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J Am Coll Cardiol, 2003; 41:633-642, doi:10.1016/S0735-1097(02)02850-4
© 2003 by the American College of Cardiology Foundation
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CLINICAL STUDY: CARDIAC ELECTROPHYSIOLOGY

Epinephrine unmasks latent mutation carriers with LQT1 form of congenital long-QT syndrome

Wataru Shimizu, MD, PhD*,*, Takashi Noda, MD*, Hiroshi Takaki, MD{dagger}, Takashi Kurita, MD, PhD*, Noritoshi Nagaya, MD, PhD*, Kazuhiro Satomi, MD*, Kazuhiro Suyama, MD, PhD*, Naohiko Aihara, MD*, Shiro Kamakura, MD, PhD*, Kenji Sunagawa, MD, PhD{dagger}, Shigeyuki Echigo, MD{ddagger}, Kazufumi Nakamura, MD, PhD§, Tohru Ohe, MD, PhD, FACC§, Jeffrey A. Towbin, MD||, Carlo Napolitano, MD, PhD and Silvia G. Priori, MD, PhD

* Division of Cardiology, Department of Internal Medicine, Suita, Japan
{dagger} Department of Cardiovascular DynamicsSuita, Japan
{ddagger} Department of Pediatrics, National Cardiovascular Center, Suita, Japan
§ Department of Cardiovascular Medicine, Okayama University Graduate School of Medical and Dentistry, Okayama, Japan
|| Department of Pediatrics (Cardiology), Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, USA
Molecular Cardiology, Salvatore Maugeri Foundation, IRCCS, Pavia, Italy

Manuscript received August 19, 2002; revised manuscript received October 14, 2002, accepted October 31, 2002.

* Reprint requests and correspondence: Dr. Wataru Shimizu, Division of Cardiology, Department of Internal Medicine, National Cardiovascular Center, 5-7-1 Fujishiro-dai, Suita, Osaka 565-8565, Japan.
wshimizu{at}hsp.ncvc.go.jp

OBJECTIVES: This study was designed to test the hypothesis that epinephrine infusion may be a provocative test able to unmask nonpenetrant KCNQ1 mutation carriers.

BACKGROUND: The LQT1 form of congenital long QT syndrome is associated with high vulnerability to sympathetic stimulation and appears with incomplete penetrance.

METHODS: The 12-lead electrocardiographic parameters before and after epinephrine infusion were compared among 19 mutation carriers with a baseline corrected QT interval (QTc) of ≥460 ms (Group I), 15 mutation carriers with a QTc of <460 ms (Group II), 12 nonmutation carriers (Group III), and 15 controls (Group IV).

RESULTS: The mean corrected Q-Tend (QTce), Q-Tpeak (QTcp), and Tpeak-end (Tcp-e) intervals among 12-leads before epinephrine were significantly larger in Group I than in the other three groups. Epinephrine (0.1 µg/kg/min) increased significantly the mean QTce, QTcp, Tcp-e, and the dispersion of QTcp in Groups I and II, but not in Groups III and IV. The sensitivity and specificity of QTce measurements to identify mutation carriers were 59% (20/34) and 100% (27/27), respectively, before epinephrine, and the sensitivity was substantially improved to 91% (31/34) without the expense of specificity (100%, 27/27) after epinephrine. The mean QTce, QTcp, and Tcp-e before and after epinephrine were significantly larger in 15 symptomatic than in 19 asymptomatic mutation carriers in Groups I and II, and the prolongation of the mean QTce with epinephrine was significantly larger in symptomatic patients.

CONCLUSIONS: Epinephrine challenge is a powerful test to establish electrocardiographic diagnosis in silent LQT1 mutation carriers, thus allowing implementation of prophylactic measures aimed at reducing sudden cardiac death.

Abbreviations and Acronyms
  APD
  action potential duration
  ECG
  electrocardiogram
  IKs
  slow component of the delayed rectifier potassium current
  INa
  sodium current
  INa-Ca
  Na+/Ca2+ exchange current
  LQTS
  long QT syndrome
  QTc
  corrected QT interval
  QTce
  corrected Q-Tend interval
  QTcp
  corrected Q-Tpeak interval
  Tcp-e
  corrected interval between Tpeak and Tend
  TdP
  torsade de pointes




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