Enhancing Communication Robustness for Leadless Pacemakers: 2-DOF Gain Compensation Across Physiologic and Pathologic...

Implantable Medical Devices (IMDs) are evolving into collaborative networks, demanding robust and ultra-low power communication in dynamic and often pathological biolog ical environments. Multi-chamber leadless pacemakers (LCPs) represent a particularly challenging case, because the intrac ardiac channel exhibits not only periodic fluctuations during healthy rhythms but also abrupt and aperiodic fades under pathological conditions such as atrioventricular (AV) block. To address this challenge, an adaptive receiver based on a Super-Regenerative Receiver (SRR) and a hybrid analog-digital Automatic Gain Control (AGC) system is proposed. At its core is a beat-synchronous two-degree-of-freedom (2-DOF) control strategy that uses peak RSSI as an electrocardiogram-free rhythm surrogate, enabling active signal stabilization through predictive feedforward and incremental Proportional-Integral Derivative (PID) control. The proposed architecture was vali dated through a three-layer framework comprising Hardware in-the-Loop (HIL) transient characterization, programmable ex vivo porcine-heart testing under a representative Mobitz Type II AV block model, and complementary ATP-provoked acute in-vivo porcine validation. Experimental results show that the proposed 2-DOF controller stabilizes the input signal to within 1% of its target under channel variations exceeding 15dB, reducing the Bit Error Rate (BER) by one to two orders of magnitude and achieving an improvement factor of more than 60 at 5kbps. In the living heart, the adaptive loop maintained stable gain control and preserved digital demodulation during ATP-provoked transient AV-block-like intervals, while supplementary in-vivo BER measurements provided additional quantitative support for end-to-end communication robustness. These results support the proposed architecture as a promising solution for robust intrac ardiac communication in future multi-chamber LCP systems.