Predictors of response to cardiac resynchronization therapy--importance of left ventricular dyssynchrony.

Background: Cardiac resynchronization therapy (CRT) is currently used in selected patients with dilated cardiomyopathy and heart failure. However, 30% of patients do not respond to CRT when selection is based on clinical and electrocardiographic criteria. Left ventricular dyssynchrony can be evaluated by tissue Doppler imaging and it has been described as a useful precdictor of response to CRT.

Objective: To evaluate whether left ventricular dyssynchrony, as measured by tissue Doppler imaging, can be used to predict response to CRT.

Methods: 23 consecutive patients (age 67 +/- 10 years, 13 male) with heart failure refractory to medical therapy and who underwent CRT were studied. Before and six months after the procedure, various characteristics - clinical (including NYHA functional class), electrocardiographic (QRS interval) and echocardiographic (left ventricular ejection fraction [EF] and respective volumes)--were evaluated. In addition, pulsed wave tissue Doppler imaging was used to assess the time interval (QS) between the beginning of the QRS complex and the beginning of the systolic wave on the Doppler signal, in the basal segments of the septal, lateral, anterior and inferior walls. Left ventricular dyssynchrony was quantified as the difference between the maximum and minimum QS interval (QS(max-min)). The patients were divide into two groups: responders, if functional class improved by at least one and EF increased by more than 10%, and non-responders for the remainder. Differences between groups were assessed and predictors of response to CRT were determined.

Results: CRT improved functional class by at least one in 87% of patients and EF improved from 21 +/- 6 to 33 +/- 9% (p < 0.001). QS(max-min) was reduced from 80 +/- 38 to 38 +/- 14 ms (p < 0.001). In 15 patients (65%), classified as responders, there was an improvement in functional class and an increase in EF of more than 10%. There were no differences between groups, except for QS(max-min). Patients in the responder group had greater left ventricular dyssynchrony (QS(max-min) 94 +/- 39 vs. 54 +/- 16 ms, p = 0.002). QSmix-min was an independent predictor of response to CRT and a cut-off of 60 ms identified responders with a sensitivity of 87% and specificity of 75%.

Conclusion: Despite the good results achieved with CRT, about one third of patients do not benefit from it. Left ventricular dyssynchrony can be quantified by tissue Doppler imaging using QS(max-min) and values greater than 60 ms can identify responders to CRT.