Treatment of hypertension in acute stage of myocardial infarction. Haemodynamic effects of labetalol.

Abstract

SUMMARY Labetalol was used to treat systemic hypertension (systolic blood pressure above 150 mmHg) in 11 patients with acute myocardial infarction; its haemodynamic effects and tolerance were studied.Increasing doses of labetalol were infused to lower systolic blood pressure to less than 130 mmHg; the optimal rate was then maintained for one hour (mean rate: 2.3 mg/min). Haemodynamic variables were measured before, during, and after labetalol infusion. Labetalol lowered blood pressure in all patients; this effect was related to a decrease both in total systemic resistance (17.7 to 14 IU) and in cardiac index (3.1 to 2.7 1/min per m2); the stroke index remained unchanged and the heart rate was reduced (94 to 81 beats/min). There was no significant change in the-mean pulmonary wedge pressure; it was decreased, however, in the six patients with an initial pressure greater than 15 mmHg. The double product was-greatly decreased (16 497 to 8598 mmHgx beats per min), which is favourable in acute myocardial infarction.We conclude that labetalol is a drug of choice to treat hypertension in acute myocardial infarction because it is very effective; its haemodynamic effects are likely to reduce myocardial oxygen requirements and suggest that labetalol administration does not worsen moderate left sided heart failure. The drug, however, may reduce the cardiac output.Systemic hypertension is frequent in the acute stage of myocardial infarction' and is associated with a higher incidence of complications.24 Labetalol which combines alpha and beta adrenoceptor blockade seems to be an effective drug in managing this type of hypertension.5 6 This study was designed to evaluate the haemodynamic changes and the clinical response after intravenous administration of labetalol to such patients. Patients and methodsEleven patients were studied (10 men and one woman), all of whom were less than 70 years of age.Criteria for inclusion were: (1) The following variables were calculated according to the usual formulae: cardiac index, stroke index, left ventricular stroke work index, total systemic resistance, and total pulmonary resistance. LABETALOL ADMINISTRATIONBefore the administration of labetalol, two series of stable haemodynamic measurements were obtained at five minute intervals; the mean of the two control observations was used as steady state value.Labetalol was administered intravenously by constant infusion. The infusion solution consisted of 200 mg labetalol in 150 ml 5% glucose in water. The infusion was initiated with a dose of 0-5 mg/min; at intervals of five minutes, labetalol dosage was increased by increments of 0-3 mg/min until the optimal dose for each individual patient was obtained. The dose was considered optimal when the systolic blood pressure was reduced below 130 mmHg. The infusion of labetalol was then given at this optimal dose over a period of 60 minutes. Complete sets ofhaemodynamic measurements were repeated at intervals 15, 30, and 60 minutes from the beginning of infusion at the optimal rate. The labetalo...