Background: The primary determinate for the indication of cardiac resynchronization therapy in symptomatic chronic heart failure currently is a prolonged QRS duration. This is based on the premise that a prolonged QRS duration is a marker of left ventricular (LV) dyssynchrony. Tissue synchronization imaging (TSI) is an emerging technology that uses tissue Doppler velocities to determine the time to peak velocity of regions of the ventricular myocardium.
Objectives: Our objectives were to determine the prevalence of dyssynchrony in a cardiomyopathic population referred for echocardiography irrespective of QRS duration, to validate the novel technique of TSI in evaluation of mechanical LV dyssynchrony and to determine the accuracy of QRS duration in predicting significant LV dyssynchrony.
Methods: A total of 100 patients with significant LV dysfunction (Simpson's ejection fraction < or = 35%) referred for echocardiography underwent TSI. Dyssynchrony was defined as a difference in time to peak contraction of greater than 105 milliseconds between opposing ventricular segments.
Results: Overall, 61 patients (61%) demonstrated significant dyssynchrony, whereas 52% had a QRS duration of greater than 120 milliseconds. Among those with a prolonged QRS duration, significant dyssynchrony was evident in 30 (58%). However, dyssynchrony was also common among those with a narrow QRS duration (<120 milliseconds) (31 patients [65%]). Of the 61 patients with dyssynchrony, 31 (51%) would have been missed if QRS criteria were used alone.
Conclusions: A substantial proportion of patients have dyssynchrony by TSI, but do not have a prolonged QRS duration. These patients may benefit from cardiac resynchronization therapy but on traditional criteria would be excluded from the therapy. Expanding the criteria for cardiac resynchronization therapy to include echocardiographic parameters may extend the benefit of this technology to a greater population in need.