Noninvasive diagnosis of ventricular arrhythmias by means of ambulatory-ECG monitoring.

Ambulatory ECG monitoring has enabled documentation of the type and frequency of ventricular arrhythmias and their relation to symptoms as well as prognosis. On 24-hour ambulatory ECG monitoring, ventricular premature beats (VPB) can be found in healthy subjects with a prevalence of 40 to 80% which is directly related to age. Complex ventricular arrhythmias are uncommon. The prevalence of VPB is higher in patients who have underlying structural heart disease; in those resuscitated from out of hospital sudden cardiac death, it is reported to be 100%. One of the most important concerns with regard to ventricular arrhythmias is the problem of spontaneous variability. There is, however, a higher degree of reproducibility on two consecutive days in patients with more than 300 VPB/hour and in patients who have experienced sustained ventricular tachycardia than in those with infrequent VPB. When ambulatory monitoring is repeated months up to one year after the initial investigation, reproducibility of arrhythmias is poor. The mechanism of sudden cardiac death has been shown to be ventricular tachycardia or ventricular fibrillation, both of which are associated with an antecedent increase in VPB. In patients with chronic coronary artery disease, idiopathic or hypertrophic cardiomyopathy, a relationship between the presence of ventricular arrhythmias and sudden cardiac death has been described but VPB are considered to be of independent prognostic value only in those with myocardial infarction. Ambulatory ECG monitoring is the preferred noninvasive method for drug evaluation in patients with frequent ventricular arrhythmias. In general, the available antiarrhythmic drugs are effective for suppression of ventricular arrhythmias in 45 to 80% of patients. As a side-effect dependent on the underlying condition, the incidence of proarrhythmic effects varies from 6 to 19%. Medical treatment may be effective in prolonging life in resuscitated patients. Limitations of ambulatory monitoring include low reliability in the presence of infrequent ventricular arrhythmias or marked spontaneous variability, low specificity with respect to prognosis, lack of standardized definition for treatment efficacy and problems of recognizing complex forms of ventricular arrhythmias.