How to ablate typical atrial flutter

Europace (1999) 1, 151 155 HOW TO... SERIES How to ablate typical atrial flutter A. Takahashi, D. C. Shah, P. Jaïs and M. Haïssaguerre Electrophysiologie Cardiaque, Hopital Cardiologique du Haut-Lévêque, Bordeaux-Pessac, France Introduction Typical atrial flutter, as referred to in this article, includes both the counterclockwise and the clockwise form of cavotricuspid isthmus-dependent right atrial flutter. The counterclockwise form is the most common and characterized by a stereotypical surface ECG pattern showing negative sawtooth flutter waves in II, III and avf at a rate between 200 350 beats.min 1. This surface ECG morphology of counterclockwise typical flutter is remarkably consistent, allowing assumptions about the circuit being entirely within the right atrium and obligatory activation through the cavotricuspid isthmus. However, in contrast, the surface ECG morphology of clockwise flutter is more variable and difficult to distinguish from non-isthmus-dependent flutters. As a result, intracardiac activation mapping and entrainment mapping is often necessary as confirmation. Importantly, since both the clockwise and the counterclockwise forms share the same obligatory cavotricuspid isthmus, a common strategy of ablation is clearly applicable and has been shown to be effective. Methodology The aim of catheter ablation for typical atrial flutter is to create a complete and stable bidirectional cavotricuspid isthmus block, because flutter termination is not enough, and recurrence is likely if isthmus conduction persists. The procedure itself can be subdivided into (a) radiofrequency (RF) delivery and lesion creation (b) identification and filling-in of residual conducting gaps (c) assessment of isthmus conduction (Table 1). RF delivery and lesion creation In our laboratory, we use a standard 4-mm tip electrode for temperature controlled sequential point-by-point RF application, targeted at the isthmus between the inferior vena cava (IVC) and the tricuspid annulus. RF delivery Correspondence: Atsushi Takahashi, Electrophysiologie Cardiaque, Hopital Cardiologique du Haut-Lévêque, Avenue de Magellan, 33604 Bordeaux-Pessac, France. begins at the right ventricular (RV) annulus where a large ventricular electrogram is recorded. To achieve a complete block, as linear and as contiguous a series of point applications as possible needs to be created. This may be facilitated by fluoroscopic monitoring or by non-fluoroscopic methods (e.g. using the Biosense system) of monitoring catheter positioning with or without the use of long introducer sheaths for superior stability. In addition to fluoroscopic monitoring, during counterclockwise flutter, RF is delivered point by point from the tricuspid valve (TV) annulus on electrograms within the isthmus region, coinciding with the centre of the surface ECG flutter wave plateau, all the way from the TV annulus to the IVC edge (Fig. 1). This ensures a lesion perpendicular to the advancing wavefront and catheter displacement to either side can be instantly and nonfluoroscopically recognized by the altered timing of the site electrogram. For example, in case of lateral displacement, the site electrogram now coincides with the beginning of the surface ECG plateau (and with the end of the plateau in case of medial displacement). Recognition of seemingly minor changes in position is certainly facilitated by the naturally lower conduction velocities in this region during flutter. During low lateral right atrial pacing in sinus rhythm, sequential RF is similarly delivered at electrogram sites in the isthmus region, with a constant stimulus electrogram time from the TV annulus to the IVC edge. It is important to recognize, however, that the mere fact of having delivered RF energy at a given point does not ensure a transmural lesion; the efficacy of RF varies according to contact, local blood flow, delivered power and myocardial thickness. During unidirectional activation in atrial myocardium (as for example in the isthmus during typical flutter or during pacing from the low lateral right atrium or the ostium of the coronary sinus), a local transmural RF lesion can be recognized by double potentials separated by an isoelectric interval (Fig. 2). Upon completion of the line of block in the isthmus, however, during pacing from the low lateral right atrium, activation passes around the TV annulus instead of through it, to give rise to the second potential. Thus widely separated double potentials can be recorded all along the line. RF delivery, therefore, should modify local electrograms, to result in double potentials during orthogonal 1099 5129/99/010151+05 r18 00/0 1999 The European Society of Cardiology

152 A. Takahashi et al. Table 1 RF delivery and lesion creation Identification and ablation of residual gap Assessment of isthmus conduction Essential catheters 4 mm ablation catheter (1) Pacing catheter placed at low lateral RA or CS 8 mm ablation catheter (2) Recording catheters (quadripolar or multielectrode) placed at ablation line, lateral RA, His region and CS Essential recording (1) Atrial Single or fractionated atrial electrograms coinciding with the centre of the surface ECG flutter wave plateau during CCW flutter or coinciding with electrogram centered on or spanning the isoelectric interval of adjacent double potentials the initial downslope of the positive flutter wave during CW flutter (2) Atrial electrogram with a constant stimulus electrogram time from the TV annulus to the IVC Optional catheter Irrigated tip ablation catheter for a resistant conducting gap (1) Only clockwise atrial activation sequence during low lateral RA pacing and only counterclockwise atrial activation sequence during CS pacing (2) Parallel double potentials with isoelectric interval all along the ablation line during low lateral RA and CS pacing CW=clockwise; CCW=counterclockwise; RA=right atrium; CS=coronary sinus; TV=tricuspid valve; IVC=inferior vena cava. unidirectional activation, and to this end, power output and/or target temperature need to be manipulated. At one extreme, when power delivery is obviously limited by local temperature (as a result of insufficient perielectrode local blood flow) the use of irrigated or cooled tip catheters, allowing the dissociation of delivered power from the endocardial surface temperatures while avoiding impedance rise, may be helpful [1]. Larger lesions with each application may also shorten the procedure: to this end, 8 mm electrodes, multielectrode catheters, and irrigated tip catheters may be useful (Fig. 3). Figure 1 An electrophysiological strategy to create a complete linear block in the cavotricuspid isthmus during counterclockwise typical flutter. This illustration depicts the technique of mapping and targeting the isthmus so as to create a series of contiguous point lesions. A series of closely spaced point lesions are created by sequentially withdrawing the catheter along a corridor defined by atrial electrograms, coinciding with the centre of the surface ECG flutter wave plateau (top tracing, lead II shown) from the RV (bottom, with a large ventricular electrogram) to the IVC edge (middle tracing, miniscule ventricular electrogram). This ensures that the created lesion is perpendicular to the advancing unidirectional wavefront in the isthmus. As the isochrones indicate during flutter, the wavefront enters the lateral isthmus at 120 ms, the centre of the plateau is at 150 ms and activation at the coronary sinus ostium occurs at 220 ms, with intervening slow conduction depicted by the closely spaced isochrones. As a result of both unidirectional activation and slow conduction in the isthmus, slight displacement of the catheter on either side of the central corridor is easily evident from the concordant change in activation timing of the atrial electrogram (stippled electrograms). CS= coronary sinus; IVC=inferior vena cava; TV=tricuspid valve annulus; V=ventricular electrogram; EC= Eustachian crest. (Reproduced with permission [5].)

Atrial flutter ablation 153 Identification and ablation of residual gaps Because of variations in isthmus anatomy and in the ability of current catheter technology to create consistent transmural lesions, isthmus conduction frequently persists despite apparently sufficient ablation. Locating and ablating residual gaps in the ablation line is therefore necessary. During typical atrial flutter, such residual gaps can be identified by local electrograms with a single or a fractionated potential centred on, or spanning, the isoelectric interval of adjacent double potentials. This has allowed efficient ablation of flutter recurrence after previous ablation [2]. The same approach has been utilized during pacing from either side of the isthmus, targeting single or fractionated potentials adjacent to double potentials and centred on their isoelectric intervals; the aim is to establish a continuous corridor of double potentials with isoelectric intervals across the full width of the isthmus. Figure 2 An electrophysiological strategy of creating a complete linear block in the cavotricuspid isthmus during counterclockwise typical flutter. Completion of a line of block during flutter. A partial line of block is depicted as a filled in black area in the centre, at the 150 ms isochrone beginning from the right ventricular edge of the isthmus. Activation passes through the remaining conducting part of the isthmus (the gap) and curves around antidromically to activate the downstream flank of the lesion after a delay. This results in low amplitude double potentials being recorded on the lesion, characteristically widest at the edge furthest from the gap (in this case, the RV edge). Thus the double potentials narrow towards the gap and a single electrogram at 150 ms coinciding with the surface ECG plateau centre is recorded from this remaining conducting tissue. Transmural ablation at this unique site could complete the line of block. CS=coronary sinus; IVC=inferior vena cava; TV=tricuspid valve annulus; V=ventricular electrogram; EC Eustachian crest. (Reproduced with permission [5].) Assessment of isthmus conduction As indicated earlier, termination of flutter during RF delivery is not a sufficient end-point because it does not result in stable isthmus block [3,4]. Mechanical ectopic induced termination, and/or transient block or conduction slowing within the isthmus are enough to terminate flutter, without, however, eliminating or affecting the substrate. During pacing from one side of the ablation lesion, time to activation on the opposite side and an activation sequence within the right atrium demonstrating a 180 change in direction of activation on the other side, have been used to demonstrate isthmus block. This activation sequence has been documented both sequentially by using mapping and simultaneously with a duodecapolar electrode catheter during low lateral atrial or coronary sinus (CS) pacing. More recently, the achievement of a complete corridor of double potentials, with isoelectric intervals in a parallel configuration from the tricuspid annulus to the inferior vena cava edge, has been effectively used as a more sensitive marker of block in the cavotricuspid isthmus than the indirect indicators described above. Follow up Recurrence rates of flutter have declined (from 44% to 9%) with the use of objective end-points based on assessment of isthmus conduction. In most cases, recurrence represents recovery of isthmus conduction after complete block; thus verification of the stability of achieved block is important. Recurrence is frequently noted within 3 months of the initial procedure and almost always represents the original flutter, though there may be variations in cycle length due to the effects of ablation on conduction or that of drugs. Ablation targeting residual gaps is effective and economical in terms of time in the above situations.

154 A. Takahashi et al. Figure 3 An example of a single discrete gap in the previous ablation line. 1 6 depict electrograms during withdrawal mapping in typical atrial flutter in the IVC-TV isthmus from the RV edge [1] to the IVC edge [6]. Note the widely separated double potentials (straddling the surface ECG flutter wave plateau) with an isoelectric interval of 95 ms in 1 and the gradual narrowing with progressive withdrawal (2 6) until the triple/fractionated potential in 5, followed by reappearance of narrower double potentials in 6 (interspike interval, 65 ms) at the IVC edge. A single RF application at site 5 (*) was successful in terminating flutter and producing bidirectional isthmus block. (Reproduced with permission [2].) Complications The procedure, as described above, is very well tolerated; a few patients require intravenous sedation and or analgesics for pain relief during RF delivery. Few side effects have been reported; and mostly minor ones relate to femoral venous catheterization. One exception is the small but significant risk of atrioventricular block when ablating in the so-called septal isthmus, falling to zero as a more lateral target is selected. In general, the embolic risk, in cases of atrial flutter, has been considered minimal; however, transoesophageal studies have shown a small incidence of atrial thrombi, and some investigators have reported systemic emboli from left atrial thrombi. Ordinarily, of course, the pulmonary circulation filters out thrombi either dislodged or produced during ablation in the right atrium. This may not occur in the presence of a right to left intracardiac shunt. Indications Since the present day ablation procedure is well tolerated, indications have expanded. While non-

Atrial flutter ablation 155 pharmacological therapy was earlier limited to refractory and incapacitated patients with haemodynamic consequences, RF catheter ablation is now offered to more and more patients with symptomatic and at least single drug refractory atrial flutter. It may even legitimately now be considered as alternative first line therapy for all those with symptomatic sustained typical atrial flutter. References [1] Jaïs P, Haïssaguerre M, Shah DC. Successful irrigated-tip catheter ablation of atrial flutter resistant to conventional radiofrequency ablation. Circulation 1998; 98: 835 8. [2] Shah DC, Haïssaguerre M, Jaïs P et al. Simplified electrophysiologically directed catheter ablation of recurrent common atrial flutter. Circulation 1997; 96: 2505. [3] Cauchemez B, Haïssaguerre M. Fischer B, Thomas O, Clémenty J, Coumel P. Electrophysiological effects of catheter ablation of inferior vena cava-tricuspid annulus isthmus in common atrial flutter. Circulation 1996; 93: 284. [4] Poty H, Saoudi N, Aziz AA, Nair M, Letac B. Radiofrequency catheter ablation of type I atrial flutter. Prediction of late success by electrophysiological criteria. Circulation 1995; 92: 1389. [5] Shah DC, Haissaguerre M, Jais P, Clementy J. Atrial flutter: contemporary electrophysiology and catheter ablation. PACE 1999; 22: 344 59.