HF Risk Drops With 'Dynamic Control' CRT Pacing in Early Study

Daniel M. Keller, PhD

June 30, 2020

In a large observational study of patients undergoing cardiac resynchronization therapy (CRT), implantation of a CRT device significantly reduced the rate of heart failure hospitalization (HFH), and even more so for those implanted with a device with adaptive atrioventricular (AV) delay (SyncAV CRT, Abbott).

The quadripolar SyncAV CRT device comes with "dynamic control" resynchronization algorithms that can vary AV delays according to the patient's intrinsic AV interval, which it does every 256 cardiac cycles, to enhance its effect on electrical and mechanical ventricular synchrony.

In patients with left bundle branch block (LBBB), the left ventricular and right ventricular wave fronts should coordinate with each other, as well as with intrinsic right bundle-branch conduction, explained Niraj Varma, MD, PhD, Cleveland Clinic, in an online presentation for the virtual congress of the European Heart Rhythm Association 2020. "We realized that the coordination of this has to be optimized on an individualized basis. Every patient is different."

"We know that the AV interval changes during the day [when] sleeping, resting, walking, eating, running, all of it. So that coordination that you so carefully customized to the patient has to be retained" throughout all of the daily variation in activity level. "Everybody's AV interval changes during the day," Varma told theheart.org | Medscape Cardiology in an interview.

Therefore, he said, the SyncAV algorithm "should improve both the quantity and the quality of paced therapies."

Varma noted that other proprietary CRT systems offer other versions of dynamic pacing, and cited in particular the AdaptivCRT dynamic pacing algorithm (Medtronic). But devices using the algorithm lack individualized programmability, which is a key feature of SyncAV, he said.

Data for the current study were obtained from the Merlin.net Patient Care Network, Abbott's proprietary telemonitoring system for cardiac implantable devices, and were crosslinked with Medicare data on cardiac disease etiology, comorbidities, and HFH.

The population consisted of 16,657 patients who were implanted from 2016 to 2019 with devices equipped with SyncAV programming, which was activated in 839 cases (the SyncAV-ON group). The remaining SyncAV-OFF patients were propensity matched to the SynchAV-ON patients in a four to one ratio according to age, gender, device type, multipoint pacing programming, baseline HFH rate, and presence or absence of LBBB.

The resulting propensity-matched cohorts of 3112 SyncAV-OFF patients and 778 SyncAV-ON patients didn't different significantly in any baseline demographic, medical history, clinical, or device variables, Varma reported. Approximately 44% had a history of atrial fibrillation and three-quarters had LBBB. They were also well matched for comorbidities, ischemic cardiomyopathy, and potential renal disease.

Across all patients, the hazard ratio (HR) for HFH, comparing the year after with the year before device implantation, was 0.64 (95% CI, 0.57 - 0.71; P < .001). The 36% reduction "is a very interesting number. It's very similar to all the randomized controlled trials," Varma noted. "So this is a good representative population."

Among SyncAV-OFF patients, the 1-year HR for HFH rate was 34% lower than in the year before device implantation (HR, 0.66; 95% CI, 0.59 - 0.74; P < .001).

For the SyncAV ON-group, there was a 45% reduction (HR, 0.55; 95% CI, 0.44 - 0.70; P < .001), "suggesting a beneficial effect of the algorithm," Varma said.

At 2 years, the SyncAV-ON group showed a greater beneficial effect, a 22% lower HFH rate compared with the SyncAV-OFF patients (HR, 0.78; 95% CI, 0.62 - 0.98; = .031).

Varma concluded that compared with "out of the box CRT," electrical optimization linked to dynamic AV control improves outcomes of patients treated with CRT.

Reasons for the SyncAV programming turned either on or off for the patients receiving CRT were unknown, a limitation with the nonrandomized study, observed Varma for theheart.org | Medscape Cardiology. Propensity matching probably did not account for many unmeasured confounders.

Because of that, Paulus Kirchhof, MD, University Heart and Vascular Center UKE Hamburg, Germany, commented to theheart.org | Medscape Cardiology, one can't conclude from the study that the SyncAV algorithm improves heart failure and prevents HFH.

"It's really only possible to say that patients who have this algorithm turned on, for whatever reason, had less heart failure hospitalization than those who did not have the algorithm turned on," he said. The possibility that the effect could result from both known and unknown confounders "is quite substantial."

Potentially confounding, he proposed, are effects from center-to-center variability. There are centers that "think more physiologically" and so are more likely to activate the SyncAV programming, for example, or perform other processes differently. And there are patients who are more involved in their heart failure treatment and ask that the algorithm be turned on, Kirchhof observed.

The current study remains hypothesis-generating only, he said. "The correct follow-up on this would be to do a randomized controlled trial of SyncAV versus standard CRT programming in unselected patients receiving a CRT."

Varma concurred, and said, in fact, that a randomized trial is currently ongoing. "So hopefully that will give us a definitive answer."

For now, patients with persistent atrial fibrillation or with heart block would not benefit from the SyncAV algorithm, "but otherwise it should be turned on," Varma said. "There's no battery cost to this, so it doesn't reduce battery longevity and has no adverse effect. So the answer is, it should be turned on in everybody in whom it can be turned on."

The study was funded by Abbott. Varma reported research funding from Abbott and honoraria/speaking/consulting fees from Biotronik and Medtronic. Kirchhof reported support for basic, translational, and clinical research projects from the European Union, the British Heart Foundation, the Leducq Foundation, the Medical Research Council (UK), and the German Centre for Cardiovascular Research, and from several drug and device companies active in atrial fibrillation, from which he has received honoraria in the past but not in the past 3 years. He is listed as inventor on two patents held by the University of Birmingham .

European Heart Rhythm Association Congress 2020. Presented online March 29-31, 2020.

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