Mahmoud Houmsse, MD
A 42-year-old man has severe symptoms of palpitations, fatigue, and dyspnea on exertion attributable to frequent premature ventricular contractions (PVCs) and was referred to for ablation of the PVCs after failing medical therapy with a β-blocker and a calcium channel blocker. Surface echocardiography found no structural heart disease and normal left ventricular ejection fraction (LVEF). A 24-hour Holter monitor showed 31% unifocal PVCs, with a morphology of right bundle, inferior axis, with presence of Q waves in lead aVL and I (Figure 24-1), suggestive of an epicardial origin. The hemodynamic impact of the PVCs is reflected by the absent cardiac output with each PVC, thus the effective heart rate is 35 bpm (Figure 24-2). The maximal deflection index (MDI), calculated by dividing the maximum deflection of the PVC complex in precordial leads by the PVC duration,1 is prolonged (>0.55) (Figure 24-3). Pseudo-delta waves in precordial leads are another feature of an epicardial origin of the PVC2-4(Figure 24-3). At electrophysiologic testing, there was no inducible supraventricular or ventricular tachycardia. Mapping of the PVC began in the left ventricle and then aortic cusp, but there was no early presystolic electrocardiogram (EGM) or optimal pace-mapping in any of these regions. It was then attempted to map the coronary sinus (CS); however, multiple manual catheter manipulations to cannulate the CS were unsuccessful. Therefore, it was decided to utilize remote magnetic navigation to access the CS ostium (Figure 24-4). This process was achieved by positioning the remote navigation mapping catheter at the infero-medial aspect of tricuspid annulus, and then a posterolateral vector navigated the catheter into the CS os with successful access, which was confirmed by the typical EGM of the CS. Further superior then anterior vector via the magnets allowed navigation of the mapping catheter to be smoothly advanced into the CS system. Electroanatomic mapping in the distal CS disclosed the earliest presystolic EGM of 31 milliseconds (ms) (Figure 24-5) and 12/12-pace map match (Figure 24-6). In the CS, the catheter impedance was quite high (170-180 Ω) consistent with the catheter wedged within the CS. The impedance was too elevated to use a conventional ablation catheter, so an irrigated catheter was used, and power was limited to a maximum of 20 watts. There was the expected drop in impedance during delivery of the RF current, and the PVC source was eliminated (Figure 24-7). During follow up, the patient had significant improvement in his symptoms, and the PVC burden on the postablation 24-hour Holter monitor was only 1.3%.
FIGURE 24-1 Baseline 12-lead ECG. Sinus rhythm with unifocal PVCs in a pattern of bigeminy.
FIGURE 24-2 Arterial pressure recording during bigeminy. The absent cardiac output with the PVCs reflects the hemodynamic impact of frequent PVCs and that the effective heart rate is only about 35 bpm.
FIGURE 24-3 Assessment of maximal deflection index (MDI) and pseudo-delta wave. Duration of the PVC complex in V5 = 134 ms (red line to red line); duration of maximum deflection, V5 = 76 ms (first red line to dashed blue line), thus the maximum deflection index = 76/134 = .57. The pseudo-delta wave is denoted by red arrows in V6. The upstroke of the PVC is slowed, as if the activation is due to conduction over an accessory pathway, yet this ECG pattern is due to slow conduction when the ectopic beat originates from the epicardium and conducts toward the endocardium with late involvement of the His-Purkinje system.
FIGURE 24-4 Fluoroscopic image of catheters during ablation procedure. HRa = quadripolar catheter in the high rate atrium catheter; Abl = magnetic-guided irrigated-tip ablation catheter; His = quadripolar catheter in the His position; RVa = quadripolar catheter in the right ventricular apex. (A) Anterior-posterior fluoroscopic image of the magnetic-guided irrigated-tip ablation catheter (Abl) in the right atrium. (B) Left anterior oblique (LAO) fluoroscopic image of the irrigated-tip ablation catheter (Abl), advanced using remote magnetic navigation, into the distal coronary sinus.
FIGURE 24-5 Pace-map of the PVC when pacing from the ablation catheter at the distal coronary sinus. Twelve-lead ECG: pace-mapping and spontaneous PVC from distal coronary sinus, 12/12 pace-map match.
FIGURE 24-6 LAO image of electroanatomic map of PVC, including right ventricle (RV), left ventricle (LV), and the distal coronary sinus (CS). Successful ablation site of PVC denoted by red dots.
FIGURE 24-7 Immediately postablation, the 12-lead ECG shows sinus rhythm without PVCs (top) and the immediate hemodynamic improvement noted by the change in the arterial pressure line (bottom).
EPIDEMIOLOGY OF EPICARDIAL IDIOPATHIC PVCs
Diagnosis of idiopathic PVCs or ventricular tachycardia (VT) is feasible only after excluding structural heart disease. In the United States, 10% of VTs are idiopathic.5 The majority of patients with idiopathic PVCs will undergo electrophysiologic testing and attempt at radiofrequency ablation because of either symptomatic high burden PVCs with normal heart function,6 or ineffective antiarrhythmic therapy or tachycardia-induced cardiomyopathy,7 which has been reported to reverse by elimination of a high burden of PVCs.8
ELECTROCARDIOGRAPHIC CRITERIA OF IDIOPATHIC EPICARDIAL PVCs
Numerous studies have described the electrocardiographic features, pharmacologic intervention, and electrophysiologic mapping and ablation of epicardial PVC/VT.5,9-12 Electrocardiographic criteria of epicardial left ventricular origin include:
• Prolonged maximum deflection index (MDI) (Figure 24-3)—more than 0.55 is an important predictor of epicardial LVT arising from perivascular origin.1
• Pseudo-delta wave pattern noted with the PVC morphology (Figure 24-3)2—related to slower activation that originates from the epicardium toward the endocardium and late involvement of the His-Purkinje conduction system.3,4
The common approach to mapping a presumed left ventricular tachycardia is to first complete endocardial mapping and then to map the aortic cusp and coronary sinus of Valsalva, followed by the CS.13,14 If these sites have poor mapping criteria, then mapping of the epicardium is completed via percutaneous epicardial access.12
REMOTE MAGNETIC NAVIGATION ABLATION OF EPICARDIAL PVCs
Mapping and ablation of epicardial PVC/VT arising from perivascular origin via CS system has been successfully completed even in patients with history of cardiac surgery.15 Open-irrigated tip radiofrequency catheter ablation is utilized because of high impedance within the CS and has been demonstrated, as in our case, to be successful and safe, including unusual sites like the anterior interventricular coronary vein.16,17 CS venous system access is an important step to be performed when mapping idiopathic PVC, especially if ECG criteria are suggestive for epicardial origin. However, access of the CS system can be difficult with manual manipulation. Lack of access to the CS can then result in extra, unnecessary steps, including mapping of the left ventricular endocardium and aortic cusp via femoral artery puncture, with the associated risk of arterial access and catheter manipulation in the left heart. Also, the operator may then decide to cannulate the epicardial space via percutaneous pericardial puncture. Therefore, the additional effort to cannulate and map the CS, including use of a remote navigation system, is quite important. Also, remote magnetic navigation system offers other advantages over manual manipulation including catheter stability, meticulous detailed mapping, and reduced fluoroscopy.18,19
Delivery of RF current within the CS system requires careful attention to power and impedance. Because of high impedance within the CS, the power is quite limited when using conventional nonirrigated RF catheters. Therefore, the ablation catheter to use within the CS is an irrigated-tip, which will cool the tip-myocardium interface, allowing delivery of RF current without further increase in impedance. The suggested settings are to start at low energy (15 watts) and high flow rates of 20 to 30 cc/minute, and to titrate up the power with close monitoring of impedance changes, reduction in EGM amplitude, and elimination of the PVC source. If RF ablation with an irrigated-tip catheter is not successful or limited, then an alternative is cryoablation.20,21
Idiopathic left ventricular outflow tract PVC that is most likely arising from a perivascular origin is best mapped first endocardially, then via the CS venous system. When manual manipulation fails, remote magnetic navigation facilitates an access of the CS as well as stability of the RF ablation catheter. Because of the unique CS anatomy and ablation within a venous structure, an irrigated-tip ablation catheter should be utilized using low energy and high irrigation flow rate, with increase in energy until achieving the desired result.
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