[Limitations of the stress test in the diagnosis of the sick sinus syndrome].

Exercise stress test in patients with sick sinus syndrome helps to evaluate the heart rate response to the increased sympathetic and to the decreased parasympathetic discharge. Aim of our study was the assessment of the diagnostic accuracy of exercise stress test in this condition. To do so, we measured the heart rate at peak stress in 18 patients with sick sinus syndrome (16 men and 2 women aged 51-78 years, mean 68). Two control groups were chosen: one of 14 healthy subjects of the same age and sex and a second one of 19 patients of the same age and sex, with comparable heart disease as the patients under study, but without sinus dysfunction. Heart rate at peak stress was expressed as percent of the expected maximal sex--and age--corrected heart rate (% max HR). The sick sinus syndrome group was characterized by the presence of: syncope and/or near-syncope in 10 patients; slight (2), moderate (9), severe (7) sinus bradycardia; corrected sinus node recovery time longer than 500 msec in 7 out of 15 patients, detected during an electrophysiological study; abnormal intrinsic heart rate in 5 out of 11 patients, obtained by means of drug-induced autonomic blockade (metoprolol 0,2 mg/Kg i.v. and atropine 0,04 mg/Kg i.v.), and evaluated according to Jose's equation; abnormal intrinsic corrected recovery time (greater than 450 msec) in 8 out of 11 patients; increase in heart rate after atropine infusion (0,02 mg/Kg i.v.) of less than 90 beats/min in 15 out of 18 patients.(ABSTRACT TRUNCATED AT 250 WORDS)