CARDIAC CHRONOTROPIC RESPONSIVENESS TO BETA-ADRENOCEPTOR STIMULATION IS NOT REDUCED IN THE ELDERLY

Objectives. This study evaluated cardiac beta adrenoceptor responsiven ess in the elderly. Background. The hypothesis of reduced cardiac beta -adrenoceptor responsiveness in the elderly is based on a smaller incr ease in heart rate after administration of isoproterenol, a nonselecti ve beta(1)- and beta(2)-adrenoceptor agonist. By means of dobutamine-s tress-echocardiography we were able to retest the hypothesis more accu rately because dobutamine is a relatively selective beta,adrenoceptor agonist with weak beta(2)- and alpha-adrenoceptor stimulant activity t hat prevents baroreflex-mediated changes in heart rate. Methods. After administration of stepwise incremental infusions of dobutamine, we me asured heart rate and blood pressure responses in 360 patients who had no beta-adrenergic blocking agent therapy and no side effects during the stress test. For each patient we calculated the dose of dobutamine required to increase heart rate by 50% of the maximal heart rate duri ng the highest dose of dobutamine. Results. No relation was found betw een age and sensitivity to dobutamine (n = 293). Power analysis reveal ed that this negative finding was not the result of inadequate sample size. In contrast to the prevailing hypothesis, an increased heart rat e response to dobutamine was found even in a subgroup of ''healthy'' e lderly subjects (i.e., those without concomitant disease or acute myoc ardial ischemia, n = 67) that was not related to changes in blood pres sure during stress. However, in subjects with acute ischemia (n = 109) , smokers (n = 151) or patients with a history of a previous myocardia l infarction (n = 148), dobutamine sensitivity was reduced in the elde rly despite a diminished change in systolic blood pressure with advanc ed age during dobutamine infusion. This phenomenon could be explained by a decrease in efferent cardiac baroreflex sensitivity, as has been observed during acute myocardial ischemia. There were no age-related d ifferences in plasma concentrations of dobutamine. Conclusions. No evi dence for reduced beta adrenoceptor responsiveness to dobutamine was f ound in ''healthy'' elderly subjects.