Exercise worsening of electromechanical disturbances : a predictor of arrhythmia in long QT syndrome

Background; Electromechanical (EM) coupling heterogeneity is significant in long QT syndrome (LQTS), particularly in symptomatic patients; EM window (EMW) has been proposed as an indicator of interaction and a better predictor of arrhythmia than QTc. Hypothesis To investigate the dynamic response of EMW to exercise in LQTS and its predictive value of arrhythmia. Methods: Forty-seven LQTS carriers (45 +/- 15 years, 20 with arrhythmic events), and 35 controls underwent exercise echocardiogram. EMW was measured as the time difference between aortic valve closure on Doppler and the end of QT interval on the superimposed electrocardiogram (ECG). Measurements were obtained at rest, peak exercise (PE) and 4 minutes into recovery. Results: Patients did not differ in age, gender, heart rate, or left ventricular ejection fraction but had a negative resting EMW compared with controls (-42 +/- 22 vs 17 +/- 5 ms, P < 0.0001). EMW became more negative at PE (-89 +/- 43 vs 16 +/- 7 ms, P = 0.0001) and recovery (-65 +/- 39 vs 16 +/- 6 ms, P = 0.001) in patients, particularly the symptomatic, but remained unchanged in controls. PE EMW was a stronger predictor of arrhythmic events than QTc (AUC:0.765 vs 0.569, P < 0.001). B-blockers did not affect EMW at rest but was less negative at PE (BB: -66 +/- 21 vs no-BB: -113 +/- 25 ms, P < 0.001). LQT1 patients had worse PE EMW negativity than LQT2. Conclusion: LQTS patients have significantly negative EMW, which worsens with exercise. These changes are more pronounced in patients with documented arrhythmic events and decrease with B-blocker therapy. Thus, EMW assessment during exercise may help improve risk stratification and management of LQTS patients