Remote monitoring trends post CRT-P upgrade: can we predict treatment response?

Background Thoracic Impedance (TI) as measured by cardiac implanted electronic devices (CIEDs) is known to correlate inversely with intrathoracic congestion, elevated pro-NT BNP and clinical heart failure (HF) worsening.1 Combining TI with other "HF diagnostics" parameters including baseline heart rate (HR), heart rate variability (HRV), patient activity (PA), atrial high rates and ventricular ectopy burden can help to predict pre-clinical HF decompensation.2 Conversely, following upgrade to Cardiac Resynchronisation Therapy (CRT), there is limited evidence regarding the role of remote monitoring in predicting treatment response, which potentially manifests as a mirror image of the findings in decompensation as the left ventricle remodels. Purpose We hypothesised that following CRT-P upgrade in patients with impaired left ventricular systolic function, trends in "HF diagnostics" and lead impedances correlate with response to CRT. Methods Single-centre retrospective observational study. All patients upgraded to CRT-P between 2018 – 2024 with complete transthoracic echo (TTE) data were included. Response to CRT was defined as improvement in ejection fraction (EF) by >5%, with super-responders improving by >15%. Exclusions due to permanent atrial fibrillation and atrial pacing rendered patient numbers insufficient to perform meaningful HR and HRV analysis. In patients where functioning right-sided leads were connected to the new CRT box, right atrial (RA) and right ventricular (RV) lead impedances were analysed at time of upgrade and at pacing check around the time of follow-up TTE. Patient activity (PA) and thoracic impedance (TI) were analysed by visual inspection of trend graphs at first post implant pacing check (Fig.1). Results 64 patients met inclusion criteria with mean age 80 (46 – 92), with 69% male. Mean ejection fraction (%) pre-upgrade was 33 (15 – 45), improving to 46 (15 – 60). 47 (73%) patients were responders with the majority being super-responders (Fig.2). 33% of patients were in permanent atrial fibrillation with associated trend towards lower likelihood of treatment response (57 vs. 81%, p 0.07). Median RV impedance change post implant (%) was 0.0 (IQR -1.7 to 10.5) in non-responders and -1.4 (IQR -5.53 to 4.64) in responders. Median RA impedance change was -0.03 (IQR -4.22 to 1.02) in non-responders and 0.00 (IQR -7.23 to 4.57%) in responders. At median 1 month post implant, 7 (58.3%) non-responders and 18 (56.3%) responders had upward trending PA while 5 (62.5%) non-responders and 13 (43.3%) responders had upward trending TI, with no statistically significant differences between the two cohorts. Conclusion In this retrospective analysis of CRT-P upgrades, 73% of patients responded to CRT. RA and RV lead impedance were stable in all patients regardless of treatment response. The majority of patients undergoing CRT-P upgrade had increasing PA and TI post implant, but trends did not corelate with CRT response.