Optimal role of rest and stress echocardiography in cardiac resynchronization therapy

Cardiac resynchronization therapy (CRT) is an effective treatment for patients with advanced heart failure (HF), depressed left ventricular (LV) function and wide QRS complex. CRT improves symptoms, exercise capacity, LV function and reduces HF hospitalization and mortality rates. However, in parallel with the impressive results for CRT in several large trials, a consistent percentage of patients do not respond to CRT when the traditional patient selection criteria are applied. The prevalence of non-responders is about 30% when clinical end-points are considered but it is much higher (≥ 45%) if echocardiographic end-points are used. Reduction of the number of non-responders is currently one of the main challenges in the field of CRT. Response to CRT has been related to the presence of cardiac dyssynchrony prior to implantation. LV dyssynchrony can be evaluated using different echocardiographic methods. When LV dyssynchrony is added to traditional patient selection criteria, the prevalence of non-responders decreases considerably. However, the value of LV dyssynchrony to predict response to CRT has shown some limitations and is possibly not sufficient. CRT response is clearly modulated by several factors. Regional and global myocardial viability are key pieces of the puzzle as well as the presence and severity of mitral regurgitation (MR). Echocardiography thus plays an important role in the care of HF patients treated with cardiac resynchronization therapy and is useful to assess acute and long-term beneficial effects of CRT. Numerous recent published reports have used echocardiographic techniques to potentially help patient selection for CRT prior to implantation and to optimize device settings afterwards. These topics are discussed in this review.