[Limits of quantitative evaluation methods]

Technical considerations limit the arrhythmias quantifiable by Holter monitoring to atrial and ventricular extrasystoles. However, benign atrial extrasystoles are often neglected and are not considered a target of importance for the study of antiarrhythmic drugs. As regards quantification of ventricular extrasystoles, possible causes of bias should be recognised: the exclusion of patients with dominant irregular and/or wide QRS rhythms, the failure to take global heart rate into account, the qualitative approach to assessment of important parameters such as QRS morphology, coupling interval, grouping which are only considered statistically in terms of prevalence. As a result of these limitations major arrhythmias both at atrial level (salvos of extrasystoles, atrial tachycardia, flutter, fibrillation) and junctional (paroxysmal reciprocating tachycardia) and ventricular levels (ventricular tachycardias of differing origins and types) are systematically disregarded by quantitative standardised protocols, although modern antiarrhythmic agents have been introduced precisely for their treatment. To consider minor arrhythmias more reliable models for study than serious ones because they are easier to quantity, is an error which has been well demonstrated, as in many respects we still do not know how to quantify relatively important parameters. A good example of this situation is the confusion and contradictions in the literature about the long-term prognosis of myocardial infarction evaluated by methods of counting ventricular extrasystoles: the most formal conclusions are drawn from reports containing the least and most qualitative data and which include bias unrelated to the techniques, chosen consciously or not by the authors.