Incidence, electrophysiological characteristics, and long-term follow-up of perimitral atrial flutter in patients with previously confirmed mitral isthmus block

Abstract

Introduction: After mitral isthmus (ΜΙ) catheter ablation, perimitral atrial flutter (PMF) circuits can be maintained due to the preservation of residual myocardial connections, even if conventional pacing criteria for complete MI block are apparently met (MI pseudo-block). We aimed to study the incidence, the electrophysiological characteristics, and the long-term outcome of these patients.

Methods: Seventy-two consecutive patients (mean age 62.4 ± 10.2, 62.5% male) underwent MI ablation, either as part of an atrial fibrillation (AF) ablation strategy (n = 35), or to treat clinical reentrant atrial tachycardia (AT) (n = 32), or to treat AT that occurred during ablation for AF (n = 5). Ιn all patients, the electrophysiological characteristics of PMF circuits were studied by high-density mapping.

Results: Mitral isthmus block was successfully achieved in 69/72 patients (95.6%). Five patients developed PMF after confirming MI block. In these patients, high-density mapping during the PMF showed a breakthrough in MI with extremely low impulse conduction velocity (CV). In contrast, in usual PMF circuits that occurred after AF ablation, the lowest CV of the reentrant circuit was of significantly higher value (0.07 ± 0.02 m/s vs 0.25 ± 0.07 m/s, respectively; P < .001). Patients presented with clinical AT had better prognosis in maintaining sinus rhythm after MI ablation compared with patients presented with AF.

Conclusion: Perimitral atrial flutter with MI pseudo-block may be present after MI ablation and has specific electrophysiological features characterized by remarkably slow CV in the MI. Thus, even after MI block is achieved, a more detailed mapping in the boundaries of the ablation line or reinduction attempts may be needed to exclude residual conduction.

Keywords: atrial fibrillation; atrial tachycardias; catheter ablation; linear lesions; mitral isthmus; perimitral atrial flutter; pseudo‐block.

FIGURE 1

The pacing maneuvers performed in all patients to confirm mitral isthmus (MI) bidirectional block. Pacing superiorly to MI line before (A) and after (B) ablation to prove conduction block in the clockwise direction. Differential pacing from coronary sinus to prove conduction block in counterclockwise direction (C, D)

FIGURE 2

Pacing maneuvers indicative of mitral isthmus (MI) block and perimitral atrial flutter (PMF). (A) Pacing from left atrial appendage (LAA) with MI conduction before MI ablation in the first procedure. (B) Pacing from LAA with complete reversal in coronary sinus sequence after MI ablation in the first procedure. (C) Pacing superiorly of the MI line at the beginning of the second procedure before any ablation. (D) Clockwise PMF with cycle length = 250 ms (E) Termination of the arrhythmia by ablating the gap in MI (Video 3). (F) Reconfirmation of MI block

FIGURE 3

Isochronal maps in two cases (A, B) of clockwise perimitral atrial flutter circuits and mitral isthmus (MI) pseudo‐block showing the impulse breakthrough from a narrow channel in the MI with very low conduction velocity (Videos 1 and 4, respectively)

FIGURE 4

Isochronal maps of clockwise (Α1) and counterclockwise (Β1) perimitral atrial flutter with the corresponding measurement of the lowest conduction velocity (CV) in each circuit (A2, B2) (Videos 5 and 6)

FIGURE 5

Comparison of the lowest CVs in usual perimitral atrial flutter (PMF) circuits and in PMF circuits after confirmed mitral isthmus block

FIGURE 6

(A) Pacing from the left atrial appendage (LAA) showing the reversal of the activation sequence in the coronary sinus (CS). The time of the counterclockwise rotation from the spike to the distal CS was 180 ms The ablation catheter is located in the mitral isthmus (MI) line and records double far‐field potentials indicative of conduction block (blue arrows) and in between a high frequency near‐field electrogram (green arrow) with total duration 50 ms The latter is possibly indicative of residual conduction through the MI ablation area; it does not have enough time to cross the MI and eventually fades colliding with the counterclockwise wavefront. (B) Clockwise perimitral atrial flutter with cycle length 240 ms that was diagnosed with high density activation mapping using the 3D mapping system