[Estimation of cardiac vagal reserve by dynamic exercise in patients with recent myocardial infarction]

In patients with coronary artery disease, the risk of sudden death is related to the degree of left ventricular dysfunction and to cardiac parasympathetic activity. The relation between these two consequences of myocardial infarction is still the matter of intense controversy. In this investigation, we have estimated the resting cardiac parasympathetic tone and assessed the left ventricular systolic function of 25 patients who had suffered an acute myocardial infarction. The absolute increase in heart rate recorded in the first 10 seconds of a programmed dynamic exercise, was considered as the resting cardiac parasympathetic tone or cardiac parasympathetic reserve. Twenty five age and sex-matched normal sedentary subjects were used as controls. Patients showed a significantly smaller increase in their heart rate (16 +/- 4 lats/min, M +/- DS) than the controls 32 +/- 5 P < 0.0001), during the first 10 seconds of exercise. Moreover, the absolute increase in heart rate was inversely related to the degree of left ventricular dilatation ( r = - 0.71, P < 0.0001) and directly related to the left ventricular ejection fraction (r = 0.84, P < 0.0001). In other words, those patients with larger left ventricles and depressed ventricular function had a more prominent reduction of their resting cardiac parasympathetic tone. These results indirectly suggest that, left ventricular size and function are indeed related to cardiac parasympathetic activity.