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Value of propranolol-induced heart rate and blood pressure changes in predicting results of tilt testing.

BACKGROUND
A degree of reduction of heart rate (HR) and blood pressure (BP) values following beta-blocker administration has been shown to indicate beta-blockade effectiveness. Whether this parameter is also useful in the identification of patients with vaso-vagal syncope (VVS) who could benefit from beta-blocker therapy, has not yet been established.


AIM
To analyse the usefulness of propranolol-induced acute changes in HR and BP in the prediction of the results of tilt testing (TT) in patients with VVS.


METHODS
The study group consisted of 37 patients with a history of at least two syncopal episodes in the past 6 months, in whom syncope was reproduced during TT. After positive baseline TT the patients were returned to supine position and were given intravenous propranolol. After 15 min supine rest the patients were tilted again using the same protocol as during the baseline test. Propranolol was considered effective when the result of the second (on drug) TT was negative or the time to syncope occurrence was longer than during baseline TT. During the whole procedure systolic BP (SBP), mean BP (MBP), diastolic BP (DBP) and HR were measured. These parameters were analysed in four different time-intervals: period I - between 13th and 15th minute of supine rest preceding the passive phase of TT, period II - between first and third minute of the passive TT, period III - following propranolol injection, between 13th and 15th minute of supine rest preceding second TT, and period IV - between first and third minute of second TT, either passive (if positive) or after NTG administration. Both, mean values and differences (Delta) in analysed parameters between various time-intervals (II-I, III-I, IV-II and IV-III) were taken into account.


RESULTS
Intravenous propranolol occurred effective in preventing syncope during second TT in 29/37 (78%) patients. The DeltaSBP, DeltaMBP and DeltaDBP values calculated from periods III and IV were significantly different between patients with or without protective effects of propranolol. The cut-off values which were computed to obtain the highest value of total predictive accuracy (the highest value of the sum of sensitivity and specificity) were -5 mmHg for DeltaSBP, -4 mmHg for DeltaMBP and -2 mmHg for DeltaDBP. A stepwise logistic regression analysis revealed that DeltaSBP of -5 mmHg or less had the highest value in the prediction of a positive response to propranolol, reaching a sensitivity of 72%, specificity of 88%, positive predictive value of 95% and negative predictive value of 48%.


CONCLUSIONS
Propranolol-induced changes in blood pressure values may predict the effectiveness of beta-blockade in preventing syncope during second TT performed after intravenous infusion of propranolol. A drug-induced reduction in systolic blood pressure of less than 5 mmHg may identify those who will benefit from beta-blocker therapy.