Continuous and Autonomous Monitoring of Changes in Left Ventricular dP/dt_max Using an Epicardial Accelerometer

Assessment of the contractile function of the heart typically requires resource demanding techniques, such as invasive left ventricular catheterisation or intermittent medical imaging, and is therefore not readily available for continuous clinical or remote monitoring. Measurement of heart wall motion by use of an epicardially attached three-axis accelerometer has emerged as a promising tool for monitoring cardiac function; however, previous methods have often underutilised the spatial and temporal information contained in the measured signals, potentially limiting its clinical reliability. This work reconstructs the position of an epicardial accelerometer in 3D space in order to enable extraction of indices of cardiac function in a Lagrangian frame of reference. The standard deviation of Lagrangian acceleration throughout a heartbeat, ${\sigma }_{\mathrm{Acc}}$ , is introduced as a novel surrogate indicator of contractility as changes in ${\sigma }_{\mathrm{Acc}}$ correlated strongly with changes in the maximum rate of change in left ventricular pressure in animal data (n=29) spanning a variety of haemodynamic conditions. The reported findings of this proof-of-principle study may represent a first step towards long-term monitoring of contractile function and expands on the current repertoire of use for epicardially attached accelerometers as versatile, continuous, and autonomous monitoring devices.