Comparison of QT peak and QT end interval responses to autonomic adaptation in asymptomatic LQT1 mutation carriers

Petri Haapalahti,Heikki Swan,Heikki Väänänen,Lauri Toivonen,Markku Mäkijärvi,Matti Viitasalo,Merja Perhonen

doi:10.1111/j.1475-097x.2010.01002.x

Petri Haapalahti, Heikki Swan + Show 5 more

Open Access

https://doi.org/10.1111/j.1475-097x.2010.01002.x

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Abstract

BackgroundLQT1 subtype of long QT syndrome is characterized by defective IKs, 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.MethodsAsymptomatic 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.ResultsIn 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.ConclusionsIn 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 IKs block.

Highlights

LQT1 subtype of long QT syndrome is characterized by defective IKs, which is intrinsically stronger in the epicardium than in the midmyocardial region
Our results show that in asymptomatic LQT1 mutation carriers, repolarization abnormalities are more detected in the QT peak than in the QT end interval during sympathetic activation
In LQT1 carriers, both QT peak and QT end intervals shortened to a similar degree, indicating impaired QT peak shortening compared to QT end

Summary

Background

LQT1 subtype of long QT syndrome is characterized by defective IKs, which is intrinsically stronger in the epicardium than in the midmyocardial region. 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. 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. LQT1 mutation carriers, using beat-to-beat measurements healthy unaffected subjects (control) participated in the study. ECG recordings and automated QT interval measurements behaved differently in LQT1 carriers and controls during any portion of a test. (QT peak) and the end (QT end) of the T wave were automatically during mental stress, 75 ± 7 during sustained handgrip and measured from every heart beat on every channel, with a 112 ± 7 during supine exercise. Subjects exhibited a greater relative shortening (in percentage) of QT peak than of QT end intervals during these tests

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