EFFECTS OF AMIODARONE ON THE CIRCADIAN-RHYTHM AND POWER SPECTRAL CHANGES OF HEART-RATE AND QT INTERVAL - SIGNIFICANCE FOR THE CONTROL OF SUDDEN CARDIAC DEATH

Effects of chronic amiodarone therapy on the circadian rhythmicity and power spectral changes of heart rate and QT intervals from Holter rec ordings were evaluated in three groups of patients: group 1 baseline ( n = 10); group 2, treated for 3 to 8 months (n = 11); and group 3, tre ated for >1 year(n = 13). Amiodarone reduced heart rate, which reached steady state at 3 to 6 months; bradycardia was evident during the ent ire 24 hours. The corrected QT (QT(c)) interval increased as a functio n of treatment duration. It was 457 +/- 39, 530 + 28 (p < 0.001), and 581 +/- 36 (p < 0.0002) msec for groups 1, 2, and 3, after 6 months, r espectively. The circadian rhythmicity of QT, was abolished in group 3 . Power spectral analysis showed a tendency for amiodarone to reduce b oth R-R and QT interval variabilities, suggesting inhibition of autono mic control on the heart by the drug. The effectiveness of amiodarone against ventricular arrhythmias may result in part from the sustained bradycardia in concert with continuous uniform prolongation of myocard ial repolarization.