EFFECT OF BETA-ADRENERGIC-RECEPTOR BLOCKADE ON CARDIAC AUTONOMIC TONEIN PATIENTS WITH CHRONIC STABLE ANGINA

Decreased heart rate variability, which may be due to increased sympat hetic and decreased parasympathetic activity, has been shown to be a p redictor of cardiac events after acute myocardial infarction. The pres ent study was undertaken to analyze the effect of beta adrenergic bloc kade on cardiac autonomic system in patients with chronic stable angin a. Nineteen patients (15 males and 4 females, age range 44-74 years) w ith chronic stable angina were enrolled. After stopping all cardiac me dications, patients had two baseline treadmill tests with both reprodu cible angina and ST depression and a baseline 48-hour ambulatory ECG r ecording. A long-acting beta-blocker (atenolol or betaxolol) was start ed and titrated to the maximal tolerated dose. After 1-2 months, a rep eat 48-hour ambulatory ECG recording on beta-blocker therapy was obtai ned. Heart rate variability analysis was performed on the baseline and drug therapy ECG recordings. The average heart rate significantly dec reased (P < 0.008), and the mean RR interval significantly increased ( P < 0.0001). in the time-domain analysis, the standard deviation, vari ance, ASDNN5, and SDANN5 were not significantly affected, although the PNN50 increased. in the frequency domain, the total power (P < 0.0001 ) and the low frequency (P < 0.001) components decreased, while the hi gh frequency spectrum was unchanged. Thus, sympathetic activity signif icantly declined in patients with chronic stable angina on beta-blocke r therapy, while parasympathetic tone demonstrated a heterogenous resp onse.