SMART-AV: SmartDelay Fails to Outwit Other CRT AV-Delay-Optimization Approaches

Reed Miller

November 15, 2010

November 15, 2010 (Chicago, Illinois) — A sophisticated programming algorithm designed to optimize the atrioventricular delay in cardiac resynchronization therapy (CRT) failed to improve upon simpler approaches [1].

Dr Kenneth Ellenbogen

Results of the SMART-AV trial, presented by Dr Kenneth Ellenbogen (Medical College of Virginia, Richmond) at a late-breaking clinical-trials session here at the American Heart Association 2010 Scientific Sessions and published online today in Circulation, showed that the SmartDelay (Boston Scientific) algorithm was not superior to either an echocardiography-based delay setting or a fixed delay of 120 ms.

"Many of these methods for optimizing AV delay have undergone fairly rigorous evaluation in hemodynamic labs and, as we've learned before, when you do something in a lab under very controlled circumstances, it doesn't automatically translate into patient outcomes. All of these algorithms made excellent sense hemodynamically in small single-center trials," Ellenbogen said. "It really points to the importance of the clinical trial to really look at the impact on outcomes."

"The bottom line [of SMART-AV] is that we can save patients a time-consuming and expensive study [to optimize AV delay] that really doesn't provide any benefit to the majority of patients with CRT devices, because the out-of-the-box settings seemed to work for most patients," he said.

The large randomized clinical trials that demonstrated the overall efficacy of CRT used several approaches to AV optimization. Some have used Doppler echocardiography of transmitral flow to select the optimal AV delay, the approach endorsed by the American Society of Echocardiography, Ellenbogen said. SmartDelay, available on Boston Scientific CRT devices, is a modified version of the algorithm investigated in the COMPANION trial. It adjusts the AV delay based on the intrinsic AV interval and baseline QRS width.

SMART-AV randomized 980 heart-failure patients indicated for a CRT device to either a fixed empirical AV delay of 120 ms, echocardiography-optimized AV delay, or AV delay optimized with SmartDelay. All patients were evaluated at three and six months after device implantation for left ventricular end-systolic volume. Secondary end points included NYHA class, quality-of-life score, six-minute-walk distance, left ventricular end-diastolic volume, and left ventricular ejection fraction.

The median reductions in left ventricular end-systolic volume at six months were 21 mL for the SmartDelay group, 19 mL for the echocardiography group, and 15 mL for the fixed-delay group, a nonsignificant difference. There were no significant differences in the secondary end points.

The only significant optimization treatment-subgroup interaction was that women in the SmartDelay and echocardiography groups had almost double the reduction in left ventricular end-systolic volume as women in the fixed-delay group. "It's unclear whether that's because they're biologically different or they have more nonischemic cardiomyopathy," Ellenbogen told heartwire .

The study shows that "SmartDelay should not be widely applied to patients who get CRT devices," Ellenbogen said. He hopes that further investigation of the data might reveal subsets of patients who do benefit from either echocardiographic-based or SmartDelay AV optimization and provide clues about why about a third of patients do not initially respond to CRT therapy.

Dr Christophe Leclercq

"We don't know how much of a difference for the nonresponders AV optimization makes. We'll go back and look at those 30% to 40% of people [in the trial] whose AV delays were way away from the mean," he said. "Maybe we need to focus more of our effort on [determining] whether we're putting these devices in some of the wrong patients or putting the LV lead in some of the wrong places. Maybe the programming isn't as important a [factor] in the nonresponders."

Commenting on the study at the conference, Dr Christophe Leclercq (Centre Hospitalier Universitaire De Rennes, France) suggested that to show a significant difference between end left ventricular systolic function may require a longer study.

Dr Douglas Zipes (Indiana University, Indianapolis) said, "What we need is some sort of a planned feedback system that will automatically adjust [the AV delay] depending upon the activity the individual is undergoing at that particular time."

Ellenbogen agreed that such a "closed-loop system" that can continually adjust the AV delay in response to the patient's stroke volume is "theoretically an ideal system. But it's been very hard to create a system that can actually measure something that is physiologically important to drive the AV intervals."

Ellenbogen disclosed research grants from Boston Scientific, Medtronic, St Jude Medical, Biosense Webster, and Sanofi-Aventis, plus consulting arrangements with Cardionet, Atricare, and EBR.

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