Exercise Induced Worsening of Mechanical Heterogeneity and Diastolic Impairment in Long QT Syndrome

Background: Electromechanical heterogeneities due to marked dispersion of ventricular repolarisation and mechanical function have been associated with symptoms in long QT syndrome (LQTS) patients; Aim: To examine the exercise response of longitudinal LV systolic and diastolic myocardial function and synchronicity in LQTS patients and its relationship with symptoms; Methods: Forty seven (age 45 ± 15 yrs, 25 female, 20 symptomatic) LQTS patients and 35 healthy individuals underwent an exercise test (Bruce protocol). ECG and echo parameters were recorded at rest, peak exercise (p.e.), and recovery; Results: LQTS patients had prolonged and markedly dispersed myocardial contraction, delayed early relaxation phase, and significantly decreased filling time at all exercise phases. Unlike controls, these electromechanical disturbances deteriorated further with exercise, during which additional decrease of the LV diastolic myocardial function and attenuated LV stroke volume were noted. Such abnormal responses to exercise were seen to a greater degree in symptomatic patients and in the LQT1 subgroup and improved with B-blocker therapy. Worsening myocardial contraction dispersion at p.e. was the strongest discriminator for previous clinical events, and its discriminating power excelled further by adding early relaxation delay; Conclusions: Electromechanical disturbances were shown to worsen during exercise in LQTS patients and were more pronounced in those with previous arrhythmic events.