EFFECT OF BETA-BLOCKADE ON BAROREFLEX SENSITIVITY AND CARDIOVASCULAR AUTONOMIC FUNCTION-TESTS IN PATIENTS WITH CORONARY-ARTERY DISEASE

We wished to assess rite effects of beta-blockade on baroreflex sensit ivity and standard rests of integrity of autonomic nervous function in patients with coronary artery disease, and to determine whether the e ffects of lipophilic (metoprolol) and hydrophilic (atenolol) beta-bloc kers differ. Beta-blocking drugs increase spontaneous heart rate varia bility in healthy subjects and in patients with coronary heart disease , but little is known about their effects on baroreflex sensitivity an d heart-rate based tests of autonomic integrity. In a randomly allocat ed double-blind crossover study with three 2-week treatment periods, m etoprolol CR 200 mg once a day, or atenolol 100 mg once a day, or plac ebo once a day, were administered to 18 male patients with stable coro nary artery disease. Baroreflex sensitivity was determined from the na tural baroreflex challenge of Valsalva strain. Heart rate reactions to standard stimuli were measured. No significant differences were found between the effects of atenolol and metoprolol. Beta-blockade did not significantly affect the baroreflex sensitivity, but it diminished th e Valsalva ratio significantly (P<0.001). The difference between mnxim um and minimum heart rate during hyperventilation was also significant ly lower during beta-blockade. The heart rate response to standing up and the ratio of maximum to minimum heart rate during deep breathing w ere not influenced by beta-blockade. Discontinuation of beta-blockade seems to be unnecessary for reliable determination of baroreflex sensi tivity in patients with coronary artery disease, when the natural pres sure challenge of Valsalva strain is used. Both hydrophilic and lipoph ilic beta-blockers interfere with certain diagnostic tests of autonomi c nervous function. These effects must be taken into account when usin g these tests in the diagnosis of autonomic dysfunction and neuropathy .