Diagnostic utility of mechanical, pharmacological and orthostatic stimulation of the carotid sinus in patients with unexplained syncope

OBJECTIVES The purpose of the present study was to systematically evaluate the diagnostic utility of mechanical, pharmacological and orthostatic stimu lation of the carotid sinus in a consecutive series of patients with recurr ent unexplained syncope. BACKGROUND Carotid sinus hypersensitivity (CSH) is an infrequently recogniz ed cause of recurrent unexplained syncope usually diagnosed by carotid sinu s massage (CSM) in the supine position. The diagnostic utility of systemati c assessment of mechanical, pharmacological and orthostatic stimulation of the carotid sinus has not been clearly established. METHODS Eighty consecutive patients (63 +/- 12 years) with a history of rec urrent unexplained syncope (mean episodes: 6 +/- 3); 30 age-matched control s (65 +/- 14 years) and 16 patients (59 +/- 12 years) with syncope not rela ted to CSH were studied. Pharmacological stimulation of the carotid sinus w as achieved by randomly administering bolus injections of nitroprusside and phenylephrine. Mechanical stimulation of the carotid sinus was performed b y CSM applied for 5 s in the supine position and after 2 min at 60 degrees. A 60 degrees low-dose isoproterenol head-up tilt test (HUTT) was also perf ormed for a total duration of 30 min. RESULTS Carotid sinus hypersensitivity was elicited by CSM in the supine po sition in seven (8.7%) patients, two (6.6%) controls and one (6.3%) patient with syncope unrelated to CSH, compared with 48 (60%) patients, two (6.6%) controls and one (6.3%) syncope unrelated to CSH patient after 60 degrees HUTT, increasing the diagnostic yield by 51%. Baroreceptor gain was signifi cantly reduced in the CSH group. Head-up tilt test was positive in 12 (25%) patients with CSH, two (6.6%) controls and two (12%) with documented synco pe but not positive in any of the patients in which syncope remained unexpl ained. Diagnostic accuracy was enhanced by 38% (31% supine vs. 69% upright) when CSM was performed at 60 degrees. CONCLUSIONS CSH was documented in 68% of patients, 8.7% in the supine posit ion and 60% in the upright position. Sensitivity was increased by 51%, and diagnostic accuracy was enhanced by 38% by performing CSM in the upright po sition. Decreased baroreceptor gain nas documented and may play a role in t he pathophysiology of CSH. (C) 1999 by the American College of Cardiology.