Effect of the calcium antagonist diltiazem on atrioventricular conduction in chronic atrial fibrillation.

The effect of oral diltiazem treatment on the mean ventricular rate was studied in 10 patients with stable atrial fibrillation (AF). The profile of mean ventricular rate was analyzed by means of 24-hour electrocardiographic recordings. Both single-dose (120 mg) and maintenance therapy (80 mg 3 times daily) reduced the mean ventricular rate significantly. After the single dose, the effect set in after 120 +/- 40 minutes (mean +/- standard deviation) and persisted for 347 +/- 84 minutes. Histograms of RR intervals were plotted and their changes after diltiazem therapy were also analyzed. The shortest and longest atrioventricular (AV) conduction times were defined as 5% and 95% values of the cumulative frequency curve, respectively. There were 2 distinct types of the RR-interval histographic changes: In 50% of the patients, the longest and shortest RR intervals prolonged proportionately; in the other 50%, the longest intervals increased disproportionately. Results indicate that oral diltiazem treatment can significantly decrease the mean ventricular rate in patients with AF by influencing the concealed conduction in the AV node. The changes of the RR-interval histograms suggest that in 50% of the patients, the increase of the concealed conduction was probably caused primarily by the increase of AF rate, and in 50% both increased AF rate and prolonged refractory period in the AV node contributed to the increase of concealed conduction.