Background: A regular distribution of ventricular ectopic beats is thought to be a relatively uncommon phenomenon, known as "concealed extrasystole". Several experimental studies suggest that the phenomenon originates from a "protected" ventricular focus. The aim of the present study was to evaluate the 24-hour ECG monitoring incidence of ventricular concealed extrasystole in patients with highly frequent ventricular ectopic beats, looking for signs useful in postulating the electrogenesis of the arrhythmia.
Methods: The 24-hour ECGs of 10 patients (pts) with highly frequent ventricular extrasystoles were analysed, searching for significant sequences in the distribution of ectopic beats (i.e., ectopic beats separated by a number of interectopic sinus beats fulfilling one of the formulas of concealed extrasystole).
Results: Five cases (50%) showed an allorhythmic distribution resulting in a prevalent pattern of concealed bigeminy (2n-1) in 3 cases, and concealed trigeminy (3n-1) in 2 cases. The phenomenon, however, showed a dynamic behaviour, alternating the distributions from patterns of concealed bigeminy to concealed trigeminy or less common patterns, and vice versa. The evidence of the pure ectopic cycle and mathematically related interectopic intervals in 2 cases, the variability of coupling intervals, and the presence of fusion beats in the remaining 3 cases, strongly suggests a parasystolic origin of the phenomenon.
Conclusions: The results suggest the following: Concealed extrasystole is a relatively common phenomenon, at least in patients with highly frequent ventricular extrasystoles; the phenomenon, however, is somewhat underestimated due to prevalent quantitative, instead of qualitative, Holter monitoring analyses. Among patients with allorhythmically distributed ventricular extrasystoles, none showed only one pattern of distribution. In fact, each single patient showed two or more patterns throughout the 24-hour recordings. Changes from one pattern to another is governed by several factors, such as sinus heart rate and/or the influence of electrotonic "modulation" upon the ectopic focus. Ventricular extrasystoles with regular allorhythmic distribution show a significantly higher variability of coupling intervals than the others (p = 0.005).