Dual-chamber leadless pacing: Atrioventricular synchrony in preclinical models of normal or blocked atrioventricular conduction

Background

Dual-chamber leadless pacemakers (LPs) require robust communication between distinct right atrial (RA) and right ventricular (RV) LPs to achieve atrioventricular (AV) synchrony.

Objective

The purpose of this preclinical study was to evaluate a novel, continuous implant-to-implant (i2i™) communication methodology for maintaining AV-synchronous, dual-chamber DDD(R) pacing by the 2 LPs.

Methods

RA and RV LPs were implanted and paired in 7 ovine subjects (4 with induced complete heart block). AV synchrony (% AV intervals <300 ms) and i2i communication success (% successful i2i transmissions between LPs) were evaluated acutely and chronically. During acute testing, 12-lead electrocardiographic and LP diagnostic data were collected from 5-minute recordings, in 4 postures and 2 rhythms (AP-VP and AS-VP, or AP-VS and AS-VS) per subject. Chronic i2i performance was evaluated through 23 weeks postimplant (final i2i evaluation period: week 16–23).

Results

Acute AV synchrony and i2i communication success across multiple postures and rhythms were median [interquartile range] 100.0% [100.0%–100.0%] and 99.9% [99.9%–99.9%], respectively. AV synchrony and i2i success rates did not differ across postures (P = .59, P = .11) or rhythms (P = 1, P = .82). During the final i2i evaluation period, the overall i2i success was 98.9% [98.1%–99.0%].

Conclusion

Successful AV-synchronous, dual-chamber DDD(R) leadless pacing using a novel, continuous, wireless communication modality was demonstrated across variations in posture and rhythm in a preclinical model.

Introduction

Appropriate timing between atrial and ventricular activity, known as atrioventricular (AV) synchrony, is necessary to maintain optimal cardiac function, notably stroke volume and cardiac output.1, 2, 3, 4, 5 To preserve this normal sequence in pacemaker-indicated patients, both atrial pacing and tracking are required. Single-chamber leadless pacemaker (LP) technologies designed to operate in VDD(R) mode, lacking atrial pacing and direct atrial sensing capabilities, have reported AV synchrony ranging from 33% to 94% of beats when a variety of postures, heart rates, pacing demands, and physical activities are included.6, 7, 8, 9, 10 Similar to traditional transvenous pacemakers, system operations (eg, rate-modulated pacing) in single-chamber LPs are performed by a single device. Expanding to synchronous dual-chamber leadless pacing, however, requires energy-efficient communication between 2 distinct LPs for them to operate in concert as a single system. To ensure continuous AV synchrony and serve as an alternative to traditional DDD(R) pacemakers, true dual-chamber leadless pacing requires bidirectional, wireless communication between LPs at each right atrial (RA) and right ventricular (RV) activation.

One technology by which multiple implants can wirelessly and efficiently operate as a single system has been termed implant-to-implant (i2i™) communication. A previous study demonstrated reliable chronic performance of this i2i communication modality using 2 LPs implanted in vivo in a healthy ovine model.¹¹ However, i2i performance has not been demonstrated under conditions expected clinically, such as AV conduction block or postural changes. This preclinical study assessed the ability of i2i to achieve synchronous, dual-chamber DDD(R) pacing using 2 LPs implanted in the RA and RV of ovine models of normal conduction and AV block. The i2i communication performance and corresponding AV synchrony were evaluated during acute conditions of induced postures and rhythms, as well as during the chronic, natural variations associated with activities of daily living. Because the i2i modality was designed to facilitate AV-synchronous pacing, AV synchrony percentage was expected to equal or exceed i2i communication performance.