Abstract 3323: Repolarization Parameters During Recovery Phase of the Epinephrine QT Stress Test: Gene-Specific Responses in Congenital Long QT Syndrome
Background Long QT syndrome (LQTS) is a potentially lethal, heritable arrhythmia affecting 1 in 3000 persons. Half of all patients (pts) with LQTS have a normal resting QTc. Previously, we demonstrated that the epinephrine (epi) QT stress test can unmask concealed LQT1 and LQT2. Here, we examine repolarization parameters during recovery following epi infusion.
Methods From 1999–2006, 177 pts [44 LQT1, 38 LQT2, 12 LQT3, and 83 gene negative (LQT0)] underwent an epi QT stress test in Mayo Clinic’s Long QT Syndrome Clinic. Sixty-three pts on beta-blockers were excluded. Analysis was performed blinded to genotype.
Results During infusion of low dose epi, the deltaQTepi-baseline was significantly greater in LQT1 (+70 ms, p < 0.0001) and significantly lower in LQT3 (−54 ms, p = 0.01) compared to LQT0 (−9 ms) and LQT2 (−12 ms). When examining the QT interval during recovery, particularly at 5 minutes recovery, LQT1 and LQT3 specific QT responses were observed. When compared to baseline, the absolute QT interval at 5 minutes of recovery was markedly longer in LQT1 (deltaQTrecovery-baseline = +58 ms, p < 0.0001) and shorter in LQT3 (−33 ms, p = 0.003) as compared to −2 ms (LQT0) and +5 ms (LQT2). When comparing the QT interval at 5 minutes of recovery to the maximum QT interval seen during low-dose epi infusion (deltaQTrecovery-epi), the QT interval shortened significantly in LQT1 (−21 ms, p < 0.0001) while there was no difference between the other subtypes at +9 ms (LQT0), +17 ms (LQT2) and +11 ms (LQT3).
Conclusion Akin to responses seen during epi infusion, there are gene-specific responses seen during recovery. The combined presence of deltaQTepi-baseline ≥ 30 ms, deltaQTrecovery-baseline ≥ 50 ms and QTrecovery-epi < 0 ms is highly predictive of LQT1 (PPV = 88%). In addition, a repolarization profile that effectively rules out LQT3 is QTepi-baseline > − 30 ms and QTrecovery-baseline > 0 ms (NPV = 99%). These QT responses during and after epi provocation facilitate a pre-genetic diagnosis of LQTS and guide initial treatment.