How to deliver optimal cardiac resynchronisation therapy

### Learning objectives Cardiac resynchronisation therapy (CRT) is a well-established treatment for heart failure (HF). The Comparison of Medical Therapy, Pacing, and Defibrillation in Heart Failure1 and Cardiac Resynchronisation Heart Failure (CARE-HF)2 trials found that CRT reduces both morbidity and mortality in HF patients. Based on current guidelines, 6%–12% of patients hospitalised with HF are eligible for CRT.3 CRT helps to restore atrioventricular (AV), interventricular (VV) and intraventricular synchrony, improve left ventricular (LV) function, reduce functional mitral regurgitation and induce LV reverse remodelling, as evidenced by increases in LV filling time and left ventricular ejection fraction (LVEF), and decreases in LV end-diastolic and end-systolic volumes, mitral regurgitation and septal dyskinesis.2 4 Up to 30% of patients receiving CRT do not attain symptomatic benefit.5 Various parameters have been used to define response to CRT, including improvement in New York Heart Association (NYHA) functional class, improvement in quality of life and echocardiographic parameters. There are five different possible clinical outcomes post-CRT implantation. Responders (70%) show a measurable improvement, whereas super-responders (5%) show excellent response up to normalisation of LV function. Non-progressors (10%) do not experience the progressive decline that is observed in non-responders (10%), and negative responders (5%) experience clinical deterioration and decline in LV function.6 7 Given the inherent risks and costs of device implantation and maintenance, a reduction in the rate of lack of response to CRT is an important goal. Factors associated with a lack of response include inappropriate patient selection, suboptimal LV lead placement, presence of myocardial scar, inadequate device programming and failure to deliver continuous biventricular (BiV) pacing.5 …