Myocardial electromechanical function in long QT syndrome

Abstract: AIM: The aim of this thesis is to assess, in LQTS and according to genotype, the myocardial electromechanical (EM) function response to exercise, its relation to symptoms and its response to b-blocker therapy. To achieve this aim, we conducted 4 studies with the following specific objectives: i. To study the ventricular repolarization (QTc interval) behaviour during stress and its potential haemodynamic effects, as reflected in left ventricular filling and stroke volume response to exercise.ii. To access the exercise response of electromechanical coupling, expressed by the electromechnical window (EMW), and its relation to symptoms.iii. To access for potential mechanical disturbances during stress by studying the myocardial contraction response to exercise, its effects on myocardial diastolic function and their relation to co-existent ventricular repolarization disturbances.iv. To investigate the myocardial behaviour during early relaxation an most particularly the longitudinal apico-basal relaxation sequence, its synamic response to exercise and any potentia contribution to the development of symptoms.v. To investigate the effect of b-blocker therapy on the above electromechanical parameters at rest and during exercise. METHODS: Forty seven (age 45±15yrs, 25 female, 20 symptomatic) LQTS mutation carriers and 35 healthy individuals (matched for age and sex) underwent an exercise test (Bruce protocol). ECG and doppler and speckle-tracking echo parameters were recorded at rest, peak exercise and recovery. RESULTS: We found that abnormal ventricular repolarization in LQTS carriers was related to marked LV mechanical dispersion and to abnormally reversed LV end-systolic electromechanical relationship and longitudinal early relaxation sequence. These phenomena worsened at peak exercise, especially in LQT1 carriers, and were related to impaired LV daistolic function and attenuated stroke volume response to exercise. Such abnormal electromechanical responses to exercise were more pronounces in LQTS subjects with previous adverse cardiac events and could better identigy these subjects than QTc interval alone. These disturbances were also less pronounced in LQTS carriers treated with b-blockers. CONCLUSION: Incorporating stress-echocardiograhic evaluation of electromechanical parameters in the routine assessment of LQTS individuals may help better stratification, symptom interpretation and management.