Assessment of Regional Myocardial Work in Rats

Abstract

Background-Left ventricular (LV) motion and deformation is dependent on mechanical load and do therefore not reflect myocardial energy consumption directly. Regional myocardial work, however, constitutes a more complete assessment of myocardial function. Methods and Results-Strain was measured using high-resolution phase-contrast MRI in 9 adult male rats with myocardial infarction (MI) and in 5 sham-operated control animals. Timing of LV valvular events and LV dimensions were evaluated by cine MRI. A separate cohort of 14 animals (MI/sham=9/5) underwent measurement of LV pressure concurrent with identification of valvular events by Doppler-echocardiography for the purpose of generating a standard LV pressure curve, normalized to valvular events. The infarctions were localized to the anterolateral LV wall. Combining strain with timing of valvular events and a measurement of peak arterial pressure, regional myocardial work could be calculated by applying the standard LV pressure curves. Cardiac output and stroke work was preserved in the MI hearts, suggesting a compensatory redistribution of myocardial work from the infarcted region to the viable tissue. In the septum, regional work was indeed increased in MI rats compared with sham (median work per unit long-axis length in a mid-ventricular slice: 241. Additionally, eccentric work was increased in the MI hearts. Conclusions-Phase-contrast MRI, in combination with measurement of peak arterial pressure and MRI-derived timing of valvular events, represent a noninvasive approach for estimation of regional myocardial work in rodents.

Elevated ventricular wall stress disrupts cardiomyocyte t-tubule structure and calcium homeostasis

“…In each sector, myocardial curvature, wall thickness, and circumferential strain were calculated as previously described in detail. 18 , 19 …”

A semiautomatic method for rapid segmentation of velocity‐encoded myocardial magnetic resonance imaging data

“…Segmentation can be done in several different ways, but manual segmentation without assistance of the underlying velocity field is common. Previously, we have applied an interpolation technique in which key time frames are identified and segmented and intermediate frames are subsequently interpolated . Comparing this approach with the semiautomatic method, we obtained an approximately 70% reduction in the segmentation workload.…”

“…The experiments were performed on a 9.4T horizontal bore magnet (Agilent Technologies, Inc., Santa Clara, California, USA) using hardware dedicated to rat cardiac imaging, as described previously .…”

“…In each animal, two short‐axis phase contrast TPM slices were acquired, one in the center of the left ventricle (midventricular slice) and one shifted 3 mm toward the base (basal slice), using a nine‐point velocity‐encoded black‐blood gradient echo cine sequence as previously described . TPM imaging parameters were as follows: echo time = 2.2–2.3 ms; pulse repetition time = 3.2 ms; field of view = 50 × 50 mm; matrix = 128 × 128; slice thickness = 1.5 mm; flip angle = 7°; velocity sensitivity (venc) = 13.9 cm/s; and number of averages = 1.…”

Cardiovascular imaging: what have we learned from animal models?

“…Also, high in-plane resolution (0.1 × 0.1 mm) cine MRI has been developed to quantify right ventricular function in murine models (Wiesmann et al, 2002 ). Other techniques for quantitative wall-motion imaging like myocardial tagging (Epstein et al, 2002 ; Zhou et al, 2003 ) or velocity-encode phase-contrast imaging (Espe et al, 2015 ) have been optimized for animal studies. These approaches permit the tracking of regional myocardium and enable the quantification of principal strains and directions (radial, circumferential, and longitudinal) to depict the extent of the changes in contractility after MI (Young et al, 2006 ).…”