Sympathomimetic infusion and cardiac repolarization: the normative effects of epinephrine and isoproterenol in healthy subjects.
BACKGROUND
Catecholamines are known to affect cardiac repolarization, and provocation with either isoproterenol or epinephrine has been proposed as a tool for uncovering latent repolarization abnormalities. This study systematically compares the effects of isoproterenol and epinephrine infusions on QT interval (QT), T waves and U waves in normal subjects.


RESULTS
Twenty-four normal subjects (29 +/- 8 years) were evaluated during graded infusions of up to 0.30 microg/kg/minute epinephrine and 5.0 microg/minute isoproterenol. Heart rates at peak doses were 81 +/- 13 bpm at 0.28 +/- 0.04 microg/kg/minute epinephrine and 104 +/- 5 bpm at 2.4 microg/minute isoproterenol. The longest absolute QT increase was 4 +/- 5 msec above baseline during isoproterenol (P < 0.001) and 12 +/- 23 msec during epinephrine (P = 0.07), while the longest corrected QT interval (QTc) increase was 67 +/- 28 msec (P < 0.0001) and 79 +/- 40 msec (P < 0.0001) above baseline during isoproterenol and epinephrine, respectively (P = 0.12 for difference). There was a 2-fold increase in U-wave amplitude during each intervention (P < 0.001). The specificity of paradoxical QT prolongation (>or=30 msec at 0.05 microg/kg/minute or >or=35 msec at 0.10 microg/kg/minute epinephrine) and an increase in QTc >or=600 msec at any dose epinephrine were 100%. However, the specificity of other proposed criteria that utilized QTc measurement (>or=30 msec at 0.10 microg/kg/minute or >or=65 msec at any dose) was poor whether all leads or only lead II were assessed.


CONCLUSIONS
Both epinephrine and isoproterenol are associated with QTc prolongation and amplification of the U wave in normal subjects. The specificity of proposed criteria for epinephrine provocation in diagnosis of the long-QT syndrome is variable; however, paradoxical QT prolongation at low-dose epinephrine or a QTc >or=600 msec is highly specific.
Magnano
Anthony R
AR
Division of Cardiology/Clinical Cardiac Electrophysiology, Columbia University College of Physicians and Surgeons, 161 Fort Washington Avenue HIP 5-551, New York, NY 10032, USA. arm6@columbia.edu
Talathoti
Naresh
N
Hallur
Ravindra
R
Bloomfield
Daniel M
DM
Garan
Hasan
H
D000328:Adult; D004562:Electrocardiography / Q000187:drug effects; D004837:Epinephrine / Q000008:administration & dosage* / Q000009:adverse effects; D005260:Female; D006339:Heart Rate / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D007262:Infusions, Intravenous; D007545:Isoproterenol / Q000008:administration & dosage* / Q000009:adverse effects; D008133:Long QT Syndrome / Q000139:chemically induced / Q000175:diagnosis / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D013566:Sympathomimetics / Q000008:administration & dosage / Q000009:adverse effects
D013566:Sympathomimetics; D007545:Isoproterenol; D004837:Epinephrine