Introduction: Cardiac accelerometers have been proposed for the characterization and monitoring of heart wall motion. Although some markers extracted from cardiac accelerometry have been associated with contractility, they are mainly based on uniaxial (1D) sensors, that not always consistently reflect this relationship.
Methods: The ECG and left ventricular (LV) pressure signals of two anesthetized pigs, together with their 3D-acceleration signals obtained from sensors located at the LV free wall, were acquired at baseline and during pharmacological inotropic stimulation by means of dobutamine infusion (5 ug/kg/min). For each cardiac cycle, contractility was estimated as the maximal LV pressure first derivative (dP/dtmax), as well as the peak of maximum energy (PE) and the peak of acceleration (PA) were acquired for each accelerometry axis and the modulus. First- and second-order polynomial curves were fitted to the relationships between dP/dtmax and each extracted feature, and the fitting quality of these curves was finally quantified by the R-squared (R2).
Results: While first-order curves were more appropriate for representing the relationship between contractility and unidimensional markers, second-order curves turned to better reflect the dependency between three-dimensional features and dP/dtmax. When all markers were taken into account, R2 was increased, on average, by a 15% when the three accelerometry axes were analyzed (R2_1D=0.62±0.25; R2_3D= 0.77±0.22). Moreover, while similar results were obtained for both unidimensional markers (R2_PE_1D=0.62±0.15; R2_PA_1D=0.63±0.34), PE seemed to better represent contractility when based on 3D data (R2_PE_3D=0.83±0.16; R2_PA_3D= 0.72±0.33).
Conclusion: Three-dimensional accelerometry seems to more consistently represent cardiac contractility. Moreover, the peak of maximum energy at each cardiac cycle is proposed as a marker of this contractility, showing good fits with data obtained during pharmacological inotropic stimulations. Although the obtained results should be validated in the future with larger databases, they already indicate that three-dimensional accelerometry may lead to more reliable LV contractility estimates.