Rationale: Reentry underlies most ventricular tachycardias (VTs) seen postmyocardial infarction (MI). Mapping studies reveal that the majority of VTs late post-MI arise from the infarct border zone (IBZ).

Objective: To investigate reentry dynamics and the role of individual ion channels on reentry in in vitro models of the "healed" IBZ.

Methods and Results: We designed in vitro models of the healed IBZ by coculturing skeletal myotubes with neonatal rat ventricular myocytes and performed optical mapping at high temporal and spatial resolution. In culture, neonatal rat ventricular myocytes mature to form striated myocytes and electrically uncoupled skeletal myotubes simulate fibrosis seen in the healed IBZ. High resolution mapping revealed that skeletal myotubes produced localized slowing of conduction velocity (CV), increased dispersion of CV and directional-dependence of activation delay without affecting myocyte excitability. Reentry was easily induced by rapid pacing in cocultures; treatment with lidocaine, a Na⁺ channel blocker, significantly decreased reentry rate and CV, increased reentry path length and terminated 30% of reentrant arrhythmias (n=18). In contrast, nitrendipine, an L-type Ca²⁺ channel blocker terminated 100% of reentry episodes while increasing reentry cycle length and path length and decreasing reentry CV (n=16). K⁺ channel blockers increased reentry action potential duration but infrequently terminated reentry (n=12).

Conclusions: Cocultures reproduce several architectural and electrophysiological features of the healed IBZ. Reentry termination by L-type Ca²⁺ channel, but not Na⁺ channel, blockers suggests a greater Ca²⁺-dependence of propagation. These results may help explain the low efficacy of pure Na⁺ channel blockers in preventing and terminating clinical VTs late after MI.