Day-to-day variability of the long-term fractal component of heart rate variability (β) and the effect of an antianginal agent in patients with silent myocardial ischemia

The deterioration of the long-term fractal component of heart rate variability (beta) is reported in patients with organic heart disease. To examine the day-to-day variability of beta and to study the effects of nipradilol (NIP), an antianginal agent, on beta in patients with coronary artery disease (CAD), we performed 24-hour ambulatory ECG (AECG) in 24 patients with silent myocardial ischemia (SMI) and obtained the conventional frequency domain heart rate variability, (HRV) indices and beta using the MemCalc system. Patients were divided into two groups: group I consisted of 10 patients (64 5 years of age) for the assessment of the day-to-day variability of beta; group II comprised 14 patients (60 6 years of age) for evaluation of the effect of NIP (3 mg b.i.d). In group I, AECG was repeated twice a week, while AECG was recorded before NIP treatment (placebo) and on the last day of the 4-week NIP treatment in group II. In group I, there was significant correlation between the values of beta on day 1 and day 2 (r=0.79, p<0.05), the difference being 0.09+/-0.15 (coefficient of variance: 6.8%). Bland and Altman's analysis indicated that the results were easily reproducible, making this approach feasible for clinical use. In group II, NIP significantly decreased the values of beta by 10.6% (from -1.23+/-0.09 to -1.18+/-0.07; p<0.05). NIP also significantly increased the conventional HRV indices. The degree of decrement of beta by NIP was larger than that of the day-to-day variability. In conclusion, a day-today variability exists in beta in patients with SMI, but its value is relatively small. A daily dose of 6 mg NIP ameliorates beta and overcomes this variability. (C) 2004 Elsevier SAS. All rights reserved.