Automatic detection of valve events by epicardial accelerometer

Measurements of the left ventricular (LV) pressure trace are rarely performed despite high clinical interest. We estimated the LV pressure trace for an individual heart by scaling the isovolumic, ejection and filling phases of a normalized, averaged LV pressure trace to the time-points of opening and closing of the aortic and mitral valves detected in the individual heart. We developed a signal processing algorithm that automatically detected the time-points of these valve events from the motion signal of a miniaturized accelerometer attached to the heart surface. Furthermore, the pressure trace was used in combination with measured displacement from the accelerometer to calculate the pressure-displacement loop area.

Publisert 19.10.2023

Monitoring of cardiac function by miniaturized accelerometers attached to the heart is becoming more frequently used, for example, these sensors can be found in pacing electrodes for cardiac resynchronization therapy1–3. Similarly, accelerometers may also be incorporated in the temporary pacemaker leads that are attached to the heart during cardiac surgery and later retracted through the chest after a few days. Addition of such a sensor to the pacemaker lead will allow measurements of cardiac motion without adding complexity to the surgical procedure, thus providing a new method for continuous monitoring of cardiac function in these patients. This can be useful for assessing the response to medication and may lead to earlier detection of cases with myocardial dysfunction.

In order to assess cardiac function by using accelerometers, functional indices need to be extracted from the sensor signal. Our group has performed several studies with epicardially attached accelerometers and demonstrated that such accelerometer recordings can be used for monitoring cardiac function. Velocity and displacement, calculated by integrating the acceleration signal once and twice, respectively, have been shown to give valuable functional information. Another functional index can be derived by combining displacement with measurements of left ventricular (LV) pressure to generate pressure–displacement loops. This builds on the classical pressure–volume loop principle for analysis of cardiac function which also has inspired other novel loop-analysis methods such as the pressure-strain loop method.