Activation sequence at the onset of arrhythmias induced by localized myocardial warming and programmed premature...

The effect of localized shortening of ventricular repolarization on arrhythmia vulnerability was studied in 10 pentobarbital anesthetized dogs. An area of the anterior right ventricle was warmed by directing a light beam through a condenser lens assembly and a rectangular aperture. Arrhythmia vulnerability was assessed with low-amplitude programmed stimulation. Activation sequence maps were constructed from electrograms recorded simultaneously from 40 epicardial sites and 24 endocardial sites in and surrounding the warmed area. Recordings were taken during regular atrial and ventricular drives and during programmed stimulation in control periods and during myocardial warming. Spontaneous activity could not be induced with low-amplitude programmed stimulation during control periods in any dog. During myocardial warming arrhythmias were induced in every dog. Most induced arrhythmias had features consistent with local reentry. However, activation sequence at the onset of some arrhythmias strongly resembled that of superventricular activation and was consistent with reentry involving the His-Purkinje system. The findings provide evidence that a localized area with short ventricular repolarization is an abnormality sufficient to increase arrhythmia vulnerability and also that even in this relatively simple setting there can be multiple mechanisms for arrhythmias.