1. Introduction
Syncope, also known as fainting, is a transient and self-limited of loss of consciousness due to reduced blood flow to the brain. Vasovagal syncope (VVS) is one of the most common types of syncope [1]. The definitive diagnosis of VVS is based on a history of syncope, clinical manifestations, and a positive head-up tilt test (HUTT) after excluding cardiac and non-cardiac causes [2]. The HUTT is a non-invasive test for VVS, but the reproducibility and sensitivity are relatively low [3]. The sensitivity of the baseline head-up tilt test (BHUT) and nitroglycerin-stimulated head-up tilt test (NHUT) are 25% and 66%, respectively, while the specificity of the BHUT and NHUT are 86% and 99%, respectively [3]. Importantly, not all VVS patients have syncopal episodes during the HUTT. Increased adrenergic tone due to emotional stress, pain, or intensive exercise may trigger and contribute to VVS [4].
The treadmill exercise test (TET) is a common, non-invasive and cost-effective test widely used in the diagnosis of coronary atherosclerotic heart disease. It is known that vasovagal syncope may occur during a TET. As such, we hypothesized that increased adrenergic tone during exercise could be an additional trigger toward orthostatic posture and venous pooling stress. The combination of a TET and a HUTT may increase the reproducibility and sensitivity for diagnosis of VVS. Therefore, the purpose of this study was to explore the diagnostic value of TET combined with HUTT for diagnosing VVS in patients with unexplained syncope or presyncope.