Table 1

Clinical Characteristics in 812 Genotyped Patients

CharacteristicLQT1 (n = 428)LQT2 (n = 302)LQT3 (n = 82)
Families, n889311
Median age at baseline ECG, yrs313330
Female gender, n (%)249 (58)178 (59)42 (51)
Baseline QTc findings
 Subjects with baseline ECG, n37026178
 QTc mean ± SD, ms485 ± 49492 ± 52506 ± 46
 95% CI of mean QTc, ms480–490486–499495–516
 ≤439 ms, n (%)41 (11)21 (8)5 (6)
 440–469 ms, n (%)103 (28)64 (25)13 (17)
 470–499 ms, n (%)102 (28)81 (31)13 (17)
 500–549 ms, n (%)85 (23)58 (22)30 (38)
 ≥550 ms, n (%)39 (11)37 (14)17 (22)
Cardiac therapy at age 18 yrs, n (%)
 Beta-blockers85 (20)53 (18)11 (13)
 Pacemaker3 (1)10 (3)2 (2)
 Sympathectomy9 (2)4 (1)1 (1)
 Implantable defibrillator4 (1)4 (1)1 (1)
Cardiac events ≥1, n (%)
 Syncope/ACA before age 18 yrs142 (34)75 (25)10 (12)
 Syncope/ACA/LQTS-death after age 18 yrs83 (20)97 (33)12 (15)
ACA/LQTS-death, n (%)
 ACA before age 18 yrs7 (2)9 (3)0
 ACA after age 18 yrs16 (3.7)13 (4.3)1 (1.2)
 Death after age 18 yrs5 (1.2)12 (3.7)3 (3.7)
 ACA or death after age 18 yrs21 (4.9)25 (8.0)4 (4.9)

ACA = aborted cardiac arrest; CI = confidence interval; ECG = electrocardiogram; QTc = corrected QT interval.

  • p < 0.01 for comparison of baseline parameters among all 3 long QT syndrome (LQTS) subtypes. No significance-level comparisons are provided for the distribution of events among the genotypes, because these end point analyses are provided in the multivariate analyses in Tables 2 and 3.