Abstract 2685: “Exercise Prestriction” in Long QT Syndrome: Impact of Genotype on Repolarization Reserve
Introduction Strict exercise restriction for patients with Long QT syndrome (LQTS) is recommended in current guidelines. However, LQTS has a variable genotype and phenotype, such that this recommendation may not be appropriate in all cases. We hypothesized that the effect of exercise on repolarization reserve will depend on genotype with potential implications for exercise prescription.
Methods Three groups of LQTS patients were studied on the basis of clinical status and genotype: LQT1, LQT2 and no evidence of LQTS (control:unaffected family members). Twenty-five age- and gender-matched patients were selected for each group. The QTc was measured during upright-bicycle exercise testing.
Results The resting QTc and maximal QTc were both significantly longer in patients with LQTS compared to controls (p<0.01). The degree of QTc prolongation during exercise was greater in LQTS patients (LQT1 80±47ms, LQT2 64±41ms, Control 46±20ms, p=0.02, Figure⇓), but not different between genotypes (LQT1 vs. LQT2 p=0.46). Maximal QTc prolongation occurred at high heart rates in LQT1, whereas QTc peaked at ~50% of maximal predicted heart rate before returning towards baseline in LQT2. This observation appeared independent of age, gender, exercise type, or beta-blockade in subgroup analysis.
Conclusions Reduced repolarization reserve is genotype and heart rate specific. Exercise prescriptions should take into account genotype when making recommendations to patients.