Comparison of QT peak and QT end interval responses to autonomic adaptation in asymptomatic LQT1 mutation carriers.
BACKGROUND
LQT1 subtype of long QT syndrome is characterized by defective I(Ks) , which is intrinsically stronger in the epicardium than in the midmyocardial region. Electrocardiographic QT peak and QT end intervals may reflect complete repolarization of epicardium and midmyocardial region of the ventricular wall, respectively. Repolarization abnormalities in LQT1 carriers may therefore be more easily detected in the QT peak intervals.


METHODS
Asymptomatic KCNQ1 mutation carriers (LQT1, n=9) and unaffected healthy controls (n=8) were studied during Valsalva manoeuvre, mental stress, handgrip and supine exercise. Global QT peak and QT end intervals derived from 25 simultaneous electrocardiographic leads were measured beat to beat with an automated method.


RESULTS
In unaffected subjects, the percentage shortening of QT peak was greater than that of QT end during mental stress and during the recovery phases of Valsalva and supine exercise. In LQT1 carriers, the percentage shortening of the intervals was similar. At the beginning of Valsalva strain under abrupt endogenous sympathetic activation, QT peak shortened in LQT1 but not in control patients yielding increased electrocardiographic transmural dispersion of repolarization in LQT1.


CONCLUSIONS
In asymptomatic KCNQ1 mutation carriers, repolarization abnormalities are more evident in the QT peak than in the QT end interval during adrenergic adaptation, possibly related to transmural differences in the degree of I(Ks) block.
Department of Cardiology, Laboratory of Clinical Physiology, Helsinki University Hospital, Helsinki, Finland. petri.haapalahti@hus.fi
Petri
P
Haapalahti
Matti
M
Viitasalo
Merja
M
Perhonen
Heikki
H
Väänänen
Markku
M
Mäkijärvi
Heikki
H
Swan
Lauri
L
Toivonen
D000200:Action Potentials; D000222:Adaptation, Physiological; D000328:Adult; D001341:Autonomic Nervous System / Q000503:physiopathology*; D016022:Case-Control Studies; D004562:Electrocardiography; D005387:Finland; D020022:Genetic Predisposition to Disease; D006321:Heart / Q000294:innervation*; D006801:Humans; D051657:KCNQ1 Potassium Channel / Q000235:genetics*; D008875:Middle Aged; D009154:Mutation; D010641:Phenotype; D029597:Romano-Ward Syndrome / Q000235:genetics / Q000503:physiopathology*; D013997:Time Factors; D055815:Young Adult
D051657:KCNQ1 Potassium Channel; C496909:KCNQ1 protein, human