Standard pacing therapy regulates heart pumping as well as costly tailored methods


Results of a late-breaking clinical trial presented at the American Heart Association’s Scientific Sessions in Chicago, USA, show that cardiac resynchronisation therapy (CRT) is as effective as two other methods that regulate the time interval between the squeezing of the heart’s upper and lower chambers.

The SMART AV trial included 1,014 heart failure patients (68% male, average age 66) at 100 sites in the United States and Europe. Each patient had suboptimal atrioventricular (AV) interval delay. In the study, researchers randomised 980 of the patients to one of the three therapies: the standard therapy of a pre-set AV interval of 120 milliseconds for the time delay between atrial and ventricle constrictions; echocardiography-customization of the AV interval determined after device implantation by an ultrasound examination of blood flow into the patient’s left ventricle and across the mitral valve; AV optimization by the SmartDelay algorithm, a technique derived from haemodynamic laboratory studies in humans.

The primary endpoint was the volume of the left ventricle at the end of contraction. Its secondary endpoints were heart function; patients’ self-reported quality of life; improvement in walking for six minutes; the left ventricle’s volume at the end of relaxation; and its squeezing force while ejecting blood.

At the end of the six-month trial, researchers found no significant difference in the primary or any of the secondary endpoints among the three patient groups.

“These conclusions are quite important,” said Kenneth A Ellenbogen, lead author of the study and Kontos professor of cardiology and department chairman at the Virginia Commonwealth University School of Medicine in Richmond. “Routine AV optimization is not worth the time, the cost, or the effort because there is no detriment to using a device as it is programmed off the shelf.” However, he said that in patients who do not respond to this therapy, some technique for optimizing the AV interval may be useful.

“We know CRT is tremendously effective,” Ellenbogen said. “It can decrease mortality and improve quality of life. It can increase heart muscle function and the amount of blood the heart pumps. In people with enlarged hearts, the size of the ventricular pumping chamber of the heart actually shrinks.”

However, only about 70% of patients respond to CRT. So researchers have sought to improve the therapy by focusing on how to best resynchronize the heart’s upper and lower contractions.

In a subanalysis of the women in the study, the researchers found that those treated with AV optimisation, both echocardiography and SmartDelay, did significantly better with respect to the primary endpoint compared to those treated with the preset program.

The results showed the importance of large clinical trials, Ellenbogen said.

“We should never assume that just because something makes sense from a physiologic point of view, or has been studied in a small numbers of patients, that we should automatically expect that it will make a big impact on patient outcomes,” he said.

Boston Scientific funded the study.