Strategies to improve cardiac resynchronization therapy

• Published in: Nature reviews cardiology Vol. 11; no. 8; pp. 481 - 493
• Main Authors: Vernooy, Kevin, van Deursen, Caroline J. M., Strik, Marc, Prinzen, Frits W.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-08-2014; Nature Publishing Group
• Subjects: 692/699/75/230; 692/699/75/29; 692/700/565/2773; Cardiac Imaging; Cardiac resynchronization therapy; Cardiac Resynchronization Therapy - methods; Cardiac Surgery; Cardiology; Cardiovascular research; Electrocardiography; Heart Failure - diagnosis; Heart Failure - etiology; Heart Failure - therapy; Humans; Medical case management; Medicine & Public Health; Methods; Pacemaker, Artificial (Heart); Patient Selection; Practice Guidelines as Topic; review-article; Treatment Outcome
• ISSN: 1759-5002; 1759-5010
• DOI: 10.1038/nrcardio.2014.67

Key Points
Cardiac resynchronization therapy (CRT) is widely used to improve cardiac pump function and prolong life in patients with heart failure, but 30–50% do not respond to treatment
Appropriate selection of patients, careful positioning of pacing leads, and optimization of resynchronization settings can notably improve response to CRT
Patients with left bundle branch block (LBBB), a QRS duration >150 ms, or both, benefit most from CRT; whether mechanical dyssynchrony provides additional useful diagnostic information is disputed
Optimal left ventricular lead positions vary considerably between individuals, but scarred regions should be avoided, and selection of a late-activated region is particularly important in patients with non-LBBB morphology
The greatest benefit from CRT might come from the optimal placement of one left ventricular pacing lead, rather than the combined effects of pacing at multiple sites
Optimization of atrioventricular and interventricular intervals increases acute haemodynamic response, but the lack of an accurate method to measure synchronization has hampered assessment of long-term effects
Cardiac resynchronization can be a useful therapy for patients with heart failure and abnormal ventricular contraction. However, up to half of patients do not respond to therapy. In this Review, Vernooy and colleagues discuss the selection of patients, positioning of pacing leads, timing of pacing, and management of patients after device implantation to improve the outcomes from cardiac resynchronization therapy.
Cardiac resynchronization therapy (CRT) emerged 2 decades ago as a useful form of device therapy for heart failure associated with abnormal ventricular conduction, indicated by a wide QRS complex. In this Review, we present insights into how to achieve the greatest benefits with this pacemaker therapy. Outcomes from CRT can be improved by appropriate patient selection, careful positioning of right and left ventricular pacing electrodes, and optimal timing of electrode stimulation. Left bundle branch block (LBBB), which can be detected on an electrocardiogram, is the predominant substrate for CRT, and patients with this conduction abnormality yield the most benefit. However, other features, such as QRS morphology, mechanical dyssynchrony, myocardial scarring, and the aetiology of heart failure, might also determine the benefit of CRT. No single left ventricular pacing site suits all patients, but a late-activated site, during either the intrinsic LBBB rhythm or right ventricular pacing, should be selected. Positioning the lead inside a scarred region substantially impairs outcomes. Optimization of stimulation intervals improves cardiac pump function in the short term, but CRT procedures must become easier and more reliable, perhaps with the use of electrocardiographic measures, to improve long-term outcomes.