Monitoring stroke volume continuously and autonomously using an epicardial accelerometer

The incorporation of miniaturised accelerometers into cardiac implants used in current clinical practice endows access to continuous measurement of heart wall motion and vibrations which may be used to monitor cardiac function without additional risk to patient safety. In this work the path length travelled throughout a heartbeat by an accelerometer attached to the lateral epicardium of the left ventricle is presented as a surrogate for stroke volume, a fundamental parameter of cardiac function. A strong correlation was found between path length and stroke volume in experimental animal data (n=13). Additionally, mathematical models for path length and stroke volume were derived using physiological and geometrical principles, and validated against a measured ground truth. Using the models, path length and stroke volume were both shown to respond similarly to changes in the size of the left ventricle and its contraction, further supporting and explaining the link between the two. The theoretical and empirical evidence presented therefore supports the use of epicardially attached accelerometers for continuous and autonomous monitoring of stroke volume, encouraging further development of epicardial motion sensors for the purpose of clinical or remote assessment of cardiac function.