Day-to-day variation of the frequency of ventricular premature contractions depends on variation of heart rates.

To examine the manner in which spontaneous variation in the frequency of ventricular premature contractions (VPCs) relates to the variation of heart rate (HR), 68 patients with frequent VPCs were studied, by using 24-hour ECG recordings. All patients had more than 40 VPCs/hour on an initial 24-hour ECG recording and a second recording was made within 2 months (mean: 15 days). For each patient, the HR-dependency of VPCs was evaluated. Plots of VPC frequency per minute (VPCs/min) vs. HR were made at 1-beat/min steps for all HRs recorded for at least 5 min during 24 hours. Based on the patterns of correlation between VPCs/min and HR observed at the first recording, patients were divided into 2 groups: 1) 26 with a positive correlation or the P group (a linear increase in VPCs/min with increasing HRs) and 2) 42 with a non-positive correlation or the NP group. The NP group included: 1) an increased VPCs/min at low HRs and a decrease at high HRs (38 patients), 2) a linear decrease in VPCs/min with increased HRs (2 patients) and 3) constant VPCs/min at all HRs (2 patients). The patterns of correlation were reproducible at the second recording period in 65 of 68 patients (96%). Variability in the VPC frequency per 24 hours between two 24-hour recording periods was significantly greater in the P than in the NP group, while the variability in the mean daily HR was similar between the 2 groups. Thus, the 95% confidence limit for spontaneous reduction in the VPC frequency was greater for the P (67%) than for the NP group (50%).(ABSTRACT TRUNCATED AT 250 WORDS)