Cardiac Resynchronization Therapy for Heart Failure: New Clinical Study Results Cardiac Resynchronization Therapy for Heart Failure: New Clinical Study Results
Cardiac Resynchronization Therapy for Heart Failure: New Clinical Study Results
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A very effective therapy for some heart failure patients has failed to improve outcomes in others, surprising many clinicians. This limits the indications for this therapy, and intensifies the search for new heart failure treatments. In a study recently reported at the annual meeting of the European Society of Cardiology and published online by the New England Journal of Medicine, cardiac resynchronization therapy was of no benefit and potentially of some harm in systolic heart failure patients with a narrow QRS duration.
Many patients with heart failure and weakness of the heart (called systolic heart failure) have an electrical abnormality resulting in prolongation of the QRS complex duration on the electrocardiogram. These abnormalities are generally called bundle branch blocks or conduction delays, and they result in cardiac dysynchrony – discoordinated pumping of the heart’s walls. This, in turn, decreases the ability of the heart to pump blood to the body.
To state this in another way, pumping of the heart is directed by electrical impulses that comprise the heartbeat. Normally, electricity travels very quickly through the heart signaling the walls of the heart to squeeze in a well-orchestrated fashion. This results in the most efficient pumping of the heart. In the case of bundle branch block or conduction delay, an electrical short-circuit delays the pumping of some walls, decreasing the performance of the heart and worsening heart failure.
Specialized Pacemakers: CRT Devices for the Heart
This situation can be treated with specialized pacemakers, called cardiac resynchronization therapy or CRT devices. Often referred to as three-lead or three-wire pacemakers, these devices bypass the electrical short circuit, causing the walls of the heart to squeeze in a more coordinated fashion again. In systolic heart failure patients with the mentioned electrical abnormalities, cardiac resynchronization therapy improves quality of life, functional status, and exercise capacity. It makes weak hearts stronger and enlarged hearts smaller. Importantly, in these patients, cardiac resynchronization therapy reduces the risk of heart failure hospitalization and prolongs life.
Many heart failure patients without bundle branch block or conduction delay (that is, with a narrow QRS duration) also demonstrate cardiac dysynchrony, visible by imaging the heart with a specialized form of ultrasound called an echocardiogram. It was postulated that these patients could also benefit from cardiac resynchronization therapy. In fact, some physicians simply recommended CRT for these patients. Others performed small observational or randomized studies to assess the effects of cardiac resynchronization therapy in these patients.
The results of this clinical experience and earlier studies were mixed. Some demonstrated benefits and others showed no improvements with CRT in heart failure patients with a narrow QRS duration. This set the stage for a large and definitive outcomes study, the Echocardiographic-guided Cardiac Resynchronization Therapy trial (EchoCRT).
New Clinical Study Results
EchoCRT is the largest investigator-initiated, international, multi-center, prospective, randomized controlled clinical trial of its kind. It enrolled patients with moderate-to-severe symptoms of systolic heart failure, a narrow QRS duration less than 130 milliseconds, and echocardiographic evidence for cardiac dysynchrony. Patients received all usual therapies for heart failure, including an implantable cardioverter defibrillator or ICD, and were randomly assigned to receive CRT or no CRT.
At study closure, there were 809 patients randomized to CRT=ON or CRT=OFF and followed for an average of 19.6 months. The primary outcome of death due to any cause or first hospitalization for worsening heart failure occurred in 116 of 404 CRT patients versus 102 of 405 control patients (28.7% vs. 25.2%) and did not demonstrate a benefit of CRT in the study population. More patients died in the CRT group, but the number of deaths was too small for the findings to be definitive.
As concluded by co-lead investigator Johannes Holzmeister, MD, from University Hospital in Zurich, Switzerland, “Compared to optimal pharmacological therapy and an ICD, the addition of CRT does not improve clinical outcomes assessed by the combined endpoint of all-cause mortality and heart failure hospitalization and it may increase mortality in patients with systolic heart failure with a QRS duration
Thus, while cardiac resynchronization therapy remains beneficial for thousands of heart failure patients with prolonged QRS duration, it can no longer be consider in those patients with a narrow QRS complex.
The search for newer therapies to help patients in this latter category of heart failure goes on.
Video: How does cardiac resynchronisation therapy work?
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