Study of Left Ventricular Dyssynchrony in Heart Failure Patients

Heart failure has become one of the major epidemics of the modern era. Despite optimal standard drug therapy, the prognosis of patients with heart failure remains poor. It has been noted that 15% of all HF patients and 30% of those with NYHA class III and IV HF have intraventricular conduction delay, with a QRS duration \>120 ms, most commonly manifested as LBBB. These electrical disturbances result in LV dyssynchrony, seen as a paradoxical septal wall motion activity, suboptimal ventricular filling and mitral regurgitation; thus further compromising an already dysfunctioning left ventricle. Ventricular dyssynchrony has been associated with increased mortality in patients with heart failure. Based on these observations, techniques have been developed to correct dyssynchrony. Cardiac resynchronization therapy (CRT) has been shown to improve subjective and objective parameters in heart failure patients with QRS duration \> 120msec. However, there is a group of heart failure patients who did not respond to CRT. Also it has been noted that approximately 30% of heart failure patients with QRS duration \> 120 msec do not have actual mechanical dyssynchrony by tissue doppler imaging. The electromechanical discrepancy of ventricular dyssynchrony has been suggested as the possible explanation for the lack of response. Also, there are heart failure patients with normal QRS duration who do have mechanical dyssynchrony. These findings bring more emphasis to the importance of mechanical dyssynchrony than electrical dyssynchrony, which is measured by QRS duration on surface EKG. There are many different modalities to quantify mechanical dyssynchrony. The most commonly used method is tissue doppler imaging (TDI). TDI measures the velocities of myocardial tissue and time to maximal velocities. Then, these are used to describe contractions of different wall segments. Strain and strain rates are more sophisticated ways to measure active segment contraction rather than passive movements. We propose to investigate the change of dyssynchrony in relation to intravascular volume status and exercise in heart failure patients. We also propose to examine dyssynchrony in the setting of acutely decompensated heart failure. The change in dyssynchrony will be followed to examine if it translates into clinical significance.