2H-2 Gradients in Radial Strain Across the Cardiac Wall Studied with Epicardial Ultrasound

Differences in radial deformation characteristics across the myocardial wall have been studied extensively in order to better understand cardiac mechanics and (patho-)physiology. To date, transmural gradients have typically been determined by invasive techniques as accurate non-invasive assessment remains a technical challenge. However, invasive methods require pericardial opening which is generally known to affect cardiac mechanics. The aim of this study was therefore to apply epicardial ultrasound in order to assess myocardial deformation at high temporal and spatial resolution. In this way, the differences in myocardial deformation across the wall could be quantified and the influence of pericardial opening could be studied. Hereto, five anesthetised, open-chest sheep were scanned using a 13 MHz epicardial transducer before and after pericardial opening. Color Doppler myocardial velocity data were acquired from the anterior wall with the probe positioned both parallel and perpendicular to the left anterior descending coronary artery. All data sets were analyzed off-line on a personal computer using dedicated software (SPEQLE). Radial end-systolic strain was extracted in the subendocardial, mid-wall and subepicardial layers. In concordance with reported observations from invasive measurements, subendocardial strain was found to be highest after pericardial opening. However, while the pericardium was intact, strain showed to be highest in the mid-myocardial layers, which is in concordance with prior observations using transthoracic ultrasound. This concept is violating local conservation of mass, which would hold for an elastic body. However, due to its structure and especially the capillary bed, myocardial might better be modelled as a poroelastic material since blood can be locally displaced within the myocardium during the cardiac cycle