Epinephrine unmasks latent mutation carriers with LQT1 form of congenital long-QT syndrome.
OBJECTIVE
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 > or =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 microg/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.
Shimizu
Wataru
W
Division of Cardiology, Department of Internal Medicine, National Cardiovascular Center, 5-7-1 Fujishiro-dai, Suita, Osaka 565-8565, Japan. wshimizu@hsp.ncvc.go.jp
Noda
Takashi
T
Takaki
Hiroshi
H
Kurita
Takashi
T
Nagaya
Noritoshi
N
Satomi
Kazuhiro
K
Suyama
Kazuhiro
K
Aihara
Naohiko
N
Kamakura
Shiro
S
Sunagawa
Kenji
K
Echigo
Shigeyuki
S
Nakamura
Kazufumi
K
Ohe
Tohru
T
Towbin
Jeffrey A
JA
Napolitano
Carlo
C
Priori
Silvia G
SG
D000293:Adolescent; D000328:Adult; D002648:Child; D004562:Electrocardiography / Q000187:drug effects*; D004837:Epinephrine; D005260:Female; D006580:Genetic Carrier Screening / Q000379:methods*; D005838:Genotype; D006801:Humans; D008297:Male; D008875:Middle Aged; D009154:Mutation / Q000187:drug effects* / Q000235:genetics*; D011930:Reaction Time / Q000187:drug effects* / Q000235:genetics*; D015203:Reproducibility of Results; D029597:Romano-Ward Syndrome / Q000175:diagnosis* / Q000235:genetics* / Q000503:physiopathology; D012680:Sensitivity and Specificity; D013566:Sympathomimetics
D013566:Sympathomimetics; D004837:Epinephrine