafted, and to decide if TMLR will be performed as an isolated procedure or as an adjunct to CABG.

      4. Myocardial perfusion scanning such as thallium scintigraphy or positron emission tomography is performed to identify areas of viable but ischemic myocardium. These tests also serve as a baseline for comparison of postoperative results.

   F. Anesthetic considerations

     1. Laser safety

        a. The operating room windows and outside doors must be marked with signs that indicate that a laser procedure is occurring.

        b. The patient’s eyes must be protected with moist gauze. In addition, all operating room personnel must wear protective goggles.

14

     2. Preoperative preparation

        a. Patients selected for TMLR present with severe coronary artery disease. In addition, there is a high incidence of coexisting diseases such as diabetes, lung disease, hypertension, prior myocardial infarction, and prior coronary bypass grafts. They require close hemodynamic control with focus on optimizing myocardial oxygen supply and consumption.

        b. Anticoagulant therapy should be discontinued prior to surgery. Antianginal, antiarrhythmic, and pulmonary medications should be continued the morning of surgery.

        c. Adequate venous access is essential as many patients have undergone previous cardiac surgery and bleeding is a significant risk.

        d. These patients are prone to acute ischemic events in the perioperative period. An ECG with computerized ST-segment analysis and trending is often utilized for ischemia detection. PACs are usually placed, as these patients often have poor ventricular function.

        e. The operating room should be warm, with every effort exercised to maintain patient normothermia.

     3. Induction and maintenance of anesthesia

        a. The goals are to maintain hemodynamic stability, facilitate early extubation, and provide reliable postoperative analgesia.

        b. Isolated TMLR is typically performed off-bypass through a left anterior thoracotomy, in which case a double-lumen endobronchial tube or left bronchial blocker is placed to permit left lung collapse in order to avert pulmonary injury from the laser beams. In contrast, combined TMLR and CABG is performed through a median sternotomy on CPB.

        c. A TEE probe is inserted after induction to monitor ventricular function, mitral valve competence, and gaseous bubbles in the LV generated by transmyocardial laser strikes.

        d. For isolated TMLR or repeat sternotomy, external defibrillation patches should be placed on the patient, and the groin should be exposed in preparation for emergency CPB or insertion of IABP.

        e. During combined TMLR and CABG, TMLR is typically performed on the beating heart (e.g., early during CPB) that is relatively full in an attempt to minimize laser channel penetration across the ventricular chamber. TMLR may cause arrhythmias and ventricular distension, in which case the procedure may be delayed until after the administration of cardioplegia.

        f. The laser probe is positioned against the epicardium. The laser is synchronized to the electrocardiogram signal and fired at the peak of the R wave. The laser energy is absorbed by blood in the LV.

        g. Transmyocardial laser channels are confirmed by the detection of ventricular bubbles by TEE and the appearance of bright red blood from the channels.

        h. It may be beneficial to avoid nitrous oxide with its attendant risk of bubble expansion during laser channel creation.

     4. Recovery

        a. For isolated TMLR, the patient may be extubated in the operated room and transported to a telemetry area for postoperative monitoring [73,74].

        b. Recovery for combined TMLR and CABG is similar to CABG.

     5. Complications

15

        a. Patients who present for isolated TMLR experience ongoing myocardial ischemia. There is no immediate physiologic benefit from the procedure; rather there may be ventricular failure, infarction, hypotension, arrhythmias, or hypoxemia related to anesthesia or myocardial manipulation. Laser vaporization can directly damage myocardium and further contribute to myocardial failure.

        b. Vasopressors, inotropes, an IABP, and CPB standby must be available to treat unexpected myocardial failure at any time in the perioperative period.

        c. TMLR may induce atrial and ventricular arrhythmias. This frequently occurs during surgical manipulation of the heart by the surgeon or the laser probe. Ventricular arrhythmias are common during the creation of transmyocardial channels. Gating of the laser to the cardiac cycle has decreased the incidence of ventricular arrhythmias. Direct injury to the Purkinje conduction system may further complicate these arrhythmias.

        d. Direct laser injury to the mitral valve apparatus causing acute mitral regurgitation may precipitate heart failure. This risk is reduced with the use of the holmium laser. A thorough intraoperative TEE exam must be performed following TMLR to diagnose this complication.

        e. Vaporization of myocardium generates bubbles in the LV cavity with a potential risk of stroke.

        f. Hemorrhage may occur secondary to surgical dissection in patients who have previously undergone CABG or from the transmyocardial laser channels. Bleeding from the laser channels can be controlled by digital pressure for isolated TMLR since systemic heparinization is not employed. However, if TMLR is performed during CPB, the risk of bleeding from the laser channels may increase.

     6. Outcome

        a. Ongoing studies continue to examine the benefit from and indications for isolated TMLR and for combined TMLR/CABG [75,76].

        b. As compared to medical therapy in patients with angina refractory to medical treatment or inoperable coronary artery disease, TMLR is associated with symptomatic and functional improvement 12 months after the procedure.

        c. In a recent comparison of patients undergoing CABG alone with those undergoing CABG and TMLR, the latter group had a significantly higher preoperative incidence of diabetes, renal failure, peripheral vascular disease, previous CABG, three-vessel disease, and hyperlipidemia. Despite the increased risk associated with these patients, the mortality rate was not significantly increased when TMLR was added to CABG [77].

     7. Future directions

        a. Percutaneous laser revascularization involving creation of the laser channels from the inside of the heart is under investigation.

        b. Augmentation of the clinical benefits of TMLR by simultaneous delivery of growth factors, gene therapy, or stem cells is under investigation.

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Robotic Surgery

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Transmyocardial Laser Revascularization

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