Comparison between subgroups
In univariate analysis (Table 2 ), TT positivity was higher among younger syncope patients <30 years, in patients with lower SBP defined as baseline SBP below the mean value of 128 mmHg, in patients with lower HR defined as baseline HR value below the mean value of 69 bpm, and in patients without history of hypertension. In multivariable-adjusted logistic regression model (Table 2 ), younger age, lower blood pressure and heart rate, and absence of hypertension remained the independent predictors of test positivity. In particular, in the quantitative analysis, positive response to TT was predicted by younger age (Odds ratio [per 10 years], OR: 1.04; 95% confidence interval (CI), 1.01-1.07, p=0.007), lower SBP (OR [per 10 mmHg]: 1.05, 95%CI, 1.01-1.08; p=0.006), and lower heart rate (OR [per 10 bpm]: 1.17; 95%CI, 1.11-1.22, p<0.001). Absence of hypertension diagnosis increased the probability of positive TT by over 50% (OR: 1.58; 95%CI, 1.38-1.81, p<0.001). Exclusion of one database did not substantially affect the overall results except for the impact of low SBP on TT positivity, which was attenuated after exclusion of Lavagna data in the multivariable-adjusted (but not in univariate) logistic regression model (p=0.083).
Table 2 . Univariable and multivariable analysis of factors predicting tilt test positivity in patients investigated for unexplained syncope using the Italian tilt test protocol.