Apex cardiogram and systolic time intervals in acute myocardial infarction and effects of practolol

Abstract

Systolic time intervals and the ratio of the height of the a wave on the apexcardiogram to the total height of the apexcardiographic deflection (a/H) derivedfrom simultaneous electrocardiogram, phonocardiogram, carotid pulse tracing, and apex cardiogram were recorded in 20 patients with uncomplicated acute myocardial infarction and 6 patients with chest pain without acute myocardial infarction over a period of 5 days. Fifteen normal subjects were investigated on one occasion. The pre-ejection period and the isometric contraction time were shortened during the first 2 days of acute myocardial infarction with a stepwise prolongation during the following days to values seen in the normal subjects. The a/H ratio was constantly raised in the patients with acute myocardial infarction compared to controls with chest pain and normal subjects. The left ventricular ejection time index corrected for heart rates in msec (LVETI and relative left ventricular ejection time in per cent (rel. LVET)) of patients with and without acute myocardial infarction decreased during the 5 days of observation. Fourteen patients with acute myocardial infarction and recurrent chest pain and two patients with status anginosus were studied before and 30 minutes after intravenous injection of the cardioselective beta-adrenergic blocking agent practolol (average I8 2 mg). An almost immediate and pronounced relief ofpain was observed in all patients and no signs of impaired left ventricular function appeared. The product of systolic blood pressure and heart rate was much decreased by the practolol injection. Pre-ejection period and isometric contraction time increased to normal values and no changes were seen in LVETI and a/H ratio. It is suggested that an inappropriate sympathetic stimulation is an important factor in provoking recurrent pain in acute myocardial infarction. Cardioselective beta-adrenergic blockade resulted in relief of pain because of reduction of heart work in these patients and it might decrease the severity of myocardial ischaemia and limit the area of infarction.