[Stratification of patients at risk for sudden cardiac death with special reference to the autonomic nervous system]

The autonomic nervous system plays a decisive role in the genesis of sudden cardiac death. During recent years, two noninvasive tests for quantitative assessment of cardiac autonomic tone have become available: analysis of heart rate variability from 24-h ambulatory recordings and determination of baroreflex-sensitivity by means of the phenylephrine method. Numerous experimental and clinical studies suggest that heart rate variability assesses tonic vagal activity whereas baroreflex-sensitivity is considered to reflect phasic or reflex vagal activity. Both methods, however, are not redundant but rather complimentary. An advantage of assessment of baroreflex-sensitivity is represented by the fact that it can be performed under controlled laboratory conditions which yields a good intra- and interindividual comparability of test results. Some retrospective as well as prospective studies have assessed the value of determination of cardiac autonomic tone with respect to risk stratification after myocardial infarction. In general, these studies indicate that the combined assessment of autonomic tone together with left ventricular function yields an improved prediction particularly of the risk of dying due to arrhythmic events. It appears that baroreflex-sensitivity is particularly useful to predict arrhythmic events whereas heart rate variability seems to be linked more to cardiovascular mortality. Preliminary results of the largest prospective study of this kind, the ATRAMI study, indicate that the combined assessment of LVEF and baroreflex-sensitivity considerably improve risk stratification after myocardial infarction. If the final analysis of this trial confirms this, prospective interventional studies should be initiated to evaluate our ability of reducing the risk of sudden death based on noninvasive risk stratification.