| Objective It is considered that head-up tilt testing(HUT) is the most valuable method for diagnosis of vasovagal syncope. Because of many factors associated with tilt testing , there is no common and standard protocol . The aim of this study is to find a new method, which should be easily performed, time-saving, more tolerable and suitable to clinical practice. And to evaluate rational dose of isosorbide dinitrate, the results of different dose isosorbide dinitrate potentiating head-up tilt testing (ISDNHUT) were compared with that of isoproterenol potentiating head-up tilt testing (ISOPHUT). Materials and Methods 100 patients with unexplained syncope (34 men and 66 women , mean age of 39.1+10.6 years, ranging from 15 to71 years ) and 60 normol subjects as control (23 men and 37 women, mean age of 27.6+4.3 years , ranging from 19 to 43 years ) were randomized into three groups , each group were tilted upright to 70 degrees for 30 minutes as baseline head-up tilt testing (BHUT). If syncope did not occur, different drugs were given : In group A (33 patients and 20 normol subjects in control group), sublingual isosorbide dinitrate (1.25mg) was administered at the end of BHUT. In group B (34 patients and 20 normol subjects in control group), sublingual isosorbide dinitrate (2.5mg) was administered at the end of BHUT. Observations of tilt testing were continued at the same angle for 20 minutes in both group Aand B. In group C (33 patients and 20 normol subjects in control group), patients were returned to supine position at the end of BHUT, intravenous isoproterenol was given at a rate of 3 U g/min for 5 minutes, then tilt testing was continued at 70 degrees for 10 minutes. Results In group A, four of thirty-three patients (12.1%) had a positive response to BHUT. another fourteen patients (42.4%) had a positive response after ISDNHUT(1.25mg). The mean time to syncope was 9.1 +3.7 minutesC from 3 to 16 minutes), and total positive rate was 54.5%, specificity was 95%. Only one patient (3%) had mild headache. In group B, four of thirty-four patients (11.8%) had positive response to BHUT, another seventeen patients (50%) had a positive response after ISDNHUT (2.5mg). The mean time to syncope was 8.4+3.2 minutes ( from 3 to 13 minutes) and total positive rate was 61.8%, specificity was 70%. Three cases had mild headache. In group C, four of thirty-three patients (12.1%) had positive response to BHUT, another thirteen patients (39.4%) had a positive response after ISOPHUT. The mean time to syncope was 3.5+2.8 minutes (from 0.5 to 9 minutes) and total positive rate was 51.5%. specificity was 90% . Two patients (6.1%) had severe side effects , including chest discomfort, angina pectoris). The differences of positive rate among three groups were not statistically significant. The specificity of group B (70%) was much lower than that of group A (95%) (P<0.05). Conclusion Shortened head-up tilt testing potentiated with sublingual low-dose isosorbide dinitrate (1.25mg) provides an adequate positivity and significant specificity. It had a lot of merits, shch as convenience, time-saving , well-toleration , etc. Thus, we recommend it may be used in routine clinical practice as a valuable method of diagnosing vasovagal syncope.
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