Minimally invasive, patient specific, beat-by-beat estimation of left ventricular time varying elastance

Abstract

Background: The aim of this paper was to establish a minimally invasive method for deriving the left ventricular time varying elastance (TVE) curve beat-by-beat, the monitoring of which's inter-beat evolution could add significant new data and insight to improve diagnosis and treatment. The method developed uses the clinically available inputs of aortic pressure, heart rate and baseline end-systolic volume (via echocardiography) to determine the outputs of left ventricular pressure, volume and dead space volume, and thus the TVE curve. This approach avoids directly assuming the shape of the TVE curve, allowing more effective capture of intra- and inter-patient variability.

Results: The resulting TVE curve was experimentally validated against the TVE curve as derived from experimentally measured left ventricular pressure and volume in animal models, a data set encompassing 46,318 heartbeats across 5 Piétrain pigs. This simulated TVE curve was able to effectively approximate the measured TVE curve, with an overall median absolute error of 11.4% and overall median signed error of -2.5%.

Conclusions: The use of clinically available inputs means there is potential for real-time implementation of the method at the patient bedside. Thus the method could be used to provide additional, patient specific information on intra- and inter-beat variation in heart function.

Keywords: Cardiovascular system; Minimally invasive; Time varying elastance.

Fig. 1

Flowchart of the proposed method. Roman numerals indicate different method regions

Fig. 2

Simulating left ventricular pressure. Note P _ao has been shifted left by δ to account for phase lag

Fig. 3

Simulating left ventricular volume

Fig. 4

The fully instrumented Piétrain Pig. The catheters for measuring P _ao, P _lv and V _lv are positioned to the left of the image

Fig. 5

Example TVE curve error. This simulated driver has an error of 7.8% and bias of −3.4%

Fig. 6

Tracking of V _es. Comparison between the three methods in 2.2.2 for Pig 1

Fig. 7

Example TVE curves for each pig. A range of error values and cardiac states are shown