Heart rate-dependent variability of cardiac events in type 2 congenital long-QT syndrome.
OBJECTIVE
We aimed to examine the validity of heart rate (HR) at rest before β-blocker therapy as a risk factor influencing cardiac events (ventricular fibrillation, torsades de pointes, or syncope) in long QT type 2 (LQT2) patients.


RESULTS
In 110 genetically confirmed LQT2 patients (45 probands), we examined the significance of variables [HR at rest, corrected QT (QTc), female gender, age of the first cardiac event, mutation site] as a risk factor for cardiac events. We also evaluated frequency of cardiac events in four groups classified by the combination of basal HR and QTc with cutoff values of 60 b.p.m. and 500 ms to estimate if these two electrocardiographic parameters in combination could be a good predictor of outcome (mean follow-up period: 50 ± 39 months). Logistic regression analysis revealed three predictors: HR < 60 b.p.m., QTc ≥ 500 ms, and female gender. When the study population was divided into four groups using the cutoff values of 60 b.p.m. for HR and 500 ms for QTc, the cumulative event-free survival by the Kaplan-Meier method was significantly higher in the group with HR ≥ 60 b.p.m. and QTc < 500 ms than in the group with HR < 60 b.p.m. and QTc < 500 ms or that with HR < 60 b.p.m. and QTc ≥ 500 m (P < 0.05). Irrespective of QTc interval, LQT2 patients with basal HR < 60 b.p.m. were at significantly higher risk.


CONCLUSIONS
The basal HR of < 60 b.p.m. is a notable risk factor for the prediction of life-threatening arrhythmias in LQT2 patients.
Nagaoka
Iori
I
Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science, Seta, Tsukinowa-cho, Otsu, Shiga 520-2192, Japan.
Shimizu
Wataru
W
Mizusawa
Yuka
Y
Sakaguchi
Tomoko
T
Itoh
Hideki
H
Ohno
Seiko
S
Makiyama
Takeru
T
Yamagata
Ken-ichiro
K
Makimoto
Hisaki
H
Miyamoto
Yoshihiro
Y
Kamakura
Shiro
S
Horie
Minoru
M
D000293:Adolescent; D000319:Adrenergic beta-Antagonists / Q000627:therapeutic use; D000328:Adult; D017668:Age of Onset; D000368:Aged; D000369:Aged, 80 and over; D018572:Disease-Free Survival; D005260:Female; D006323:Heart Arrest / Q000235:genetics / Q000503:physiopathology; D006339:Heart Rate / Q000235:genetics / Q000502:physiology*; D006801:Humans; D008133:Long QT Syndrome / Q000150:complications / Q000188:drug therapy / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009154:Mutation; D012189:Retrospective Studies; D012307:Risk Factors; D013575:Syncope / Q000453:epidemiology / Q000209:etiology; D016171:Torsades de Pointes / Q000453:epidemiology / Q000209:etiology; D014693:Ventricular Fibrillation / Q000453:epidemiology / Q000209:etiology; D055815:Young Adult
D000319:Adrenergic beta-Antagonists