Induction of cardiac memory by 3 weeks of AV-sequential pacing in dogs resulted in a significant left ventricular transmural repolarization gradient compared to sham controls (12.4 vs 2.7 ms; p<0.01).
Does AV-sequential pacing induce transmural repolarization gradients associated with long-term cardiac memory in a canine model?
Long-term cardiac memory T-wave changes are driven by the evolution of transmural repolarization gradients that are maximal near the site of ventricular pacing.
Absolute Event Rate: 12.4% vs 2.7%
p-value: p=<0.01
OBJECTIVE: The contribution of regional electrophysiologic heterogeneity to the T-wave changes of long-term cardiac memory (CM) is not known. We mapped activation and repolarization in dogs after induction of CM and in sham animals. METHODS AND RESULTS: CM was induced by three weeks of AV-sequential pacing at the anterior free wall of the left ventricle (LV), midway between apex and base in 5 dogs. In 4 sham controls a pacemaker was implanted but ventricular pacing was not performed. At 3 weeks, unipolar electrograms were recorded (98 epicardial, 120 intramural and endocardial electrodes) during atrial stimulation (cycle length 450 ms). Activation times (AT) and repolarization times (RT) were measured and activation recovery intervals (ARIs) calculated. CM was associated with 1) deeper T waves on ECG, with no change in QT interval; 2) longer activation time at the site of stimulation in CM (29.7+/-1.0, X+/-SEM) than sham (23.9+/-1.3 ms p<0.01); 3) an LV transmural gradient in repolarization time such that repolarization at the epicardium terminated 12.4+/-2.4 ms later than at the endocardium p<0.01), in contrast to no gradient in shams (2.7+/-4.2 ms); in memory dogs, the repolarization time gradient was greatest at sites around the pacing electrode varying from 13.1+/-2.3 ms to 25.5+/-3.8 ms; 4) more negative left ventricular potentials at the peak of the body surface T wave (-4.9+/-0.8 vs -2.2+/-0.4 mV; p<0.05) but no altered right ventricular epicardial T-wave potentials. ARIs did not differ between groups. Right ventricular activation was delayed but was not associated with altered repolarization because of compensatory shortening of the right ventricular ARIs. CONCLUSION: CM-induced T-wave changes are caused by evolution of transmural repolarization gradients manifested during atrial stimulation that are maximal near the site of ventricular pacing.
Coronel et al. (Thu,) conducted a other in Cardiac memory (n=9). AV-sequential pacing vs. Sham pacemaker implantation without ventricular pacing was evaluated on Left ventricular transmural gradient in repolarization time (p=<0.01). Induction of cardiac memory by 3 weeks of AV-sequential pacing in dogs resulted in a significant left ventricular transmural repolarization gradient compared to sham controls (12.4 vs 2.7 ms; p<0.01).