Comparison between isoproterenol and nitroglycerin sensitized head-upright tilt in patients with unexplained syncope and negative or positive passive head-up tilt response

It is unknown if the head-upright tilt test in patients who receive isoproterenol and nitroglycerin can identify different populations with vasovagal syncope. The aim of this study was to compare the positive or negative responses to passive tilt between