Dependency of Premature Ventricular Contractions on Heart Rate and Circadian Rhythms during Childhood

The aim of the present study was to identify and quantify the rate dependence of premature ventricular contractions (PVC) during childhood. A 24-hour Holter recording was performed in 16 consecutive children, aged 22 days to 11 years (mean age 5.6 years), with frequent (>5,000/day), isolated monomorphic PVC. Those PVC were identified and the length of the preceding sinus cycle was measured. The values were ordered into 50-ms class intervals, and the percentage of PVC for each class was calculated and then analyzed by linear regression analysis. On the basis of the significance of the p value, and the positive or negative value of the slope, we identified a tachycardia-enhanced, a bradycardia-enhanced, and an indifferent pattern. Chronobiologic analysis was made by the cosinor method. All the patients had upper and lower limits of cycle length beyond which PVC disappeared. A tachycardia-enhanced pattern was present in 7 patients and an indifferent one in 9 patients. In the latter a second-degree polynomial correlation was systematically found. Children but not infants had a significant circadian variation in the frequency of PVC with a very variable time of highest incidence. In conclusion, it is possible to identify a circadian rhythm of PVC and a spontaneous trend between their incidence and the length of the preceding cardiac cycle in children.