Abstract 16314: Do LQTS Gene Polymorphisms Alter QT Interval Adaptation During Exercise Stress Testing?
Introduction: The significance of genetic polymorphisms (PM) in the spectrum of long QT syndrome (LQTS) mutations is unknown. We sought to assess the repolarization reserve manifested by QT interval adaptation during exercise stress test (EST) in children with LQTS PM compared to a group of age and gender matched normal controls.
Hypothesis: Patients with LQTS polymorphisms have abnormal QTc adaptation during EST.
Methods: Patients who underwent genetic testing for suspected LQTS with identified polymorphisms and EST were included in the study. Control group consisted of age and gender matched normal children who had EST. Patients with disease causing LQTS mutations were excluded. Cycle ergometer with a graded exercise protocol was used. First EST at evaluation was analyzed for QT, RR and QTc intervals at rest (supine and standing), warm-up, peak exercise and recovery (1, 3, 5, 7 and 9 minutes) .
Results: Forty-three (49% female) patients were identified as having LQTS polymorphisms. Eighteen (42%) had a single mutation, 18 (42%) had two mutations and 7 (16%) had three mutations. A total of 125 mutations were identified: KCNE1 n=43 (34%), SCN5A n=43 (34%), KCNH2 n=36 (29%), KCNQ1 n=2 (2%), KCNE2 n=1 (1%). Average age of study group was 13.2±4.3 years. QTc (msec) intervals were 420±22 (supine), 456±34 (standing), 442±26 (warm-up), 419±31 (peak exercise), 414±25 (1 minute recovery), 429±29 (3 minute recovery), 442±26 (5 minute recovery), 444±27 (7 minute recovery) and 442±31 (9 minute recovery). Control group QTc (msec) intervals were 407±20 (supine), 439±29 (standing), 425±21 (warm-up), 406±25 (peak exercise), 401±22 (1 minute recovery), 408±22 (3 minute recovery), 427±19 (5 minute recovery), 431±18 (7 minute recovery) and 432±18 (9 minute recovery) with p –value <0.05 at all points.
Conclusions: Patients with LQTS polymorphisms may have reduced repolarization reserve manifested as increased QTc intervals at peak exercise and during all phases of the recovery period as compared to age and gender matched controls. Interpretation of EST for evaluation of LQTS disease should be performed with caution as QTc prolongation may occur in the presence of LQTS polymorphisms .
- © 2010 by American Heart Association, Inc.