BAROREFLEX SENSITIVITY AND NEUROHORMONAL ACTIVATION IN PATIENTS WITH ACUTE MYOCARDIAL-INFARCTION

Objective-To examine the relationship between baroreflex sensitivity a nd neurohormonal activation in patients with an acute myocardial infar ction. Methods-Baroreflex sensitivity, plasma noradrenaline, atrial na triuretic factor, endothelin-1, and plasma renin activity were measure d in 37 male patients about 10 days after their first myocardial infar ction, and in 15 healthy controls. Baroreflex sensitivity was assessed from the regression line relating the change in RR interval to the ch ange in systolic blood pressure following an intravenous bolus injecti on of phenylephrine. The measurements were repeated after a follow up of three months. Results-There was a significant inverse correlation b etween baroreflex sensitivity and plasma noradrenaline measured before hospital discharge (r = -0.43, P < 0.01). Patients with increased pla sma noradrenaline (greater than or equal to 2SD above the mean of the age matched control group) had significantly lower baroreflex sensitiv ity than patients with normal plasma noradrenaline (8.7 (SD 4.6) v 12. 1 (6.1) P < 0.05). The change in baroreflex sensitivity during the fol low up showed a significant inverse correlation with the change of pla sma nor-adrenaline (r = -0.450, P < 0.01). Furthermore, when patients with increased plasma noradrenaline before hospital discharge were ana lysed separately, baroreflex sensitivity at three months in patients i n whom plasma noradrenaline had decreased to normal values was signifi cantly higher than in patients in whom plasma noradrenaline had remain ed increased (14.6 (5.7) v 8.1 (8.1) ms/mm Hg, P < 0.05). On the other hand, baroreflex sensitivity was not related to the levels of plasma atrial natriuretic factor, plasma endothelin-1, or plasma renin activi ty. Neither was any relationship found between change in baroreflex se nsitivity and change in plasma atrial natriuretic factor, endothelin-1 , or plasma renin activity during the follow up. Conclusions-The impai rment baroreflex sensitivity after myocardial infarction was associate d with increased concentration of plasma noradrenaline, that is, sympa thetic activation, but not with plasma atrial natriuretic factor, endo thelin-1, or plasma renin activity. Baroreflex sensitivity provides in formation about cardiac vagal control as well as about the balance of cardiac sympathetic-parasympathetic regulation.