Color Atlas and Synopsis of Electrophysiology, 1st Ed.

43. ISTHMUS-DEPENDENT ATRIAL FLUTTER

Thomas McGarry, MD, and Gregory K. Feld, MD

CASE PRESENTATION

The patient, a 65-year-old retired physician, presented to our institution for evaluation of recurrent palpitations. The patient had a history of typical atrial flutter (AFL) documented by electrocardiogram (ECG) on several previous occasions (Figure 43-1A), including several emergency department visits during which he had undergone cardioversion. After failure of antiarrhythmic therapy, the patient underwent electrophysiology study (EPS) and cavotricuspid isthmus (CTI) ablation at another institution, in an attempt to cure the atrial flutter. The initial EPS confirmed the mechanism of typical AFL, but attempted ablation of the CTI was unsuccessful in producing bidirectional CTI conduction block. The patient continued to have recurrent palpitations and presented to our institution for further evaluation with an ECG showing a slightly modified flutter pattern suggesting an atypical AFL (Figure 43-2A). Repeat EPS with three-dimensional (3-D) electroanatomical mapping in this case demonstrated incomplete CTI ablation with a large area of low voltage (ie, <0.5 mV) due to scarring in the CTI from prior ablation, but with persistent CTI conduction along a rim of viable myocardium near the tricuspid valve annulus, resulting in reinducibility of typical AFL (Figure 43-2B). Additional ablation of the CTI near the tricuspid valve annulus terminated AFL (Figure 43-3), and eliminated further clinical recurrences in this patient.

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FIGURE 43-1 (A) A 12-lead ECG recorded during typical AFL, with typical saw-toothed pattern of inverted F waves in the inferior leads II, III, and aVF. (B) A 12-lead ECG recorded during reverse typical AFL, with atypical F wave pattern in the inferior leads. (Reproduced with permission from Feld GK, Srivatsa U, Hoppe B. Ablation of isthmus dependent atrial flutters. In: Huang SS, Wood MA, eds. Catheter Ablation of Cardiac Arrhythmias. Philadelphia, PA: Elsevier; 2011.)

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FIGURE 43-2 (A) A 12-lead ECG recorded during AFL following initial CTI ablation attempt. Note the biphasic F waves in the inferior leads II, III, and aVF, an atypical AFL pattern suggesting possible non–isthmus-dependent AFL. (B) During EPS a CARTO map of induced atrial flutter demonstrates an area of scarring (grey area) throughout the CTI near the Eustachian ridge, but continued activation of the CTI near the tricuspid valve annulus in a counterclockwise direction producing typical AFL. Color red = earliest activation, color purple = latest activation, reference coronary sinus electrogram. [(B) Reproduced with permission from Feld GK, Birgersdotter-Green U, Narayan S. Diagnosis and ablation of typical and reverse typical (type 1) atrial flutter. In: Wilber D, Packer D, Stevenson W, eds. Catheter Ablation of Cardiac Arrhythmias: Basic Concepts and Clinical Applications. 3rd ed. Oxford, England: Blackwell Publishing; 2007:173-192.]

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FIGURE 43-3 Surface ECG leads I, aVF, and V1 and endocardial electrograms from the coronary sinus catheter (CSP-D), the ablation catheter (CARTO P&D), and power, impedance, and temperature readouts, show termination of AFL and restoration of sinus rhythm immediately after initiating ablation near the tricuspid valve annulus.

ELECTROPHYSIOLOGIC MECHANISMS OF ISTHMUS-DEPENDENT (TYPICAL AND REVERSE TYPICAL) ATRIAL FLUTTER

Electrophysiologic studies have shown typical and reverse typical AFL to be due to counterclockwise (typical) or clockwise (reverse typical) macroreentry around the tricuspid valve annulus (Figure 43-4, left and right), with an area of slow conduction in the CTI accounting for one-third to one-half of the AFL cycle length.1-10 The CTI is bounded by the inferior vena cava and Eustachian ridge posteriorly and the tricuspid valve annulus (TVA) anteriorly (see Figure 43-4, left and right), forming barriers delineating a protected zone in the reentry circuit.5,11-13 Lines of block, including the Eustachian ridge and the crista terminalis, along which double potentials are typically recorded during AFL (Figure 43-5A and B), are necessary to establish an adequate path-length for reentry to be sustained and to prevent short circuiting of the reentrant circuit.12-14

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FIGURE 43-4 Schematic diagrams demonstrating right atrial activation patterns in typical (left) and reverse typical (right) forms of CTI-dependent AFL. In typical AFL, reentry occurs in a counterclockwise direction around the tricuspid valve annulus (TVA), whereas in reverse typical AFL reentry is clockwise. The Eustachian ridge (ER) and crista terminalis (CT) form lines of block, and an area of slow conduction (wavy line) is present in the CTI between the inferior vena cava (IVC) and Eustachian ridge and the tricuspid valve annulus. Abbreviations: CS, coronary sinus ostium; His, His bundle, SVC, superior vena cava. (Reproduced with permission from Feld GK, Srivatsa U, Hoppe B. Ablation of isthmus dependent atrial flutters. In: Huang SS, Wood MA, eds. Catheter Ablation of Cardiac Arrhythmias. Philadelphia: Elsevier; 2011.)

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FIGURE 43-5 (A) Schematic diagram demonstrating where double potentials (x, y) are recorded during typical AFL along the Eustachian ridge and crista terminalis. (B) Double potentials recorded from an ablation catheter (RFp&d) positioned at the Eustachian ridge during typical AFL. Abbreviations: I, aVF, V1, surface ECG leads; RFp&d, proximal and distal bipolar recordings from the ablation catheter; CSp-d, proximal to distal CS electrogram recordings; RV, right ventricular electrogram recording. (Reproduced with permission from Feld GK, Srivatsa U, Hoppe B. Ablation of isthmus dependent atrial flutters. In: Huang SS, Wood MA, eds. Catheter Ablation of Cardiac Arrhythmias. Philadelphia: Elsevier; 2011.)

Slow conduction in the CTI may be caused by anisotropic fiber orientation, predisposing it to development of unidirectional block during rapid activation.2,8-10,15-19 The predominate clinical presentation of isthmus-dependent AFL is typical AFL, likely triggered by premature atrial contractions originating from the left atrium (LA) or nonsustained atrial fibrillation (AF),20 both of which result in clockwise unidirectional block in the CTI and initiation of counterclockwise macroreentry.

ECG PATTERNS OF TYPICAL (AND REVERSE TYPICAL) ATRIAL FLUTTER

In typical AFL, there is a characteristic inverted saw-tooth F wave pattern in the inferior leads II, III, and aVF. In reverse typical AFL, in contrast, the F wave pattern on the 12-lead ECG is less specific, often with a sine wave pattern in the inferior ECG leads (Figure 43-1A and B). The F wave pattern on ECG is dependent in part on the activation sequence of the LA, with inverted F waves in the inferior leads in typical AFL the result of activation of the left atrium initially near the coronary sinus (CS), and upright F waves in the inferior leads in reverse typical AFL resulting from activation of the LA near Bachman bundle.21,22 However, following LA ablation, and even right atrial ablation as in this case, the ECG presentation of isthmus-dependent AFL may be significantly different from the characteristic patterns described above.23

STANDARD CATHETER MAPPING OF ISTHMUS- DEPENDENT ATRIAL FLUTTER

Despite the characteristic 12-lead ECG pattern, electrophysiologic mapping and entrainment must be performed prior to radiofrequency catheter ablation of AFL. For standard catheter mapping, multielectrode catheters are typically positioned in the right atrium (RA), His bundle region, CS, and around the TVA (Figure 43-6). Recordings obtained during AFL (ie, spontaneous or induced) are then analyzed to determine the RA activation sequence. Typical or reverse typical AFL is confirmed by observing a counterclockwise or clockwise activation pattern in the RA around the TVA, respectively, (Figures 43-7Aand B) and demonstration of concealed entrainment during pacing from the CTI (Figures 43-8 A and B).5

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FIGURE 43-6 Left anterior oblique (LAO) and right anterior oblique (RAO) fluoroscopic projections showing common intracardiac positions of the right ventricular (RV), His bundle (HIS), coronary sinus (CS), Halo (HALO), and mapping/ablation catheters (RF). (Reproduced with permission from Feld GK, Srivatsa U, Hoppe B. Ablation of isthmus dependent atrial flutters. In: Huang SS, Wood MA, eds.Catheter Ablation of Cardiac Arrhythmias. Philadelphia: Elsevier; 2006:195-218.)

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FIGURE 43-7 Endocardial electrograms from the mapping/ablation, Halo, CS, and His bundle catheters, and surface ECG leads I and aVF, during typical AFL (A) and reverse typical AFL (B). The atrial cycle length was 256 ms for both, and the arrows demonstrate the activation sequence. Abbreviations: CSP, electrograms recorded from the CS ostium; HISP, electrograms recorded at the proximal His bundle; RF, electrograms recorded from the mapping/ablation catheter in the CTI. (Reproduced with permission from Feld GK, Srivatsa U, Hoppe B. Ablation of isthmus dependent atrial flutters. In: Huang SS, Wood MA, editors. Catheter ablation of cardiac arrhythmias. Philadelphia: Elsevier; 2011.)

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FIGURE 43-8 Endocardial electrograms from the RF, Halo, CS, and His bundle catheters, and surface ECG leads I, aVF, and V1, demonstrating concealed entrainment during pacing at the CTI in typical AFL (A) and reverse typical AFL (B). Abbreviations: Halo D-Halo P, bipolar electrograms from the distal to proximal poles of the Halo catheter around the TVA; CSP-D, bipolar electrograms recorded from the proximal to distal CS catheter electrode pairs; HISP&D, bipolar electrograms recorded from the proximal and distal His bundle catheter; RFAP&D, bipolar electrograms recorded from the proximal and distal electrode pairs of the mapping/ablation catheter at the CTI. (Reproduced with permission from Feld GK, Srivatsa U, Hoppe B. Ablation of isthmus dependent atrial flutters. In: Huang SS, Wood MA, editors. Catheter ablation of cardiac arrhythmias. Philadelphia: Elsevier; 2011.)

RADIOFREQUENCY CATHETER ABLATION OF TYPICAL ATRIAL FLUTTER

Radiofrequency catheter ablation (RFCA) of isthmus-dependent AFL is performed with a steerable mapping/ablation catheter positioned across the CTI via a femoral vein.3,5-7,24-26 Catheters with either saline-irrigated ablation electrodes (Thermocool Classic or SF, Biosense Webster, Inc, Diamond Bar, CA, or Chili, Boston Scientific, Inc., Natick, MA), or large distal ablation electrodes (ie, 8-10 mm Blazer, Boston Scientific, Inc, Natick, MA) are preferred for CTI ablation.27,29,30-33

The preferred target for isthmus-dependent AFL ablation is the CTI (Figure 43-9A).3,5-7,24-30,32,33 The ablation catheter is positioned across the CTI (Figure 43-6) with the ablation electrode near the TVA, midway between the septum and RA free wall, in order to record an atrial-to-ventricular electrogram amplitude ratio of 1:2 to 1:4 (Figure 43-6). The ablation catheter is then withdrawn a few millimeters at a time, pausing for 30 to 60 seconds at each location during a continuous or interrupted RF energy application. The catheter should be withdrawn until the ablation electrode records no atrial electrogram or until it is noted to abruptly slip off the Eustachian ridge. Radiofrequency energy application should be immediately interrupted when the catheter reaches the inferior vena cava, since ablation in venous structures may cause significant pain.

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FIGURE 43-9 (A) A schematic diagram of the right atrium demonstrating the potential targets for ablation of CTI-dependent AFL. The preferred target for ablation is the CTI. (B) Surface ECG and endocardial electrogram recordings during ablation of the CTI showing termination of AFL. Abbreviations: I, aVF, V1, surface ECG leads; RFAP, proximal ablation electrogram; Hisp&d, proximal and distal His bundle electrograms; CSd-p, distal to proximal CS electrograms; Halo d-p, distal to proximal Halo catheter electrograms (Reproduced with permission from Feld GK, Srivatsa U, Hoppe B. Ablation of isthmus dependent atrial flutters. In: Huang SS, Wood MA, editors. Catheter ablation of cardiac arrhythmias. Philadelphia: Elsevier; 2011.)

PROCEDURE END POINTS FOR RADIOFREQUENCY CATHETER ABLATION OF TYPICAL ATRIAL FLUTTER

Ablation may be performed during AFL or sinus rhythm. If performed during AFL, the first end point is its termination (Figure 43-9B). After CTI ablation, electrophysiologic testing is required to ensure the presence of bidirectional conduction block (Figures 43-10A and B and 43-11A and B), which is confirmed by demonstrating a strictly cranial-to-caudal activation sequence in the contralateral RA, and widely spaced double potentials (ie, usually ≥120 ms apart) along the ablation line, during pacing from the low lateral right atrium and CS ostium, respectively (Figure 43-12).34-38 Electrophysiologic testing should be repeated up to 30 to 60 minutes after ablation to ensure that bidirectional CTI block persists, and that AFL cannot be reinduced, in order to significantly lower the risk of recurrent AFL during long-term follow-up.3,5-7,24-28,30-36,39-40

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FIGURE 43-10 (A) A schematic diagram of the expected right atrial activation sequence during pacing in sinus rhythm from the CS ostium before (left) and after (right) ablation of the CTI. Abbreviations: CT, crista terminalis; ER, Eustachian ridge; His, His bundle; IVC, inferior vena cava; SVC, superior vena cava. (B) Surface ECG and right atrial endocardial electrograms recorded during pacing in sinus rhythm from the CS ostium before (left) and after (right) CTI ablation. (Reproduced with permission from Feld GK, Srivatsa U, Hoppe B. Ablation of isthmus dependent atrial flutters. In: Huang SS, Wood MA, editors. Catheter ablation of cardiac arrhythmias. Philadelphia: Elsevier; 2011.)

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FIGURE 43-11 (A) A schematic diagram of the expected right atrial activation sequence during pacing in sinus rhythm from the low lateral right atrium before (left) and after (right) ablation of the CTI. Abbreviations: CT, crista terminalis; ER, Eustachian ridge; His, His bundle; SVC, superior vena cava; IVC, inferior vena cava. (B) Surface ECG and right atrial endocardial electrograms recorded during pacing in sinus rhythm from the low lateral right atrium before (left) and after (right) ablation of the CTI. (Reproduced with permission from Feld GK, Srivatsa U, Hoppe B. Ablation of isthmus dependent atrial flutters. In: Huang SS, Wood MA, editors. Catheter ablation of cardiac arrhythmias. Philadelphia: Elsevier; 2011.)

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FIGURE 43-12 Surface ECG leads I, aVF, and V1, and endocardial electrograms from the CS sinus, His bundle, Halo, mapping/ablation (RF), and right ventricular (RV) catheters during ablation of the CTI while pacing from the CS ostium. Note the change in activation sequence in the lateral right atrium on the Halo catheter from bidirectional to unidirectional, indicating development of clockwise block in the CTI. This was associated with development of widely spaced (170 ms) double potentials (x and y) on the RF catheter along the ablation line, confirming medial to lateral conduction block. All abbreviations are the same as in previous figures. (Reproduced with permission from Feld GK, Srivatsa U, Hoppe B. Ablation of isthmus dependent atrial flutters. In: Huang SS, Wood MA, editors. Catheter ablation of cardiac arrhythmias. Philadelphia: Elsevier; 2011.)

OUTCOMES AND COMPLICATIONS OF CTI ABLATION FOR ISTHMUS-DEPENDENT ATRIAL FLUTTER

Although early reports of RFCA for AFL revealed recurrence rates up to 20% to 45%, subsequent studies have demonstrated acute and chronic efficacy in excess of 95% (Table 43-1), although patients with complex CTI anatomy may have higher recurrence rates in long-term follow-up.41 Randomized comparisons of internally cooled, externally cooled, and large-tip ablation catheters, suggest a slightly better acute and chronic success rate with externally cooled ablation catheters, compared to internally cooled or large-tip ablation catheters.27,28,30,33,40,42

TABLE 43-1 Success Rates for Radiofrequency Catheter Ablation of Atrial Flutter

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Radiofrequency catheter ablation for typical AFL is relatively safe, but serious complications can occur, including AV block, cardiac perforation, pericardial tamponade, and thromboembolic events, including pulmonary embolism and stroke. In recent large-scale studies, including those using large-tip ablation catheters and high power generators, major complications have been observed in only 2.5% to 3.0% of patients.32,33,40

ALTERNATIVE ENERGY SOURCES FOR ABLATION OF TYPICAL ATRIAL FLUTTER

Alternate energy sources for CTI ablation are being studied due to the disadvantages of RFCA, including pain, risk of coagulum formation and embolization, tissue charring, and subendocardial steam pops resulting in perforation. Several studies have been published on cryoablation and microwave ablation of AFL.43-46 Cryoablation of isthmus-dependent AFL can achieve results similar to RFCA.43,44Cryoablation produces less pain during ablation and does not cause tissue charring or coagulum formation, or steam pops.43,44 In addition, the CTI may be ablated with microwave energy (Medwaves, Inc., San Diego, CA) using a catheter-mounted antennae with lengths up to 4 cm.45,46Microwave ablation might reduce procedure time considering the length of the electrodes that can effectively ablate tissue.45,46

COMPUTERIZED 3-D MAPPING AND INTRACARDIAC ECHOCARDIOGRAPHY (ICE) GUIDANCE FOR CTI ABLATION

Three-dimensional (3-D) electroanatomical activation mapping systems (CARTO, BioSense-Webster, Diamond Bar, CA, and ESI NavX, St. Jude, Inc., St. Paul, MN) and noncontact balloon (Ensite, St. Jude, Inc., St. Paul, MN), although not required for isthmus-dependent AFL ablation, are now widely used. Although it is not within the scope of this chapter to describe the technological basis of these systems in detail, there are unique characteristics of each system that make them more or less suitable for mapping and ablation of atrial flutter.

A 3-D mapping system may be particularly useful in difficult cases such as those where prior ablation has failed, similar to the case described herein (Figure 43-2B), those with complex CTI anatomy, or those with surgically corrected congenital heart disease such as an atrial septal defect. Voltage mapping, alone or in combination with activation mapping, may also be helpful to identify areas of thinner muscle in the CTI that may be more easily ablated. Following CTI ablation, 3-D mapping may also be used to confirm CTI block, when pacing from the proximal CS catheter electrodes (Figure 43-13) or the low lateral right atrium. ICE may also be used to identify anatomical variations in the CTI, such as a wide or thickened CTI or deep pouches in the CTI that may make ablation difficult using standard techniques. Visualization of these anatomical variations with ICE may allow their avoidance or better catheter contact with the CTI, increasing the acute and long-term success rates of ablation (Figure 43-14).

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FIGURE 43-13 A 3-D electroanatomical (CARTO) map of the right atrium is shown in a patient with typical AFL after CTI ablation. Following ablation of the CTI, during pacing from the coronary sinus ostium, there is evidence of medial-to-lateral isthmus block as indicated by juxtaposition of orange and purple color in the CTI, indicating early and late activation, respectively. (Reproduced with permission from Feld GK, Birgersdotter-Green U, Narayan S. Diagnosis and Ablation of Typical and Reverse Typical (Type 1) Atrial Flutter. In: Catheter Ablation of Cardiac Arrhythmias: Basic Concepts and Clinical Applications, 3rd Edition, Wilber D, Packer D, Stevenson W, eds., Blackwell Publishing, Oxford, England, pp:173-192, 2007.)

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FIGURE 43-14 Intracardiac echo (ICE) image of a deep pouch preventing complete CTI ablation using a standard approach, due to difficulty in achieving adequate contact between the ablation catheter tip and the CTI in the pouch near the Eustachian ridge (ER). Positioning the ablation catheter in the CTI under ICE guidance, with a reverse curl from the inferior vena cava, such that the ablation electrode was just beneath the ER resulted in improved catheter-tissue contact with complete CTI ablation and bidirectional conduction block. Abbreviations: CTI, cavotricuspid isthmus; RF, radiofrequency; TVA, tricuspid valve annulus.

ATYPICAL FORMS OF ISTHMUS-DEPENDENT ATRIAL FLUTTER

In lower loop reentrant AFL, the activation wave front spreads through the crista terminalis and around the inferior vena cava through the CTI (Figure 43-15A). This is in contrast to typical AFL, where the crista terminalis behaves as a line of block, albeit functional in most cases. The diagnosis of lower loop reentrant AFL is confirmed by the demonstration of concealed entrainment of the tachycardia from not only the CTI but also the inferior-posterior right atrium.47 In lower loop reentry, the posterior right atrium is part of the reentry circuit, and wave fronts collide in the lateral right atrium47 (Figure 15B). Lower loop reentrant AFL may be slowed or terminated by ablation posteriorly along the crista terminalis from the superior vena cava to the inferior vena cava, but will usually convert to typical AFL and require CTI ablation for cure.

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FIGURE 43-15 A CARTO 3-D activation sequence map (posterior caudal view) is shown in a patient with lower loop reentry. Note that the activation wave front spreads counterclockwise in the right atrium and horizontally across the crista terminalis between two (superior and inferior) areas of scarring in the posterior right atrial wall. Ablation between the scarred areas converted this atypical AFL into a typical AFL, which was ablated at the CTI. Abbreviation: IVC, inferior vena cava. (Reproduced with permission from Feld GK, Birgersdotter-Green U, Narayan S. Diagnosis and Ablation of Typical and Reverse Typical (Type 1) Atrial Flutter. In: Catheter Ablation of Cardiac Arrhythmias: Basic Concepts and Clinical Applications, 3rd Edition, Wilber D, Packer D, Stevenson W, eds., Blackwell Publishing, Oxford, England, pp:173-192, 2007)

In partial isthmus-dependent AFL, the wave front bypasses the (CTI) to enter it laterally and medially in opposite directions, with collision of wave fronts near the middle of the CTI48 (Figure 43-16). Partial isthmus-dependent AFL is confirmed by the demonstration of concealed entrainment from the lateral margin of the CTI but not from the medial portion near the tricuspid valve.48 In addition, there is early activation of the CS ostium and evidence of collision with double potentials recorded within the medial CTI.48 Cure of partial isthmus-dependent AFL can be achieved by ablation at the lateral CTI.

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FIGURE 43-16 Electrograms and schematic representation of atrial activation in lower loop reentry and partial isthmus-dependent flutter. (A) In lower loop reentry, the posterior right atrium is part of the reentry circuit and wave fronts collide in the lateral right atrium. The electrograms show multiple collisions at TA1 and TA8 (stars). (B) In partial isthmus-dependent flutter, the wave front bypasses the cavotricuspid isthmus (CTI) to enter it laterally and medially. The coronary sinus (CS) ostium is activated prematurely, and the tachycardia is not entrained from the CTI itself. Abbreviations: IVC, inferior vena cava; SVC, superior vena cava; TA10, proximal recording electrodes on Halo catheter near upper septum; TA1, distal recording electrodes on Halo catheter near lateral aspect of the CTI. (Reproduced with permission from Yang Y, Cheng J, Bochoeyer A, et al. Atypical right atrial flutter patterns. Circulation 2001;Jun 26;103(25):3092-3098.)

SIMPLIFIED APPROACH TO ABLATION OF TYPICAL (AND REVERSE TYPICAL) AFL

We have developed a simplified approach for CTI ablation in patients with isthmus-dependent AFL, using only two catheters. CTI ablation can be rapidly achieved with minimal fluoroscopy time using this approach. After percutaneous insertion via the right femoral vein, a steerable decapolar catheter is positioned in the CS with the proximal electrode pair at the ostium near the medial CTI, and an ablation catheter is flexed in the low lateral right atrium with the distal pair near the lateral CTI (Figure 43-17A). Pacing from the proximal CS and the ablation catheter demonstrates bidirectional CTI conduction before and block after CTI ablation (Figure 43-17B and C). Using this simplified catheter approach, medial to lateral CTI conduction block is defined by both the presence of a high to low (ie, proximal to distal) activation sequence on the ablation catheter during pacing from the proximal CS, and by equal conduction times (ie, >130 ms) from medial to lateral and from lateral to medial, during pacing from the proximal CS and low lateral RA, respectively. In addition, pacing from the proximal CS with the ablation catheter positioned on the ablation line will demonstrate widely spaced double potentials (Figure 43-17D).

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FIGURE 43-17 (A) Left anterior oblique fluoroscopic projection showing the positions of the CS and ablation catheter after CTI ablation to demonstrate conduction block. The proximal CS catheter electrode is positioned near the CS ostium, and the ablation catheter is positioned at the lateral CTI. (B) Surface ECG and endocardial electrogram recordings during pacing from the proximal CS demonstrating a proximal to distal (high to low) activation sequence on the ablation catheter with a conduction time of 136 ms confirming medial to lateral CTI conduction block. Abbreviations: I, aVF, V1, surface ECG leads; RFd&p, distal and proximal ablation catheter electrograms; CSd-p, distal to proximal CS electrograms. (C) Surface ECG and endocardial electrogram recordings during pacing from the ablation catheter at the low lateral right atrium demonstrating a conduction time to the proximal CS of 138 ms, similar to the medial to lateral conduction time, confirming lateral to medial CTI conduction block. Abbreviations same as in Figure 43-16B. (D) Surface ECG and endocardial electrogram recordings during pacing from the proximal CS demonstrating widely spaced (130 ms) double potentials (x and y) at the ablation line, confirming medial to lateral conduction block. Abbreviations same as in previous figures. (Reproduced with permission from Sawhney NS, Wayne Whitwam W, Feld GK. Mapping of Human Atrial Flutter and Its Variants, In: Cardiac Mapping, 4th Edition, Shenasa M, Hindricks G, Borggrefe M, Briethardt G, eds., Wiley-Blackwell, Hoboken, NJ, 2012, pp: 191-212.)

SUMMARY

Mapping of isthmus-dependent AFL can be performed using standard catheter techniques, allowing one to make an accurate diagnosis that will result in successful ablation. Computerized 3-D activation mapping is an adjunctive method, which, while not mandatory, may have significant advantages in some cases resulting in improved success rates overall. Radiofrequency catheter ablation has become a first-line treatment for AFL with nearly uniform acute and chronic success and low complication rates. Currently, the use of large-tip or irrigated ablation catheters is recommended for optimal success. Alternate energy sources including cryoablation and microwave ablation are under investigation with the hope of further improving procedure times and success rates and potentially reducing the risk of complications during AFL ablation.

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