[Interrelationship between changes of rate and variability of cardiac rhythm under influence of beta-adrenoblockers]

Beta-blocking agents (BB) decrease mortality particularly sudden in post-myocardial infarction patients and in patients with chronic heart failure that is closely related to heart rate (HR) lowering at rest. The hypothesis exists that BB decrease mortality due to increase of cardiac vagal activity.

To evaluate the relation between HR changes on therapy with BB and changes in heart rate variability (HRV).

Sixty patients with arterial hypertension randomized in three groups were studied before and after treatment with atenolol (AT), acebutolol (AC) or talinolol (TL) until doses of 100, 600 and 300 mg/d correspondingly were reached or resting HR was decreased by 10 bpm. 24-hour Holter monitoring was used to measure HR and HRV indexes.

Arterial blood pressure decreased significantly in every group. HR max, min and average decreased significantly on AT. AC and TL lowered HR max and AT average but did not change HR min. AT did not change SDNN, SDANN, TotP and ULFP, but AC and NL decreased them significantly (p < 0.001). AT increased SDNNind, VLFP (p < 0.002), rMSSD, pNNSO and HFP (p < 0.003), but did not change LFP. AC and TL did not change these indexes. Changes of HRV indexes were closely related to changes of HR particularly HR min (r=0.53 - 0.84). Linear regressions of these relations did not differ between three drugs except for low frequency indexes of HRV between AC and TL. According to the equations the differences in HRV indexes between the drugs were well explained by the differences in HR changes. When all patients were evaluated together statistical significance of increase in rMSSD, pNN50 and HFP was not reached until HR average decreased by 10 bpm or more. The effect of TL on HR and HRV is very similar to AC what suggests its intrinsic sympathomimetic activity or anticholinergic properties.