Baroreflex sensitivity

Background: Arterial baroreceptors play a central role in governing autonomic outflow to the heart and are involved in the electrophysiological mechanisms by which sympathetic activation may initiate a ventricular tachyarrhythmia and vagal activation may have antifibrillatory effects. Stimulation of arterial baroreceptors results in sympathoinhibition and efferent vagal activation. Cardiovascular disease may alter baroreceptor function leading to inappropriate or excessive autonomic activity in response to blood pressure changes. Methods: Evidence obtained in an experimental preparation in chronically infarcted dogs opened the way to the understanding of the importance of the analysis of baroreceptor control of heart rate in risk stratification. Among several methodologies, the measurement of the reflex R-R interval lengthening following a blood pressure rise induced by bolus injections of phenylephrine has been shown to provide clinically relevant information as a measure of the capability to augment vagal activity. Results: Following pilot studies conducted by different groups of investigators, the Autonomic Tone and Reflexes After Myocardial Infarction (ATRAMI) trial in a series of 1284 myocardial infarction patients has demonstrated that the prognostic value of baroreflex sensitivity is largely independent from the established clinical predictors Such as left ventricular ejection fraction and ventricular arrhythmias. Conclusions: In these patients, the value of the information obtained by the combination between left ventricular function and baroreflex sensitivity suggests that this analysis should be included in the risk stratification strategy for identification of patients who may need an implantable automatic defibrillator for primary prevention of sudden cardiac death. The analysis of baroreceptor reflexes is of prognostic value also in patients with chronic heart failure.