Monitoring Canine Myocardial Infarction Formation and Recovery via Transthoracic Cardiac Strain Imaging

Abstract

Myocardial Elastography (ME) is an ultrasound-based strain imaging method. A survival canine model (n=11) was employed to investigate ME's ability to image myocardial infarction (MI) formation and recovery. Infarcts were generated by ligation of the left anterior descending coronary artery. Canines were survived and imaged for four days (n=7) or four weeks (n=4), allowing sufficient time for recovery via collateral perfusion. A radial strain-based metric, percentage of healthy myocardium by strain (PHM ε ), was developed as a marker for healthy myocardial tissue. PHM ε was strongly linearly correlated with actual infarct size as determined by gross pathology (R 2 = 0.80). Mean PHM ε was reduced 1-3 days postinfarction (p<0.05) at the papillary and apical short-axis levels; full recovery was achieved by day 28, with mean PHM ε returning to baseline levels. ME was capable of diagnosing individual myocardial segments as non-infarcted or infarcted with high sensitivity (82%), specificity (92%), and precision (85%) (ROC AUC = 0.90).

Segmental and transmural motion of the rat myocardium estimated using quantitative ultrasound with new strategies for infarct detection

“…Additionally, an improvement in segmental and transmural myocardial motions was detected in 1-day versus 28-day results. A similar increase in mechanical properties during myocardial infarction recovery was also reported in recent studies using the ME technique ( Sayseng et al, 2020 ).…”

Murine cardiac fibrosis localization using adaptive Bayesian cardiac strain imaging in vivo

“…Vincent et al . also corroborates our approach of using ES strain images 24 . Two separate threshold values had to be chosen for radial ( = 4%) and longitudinal ( = − 4%) strain images due to their opposing BL strain direction (myocardial thickening and shortening 10 respectively).…”

“…Threshold values were chosen based on maximizing the correlation between PFM Radial and PFM Longitudinal against PFM Histopathology separately for this study. In the absence of ground truth histopathology images, BL data collected from a larger cohort of mice can be employed for choosing the threshold 24 . Quantitative analysis of fibrosis maps was performed regionally rather than globally due to the non-uniform LV structural and functional remodeling expected in MI and IR 6 .…”

“…Segmental analysis was performed by dividing the myocardium into six equal segments following the American Heart Association recommendation 34 . For each segment, percentage fibrotic myocardium (PFM) 24 was calculated as an in vivo surrogate measurement of cardiac fibrosis using the following equation. …”

“…However, CSI using ultrasound RF data is more sensitive to subtle myocardial motion abnormalities compared to envelope-based STE 16 – 18 . RF-based CSI 8 , 9 has been shown to be feasible in humans 22 , 23 and large animal models 24 , 25 . However, very few RF-based CSI studies have been performed in mice due to this method’s increased sensitivity to signal decorrelation associated with large deformations 26 , 27 .…”