LOW-DOSE DISOPYRAMIDE OFTEN FAILS TO PREVENT NEUROGENIC SYNCOPE DURING HEAD-UP TILT TESTING

Low dose disopyramide has been used to prevent neurally-mediated synco pe during head-up tilt testing but a correlation between blood levels and efficacy has not been described. We measured disopyramide levels i n 15 patients with recurrent syncope and positive 70 degrees head-up t ilt tests who under-went one or more repeat tests on the drug. There w ere 9 males and 6 females, age range 15-78 years. Fourteen of the 15 p atients had structurally normal hearts. The daily disopyramide dose wa s 645 +/- 165 mg (mean +/- SD). Patients developed syncope during 9 te sts and had no syncope during 12 tests. The mean disopyramide level in patients with positive tests was significantly lower than the level i n patients with negative tests (2.4 +/- 0.15 mu/mL vs 3.2 +/- 0.22 mu/ mL, P = 0.018). Six patients were tested twice on different disopyrami de doses. Five of these six patients had syncope during head-up tilt t esting on the lower dose and negative tests on the higher dose (disopy ramide levels 2.2 +/- 0.17 mu/mL vs 3.2 +/- 0.17 mu/mL, P = 0.004). Th us, disopyramide is effective in preventing neurogenic syncope during head-up tilt testing but higher blood levels are often necessary for e fficacy. In a given patient, failure to respond to low dose disopyrami de does not preclude success on higher doses.