Assessing antiarrhythmic drug efficacy: multivariate considerations

The spontaneous variability of ventricular arrhythmias is the major problem in assessing antiarrhythmic drug efficacy. Efficacy is usually assessed on one form of ventricular premature beats, namely either single beats (VPC) or more complex forms like couplets or salvos. The reduction rates required to assume efficacy with a confidence of 95 per cent are 63 per cent for VPCs, 92 per cent for couples or 96 per cent for salvos. These rates are valid for two Holter electrocardiogram recordings within one week; otherwise the rates are higher and close to 100 per cent. In this paper we extend our ratio method for calculating these criteria to consider two or all three forms of ventricular premature beats simultaneously. The method is based on the first principal component. For use in practice we decided to calculate fixed criteria for each form of ventricular premature beats. For the combination of VPCs and couplets and a confidence level of 95 per cent, reduction rates of 42 per cent for VPC and 87 per cent for couplets are required. Both criteria must be fulfilled to assume the efficacy of a drug. These criteria are lower than those for each form alone. For all three forms together, reduction rates of 28, 72 and 88 per cent for VPC, couplets and salvos respectively are required.