Reduced systemic vascular resistance in healthy volunteers with presyncopal symptoms during a nitrate‐stimulated tilt‐table test

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT • Nitrates may facilitate syncope through various pathways, but the precise mechanism of nitrate‐induced syncope is still under debate. The purpose of the present study was to compare the underlying haemodynamic mechanisms in subjects without and with presyncopal symptoms during a nitroglycerin‐stimulated tilt‐table test. WHAT THIS STUDY ADDS • A major decrease in systemic vascular resistance was documented in subjects with presyncope during 0.25 mg nitroglycerin‐stimulated tilt‐table test, in the absence of changes in cardiac output. These findings indicated that even a small dose of nitroglycerin significantly decreased arterial resistance and cardiac afterload. AIMS The mechanism of nitrate‐induced syncope remains controversial. We examined the haemodynamic changes in healthy volunteers during nitroglycerin‐stimulated tilt‐table test. METHODS Continuous radial pulse wave analysis, whole‐body impedance cardiography and plethysmographic finger blood pressure were recorded in a supine position and during head‐up tilt in 21 subjects with presyncopal symptoms (6 male/15 female, age 43 ± 3 years) after 0.25 mg sublingual nitroglycerin and 21 control subjects (6 male/15 female, age 43 ± 2 years). The drug was administered in the supine position and a passive head‐up tilt followed 5 min later. Additionally, nitroglycerin was only administered during head‐up tilt in 19 subjects and the haemodynamics were recorded. RESULTS Supine and upright haemodynamics were similar before nitroglycerin administration in the two groups. During the nitroglycerin‐stimulated tilt test, aortic and radial mean blood pressure decreased significantly more in the presyncope group when compared with the controls (P= 0.0006 and P= 0.0004, respectively). The decreases in systemic vascular resistance (P= 0.0008) and heart rate (P= 0.002), and increase in aortic reflection time (P= 0.0002) were greater in the presyncope group, while the change in cardiac index was not different between the groups (P= 0.14). If nitroglycerin was administered during the upright tilt and not in supine position, the haemodynamic changes were quite corresponding. CONCLUSIONS Presyncopal symptoms during nitrate‐stimulated tilt test were explained by decreased systemic vascular resistance and increased aortic reflection time, while cardiac output remained unchanged. These findings indicated reduced arterial resistance in nitroglycerin‐induced presyncope.