Usefulness of head up tilt test in the diagnosis of neurocardiogenic syncope.

Sir, I read with interest the article published by Udani V et al, which is a retrospective and part prospective study, evaluating the usefulness of head up tilt test in the diagnosis of neurocardiogenic syncope. The authors have made a good attempt to analyze the significance of HUTT in ruling out other perturbing causes of syncope in children and adolescents such as seizure disorders and vertigo. But there are many aspects in this study which are unclear. The study being partly prospective, investigators had an opportunity to include a control group. Without an appropriate control group, it is certainly inappropriate to attribute any significance to the positive test obtained in 16 children. It is not clear why the investigators choose to define a positive test as > 30% drop in blood pressure or heart rate and neither is it mentioned whether they were considering systolic or diastolic blood pressure. Moreover, measurement of blood pressure with a standard sphygmomanometer can produce considerable interpersonal subjective variation in the BP values. As many as 11 children showed a positive test on provocation with nitroglycerin. I would like to know the dose of the S/L nitroglycerin used and whether it is adjusted according to the body weight in this age group. Higher doses of nitroglycerin cause further venous pooling and may decrease arteriolar resistance as well, decreasing systolic and diastolic blood pressure and cardiac output and resulting in pallor, weakness and dizziness. This can lead to more number of false positive tests if the dose is not appropriately adjusted. Considering these ambiguities, this study does not provide any definitive evidence of usefulness of HUTT in the diagnosis of neurocardiogenic syncope.