September 26, 2013

ORLANDO, FL — A pacemaker-defibrillator implant with proprietary programming that aims to minimize right ventricular (RV) pacing during cardiac resynchronization therapy (CRT) appeared to cut the prevalence of atrial fibrillation (AF) by about one-half over a 20-month follow-up compared with more traditional echo-optimized CRT, in a post hoc finding from a randomized trial[1]. In its published primary analysis[2], the device with novel programming (AdaptivCRT, Medtronic) had been noninferior in achieving functional and clinical improvement over six months.

Although the study couldn't determine whether the AF reduction made a clinical impact, Dr David O Martin (Cleveland Clinic, OH) said in an interview, "A nearly 50% reduction I'd think is clinically relevant. It was an absolute change from 16.2% [with conventional CRT] to 8.7% [with the novel algorithm]."

Nor is it known whether resynchronization or symptom improvement achieved with the novel CRT algorithm is any better than with standard biventricular (BiV) pacing for CRT; its use is based entirely on a body of research suggesting that LV pacing synchronized to intrinsic RV activation may lead to better outcomes than the standard approach, Martin said.

"My hope is that [the algorithm] will increase the responder rate [for patients receiving CRT]," he said. "The patients that you'd think would benefit the most would be those with left bundle-branch block and a normal [atrioventricular] AV interval. And in a subgroup analysis [in the study's primary publication], they did do better."

Martin presented the Adaptive CRT Trial update featuring the AF-reduction results here at the Heart Failure Society of America 2013 Scientific Meeting .

The prevalence of AF using the novel algorithm dropped by half, give or take, depending on the definition of AF. The hazard ratio (HR) for development of AF or atrial flutter lasting 48 hours was 0.54 (95% CI 0.31–0.93, p=0.03). The HR for AF or atrial flutter lasting at least seven days ("persistent" AF), solely in patients without a prior history of AF, was 0.44 (95% CI 0.19–1.03, p=0.05). There were no significant differences in time to heart-failure hospitalization or death from any cause.

The findings are important, given that about 30% of patients treated with CRT show a poor response to the invasive therapy, according to the assigned discussant for Martin's presentation, Dr Jag Singh (Harvard Medical School, Boston MA). Whether pacing is optimized for individual patients is only one of the determinants of CRT success. Optimization guided by echocardiography has long been available, but its broad adoption has been limited: "It's resource intensive and logistically challenging," he said. It's also possible that echo-optimized mechanical and hemodynamic parameters "are not necessarily translatable when patients are ambulatory." The AdaptivCRT feature on CRT devices potentially addresses those limitations.

Martin explained that all the implantable cardiac rhythm-management device companies have models with algorithms for reducing RV pacing during conventional pacemaker therapy; such RV pacing can worsen cardiac function and heart failure, perhaps by exacerbating ventricular dyssynchrony. But a feature that reduces RV pacing during CRT is novel, he said; so is the dynamic adjustment of AV and interventricular (VV) delays.

The algorithm monitors AV conduction and guides the CRT device to pace only the left ventricle when it can be synchronized to intrinsic RV activation, but only when the patient is in sinus rhythm with normal AV conduction, Martin noted. When AV conduction is prolonged, the device goes to BiV pacing with optimization of AV and VV delays at one-minute intervals. The strategy seems to work; in the noninferiority trial's primary analysis, the prevalence of RV pacing had been 94.3% with conventional CRT but only 60% with the novel algorithm (p<0.0001).

Medtronic sponsored the trial. Martin discloses serving on a Medtronic advisory board. Singh discloses receiving research grants from Boston Scientific, Biotronik, Medtronic, and St Jude Medical; serving on a steering committee or data safety monitoring board or consulting for Boston Scientific, Cardioinsight, Medtronic, St Jude Medical, the Sorin Group, Biosense Webster, theheart.org, and Respicardia; and participating in educational symposia for Boston Scientific, Biotronik, Medtronic, St Jude Medical, and the Sorin Group.

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