Effect of dynamic myocardial dyssynchrony on mitral regurgitation during supine bicycle exercise stress echocardiography in patients with idiopathic dilated cardiomyopathy and 'narrow' QRS

Aims: Cardiac resynchronization therapy (CRT) has become an attractive therapeutic option for patients with end-stage heart failure (HF). Currently, patients are selected for CRT on ECG and on echocardiographic criteria analysed at rest. Whether the physical effort may further increase myocardial dyssynchrony is not fully established. The aim of the study was to test by the use of Doppler myocardial imaging (DMI) if dynamic left ventricular (LV) dyssynchrony during physical effort may be a determinant of dynamic mitral regurgitation in patients with dilated cardiomyopathy and 'narrow' QRS. Methods and results: Sixty patients (62.3 ± 8.3 years) with idiopathic dilated cardiomyopathy and narrow QRS duration (< 120 ms) were selected. All the patients underwent standard Doppler echo, colour DMI, supine bicycle exercise stress echocardiography, and cardiopulmonary exercise testing. Cardiac synchronicity was assessed, at rest and at peak exercise, from measurements of time intervals (Ts) between the onset of the QRS complex and the peak myocardial systolic velocity, in a six-basal-six-mid-segmental model. Standard deviation of Ts of the 12 LV segments (Ts-SD-12) was also calculated. In baseline conditions, HF patients showed an LV ejection fraction of 30.1 ± 4%, and a significant electromechanical delay (Ts-SD-12 ≥ 34.4 ms) in 20 patients (33.3%). At peak of physical exercise, a significant electromechanical delay was detected in 35 patients (58.3%), whereas in 47 patients (78.3%) exercise-induced increase in mitral valve effective regurgitant orifice (ERO) was observed. By multivariable analysis, an independent positive association between changes in Ts-SD-12 and in mitral valve ERO (P < 0.0001), as well as an independent inverse correlation of the same changes in Ts-SD-12 with LV stroke volume (P < 0.0001) were detected. In addition, changes in Ts-SD-12 were also independent determinants of peak VO2 (P < 0.0001) during cardiopulmonary exercise testing. Conclusion: Colour DMI is an effective technique for assessing the severity of regional delay in activation of LV walls in HF patients with narrow QRS both at rest and during stress test. The increase in LV dyssynchrony during exercise strongly correlates with the increase in mitral regurgitation severity and with the impairment of LV stroke volume. © The European Society of Cardiology 2007. All rights reserved.