A novel septal sensor for continuous cardiac function monitoring

Background Miniaturized sensors can be implanted in the heart for direct monitoring of cardiac function. Purpose We developed a miniaturized motion sensor with potential to be incorporated in pacemaker leads screwed into the septum and investigated how such a sensor can be used to monitor cardiac function. Methods A miniaturized sensor (2.5 × 3 × 0.71 mm) capable of measuring three-axis acceleration was integrated into a flexible printed circuit board and encapsulated in silicone rubber (Figure 1A). The sensor was inserted into the interventricular septum in anesthetized open-chest animals (>35 kg) (Figure 1B). A microtip pressure catheter was placed through the left ventricular apex for continuous pressure measurement. Myocardial contractility was increased by intravenous dobutamine and reduced by inhaled isoflurane. Additionally, transient preload reductions were induced by brief constriction of the inferior vena cava. Heart function was evaluated using maximal rise of the first derivative of left ventricular pressure (LV dP/dtmax). Sensor signals (Figure 1C) were processed to derive four indices: principal components (PC), root mean square (RMS), ʃpower spectral density (PSD) and maximum 3D acceleration (Amax), using R peaks on ECG as reference. The relationship between dP/dtmax and each index was quantified using Pearson’s coefficients. Results Four animal experiments were performed, yielding a total of 5,647 heartbeats for analysis. Acceleration signals decreased during isoflurane and increased during dobutamine, mirroring intervention-related changes in left ventricular pressure (Figure 1C). Figure 2 shows an example of the sensor ability to track dP/dtmax from 2800 mmHg/s to 1050 mmHg/s over a 7-minute continuous recording of isoflurane ventilation in one animal. All indices demonstrated an excellent correlation with dP/dtmax (r>0.98, p<0.001). Similar results were observed across all animals with correlation coefficients ranging between 0.796 – 0.993 (all p<0.001) during the isoflurane intervention, and between 0.746 – 0.902 (all p<0.001) during the dobutamine intervention. The best index (PSD) had a correlation coefficient of 0.843 ±0.098 averaged over animals and interventions. Conclusions This proof-of-concept study shows that septal acceleration sensor signals closely track LV systolic function across a series of interventions. Such a sensor could be integrated into pacing leads to provide continuous home monitoring of cardiac function in pacemaker recipients.