PMC5412655_01
Right panels show intracardiac electrograms from the distal (Map D) and proximal (Map P) tip of the ablation catheter and surface electrocardiogram lead III. 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). 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. B: After ablation the CTI block is created and the impulse travels along the tricuspid annulus, first reaching Map P and later Map D. Thus, CTI block in the clockwise direction is documented. AVN = atrioventricular node; PS = pacing site (pacemaker ventricular lead).
gr1.jpg
PMC5412655_01_gr1.jpg
f0005
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).
Right panel shows intracardiac electrograms from the ablation electrode before (A) and after (B) creating cavotricuspid isthmus (CTI) block. A: Before ablation there is a single atrial signal (SP = single potential) because the activation wavefront approaches the tip of the ablation electrode only from 1 side. B: After creation of the CTI block, the impulse reaches the CTI first from the septal side, and after 101 msec from the other side of the block, resulting in 2 split atrial potentials (DP = double potentials). Thus, the CTI block in the clockwise direction is documented and strongly suggest true bidirectional block. Abbreviations as in Figure 1.
gr2.jpg
PMC5412655_01_gr2.jpg
f0010
Moreover, double potentials (AA':101 msec) were recorded at the ablation line (Figure 2).
Right panel shows intracardiac electrograms from the distal (Map D) and proximal (Map P) tip of the ablation catheter and surface electrocardiogram (ECG) lead I during differential pacing, after completing the cavotricuspid isthmus (CTI) ablation line. A: Pacing from Map P shows 205 msec distance to QRS complex recorded on surface ECG. B: During Map D pacing, owing to existence of counterclockwise CTI block, the impulse travels only in the clockwise direction, arrives into the atrioventricular node, and activates the ventricles, which is unveiled by prolongation of the measured distance from Map P to QRS complex recorded on surface ECG. Thus, CTI block in the counterclockwise direction is also confirmed. PS = pacing site.
gr3.jpg
PMC5412655_01_gr3.jpg
f0015
TA and measuring the distance to ventricular activation occurring through the AVN (Figure 3). The patient was discharged home the next day and continues to be free of symptoms 6 months after the procedure.