EFFECTS OF ACETYLSTROPHANTHIDIN ON BAROREFLEX SENSITIVITY IN PATIENTSWITH ACUTE MYOCARDIAL-INFARCTION

We evaluated the effects of acetylstrophanthidin on baroreflex sensiti vity in patients soon after an acute myocardial infarction. Baroreflex control of heart rate is frequently depressed after acute myocardial infarction and few data are available as to the effects of pharmacolog ical intervention on this parameter. The reflex chronotropic response to arterial baroreceptor stimulation was assessed in 29 patients with uncomplicated acute myocardial infarction in control conditions (72-96 h after symptom onset) and 30 min after acetylstrophanthidin administ ration. To check for spontaneous baroreflex sensitivity variations, 24 patients with the same characteristics were evaluated at the same tim e intervals before and after a 10-cc bolus of saline placebo. Barorefl ex sensitivity was assessed by calculating the regression line relatin g phenylephrine-induced increases in systolic blood pressure to the at tendant changes in RR intervals. Mean baseline baroreflex sensitivity value for the whole study population was 7.4 +/- 4.5 ms/mmHg and was u nchanged, 7.0 +/- 4.5 ms/mmHg, after acetylstrophanthidin (P = NS). Me an baroreflex sensitivity values were also comparable dividing patient s according to the site of infarction both before and after acetylstro phanthidin. Despite the lack of difference in mean baroreflex sensitiv ity values between the two studies, at a post hoc analysis an inverse relation was found in the total study population between baseline baro reflex sensitivity values and their changes after acetylstrophanthidin (r = -0.62; P < 0.005). The inverse relation was also evident separat ely in anterior (r = -0.57; P < 0.05) and in inferior (r = -0.70; P < 0.005) myocardial infarction patients. In the control group no differe nce was observed between mean baroreflex sensitivity values obtained i n the two studies, nor was there any relationship between baseline bar oreflex sensitivity values and their changes after placebo administrat ion. These data demonstrate that after myocardial infarction acetylstr ophanthidin administration had no effect on mean baroreflex sensitivit y value. However, this drug seems to improve baroreflex sensitivity wh en it is depressed and to worsen it when normal or nearly normal.