Baroreflex sensitivity in the elderly with silent myocardial ischemia.

In order to assess high-pressure baroceptor sensitivity and parasympathetic function in elderly patients with silent myocardial ischemia, we selected 45 inpatients in our geriatric unit for a prospective cohort study of patients with coronary heart disease. All patients were over 65 years of age (37 men and 8 women) and had coronary heart disease, documented by an angiographic study and electrocardiographic evidence of myocardial ischemia during exercise stress testing, performed according to the Bruce protocol. The subjects were divided in three subgroups: group 1 (22 patients) with electrocardiographic and echocardiographic history of myocardial infarction but no angina chest pain during exercise testing; group 2 (13 patients) with no exercise induced chest pain; and group 3 (10 patients) with exercise-induced chest pain. Baroceptor sensitivity was assessed in all subjects, by evaluating heart rate changes expressed in RR interval on the basis of changes in the mean arterial pressure during intravenous infusion of stepwise doses (50-100 and 150 microg) of phenylephrine hydrochloride. Heart rate changes were also evaluated during overshoot of the Valsalva maneuver (Valsalva max.), providing an index of parasympathetic activity. Our results showed that group two patients (only silent ischemia) had significantly (P>0.001) greater baroceptor sensitivity than the other two groups (group 2; 15.2+/-1.9 ms/mmHg; group 1: 10.0+/-1.7 ms/mmHg; and group 3: 9.8+/-1.7 ms/mmHg). Group two also showed a significant positive correlation (r=0.58; P<0.05) between baroceptor sensitivity and end-diastolic pressure and a significant inverse correlation (r=-0.672; P<0.05) between baroceptor sensitivity and the ejection fraction. Group 2 patients had a significantly longer RR interval than group 1 (P<0.05) and group 3 (P<0.05); a significant positive correlation (r=0.620; P<0.05) between Valsalva max. and end-diastolic pressure; and a significant inverse correlation (r=0.694; P<0.05) between Valsalva max. and the ejection fraction. Valsalva max. and baroceptor sensitivity correlated significantly in all three groups (group 1, r=0.707; P<0.001; group 2, r=0.94; P<0.001; and group 3; r=0.833; P<0.05). In conclusion our data suggest that elderly patients with silent ischemia appear to have an increased capacity for evoking parasympathetic reflexes that could inhibit pain perception.