Please click here to obtain permission to reproduce this image.
Click on image to view larger version.
Figure 3 Pacing from a bystander dead-end pathway in the computer simulation of the same circuit as in Figure 2 is shown. (A) The S-QRSn interval is produced by conduction of the stimulated wavefront from the pacing site to the circuit exit (arrow). Entrainment occurs with concealed fusion. X is the conduction time from the pacing site to the circuit common pathway, and y is the conduction time from the junction of the bystander pathway and circuit to the circuit exit, which produces the onset of the QRS. (B) The wavefront continues through the circuit, returning to the exit to produce QRSn+1. S-QRSn+1 is the sum of the S-QRSn (x + y) plus the TCL. (C) The PPI is the sum of the conduction times from the pacing site to the circuit, through the circuit and back to the pacing site. (D) The S-QRSn+1 interval is 484 ms and is longer than the Egn+1-QRSn+2 and Egn+2-QRSn+3 interval, which is 434 ms. The N + 1 difference is 484 – 434 = 50 ms. The PPI-TCL difference is 473 – 423 = 50 ms. See text for discussion. Eg = electrogram; PPI = postpacing interval; S = stimulus; TCL = tachycardia cycle length; VT = ventricular tachycardia.
|
