Fixed intercaval block in the setting of atrial fibrillation promotes the development of atrial flutter.

BACKGROUND: In the canine sterile pericarditis model, typically only atrial fibrillation (AF) is inducible on postoperative day 2. OBJECTIVE: In this model, we tested the hypothesis that on postoperative day 2, placing a fixed line of block (LoB) between the vena cavae critically alters the atrial substrate, favoring the induction of sustained atrial flutter (AFL) instead of AF. METHODS: In 6 sterile pericarditis dogs, sustained AF was induced by rapid atrial pacing. After terminating AF, a fixed LoB between the vena cavae was created (cryoablation), and AF reinduction was attempted. Simultaneous mapping from 400 to 420 electrodes on the right and left atrial epicardium and the interatrial atrial septum was performed during all studies. RESULTS: Before creation of the LoB, in all 6 dogs, rapid atrial pacing induced sustained AF because of a rapid (mean cycle length [CL] 110 +/- 10 ms), regular, left atrial reentrant driver, which caused fibrillatory conduction. After creation of the LoB, in 5 dogs, rapid atrial pacing now induced sustained AFL (mean CL 167 +/- 13 ms). In the 6th dog, AFL failed to develop because the left atrial driver that was induced before the LoB was still reproducibly induced despite the LoB. CONCLUSION: In this model of sustained AF, altering the substrate to create a fixed LoB between the vena cavae creates a substrate favoring the induction of AFL.

Biventricular pacing attenuates T-wave alternans and T-wave amplitude compared to other pacing modes.

BACKGROUND: The impact of altered ventricular activation, including biventricular (BV) pacing, on T-wave alternans (TWA) and arrhythmic substrates is unclear. We studied how differing ventricular activation sequence alters TWA; the interval from peak-to-end of the T-wave (TpTe) and T-wave amplitude during right (RV), left (LV), and biventricular (BV) pacing; and right atrial (RA) pacing in patients with preexisting conduction delay. METHODS AND RESULTS: We measured TWA during RA, RV, LV, and BV pacing in 33 patients receiving cardiac-resynchronization-therapy-defibrillators. TWA magnitude (V(alt)) was lower during BV than RV (P < 0.01), RA (P < 0.01), or LV pacing. As a result, BV-TWA was more often negative than RV-TWA (P < 0.01), LV-TWA, and RA-TWA, particularly when discordant between pacing modes (P < 0.01). Overall, 83% of TWA recordings were abnormal (25% indeterminate), and 17% negative. BV pacing reduced T-wave amplitude (P < 0.05) and TpTe (P < 0.005) compared to RV pacing and LV pacing (P < 0.05; P < 0.005 respectively). Notably, TWA magnitude varied linearly with T-wave amplitude for all pacing modes (P < 0.001). Over 410 +/- 252 days' follow-up, RV-TWA predicted the combined endpoint of death and ICD therapy with 86% negative predictive value (P < 0.05). BV-TWA, RA-TWA, and other repolarization indices were not predictive. CONCLUSIONS: BV pacing attenuates TWA in tandem with reduced T-wave magnitude. In these patients with baseline QRS prolongation, RV-TWA predicted events more effectively than BV-TWA and RA-TWA. Further studies are required to understand how altered ventricular activation influences repolarization dynamics and arrhythmic tendency.