Days required for 75% suppression of ventricular premature contractions by antiarrhythmic agents obtained from continuous in-hospital ECG monitoring.

To determine the number of days required to obtain 75% suppression of ventricular premature contractions (VPCs) by antiarrhythmic agents, which was expressed as t1/4, we performed 32 in-hospital continuous all day ECG monitoring trials in four groups of 28 symptomatic patients (ages; 54 +/- 20 years-old) with frequent VPCs. Nine patients had no organic heart disease (group 1, 11 trials), nine had valvular heart disease (group 2, 10 trials), three had dilated cardiomyopathy (group 3, 3 trials) and seven had myocardial infarction within two to four weeks onset (group 4, 8 trials). All patients were monitored by ECG telemetry with an arrhythmia analyzer, which could count hourly and daily VPCs. Class I antiarrhythmic agents were given in 18 trials, class II in two trials and class I+ class II in 12 trials. Plasma concentrations of the antiarrhythmic agents were monitored in 11 trials. In 21 trials, t1/4 could be obtained; ten (91%), six (60%), three (100%) and two trials (25%) in the four groups, respectively (p < 0.05). The value of t1/4 in the four groups was 6 +/- 6, 7 +/- 6, 14 +/- 11 and 13 +/- 2 days, respectively (mean 8 +/- 7 days; N.S.). Immediate response to the initial antiarrhythmic agent administration, expressed as percent VPC count after three hours, correlated significantly with t1/4 (r = 0.696, p = 0.0006), but ejection fraction, patient's age, control VPC counts or plasma antiarrhythmic agent level did not correlate with t1/4. In conclusion, t1/4 is a useful index for the evaluation of VPC suppression, revealing wide inter-individual variations and can be roughly estimated from the immediate response to the initial antiarrhythmic agent administration.