The first modular cardiac rhythm management (mCRM) system showed an acceptable safety profile and stable device-device communication over 18 months. Results from the preclinical evaluation were presented at the American Heart Association (AHA) Scientific Sessions 2021, held virtually from November 13 to 15, 2021.

The mCRM system comprises 2 devices that work together to coordinate therapy: a subcutaneous implantable cardioverter-defibrillator (S-ICD) and a modular pacing system (MPS). Leadless pacemakers are designed to reduce complications due to transvenous leads by providing protection without coming in contact with the heart or substernal space. However, currently available leadless pacemakers are unable to deliver antibradycardia or antitachycardia pacing, so there are no leadless options for patients with a defibrillator who have or are expected to have pacing needs.

Researchers from Boston Scientific Corporation implanted a leadless pacemaker in canine subjects (N=63). A subset of dogs (n=38) received a concomitant S-ICD device. Clinical outcomes and mCRM communication were assessed at multiple visits over 18 months. The mCRM communication was determined to be successful if the communication threshold was less than or equal to 6.0 V post-implant and at least 1.0 V at subsequent visits (as measured in 3 postures).

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The mCRM communication was successful in 99.8% (1022/1024) of assessments over the study duration. At the 18-month follow-up, the communication had a 100% success rate.

At implantation, the median communication threshold was 2.0 V (IQR, 1.5-2.0). During later follow-ups, the communication threshold was stable at 1.5 V (IQR, 1.0-2.0).

At implantation, the median pacing capture threshold was 0.3 V at 0.5 ms (IQR, 0.2-0.3), impedance was 877 W (IQR, 739-1041), and R-wave was 25 mV (IQR, 14-34). During subsequent follow-ups, the pacing threshold remained stable (median, 0.5 V at 0.5 ms; IQR, 0.1-0.9) and acceptable ranges were observed for impedance (median, 765W; IQR, 578-953) and R-wave (median, 25 mV; IQR, 13-37).

There were 2 complications due to prototype leadless pacemaker accelerometer malfunctions.

This study demonstrated that the first mCRM system had a stable and safe performance up to 18 months and may be a viable approach for patients who have pacing needs.

“Our preclinical evaluation demonstrated excellent long-term performance and safety of the first modular cardiac rhythm management (mCRM) system, with low, stable device-device communication thresholds and acceptable leadless pacemaker electrical parameters,” Dr Karel Breeman, lead investigator of the mCRM preclinical evaluation, said. “These results are particularly promising as there currently are no minimally-invasive, leadless options for patients requiring a defibrillator and expected pacing. We look forward to building on this strong preclinical foundation to evaluate the mCRM system in human subjects with both ICD and pacing indications in the MODULAR ATP study, which will begin enrollment by the end of 2021.”

Disclosure: Multiple authors declared affiliations with industry. Please refer to the original article for a full list of disclosures.


Breeman KTN, Tjong FVY, Knops RE, et al. Novel communicating leadless pacemaker and subcutaneous implantable cardioverter-defibrillator system provide stable long-term performance. Presented at: AHA Scientific Sessions 2021. Abstract LBP22