Mechanical dyssynchrony in heart failure: Still a valid concept for optimizing treatment?

Cardiac resynchronization therapy (CRT) has had a major favourable impact on the care of patients with symptomatic heart failure, left ventricular ejection fraction<35% and enlarged QRS. Despite this, about 35% of patients who undergo CRT in accordance with current guidelines are "non-responders". Therefore, more accurate selection of CRT candidates would significantly improve patient benefit and decrease costs. In the past decade, some small non-randomized studies have shown that estimation of left ventricular dyssynchrony by echocardiography might be useful to ameliorate the selection of patients for CRT. These preliminary findings have been challenged by the results of large randomized surveys, such as the Prospect and EchoCRT trials, which demonstrated that no left ventricular mechanical dyssynchrony variable could accurately predict CRT response. In recent years, improvements in myocardial imaging techniques, and the potential of fusion imaging to facilitate our understanding of the physiological basis of dyssynchrony and plan lead delivery, have let us suppose that imaging might play a role in the future of CRT. The aim of the present paper is to provide an overview of recent advances in the field of imaging-guided CRT. The role of imaging in the assessment of CRT candidates, in guiding lead implantation, and in the optimization of CRT delivery will be addressed, together with the limitations of these new techniques.