Patients with premature ventricular complexes (PVCs) usually experience accompanying alterations of the autonomic nerve system. The timing of PVC occurrence is associated with different circadian rhythms, which may be related to the autonomic nerve imbalance. The relationship between night-time PVC and cardiac autonomic nervous activity is still obscure. Our study aimed to investigate the relationship between the number of night-time PVCs and cardiac autonomic nervous activity.

We enrolled 72 patients with frequent PVCs and 27 without PVCs. The patients with PVCs were divided into two groups based on the number of night-time PVCs (i.e., PVCs occurring between 10 pm and 6 am/24-hr total PVCs; group 1: n=34, <30%; group 2: n=38, >30%). At baseline, 12-lead electrocardiogram and 24-hour Holter recording were performed. When the number of PVCs declined significantly after radiofrequency catheter ablation, Holter monitoring was performed again. Heart rate (HR) variability, mean 24-hour HR, mean daytime HR, and mean night-time HR were analysed.

With a greater number of night-time PVCs, group 2 had a lower standard deviation of all NN intervals (SDNN; 116.5±38.3 vs 135.3±37.8 ms; p=0.035) and increased mean 24-hour HR (77.3±9.2 vs 73.4±7.5 beats per min; p=0.05) than group 1. The SDNN was negatively correlated with the number of night-time PVCs and mean night-time HR (r= –3.04 and r= –0.504, respectively; p=0.009 and p=<0.001, respectively), and night-time PVC proportion was positively correlated with the ratio of low-frequency power (LF)/high-frequency power (HF; r=0.319 [p=0.013]). Multivariate linear regression analysis showed that the number of night-time PVCs was an independent predictor of decreased SDNN (β= –0.446, p=0.030) and increased LF/HF ratio (β=0.027, p=0.038). After PVCs disappeared, SDNN increased significantly and the frequency domain of the square root of the mean of the sum of the squares of differences between adjacent NN intervals, NN50 count divided by the total number of all NN intervals, the time domain of natural logarithm of HF, natural logarithm of LF, and mean 24-hour HR were significantly decreased in the two PVC groups.

An increased number of night-time PVCs was accompanied by enhanced cardiac sympathetic activity. After PVCs diminished, both cardiac parasympathetic and sympathetic nervous activity declined.