Cardiac Resynchronization Therapy: Who is and who is not a Candidate? Who Decides?

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William F. McIntyre MD, FRCPC
Colette M. Seifer MB (Hons), FRCP(UK)

living with heart failure, systolic heart failure, Cardiac resynchronization therapy, CRT,

Abstract

It is estimated that nearly 500,000 Canadians are currently living with heart failure, a disease process associated with considerable morbidity and mortality. Despite significant evidence for effective medical therapies, heart failure remains one of the leading causes of hospitalization in Canada and patients with the disease experience an annual mortality of up to 10%.

Approximately one in three patients with systolic heart failure have some degree of intraventricular conduction delay, manifest as increased QRS duration on electrocardiogram (ECG), the most common of which is left bundle branch block (LBBB). This conduction delay, or electrical dyssynchrony, can lead to mechanical uncoupling and inefficiency, which, in turn, can lead to exacerbation of systolic dysfunction, altered myocardial metabolism, functional mitral regurgitation, negative remodeling and worsening clinical outcomes.Cardiac resynchronization therapy (CRT), also known as biventricular pacing, involves coordinating contraction between the left (LV) and right ventricles (RV) through programmed pacing of both ventricles. CRT is an established non-pharmacological therapy for patients with systolic heart failure due to a low ejection fraction, who have a QRS >130 ms and who are symptomatic despite optimal medical therapy. In carefully selected patients, CRT has been shown to promote positive LV remodeling, increase functional capacity, improve quality of life, reduce heart failure hospitalizations and reduce mortality.2 CRT systems can include defibrillator capabilities (CRT-D) or act as a stand-alone pacemaker (CRT-P).

The insertion of a CRT system consumes significant resource (costs), requires a commitment to regular clinical follow-up, and the acceptance of permanent implantation of a large medical device. Clinicians are tasked with identifying patients who would be expected to benefit from CRT and making the decision whether to proceed with CRT implantation. Therefore a careful consideration of the risks and benefits of this technology is required by both the healthcare providers and the patient.

Herein we hope to offer guidance on identifying ideal candidates for CRT and to remind health care providers that the patients’ goals must be taken into consideration when counseling a patient for treatment with CRT.

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