How to visually diagnose mechanical dyssynchrony in cardiac resynchronization therapy candidates using echocardiography

Cardiac resynchronization therapy (CRT) improves outcomes in patients with heart failure and broad QRS complex, yet 20-45% do not respond. Mechanical dyssynchrony (MechDys)-identified visually by septal flash and/or apical rocking (SFoAR)-is strongly associated with CRT benefit. This 'How to' paper outlines a practical four-step workflow for the visual assessment of MechDys. First, a high-quality, multi-view echocardiographic acquisition is essential. Second, septal flash4 (SF) is recognized as an early leftward septal motion, often with rebound, preceding lateral wall contraction; its magnitude depends on conduction delay, myocardial contractility, and right heart loading. Third, ApR is identified as a biphasic apical motion reflecting sequential septal and lateral wall contractions; its appearance may be modified by scarring, pacing, or imaging artefacts. MechDys is confirmed when either motion pattern is present. Clinically, the visual assessment of MechDys may improve patient selection for CRT, thus improving response rates. The ongoing AMEND-CRT trial is evaluating whether incorporating SFoAR assessment is non-inferior to guideline recommendations. Pending prospective evidence, existing observational data supports the use of visual assessment of MechDys to guide decision-making in patients with intermediate CRT indications.