Excessive myocardial contraction in vasovagal syncope demonstrated by echocardiography during head-up tilt test

The purpose of this study was to gain insight into the mechanism of vasovagal syncope and to test the efficacy of theophylline to prevent syncope. Twenty-six patients with vasovagal syncope underwent two-dimensional echocardiography and theophylline test during head-up tilt test. A standard parasternal short-axis view of echocardiography at the level of the papillary muscle was recorded to measure fraction shorting of the left ventricle, and left ventricular end-diastolic and end-systolic dimensions. Heart rate, blood pressure, and symptoms were recorded. There were three groups; Group 1: no syncope with and without isoproterenol (n = 5); Group 2: syncope only after the infusion of isoproterenol (n = 16); Group 3: syncope without isoproterenol (n = 5). Groups 2 and 3 proceeded to theophylline injection (250 mg). The study showed that the 80 degrees tilt induced an increase in heart rate of 6.6 +/- 4.0, 12.4 +/- 6.6, and 25.4 +/- 4.5 beats/min in Groups 1,2, and 3, respectively (p <0.05 in Groups 1 and 2, p < 0.05 in Groups 1 and 3). The addition of isoproterenol during posture change from supine to an 80 degrees tilt made the significant change of fractional shortening from 0.4 +/- 5% to 6 +/- 13% in Group 2 (p = 0.05), compared with no significant change in Group 1. There were no significant differences in left ventricular end-diastolic dimension and end-systolic dimension in each group between baseline and isoproterenol infusion during posture change. Vasovagal syncope was associated with vigorous myocardial contraction, rather than with contraction against an empty left ventricle. The acute loading of theophylline was not effective in preventing vasovagal syncope.