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  • In patients with typical atrial


    In patients with typical atrial flutter circulating around the tricuspid valve, the verification of a bidirectional conduction block is recommended for cavotricuspid isthmus (CTI) ablation, because a unidirectional conduction block at the CTI has been previously reported to cause recurrence of atrial flutter [5]. Linear ablations in the LA, including that in the “roof line” that joins the left and right superior PVs and that in the “MI line,” have been developed to treat AF patients. The endpoint of the linear ablation in the LA region should also be the completion of the bidirectional block to prevent any subsequent recurrence of the tachycardia [6]. We herein report a case of a unidirectional conduction block during linear ablation at the mitral isthmus.
    Case report A 46-year-old man who was experiencing palpitations for 6 months after undergoing catheter ablation for persistent AF was admitted to our hospital for treatment of recurrent arrhythmia. During the initial ablation procedure, the PVs were individually isolated from the LA and electrogram-based ablation was performed in all aspects of the LA, including the LA appendage and coronary sinus (CS). No linear ablation was performed in the LA during the initial procedure. A surface electrocardiogram during palpitation showed the presence of a regular, narrow QRS tachycardia, with a inno-206 rate of 125bpm (Fig. 1A). This tachycardia was resistant to oral bepridil antiarrhythmic therapy. The intravenous administration of adenosine triphosphate (20mg) did not terminate the tachycardia, but it revealed the morphology of positive P-waves in leads II, III, and aVF and negative P-waves in I, aVL, and V1-6 (Fig. 1B). A chest radiograph showed no cardiomegaly (cardiothoracic ratio: 50%), and echocardiography revealed normal left ventricular function with an ejection fraction of 61% and mild LA dilatation with a dimension of 42mm. The electrophysiological study and catheter ablation were performed after informed consent was obtained from the patient. The anti-arrhythmic medication was discontinued for 7 days before the procedure. A decapolar electrode catheter was positioned in the CS via the right subclavian vein. Following transseptal access, all four PVs were visualized using selective venography and did not reveal any PV stenosis, and selective venography was used during the procedure to show venous anatomy and the location of the LA–PV junction. A steerable 20-polar circular mapping catheter was introduced into the LA. An 8-mm-tip ablation catheter (Fantasista, Japan Lifeline, Japan) was used for mapping and ablation. The bipolar and unipolar electrograms were filtered at 30–400Hz and 0.05–400Hz, respectively. Tachycardia with an atrial cycle length (CL) of 245ms demonstrated an atrial activation sequence from the septal to the lateral areas of the posterior LA (Fig. 2A). Entrainment mapping was first performed to distinguish reentrant ATs in the right atrium (RA). The post-pacing interval (PPI) at the CTI and the lateral RA were both longer than the tachycardia CL (300 and 410ms, respectively). Activation mapping in the LA revealed that both the posterior and anterior left atria were activated from the low to high direction, whereas the activation of the anterior LA was propagated from the lateral region to the septum. These findings were compatible with the macroreentrant AT circulating around the mitral annulus (perimitral AT), and 100% of the circuit could be mapped around the mitral annulus. Subsequent entrainment mapping at two different sites on the mitral annulus confirmed that this tachycardia was a perimitral AT circulating around the mitral annulus in a counterclockwise direction. Linear ablation at the MI line from the lateral mitral annulus to the ostium of the left inferior PV was then performed to eliminate the tachycardia. Radiofrequency (RF) energy was delivered with a target temperature of 50°C and a power limit of 35W. The tachycardia was terminated during the fifth RF application near the CS 5–6 electrodes on the MI (Figs. 2B and 3). An atrial pacing maneuver was then attempted to verify the completion of the MI block. During pacing at the most distal CS electrodes (CS 1–2), both the prolonged activation time to the proximal CS electrodes and the septal to lateral activation sequence (CS 9–10 to CS 7–8) suggested the absence of conduction in a clockwise direction (Fig. 3A).