Transmural Distribution of Coronary Perfusion and Myocardial Work Density Due to Alterations in Ventricular Loading, Geometry and Contractility.

Lei Fan,Ghassan S Kassab,Lik Chuan Lee,Ravi Namani,Jenny S Choy

doi:10.3389/fphys.2021.744855

Lei Fan, Ghassan S Kassab + Show 3 more

Open Access

https://doi.org/10.3389/fphys.2021.744855

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Abstract

Myocardial supply changes to accommodate the variation of myocardial demand across the heart wall to maintain normal cardiac function. A computational framework that couples the systemic circulation of a left ventricular (LV) finite element model and coronary perfusion in a closed loop is developed to investigate the transmural distribution of the myocardial demand (work density) and supply (perfusion) ratio. Calibrated and validated against measurements of LV mechanics and coronary perfusion, the model is applied to investigate changes in the transmural distribution of passive coronary perfusion, myocardial work density, and their ratio in response to changes in LV contractility, preload, afterload, wall thickness, and cavity volume. The model predicts the following: (1) Total passive coronary flow varies from a minimum value at the endocardium to a maximum value at the epicardium transmurally that is consistent with the transmural distribution of IMP; (2) Total passive coronary flow at different transmural locations is increased with an increase in either contractility, afterload, or preload of the LV, whereas is reduced with an increase in wall thickness or cavity volume; (3) Myocardial work density at different transmural locations is increased transmurally with an increase in either contractility, afterload, preload or cavity volume of the LV, but is reduced with an increase in wall thickness; (4) Myocardial work density-perfusion mismatch ratio at different transmural locations is increased with an increase in contractility, preload, wall thickness or cavity volume of the LV, and the ratio is higher at the endocardium than the epicardium. These results suggest that an increase in either contractility, preload, wall thickness, or cavity volume of the LV can increase the vulnerability of the subendocardial region to ischemia.

Highlights

Myocardial blood flow across the left ventricular (LV) wall is affected by many factors that depend on LV mechanics
Given that the coronary flow is a compromise between perfusion pressure and intramyocardial (extravascular) pressure (IMP), increasing Tmax from 65 to 130 kPa produced an increase in the coronary flow at endocardium (14.3%)
The specific key findings are: (1) Transmural distribution of IMP across the LV wall can explain the transmural distribution of passive coronary flow measured experimentally (Heineman and Grayson, 1985; Krams et al, 1989b; Vatner and Hittinger, 1993); (2) Coronary flow Q at all transmural positions across the myocardial wall increases with either increasing LV contractility, afterload or preload, while it decreases with increasing wall thickness or cavity volume; (3) Myocardial work density Wf at all transmural positions increases with either increasing

Summary

Introduction

Myocardial blood flow across the left ventricular (LV) wall is affected by many factors that depend on LV mechanics. Transmural Distribution of Myocardial Demand/Supply (Namani et al, 2020) which varies from its maximum value at the endocardium to its minimum value at the epicardium (Downey et al, 1975; Algranati et al, 2010). This trend is widely used to explain the transmural distribution of myocardial blood flow across the LV wall under maximally dilated conditions, where flow is small at the endocardium and large at the epicardium (Bache et al, 1981a). CFR is exhausted first at the endocardium (Gallagher et al, 1980) compared to epicardium, which can explain the observation that the endocardium is more vulnerable to ischemia than the epicardium (Algranati et al, 2011)

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