Role of wavelength adaptation in the initiation, maintenance, and pharmacologic suppression of reentry

Introduction: The stability of reentry is thought to depend on a critical balance between the spatial extent of refractory tissue in a reentrant wave (i.e., wavelength lambda) and the reentrant path length. Because considerable evidence suggests that lambda changes continuously in space and time during abrupt rate changes associated with the onset of tachycardia, we hypothesized that beat-by-beat adaptation of A to the dimensions of the reentrant path plays a central role in the mechanism of initiation of reentry, Methods and Results: To investigate the dynamic relationship between lambda and path length during initiation of reentry, optical mapping with voltage-sensitive dyes was used in a guinea pig model of reentrant ventricular tachycardia (VT), In this model, a computer-guided laser obstacle precisely controlled the position and dimensions of the reentrant path. Under control perfusion and after addition of 15 muM d-sotalol, lambda was monitored during steady-state pacing, premature stimulation, and the initiating beats leading to nonsustained and sustained VT. During control perfusion, reentrant VT was reproducibly induced in 8 of 8 hearts, whereas in the presence of d-sotalol, reentry could only be initiated in 1 of 8 hearts due primarily to the failure of lambda to adapt to the reentrant path length, During successful initiation of VT, a consistent sequence was observed. The sequence was characterized by antidromic and orthodromic propagation around both sides of the anatomic obstacle, followed by unidirectional block of the antidromic impulse and persistence of reentry only if the lambda of the orthodromic impulse adapted to the reentrant path (lambda < path length). d-Sotalol prevented initiation of VT by altering lambda adaptation of the orthodromic wave; however, it failed to terminate ongoing VT because reverse use-dependence developed after several beats of tachycardia. Conclusion: In an experimental model where lambda, path length, and cellular action potentials were monitored during initiation of reentry, we found that, in contrast to termination, the initiation of reentry and the transition from nonsustained to sustained VT is strongly dependent on beat-to-beat adaptation of lambda to the dimensions of the reentrant path.