Impact of chronic DDD pacing on time-domain indexes of heart rate variability in patients with hypertrophic obstructive cardiomyopathy

The aim of this study was to examine whether DDD pacing affects time-domain indexes of heart rate variability (HRV) in patients with hypertrophic obst ructive cardiomyopathy (HOCM). We studied 11 patients (7 men, age 52 +/- 8 years) with HOCM refractory to drugs. In all patients a DDD pacemaker was i mplanted and the atrioventricular delay was programmed to ensure a full ven tricular activation sequence. Time-domain indexes of HRV (mean NN, SDANN, S DNN, SD, rMSSD, pNN50) were determined from 24-hour Holter recordings 3 day s before and 1 year after pacemaker implantation. The pacemaker was turned off during the second recordings. The same indexes were determined in ten h ealthy controls at the same time points. The controls showed no significant differences in any of the measured parameters between the two time points. The HOCM patients showed an increase in SD (from 27 +/- 13 to 41 +/- 13 ms , P < 0.001), rMSSD (from 18 +/- 5 to 32 +/- 8 ms, P < 0.001), and pNN50 (f rom 1.03 +/- 1.06 to 8.52 +/- 4.84%, P < 0.0001). As a result, the values o f these three parameters, which were lower in the HOCM patients than in the controls before pacing, were restored to normal levels by the end of the s tudy. In conclusion, our findings indicate that long-term pacing in HOCM pa tients restores the sympathovagal balance in the heart by increasing vagal activity.