Cardiac Resynchronization Therapy Targeting for Electrical Cardiac Dyssynchrony

Abstract

　Cardiac resynchronization therapy (CRT) is an established treatment for symptomatic chronic heart failure (HF) patients with cardiac dyssynchrony. Since CRT is considered as one of the treatments for HF, several endpoints about HF improvement are often used to assess the therapeutic effects of CRT. However, identification of the HF precipitating factor that CRT can attenuate is crucial because HF can be attributed to multiple predisposing factors. The precipitating factor targeted by CRT is cardiac dyssynchrony. Cardiac dyssynchrony can be classified into electrical cardiac dyssynchrony and mechanical cardiac dyssynchrony, but CRT directly affects electrical cardiac dyssynchrony. Mechanical cardiac dyssynchrony can be indirectly alleviated by CRT as a result of improvement of electrical cardiac dyssynchrony. Therefore, recent guidelines about cardiac pacing does not recommend pre-procedural echocardiographic assessment of cardiac dyssynchrony to indicate CRT or to predict CRT outcome. Because electrical cardiac dyssynchrony is an adequate index for CRT indication, CRT can be applicable not only for patients with left bundle branch block, but also patients with other electrical cardiac dyssynchrony beyond current guideline recommendations. Identifying the site of the latest activation site in left ventricle, subsequent placing a left ventricular lead at that site, and appropriate device programming, may significantly expand indications for CRT.