Catheter Ablation of Left Atrial Flutter Occurring Late After Surgical Maze

Introduction

Atrial flutter is a common macroreentrant atrial tachyarrhythmia. Typical atrial flutter, where the reentrant circuit involves the cavotricuspid isthmus and circles counter- clockwise around the crista terminalis, is the most common form of atrial flutter, particularly in patients with no prior interventions. Atypical atrial flutter, in which the macroreentrant circuit involves another location in either atrium, most commonly involves reentry around a scar from prior surgery, catheter ablation, or congenital heart disease. As the atypical atrial flutter reentry circuit may involve various locations in either atrium, mapping the activation of the flutter circuit is important to confirm that ablation is being performed at an isthmus involved in the circuit.

Also, because the same substrate can give rise to multiple flutters, stimulating the atria to ensure that other atypical flutters are not inducible is important prior to completing the procedure. We describe a case of a patient with atypical atrial flutter which developed after a maze procedure that demonstrates the importance of a systematic approach to mapping and ablating atypical atrial flutter to prevent a recurrence of symptomatic arrhythmia.

Case Presentation

A 68-year-old man presented with worsening shortness of breath on exertion. He had a history of severe myxomatous degeneration of the mitral valve, resulting in severe valvular regurgitation requiring mitral valve replacement with a 31 mm pericardial prosthetic valve at age 63. At the time of his valve surgery, the left atrial appendage was removed and a Cox III maze procedure was performed because he also had paroxysmal atrial fibrillation. He developed atypical atrial flutter that was initially refractory to cardioversion, and so he was discharged on warfarin, amiodarone, and metoprolol. After completing the amiodarone load, he was successfully cardioverted. Atypical atrial flutter recurred, and the patient was cardioverted again after 3 months of amiodarone. After 3 months of maintaining sinus rhythm, amiodarone was discontinued. He remained in sinus rhythm for 3.5 years, and then presented again with dyspnea on exertion, and was again found to be in atypical atrial flutter, as shown in Figure 1. Anticoagulation was reinitiated upon the discovery of a right atrial thrombus, and he was scheduled for atrial flutter ablation after repeat transesophageal echocardiogram demonstrated that the thrombus had resolved.

The patient was brought to the electrophysiology lab in sinus rhythm. A 6 French (Fr) duodecapolar Halo catheter was placed from the left femoral vein into the right atrium, and a 6 Fr decapolar Orbiter (C. R. Bard, Inc.) catheter was placed from the right internal jugular vein into the coronary sinus. Transseptal puncture was performed guided by intracardiac echocardiography, and a 6 Fr duodecapolar crista catheter was placed from the transseptal sheath to the left atrium. Heparin was used for anticoagulation after transseptal puncture to maintain an activated clotting time >300 sec. Programmed atrial stimulation was used to induce an atrial flutter with negative F waves in leads I and aVL and isoelectric in leads II, aVF, and V1 (atrial flutter 1) (Figure 2). Entrainment of the tachycardia was performed from the right atrium as well as from the roof of the left atrium. The difference of the post-pacing interval (PPI) and the tachycardia cycle length (TCL) after the entrainment pacing indicates the proximity of the entrainment catheter to the reentry circuit, and the PPI – TCL at the roof of the left atrium was <10 ms, with concealed entrainment and markedly fractionated electrograms (Figure 3). These findings are all indicative of the roof of the left atrium being part of the critical zone of the reentry circuit. Carto activation mapping demonstrated that this was located between the right superior and left superior pulmonary veins (Figure 4). A linear radiofrequency ablation line was created with a 7 Fr 3.5 mm tip asymmetric ThermoCool catheter (Biosense Webster, Inc., a Johnson & Johnson company). The atrial flutter terminated during ablation (Figure 5), and the ablation line was completed from vein to vein. Repeat atrial stimulation induced another atrial flutter (atrial flutter 2), this time with F waves that were positive in leads III, aVF, and V1, negative in leads I and aVL, and isoelectric in lead II (Figures 6 and 7). Concealed entrainment was demonstrated by pacing the lateral wall of the left atrium, with a PPI – TCL of 10 ms (Figure 8). A second ablation line connecting the left inferior pulmonary vein and the mitral annulus did not terminate this second flutter, even though completion of the line was confirmed by failure to capture at maximal output on the line, and a delay of >100 ms was recorded while pacing the atrium across the line. Activation sequence reversal was not confirmed. At this juncture repeat entrainment and activation mapping identified an anterior critical zone of concealed entrainment and slow conduction, which required a third ablation line connecting the left superior pulmonary vein with the mitral annulus anteriorly. This third line successfully terminated atrial flutter 2 (Figure 9). Although the possibility that atypical flutter 1 became flutter 2 was considered, the different cycle lengths, different activation sequences, and the locations of the concealed entrainment sites far apart all suggest that these are likely two different flutters. Repeat atrial stimulation demonstrated no inducible atrial flutters or other tachyarrhythmias. Bidirectional conduction block at the cavotricuspid isthmus and the completeness of the pulmonary vein isolation was confirmed prior to the conclusion of the procedure. Postprocedure, the patient recovered well with no complications. His dyspnea on exertion resolved, and he remains symptom-free in sinus rhythm after 4 months of follow-up (Figure 10).

Discussion

The “cut-and-sew” surgeries for atrial fibrillation have a high success rate at preventing recurrent arrhythmia. Raanani et al found after 26-month mean follow-up, 75% of patients remained in sinus rhythm after receiving concomitant Cox III maze and mitral valve surgery.¹ The most common arrhythmias following a Cox III maze surgery include atypical atrial flutter from reentry around the surgical incisions, atrial fibrillation from electrical reconnection across the pulmonary veins, and focal atrial tachycardia. Wazni et al found in their cohort of 23 patients with atrial arrhythmias after surgical maze that 43% had atypical atrial flutter, with more patients having left atrial flutter than right atrial flutter.² In this study, all patients with atrial flutter underwent both activation mapping with Biosense Webster’s Carto system, and the reentry circuit was confirmed by entrainment. As in our patient, the combination of activation mapping and entrainment mapping was crucial to identifying the isthmus where ablation would successfully terminate the arrhythmia.

On ECG, left atrial flutters can be distinguished from right atrial flutters by the small amplitude of the flutter waves in inferior leads, compared to the large negative flutter waves seen in the inferior leads during typical right atrial flutter.³ Reverse typical and upper loop reentry right atrial flutters demonstrate large positive flutter waves in the inferior leads, which distinguish these from left atrial flutters. However, there are many different potential left atrial reentry circuits that involve various pathways around pulmonary veins, the septum, the mitral valve annulus, and silent areas in the posterior and anterior aspects; figure-of-8 and multiple loop circuits also occur, making precise noninvasive localization of an atrial flutter circuit difficult,⁴ particularly after a surgical maze procedure. Our patient’s low amplitude flutter waves in the inferior leads were consistent with left atrial flutter.

Entrainment, first described in 1977, refers to the concept that pacing at a slightly shorter cycle length than a reentrant tachycardia will accelerate the tachycardia without interrupting it.⁵ While manifest entrainment is demonstrated by fusion beats during pacing until the last paced beat (which entrains but does not cause fusion), concealed entrainment accelerates the tachycardia without producing fusion on the ECG. If concealed entrainment occurs with pacing, and if the PPI is equal to the TCL, then the pacing electrode is likely at an isthmus of slow conduction within the reentry circuit.⁶ In atypical atrial flutter, without a specifically defined anatomic isthmus, confirming that the ablation catheter is within the reentry circuit by demonstrating concealed entrainment and a PPI – TCL of ≤20 ms is important for the success of the procedure. In a recently published multicenter retrospective review of 91 patients with atypical atrial flutter who were mapped with an impedance-based multielectrode array catheter and suspected critical isthmuses confirmed with entrainment pacing, 90% of all tachycardias were terminated by ablation, with a long-term atrial tachycardia-free survival of 77%.⁷ In this study, of all the potential substrates of atypical atrial flutter, the patients with a history of a surgical maze procedure had the highest long-term success rate, at 88% over 16 ± 12 months.⁷ Thus, when electroanatomic mapping techniques are used with entrainment mapping, atypical atrial flutter ablation can lead to long-term freedom from atrial arrhythmia in a majority of patients.

The choice of ablation catheter is also a factor in the success of an atrial flutter ablation. Bai et al demonstrated a 94.4% acute success rate with an open-tip irrigated catheter compared to a 76.5% acute success rate with a standard 8-mm tip ablation catheter. The arrhythmia-free rate remained high at 91.7% at 10 months after ablation.⁸

It is important, prior to concluding the flutter ablation, to attempt to induce other flutters. Frequently, as in our case, more than one flutter or atrial tachycardia is inducible, and failure to ablate potential reentry circuits increases the risk of recurrence of atypical atrial flutter. Furthermore, it is also important to confirm cavotricuspid isthmus block. Akar et al demonstrated a recurrence of cavotricuspid isthmus-dependent atrial flutter in 33% of patients who developed recurrent atrial arrhythmias after a modified radiofrequency maze procedure.⁹

Conclusion

Although ablation of left atrial flutter has a somewhat lower success rate compared to that of typical cavotricuspid isthmus-dependent atrial flutter, several factors enhanced the success of the atypical atrial flutter ablation in this patient. The history of the Cox III maze procedure, the successful use of entrainment mapping, the repeated attempt to stimulate additional atrial flutters, the confirmation of cavotricuspid isthmus block and pulmonary vein isolation, and the use of an open-tip irrigated catheter all led to an ablation that was acutely successful. The patient achieved relief of his symptoms and remains arrhythmia free.

Editor’s Note: This article underwent peer review by one or more members of EP Lab Digest^®’s editorial board.

Disclosure: The authors have no conflicts of interest to report.

References 

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