The rule of bigeminy revisited: analysis in sudden cardiac death syndrome

Background

The rule of bigeminy is commonly explained by a reentrant mechanism. We hypothesize that in patients with prolonged ventricular repolarization, the rule of bigeminy may be caused by premature ventricular complexes (PVCs) due to early afterdepolarizations. We evaluated these ventricular arrhythmias over extended periods in patients with sudden cardiac death syndrome.

Methods

The electrocardiographic (ECG) characteristics of 15 recordings from the PhysioNet Sudden Cardiac Death Holter Database were analyzed for the persistence of bigeminy, interaction between the underlying cardiac rhythm and the coupling interval, and influence of a prolonged initiating RR cycle on the self-perpetuation of the arrhythmias.

Results

Eight (53%) patients had classic torsade de pointes (TdP), 5 (33%) had other polymorphic ventricular tachycardia (VT), and 2 (13%) had monomorphic VT. Group A, which comprised 6 of the patients with TdP, had the following ECG tetrad: (1) frequent ventricular bigeminy (>5% of total ventricular arrhythmias), (2) long corrected QT interval (>0.5 second), (3) relatively fixed coupling interval, and (4) onset of bigeminy (n = 4) and TdP (n = 6) after a short-long RR sequence. Patients in group A had slower heart rates (mean RR = 1.12 ± 0.26 vs 0.77 ± 0.13 seconds, P < .01), longer QT intervals (corrected QT = 0.57 ± 0.06 vs 0.45 ± 0.06 second; P < .01) and more cases with prominent U waves (83% vs 33%, P < .05) than patients in group B (n = 9), composed of patients who had other types of VT, or TdP without frequent bigeminy.

Conclusions

We identified a set of ECG characteristics that supports the notion that premature ventricular complexes during self-perpetuating ventricular bigeminy (“rule of bigeminy”) in long QT syndromes may be due to early afterdepolarizations.