Introduction: Infusion of epinephrine has been used to unmask patients with LQTS. Our aim was to assess if the use of different formulas to correct the QT could modify the results of epinephrine-test.
Methods : 15 patients underwent to epinephrine-test using the protocol previously described (bolus 0.1µg/kg/min followed by continuous infusion 0.1µg/kg/min). QTcorrected(QTc) was measured using Bazett´s(BF), Fridericia´s(FriF) and Framingham´s(FraF) formulas at baseline, peak and steady-state. ?QTcsteadystate-baseline(QTc steady state-QTc baseline) and ?QTc peak-baseline(QTc peak-QTc baseline) were calculated. ?QTcsteadystate-baseline?35ms was diagnostic of LQT1, and if it was <35ms a ?QTcpeak-baseline?80ms was diagnostic of LQT2.
Results: Mean QTc(ms) were: QTcbaseline 402±19(BF), 399±18(FriF), 399±18(FraF); QTcpeak 496±46(BF), 458±44(FriF), 449±40(FraF); QTcsteady-state 444±29(B), 427±28(Fri), 426±25(Fra). 13(87%) patients showed a positive test using BF (11 LQT1, 2 LQT2), and 6(40%) with FriF and FraF (5 LQT1 and 1 LQT2). In the subgroup of patients with heart rate(HR) < 60bpm (n=7), the test was positive in 6(86%) with BF and in 2(29%) with both FriF and FraF.
Conclusions: Underestimation and overestimation the duration of cardiac repolarization at extreme low and high HR using BF could produce false positive response to epinephrine-test.