Heart rate variability in left ventricular hypertrophy and heart failure, and the effects of beta-blockade

Abstract

An analysis of heart rate (HR) variability (HRV) was based on quantifying the number and amplitude of HR fluctuations over long (8-30 cycles) and short (2-4 cycles) sequences of acceleration and deceleration-forming oscillations. The 'product' (number times amplitude) is an equivalent of the power spectrum in the frequency domain. In the time domain, positive correlations with HR were found for the number of long (L) sympathetic-mediated oscillations, whereas they were negative for short (S) vagally-mediated oscillations. The L/S ratio, an index of the autonomic nervous system (ANS) balance, closely paralleled the circadian HR values. HRV was studied in the ambulatory ECG of three groups of 15 normal adults (group I), 13 patients with left ventricular hypertrophy (LVH, group II) and 13 patients with heart failure (HF, group III). In basic conditions the mean HR was 77.1 +/- 1.9 beats min-1 (mean +/- SEM) in group I, 76.8 +/- 3.3 in II, 79.5 +/- 3.5 in III (P = NS). The different types of oscillations had smaller 24-h average values of the product in groups II and III than in group I, but the trends did not reach significance. However, the pooled 24 hourly values of the L/S ratio in group I (1.17 +/- 0.09) were lower than in group II (1.33 +/- 0.06, P less than 0.05 at Ancova) and higher than in group III (1.06 +/- 0.09, P less than 0.001). A 3-day treatment with acebutolol non-uniformly slowed the mean HR:--9.5% in group I, --18.1% in II and -19.1% in III (P less than 0.001), and uniformly diminished the L/S ratio by 17% to 20% (P less than 0.01). In conclusion, the sympathetic predominance of the ANS balance in LVH and HF is reflected by the beta-blockade induced HR decrease that is twice as marked in patients as in controls. In basic conditions HRV tends to be depressed in LVH and even more in HF. The ANS imbalance, however, has different modalities depending on the presence of HF, probably because of the different status of beta-adrenergic receptors in this condition.