Cycle length dynamics at the onset of postinfarction ventricular tachycardias induced in canines: dependence on interval-dependent excitation properties of the reentrant substrate.

INTRODUCTION

Postinfarction monomorphic ventricular tachycardias induced by programmed stimulation may display initial cycle length (CL) variations before stabilizing.

METHODS AND

RESULTS

To show that tachycardia onset dynamics depend on rate-dependent electrical properties of the reentrant substrate, we extracted activation times and maximum negative slopes of local activation complexes (-dV/dt(max)) from 191 unipolar electrograms recorded in the anterior left ventricular wall of anesthetized, 3-day-old infarct canine preparations. Measurements were made of the responses to programmed stimulation, as well as in early and later beats of tachycardias, which displayed either a constant trend in CL (group A, n = 5 preparations) or one in which CL prolongation occurred according to an exponential course before stabilizing (group B, n = 9). Stimulation protocols inducing the tachycardias were more aggressive and their CL was significantly shorter (CL = 159 +/- 24 msec) in group A than in group B (stabilized CL = 206 +/- 34 msec). Reentrant activity occurred in subepicardial areas in which the absolute value of -dV/dt(max) (absolute value(-dV/dtmax)) was heterogeneously depressed (<2 mV/msec). Absolute value(-dV/dtmax) was reduced and activation delay increased in the successive responses to extrastimuli. Further reductions in absolute value(-dV/dtmax) (10% to 23%) were shown to occur between early and later beats in 5 of the 9 tachycardias in group B (no change in the 4 others), and they were associated with localized prolongation of conduction times in reentrant pathways. In contrast, absolute value(-dV/dtmax) improved in all group A tachycardias (7% to 25%).

CONCLUSION

This study provides evidence that the onset dynamics of postinfarction ventricular tachycardias are determined by interval-dependent electrical changes occurring in the reentrant substrate.