Continuous monitoring of an endocardial index of myocardial contractility during head-up tilt test

Background Previous studies suggest that vigorous myocardial contractions stimulate ventricular mechanoreceptors and lead to vasovagal syncope. We studied an endocardial index of myocardial contractility during the head-up tilt test in vasovagal patients and control patients, and we evaluated the effect of negative inotropic drugs on myocardial contractility and tilt test outcome. Methods and Results We investigated 19 patients with recurrent vasovagal syncope and positive tilt test (group 1) and 11 patients with no syncope and negative tilt test (group 2). Myocardial contractility was continuously measured during a tilt test (60°) through a microaccelerometer incorporated in the tip of a right ventricular electrode to sense left ventricular contractility. Patients in groups 1 and 2 were evaluated during an unmedicated tilt test, and patients in group 1 were reevaluated during a tilt test with infusion of esmolol (n = 10) or disopyramide (n = 9). During the unmedicated test, patients in group 1 exhibited a significant increase in myocardial contractility immediately on postural change (P