![]() AVN = atrioventricular node PS = pacing site (pacemaker ventricular lead).Ĭlockwise CTI block is usually confirmed by measurements on the TA and in CTI during coronary sinus pacing. Thus, CTI block in the clockwise direction is documented. B: After ablation the CTI block is created and the impulse travels along the tricuspid annulus, first reaching Map P and later Map D. A: Before ablation during pacing from the ventricular pacing lead, atrial electrogram is earlier in Map D than in Map P because there is no block in the cavotricuspid isthmus (CTI), the distance from septum to ablation electrode tip is shorter through the CTI than along the tricuspid annulus in the counterclockwise direction, and therefore the impulse first reaches Map D and later Map P. Left panels show fluoroscopic images of the right atrium in the left lateral oblique projection (45 degrees) showing 2 permanent pacemaker leads in the right ventricle and in the right atrium, ablation electrode, with superimposed arrows showing direction of depolarization wave, important structures, and site of block ( zig-zag arrow). Right panels show intracardiac electrograms from the distal (Map D) and proximal (Map P) tip of the ablation catheter and surface electrocardiogram lead III. The patient was discharged home the next day and continues to be free of symptoms 6 months after the procedure. The conduction block through CTI in the counterclockwise direction was further documented by differential pacing from the ablation catheter positioned at the TA and measuring the distance to ventricular activation occurring through the AVN ( Figure 3). Moreover, double potentials (AA′-101 msec) were recorded at the ablation line ( Figure 2). After completing the CTI ablation line, the distance between ventricular paced signal to low right atrium increased to 197 msec and the reversed activation pattern on ablation catheter confirmed CTI block in the clockwise direction ( Figure 1). Before RFCA, the PM was programmed to VVI 90/min mode-retrograde conduction via the atrioventricular node (AVN) was confirmed, with activation on the ablation catheter located at the tricuspid annulus (TA) suggesting conduction via CTI, with the distance from the ventricular pacing signal to low right atrium of 136 msec, and with the absence of atrial double potentials in the CTI. Pacing using PM leads was performed before and after ablation in order to confirm block in the CTI. Because of massive leg varices, problems with femoral vein access, and increased risk of periprocedural deep vein thrombosis, a single-catheter procedure was undertaken. A 61-year-old woman with a dual-chamber pacemaker (PM) was referred for RFCA owing to recurrent typical AFL. ![]()
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