Detection of patients at risk for sudden heart death by long-term ECG. The role of life-threatening ventricular arrhythmias]

Recognition of patients at risk of sudden cardiac death and prevention of such lethal events represent important and, for the most part, unresolved problems in clinical cardiology. From pathologic-anatomical and clinical studies of instances of sudden death it is known that in more than 80% the lethal electrical events, that is ventricular fibrillation, are attributable to myocardial ischemia, usually due to coronary artery disease. Experience in experimental studies as well as in treatment of patients with myocardial infarction on coronary care units has shown that certain types of arrhythmias such as frequent, multiform, repetitive and early-occurring (R-on-T) ventricular premature beats, in particular, may be associated with sudden arrhythmic cardiac death. Accordingly, in 1971, Lown and Wolf proposed a system for grading of ventricular arrhythmias and their severity which assumed world-wide importance for clinical and prognostic studies. This system of classification contains quantitative and qualitative criteria and is ordered in part on exclusion and in part on hierarchy, in which it is implied that the hierarchy of ventricular premature beats corresponds with that of the risk of death. Since the system enables only semiquantitative delineation of ventricular arrhythmias whose absolute number, however, within a given observation period appears to be of prognostic relevance and, additionally, since the Lown system is encumbered by the fact that classification is based only on the most severe arrhythmia with subsequent loss of information regarding concurrent arrhythmias of lesser severity, Bigger and his associates, in 1978, suggested a modification to provide quantification of all ventricular premature beats. In addition to the problems inherent to grading ventricular premature beats, further problems are also incurred with respect to spontaneous variability of ventricular arrhythmias. Based on statistical considerations and clinical studies accordingly, adequate assessment of complex ventricular arrhythmias prerequisites continuous monitoring for a period of 24 to 48 hours. Furthermore, for the exact recognition and quantitative detection of ventricular arrhythmias, the reliability of the individual systems for continuous ECG monitoring plays an important role since, by no means, have they all been validated in arrhythmia-detection capabilities. Since 1971, a number of clinical studies have shown, in particular, that complex ventricular arrhythmias are of important prognostic relevance in characterization of patients at risk of sudden cardiac death. The results may be summarized as follows: Ventricular premature beats can be found frequently in