Epinephrine-induced T-wave notching in congenital long QT syndrome.
OBJECTIVE
The purpose of this study was to characterize the effect of epinephrine on T-wave morphology in patients with congenital long QT syndrome (LQTS).


BACKGROUND
QT prolongation is a paradoxical, LQT1-specific response to low-dose epinephrine infusion. At rest, notched T waves are more common in LQT2.


METHODS
Thirty subjects with LQT1, 28 with LQT2, and 32 controls were studied using epinephrine provocation. Twelve-lead ECG was recorded continuously, and QT, QTc, and heart rate were obtained during each stage. Blinded to phenotype and genotype, T-wave morphology was classified as normal, biphasic, G1 (notch at or below the apex), or G2 (distinct protuberance above the apex).


RESULTS
At baseline, 97% LQT1, 71% LQT2, and 94% control had normal T-wave profiles. During epinephrine infusion, G1- and G2-T waves were more common in LQT2 than in LQT1 (75% vs 26%, P = .009). However, epinephrine-induced G1-T waves were present in 34% of control. Epinephrine-precipitated biphasic T waves were observed similarly in all groups: LQT1 (6/30), LQT2 (3/28), and control (4/32). During low-dose epinephrine infusion (< or =0.05 microg/kg/min), G1-T waves occurred more frequently in LQT2 (LQT1: 25% vs 3%; control 9%, P = .02). Low-dose epinephrine-induced G2-T waves were detected exclusively in LQT2 (18%). Low-dose epinephrine elicited G1/G2-T waves in 8 of 15 LQT2 patients with a nondiagnostic baseline QTc.


CONCLUSIONS
Biphasic and G1-T waves are nonspecific responses to high-dose epinephrine. Changes in T-wave morphology during low-dose epinephrine (<0.05 microg/kg/min) may yield diagnostic information. G2-notched T waves elicited during low-dose epinephrine may unmask some patients with concealed LQT2.
Khositseth
Anant
A
Department of Pediatric and Adolescent Medicine, Division of Pediatric Cardiology, Mayo Clinic College of Medicine, Rochester, MN 55905, USA.
Hejlik
Joseph
J
Shen
Win-Kuang
WK
Ackerman
Michael J
MJ
D000328:Adult; D004562:Electrocardiography; D004837:Epinephrine; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008133:Long QT Syndrome / Q000503:physiopathology*; D008297:Male; D013566:Sympathomimetics
D013566:Sympathomimetics; D004837:Epinephrine