NONSTATIONARY VORTEX-LIKE REENTRANT ACTIVITY AS A MECHANISM OF POLYMORPHIC VENTRICULAR-TACHYCARDIA IN THE ISOLATED RABBIT HEART

Background Ventricular tachycardia may result from vortexlike reentran t excitation of the myocardium. Our general hypothesis is that in the structurally normal heart, these arrhythmias are the result of one or two nonstationary three-dimensional electrical scroll waves activating the heart muscle at very high frequencies. Methods and Results We use d a combination of high-resolution video imaging, electrocardiography, and image processing in the isolated rabbit heart, together with math ematical modeling. We characterized the dynamics of changes in transme mbrane potential patterns on the epicardial surface of the ventricles using optical mapping. Image processing techniques were used to identi fy the surface manifestation of the reentrant organizing centers, and the location of these centers was used to determine the movement of th e reentrant pathway. We also used numerical simulations incorporating Fitzhugh-Nagumo kinetics and realistic heart geometry to study how sta tionary and nonstationary scroll waves are manifest on the epicardial surface and in the simulated EGG. We present epicardial surface manife stations (reentrant spiral waves) and ECG patterns of nonstationary re entrant activity that are consistent with those generated by scroll wa ves established at the right and left ventricles. We identified the or ganizing centers of the reentrant circuits on the epicardial surface d uring polymorphic tachycardia, and these centers moved during the epis odes. In addition, the arrhythmias that showed the greatest movement o f the reentrant centers displayed the largest changes in QRS morpholog y. The numerical simulations showed that stationary scroll waves give rise to monomorphic ECG signals, but nonstationary meandering scroll w aves give rise to undulating ECGs characteristic of torsade de pointes . Conclusions Polymorphic ventricular tachycardia in the healthy, isol ated rabbit heart is the result of either a single or paired (''figure -of-eight'') nonstationary scroll waves, The extent of the scroll wave movement corresponds to the degree of polymorphism in the EGG. These results are consistent with our numerical simulations that showed mono morphic ECG patterns of activity for stationary scroll waves but polym orphic patterns for scroll waves that were nonstationary.