Sukenobu Ito

Effects of oral diltiazem on ventricular premature contractions.

The effects of oral diltiazem (90-180 mg/day for four weeks) on ventricular premature contractions (VPCs) were studied in 16 patients with frequent VPCs using 24-hour ambulatory ECG recordings. VPC frequency was evaluated as a function of underlying heart rate. Plots of VPC frequency vs. heart rate were made at 1-beat/min intervals for all heart rates recorded for at least five minutes during 24 hours. Patterns of correlation between VPC frequency and heart rate observed before diltiazem therapy included: 1) a relatively linear increase in VPCs with heart rate (positive correlation) in ten patients, 2) a linear decrease (negative correlation) in one patient, and 3) an increase at low heart rates and a decrease at high heart rates (bidirectional correlation) in five patients. Diltiazem significantly reduced the mean VPC frequency per 24 hours for patients with a positive correlation, but induced no significant change for patients with a negative or a bidirectional correlation. At the 65% level of VPC reduction, diltiazem was effective in eight of ten patients with a positive correlation but was not effective in the six patients with other correlations (p less than 0.01). These results suggest that an evaluation of VPC frequency as a function of heart rate predicts the response of VPCs to diltiazem.

Diabetes Prolongs the Action Potential Duration in Rat Ventricular Muscle Probably Via Enhanced Calcium Current

Diabetic cardiomyopathy arises in patients suffering from diabetes mellitus for relatively long periods, and it is not secondary to hypertension, coronary artery disease, or valvular disease (1–4). A number of studies using diabetic rats as an experimental model, disclosed mechanical, biochemical and morphological changes in the heart (5,6). Fein et al. (7) found a marked slowing of relaxation and a substantial decrease of shortening velocity in the ventricular papillary muscles obtained from streptozotocin-induced diabetic rats, in which prolongation of action potential duration (APD) was also shown (8.)