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.