A GMSK-based conductive intracardiac communication method

Conductive intracardiac communication (CIC) can be utilized for the synchronization of multi-chamber leadless pacemakers (LLPMs) to overcome complications arising from traditional pacemaker lead connections. Current CIC methods are mainly based on pulse modulation (PM) and On-Off Keying (OOK), which suffer from high power consumption and poor interference resilience, with transmitter output bit energy (E_bit) exceeding 5 pJ. Addressing these concerns, we proposed a method of conductive intracardiac communication based on Gaussian Minimum Shift Keying (GMSK). In the transmitter, a power-optimized GMSK modulation method is employed for signal transmission. In the receiver, a variable gain amplifier is utilized for CIC signal reception, and signal recovery is achieved through low-power demodulation and bit synchronization methods. A prototype transceiver was designed for measuring the bit error ratio (BER) and transmitter output E_bit of GMSK and OOK methods in in-vitro experiments using porcine hearts as channels. The transceiver was connected to the right atrium and right ventricle via stainless steel needle electrodes. At data rates of 75-500 kbps and a BER of 1e-4, the average E_bit for OOK ranged from 0.06-0.61 pJ, whereas for GMSK, it was lower, ranging from 0.02-0.35 pJ. This study demonstrates that LLPM achieving reliable CIC using GMSK at transmission powers below 35 pW is feasible in practical channel conditions. The proposed GMSK-based CIC method is more preferable to PM and OOK due to its higher reliability and lower transmission power requirements.