DAYS REQUIRED FOR 75-PERCENT 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, wh ich was expressed as tin, we performed 32 in-hospital continuous all d ay ECG monitoring trials in four groups of 28 symptomatic patients (ag es; 5+/-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 tria ls) and seven had myocardial infarction within two to four weeks onset (group 4, 8 trials). All patients were monitored by ECG telemetry wit h an arrhythmia analyzer, which could count hourly and daily VPCs. Cla ss I antiarrhythmic agents were given in 18 trials, class II in two tr ials 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 t he 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 antiarrhyt hmic agent administration, expressed as percent VPC count after three hours, correlated significantly with t1/4 (r=0.696, p=0.0006), but eje ction fraction, patient's age, control VPC counts or plasma antiarrhyt hmic agent level did not correlate with t1/4. In conclusion, t1/4 is a useful index for the evaluation of VPC suppression, revealing wide in terindividual variations and can be roughly estimated from the immedia te response to the initial antiarrhythmic agent administration.