[Polymorphic ventricular tachycardia. Analysis of the onset of the episodes]

To analyze the spontaneous onset of events for polymorphous ventricular tachycardia, to determine the importance of this parameter in the clinical and electrophysiologic context.

We evaluated 124 modes of onset of polymorphous ventricular tachycardias recorded by 24 hr of continuous ECG monitoring in 6 patients. Four patients were using quinidine and diuretics, and two patients only diuretics. We determined the two preceding cycle in milliseconds from the initiating events and also the induced cycle (cycles A, B and C). Careful analyses of T and U waves alternans and QT ou QTU intervals inside and outside the episodes of tachycardia.

In 105 episodes (84%) the events were pause-dependent; in 12 episodes (10%) they occurred without pauses but after a ventricular fusion and in 7 episodes (6%) also without pauses but with sudden cycle (C) shortening (R on T phenomena). The pause-dependent episodes were only seen in patients using quinidine with the association of diuretics and non-pause related episodes were registered in patients using diuretics. All patients had prolonged QTU intervals outside the episodes. There were a linear correlation (r = 0.865) between the amplitude of the U waves of the cycles C and duration of cycles A and B, in pause-dependent episodes.

The contribution of this study is that: the analyses of the spontaneous onset of polymorphous ventricular tachycardia can allow the differentiation of typic forms of torsades des de pointes (pause-dependent) and other atipic forms. The former type occurred probably as a result of EADs provoking triggered rhythms. The latter could be better explained as polymorphous ventricular tachycardia due to reentry mechanisms or enhanced automatic focus. Only the tipic forms should be acutely benefited with regularization of cardiac cycles with cardiac pacing.