Assessment of the variability in coupling intervals of ventricular premature contractions

The coupling interval of ventricular premature contraction is relatively constant in some patients, while it varies in others. The clinical implications of this variability in the coupling intervals of ventricular premature contractions remains to be clarified.

Ambulatory electrocardiograms were recorded in 48 patients who had 2000 or more ventricular premature contractions per day. In each subject, 24 h ambulatory electrocardiograms were recorded in the absence of antiarrhythmic drug (control), and during treatment with various antiarrhythmic drugs. Data on R-R intervals were obtained using a Marquette 8000T, and transmitted to a personal computer. For each of the control recording, an R-R interval scatterplot was constructed by plotting the coupling intervals of ventricular premature contractions as a function of the preceding R-R intervals of normal sinus beats. The standard deviation of the coupling intervals (SDNV), that of the preceding R-R intervals (SDNN), and their ratio (SDNV/SDNN) were calculated.

At control recording, two primary R-R scatterplot patterns were recognized; 1) Fixed, where the coupling intervals remained constant at various preceding R-R intervals (SDNV/SDNN < 0.5 and SDNV < 50 msec) (n = 29), and 2) Variable, where the coupling intervals showed a much greater (n = 19). The prevalence of organic heart disease was higher in the Variable group than in the Fixed group (47% vs 14%, p < 0.05). SDNV/SDNN was higher in patients with organic heart disease than in those without (0.62 +/- 0.34 vs 0.44 +/- 0.23, p < 0.05). The efficacy of antiarrhythmic drugs was compared between the two groups. A reduction of 80% or more in the total number of ventricular premature contractions was considered effective. Class Ia, Ib, and Ic drugs had almost the same efficacy in the Fixed and Variable groups (Ia, 43% and 41%; Ib, 36% and 22%; Ic, 64% and 63%, respectively). Class II drugs (beta-blockers) were more effective in the Fixed group than in the Variable group (50% vs 0%, p < 0.05).

The R-R interval scatterplot of ambulatory electrocardiograms was useful in exploring the variability in the coupling intervals of ventricular premature contractions, and may help to predict the efficacy of antiarrhythmic drugs.