Isoprenaline versus nitroglycerine in head-up tilt test

HUTT test is used in evaluation of syncope. Isoprenaline and isosorbide dinitrate are used to increase the sensitivity of the test. These drugs act by different mechanisms. We aimed to compare the results of isoprenaline with isosorbide dinitrate.

We studied 198 subjects referred for HUTT to our institute; those above the age of 35 years were not included in our study, because isoprenaline was not used commonly above this age; thus, only 90 subjects were analyzed. We found that isosorbide dinitrate resulted in more HUTT-positive results than isoprenaline by absolute risk difference of 26%; relative risk for positive isoprenaline was 60%, confidence interval 0.38-0.93, and P value of 0.03. There was no difference in frequency of types of responses, i.e. Type 1, Type 2, and Type 3 between passive testing, isosorbide dinitrate, and isoprenaline, confidence interval 1.53-2.02, and P value 0.71. Time to get positive response was highest for passive testing followed by ISO and ISDN; the mean was 16.85±7.00min, 9.85±5.84min, and 7.00±3.35min, respectively. Statistically, ISDN versus ISO time to get positive response was not significant; P value was 0.074 and 95% confidence interval was -0.28 to 5.98.

Isosorbide dinitrate yields more positive HUTT than isoprenaline. The frequencies of type of responses are not different between passive testing, isosorbide dinitrate, and isoprenaline. There is no difference in time taken for positive response between isosorbide dinitrate and isoprenaline. In comparison to isosorbide dinitrate and isoprenaline, passive testing showed longest time for positive response.