Prediction of non-occurrence of syncope during a tilt-table test by early heart rate variations

A recent study showed that, in a select patient population with no drug use and no cardiac or other illness, an increase in heart rate equal to or less than 18 beats per minute from baseline in the first 6 minutes of a tilt-table test at 60 degrees identifies patients who will not develop syncope during prolonged tilting, with specificity and positive predictive value nearing 100 percent. We retrospectively reviewed 110 consecutive tilt-table tests at an angle of 70 degrees or more, performed at our institutions between 1994 and 1999 in patients with and without cardiac disease or drug use. Excluded were 320 additional patients due to either incomplete heart rate documentation or development of syncope in the first ten minutes of tilting. The difference between maximal heart rate in the first ten minutes during tilting and the average of at least two baseline heart rate measurements was used to assess correlation with the non-occurrence of syncope during the same test. The tilt-table angle used varied from 70 degrees to 90 degrees (80 degrees in 89 percent of patients). There was a strongly significant (p < 0.0001) correlation between a sustained rise in heart rate equal to or less than 18 beats per minute in the first ten minutes of tilting and the non-occurrence of subsequent syncope during the test. The sensitivity, specificity, positive and negative predictive values were 75.7 percent, 65.0 percent, 79.1 percent and 60.47 percent, respectively. These data indicate that even in the routine setting, that is, a non-select population and at a higher tilt-table angle, an increase in heart rate equal to or less than 18 beats per minute in the first ten minutes of tilting constitutes a good predictor of a negative test. However, the specificity and positive predictive value of this criterion were not high enough to justify an early termination of the test.