Contribution of decreased atrial function in the pathogenesis of neurally mediated syncope

One of the most important mechanisms proposed in the pathogenesis of neurally mediated syncope considers the stimulation of myocardial mechanoreceptors as the final trigger leading to reflex hypotension and bradycardia. The aim of our study was to analyze the modifications of systolic and diastolic velocities of the left ventricle by tissue Doppler echocardiography, during the upright tilt test, to confirm the presence of an increased ventricular contractility before syncope. We evaluated 47 patients (mean age 43 years) with unexplained syncope and 13 healthy subjects. Three echocardiographic recordings were collected: at baseline, during the initial 5 minutes of the test, and after 15 minutes of tilt. The upright tilt test was positive in 28 patients. During the test, all of them had a similar, significant, progressive reduction of left ventricular end-diastolic volume, left atrial area, and left atrial volume. In contrast, the left ventricular ejection fraction showed an early, more pronounced decrease in those with positive tests. By tissue Doppler echocardiography, the systolic waves remained almost unchanged, and the early filling waves decreased similarly in those with positive or negative findings and the controls. In contrast, the atrial filling waves showed a significant decrease only in patients with positive tests. In conclusion, our study did not find increased ventricular contractility before syncope. In contrast, a decreased atrial contribution to ventricular filling characterized patients with positive upright tilt test results, which, we postulate, may be an important contributory factor to vasovagal syncope.