Mechanisms in Simulated Torsade de Pointes

Torsade de Pointes. A mechanism of torsade de pointes consisting of moving sites of reentrant excitation has been proposed on the basis of findings with a computer model. Substantialadditions to that mechanism are now proposed based on further studies with the same model.The model simulated propagation, cycle length‐dependent recovery of excitability, and slowpropagation during incomplete recovery. Regions of relatively short and long recovery wereassigned because of evidence of regional prolongation of recovery in long QT syndromes inwhich torsade dc pointes is frequent. As previously reported, premature excitation in the shortrecovery region initially propagated independently, then entered the long recovery region andreentered the short recovery region distal to the site of origin. Reentrant excitation initiated asimilar series of events, and serial reentry at systematically changing locations resulted inchanging patterns of excitation compatible with the changing QRS waveform in torsade depointes. Episodes terminated when reentrant excitation reached the end of unclosed shortrecovery paths, collided in closed paths, or encountered refractoriness in the presence ofnonuniform short recovery. In this study, it was shown that excitation preceding reentry hadimportant effects on the mechanism. These included reversal of the direction of serial reentry, bidirectional serial reentry, reentry at multiple sites from the same parent conditions, andoccurrence of reentry without the requirement of slow propagation. Evidence for a Dopplershift of cycle lengths in regions from which serial reentry was receding or approaching wasobtained. Sustained serial reentry was also demonstrated and is a possible mechanism for polymorphic ventricular tachycardia. Findings further define a possible mechanism of torsade depointes.