Effect of labetalol on preload in acute myocardial infarction with systemic hypertension

We assessed the effects of labetalol on pulmonary wedge pressure (PWP) and other hemodynamic variables in 18 patients with acute myocardial infarction (AMI) and systemic hypertension (systolic blood pressure greater than 150 mm Hg). According to the initial value of PWP, the patients were separated into two groups of nine patients each: Group 1 (PWP greater than or equal to 15 mm Hg) and Group 2 (PWP less than or equal to 12 mm Hg). Labetalol was infused at increasing rates to lower systolic blood pressure below 130 mm Hg; this optimal rate (mean rates for Groups 1 and 2: 1.8 and 2.1 mg/min, respectively) was maintained for 1 h. Hemodynamic variables were measured before and after 1 h of infusion. Labetalol normalized blood pressure in both groups by a significant decrease in total systemic resistance [22% (p less than 0.001) and 13% (p less than 0.02)] and in cardiac index [17% (p less than 0.005) and 12% (p less than 0.02)]. While the hemodynamic responses were rather similar in both groups, the PWP decreased significantly (from 22 to 15 mm Hg, p less than 0.01) in Group 1, but did not change significantly in Group 2 (from 7 to 10 mm Hg, NS). The possible mechanisms behind these different responses are discussed. We conclude that labetalol is an effective drug for treating systemic hypertension in AMI which acutely decreases total systemic resistance and preload in patients with moderate left ventricular failure.