Diagnostic utility of mechanical, pharmacological and orthostatic stimulation of the carotid sinus in patients with unexplained syncope
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OBJECTIVES: The purpose of the present study was to systematically evaluate the diagnostic utility of mechanical, pharmacological and orthostatic stimulation of the carotid sinus in a consecutive series of patients with recurrent unexplained syncope. BACKGROUND: Carotid sinus hypersensitivity (CSH) is an infrequently recognized cause of recurrent unexplained syncope usually diagnosed by carotid sinus massage (CSM) in the supine position. The diagnostic utility of systematic 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 recurrent unexplained syncope (mean episodes: 6 +/- 3); 30 age-matched controls (65 +/- 14 years) and 16 patients (59 +/- 12 years) with syncope not related to CSH were studied. Pharmacological stimulation of the carotid sinus was achieved by randomly administering bolus injections of nitroprusside and phenylephrine. Mechanical stimulation of the carotid sinus was performed by CSM applied for 5 s in the supine position and after 2 min at 60 degrees. A 60 degree low-dose isoproterenol head-up tilt test (HUTT) was also performed for a total duration of 30 min. RESULTS: Carotid sinus hypersensitivity was elicited by CSM in the supine position 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 degree HUTT, increasing the diagnostic yield by 51%. Baroreceptor gain was significantly 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 syncope but not positive in any of the patients in which syncope remained unexplained. 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 position and 60% in the upright position. Sensitivity was increased by 51%, and diagnostic accuracy was enhanced by 38% by performing CSM in the upright position. Decreased baroreceptor gain was documented and may play a role in the pathophysiology of CSH.
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