RESPONSE OF NEUROCARDIAC SYNCOPE TO BETA-BLOCKER THERAPY - INTERACTION BETWEEN AGE AND PARASYMPATHETIC TONE

Beta-blockers are a first line therapy for neurocardiac syncope, but a re not always effective. The purpose of this study was to determine wh ether differential autonomic responses to orthostasis predict the resp onse of patients with neurocardiac syncope to beta-adrenergic blockade . We computed the RMS successive difference of the RR intervals (RMSSD : a measure of cardiac parasympathetic tone) during supine and upright phases of the initial tilt test in 28 patients with syncope and posit ive till tests who were treated with atenolol. Follow-up tilt testing was performed to assess the efficacy of the drug in preventing lilt in duced neurocardiac syncope. RMSSD did not differ at baseline (supine) between those who did (n = 20) and did not (n = 8) respond to beta-blo ckade. However, withdrawal of parasympathetic tone in response to tilt varied inversely with age (r = -0.69; P < 0.01). Reduced age adjusted parasympathetic withdrawal during orthostasis was associated with a 4 7% versus 8% risk of beta-blockade failure (odds ratio = 11; P = 0.01) , Patients with diminished age adjusted parasympathetic withdrawal al during orthostatic stress are less likely to respond to beta-blocker t herapy of neurocardiac syncope than their counterparts. This may refle ct a correspondingly greater sympathetic response to orthostasis in th ese patients, but the mechanism for this interaction is undetermined.