The Active Stand and Tilt Tests

A critical step in the clinical evaluation of postural tachycardia syndrome (PoTS) is the assessment of orthostatic tachycardia. Active stand testing (AST) and head up tilt table testing (HUT) can both be used to evaluate the presence of this tachycardia. Drugs that affect heart rate (HR), sympathetic nervous system activity, or blood volume should be withheld prior to the orthostatic test. There are several important methodological and physiological differences with HUT versus AST. Orthostatic heart rate is typically higher during HUT than with AST, and requires specialized equipment that is not available to all clinicians. Conversely, AST is convenient, cost-effective and can be performed in the primary care physician office. Reflex tachycardia specific to initial orthostatic hypotension may be greater in the initial minutes of AST, compared to HUT, and this should be considered in the evaluation of early AST HR responses. The AST has similar sensitivity and greater specificity than HUT. Overall, AST should be used as the first line diagnostic tool during assessment of orthostatic tachycardia in PoTS.