An overview on development and application of an experimental platform for quantitative cardiac imaging research in rabbit models of myocardial infarction

Three-dimensional quantitative assessment of myocardial infarction via multimodality fusion imaging: methodology, validation, and preliminary clinical application

Background

The precise assessment of myocardial infarction (MI) is crucial both for therapeutic interventions in old MI and the development of new and effective techniques to repair injured myocardium. A novel method was developed to assess left ventricular (LV) quantitatively infarction through three-dimensional (3D) multimodality fusion based on computed tomography angiography (CTA) and technetium-99m methoxyisobutylisonitrile (^99mTc-MIBI) single-photon emission computed tomography (SPECT) images. This study sought to develop a 3D quantitative method for MI for pre-clinical study and clinical application.

Methods

Three months after the MI models were established in 20 minipigs, CTA and SPECT images were acquired separately, which were then aligned automatically with the constraints of the shape and the whole heart and LV myocardium position. Infarct ratios were quantified based on the 3D fusion images. The quantitative assessment was then experimentally validated via an ex vivo histology analysis using triphenyl-tetrazolium-chloride staining and subsequently applied to post-MI patients (n=8).

Results

The location of an infarct identified by the SPECT was consistent with that identified by an ex vivo heart in a 3D space. Infarct size determined by CTA-SPECT was correlated with infarct size assessed by triphenyl-tetrazolium-chloride pathology {27.6% [interquartile range (IQR) 17.1-34.7%] vs. 24.1% (IQR 14.7-32.5%), r²=0.99, P<0.01}. In clinical cases, the CTA-SPECT 3D fusion quantitative results were significantly correlated with the quantitative perfusion SPECT results (r=0.976, P<0.01).

Conclusions

The proposed 3D fusion quantitative assessment method provides reliable and intuitive evaluations of infarction. This novel quantification technique enables whole heart quantification for the pre-operation evaluation and post-diagnosis management of old MI patients. It could also be applied to the design of 3D-printed cardiac patches.

An Under-Recognized Sequela of Myocardial Infarction: Lipomatous Metaplasia

Lipomatous metaplasia is an infrequently discussed condition characterized by adipose tissue replacing scar tissue from ischemic events. Lipomatous metaplasia specifically of the myocardium is an adverse physiological result of myocardial infarction. In the past, several different imaging and diagnostic techniques were utilized to recognize lipomatous metaplasia of the myocardium. The aim of this study is to discuss an individual case with this condition to highlight several key aspects that are under-discussed in current literature, such as determining the most suitable modality for the recognition of lipomatous metaplasia.

Development and Long-Term Follow-Up of an Experimental Model of Myocardial Infarction in Rabbits

Simple Summary

Ischemic heart disease is one of the leading causes of death. A series of processes occur during acute myocardial infarction that contribute to the development of ventricular dysfunction, with subsequent heart failure and ventricular arrhythmias, which account for most episodes of sudden cardiac death in these patients. These complications are associated with the adverse cardiac remodeling that occurs during the healing process following an acute episode. The remodeling causes the appearance of a substrate that can trigger life-threatening arrhythmias, such as tachycardia and/or ventricular fibrillation. The development of experimental models for analyzing the basic mechanisms involved in the pathophysiology of myocardial infarction enables the study of different therapeutic approaches aimed at improving the patient´s prognosis. The present study describes the methodology and the results obtained in a 5-week chronic infarction (one hour followed by reperfusion) in a rabbit model. The viability of the model, the care provided, the characteristics and extent of the lesions, the inducibility of arrhythmias, and the reproducibility of the methods and results have been analyzed.

Abstract

A chronic model of acute myocardial infarction was developed to study the mechanisms involved in adverse postinfarction ventricular remodeling. In an acute myocardial infarction (AMI), the left circumflex coronary artery of New Zealand White rabbits (n = 9) was occluded by ligature for 1 h, followed by reperfusion. A specific care protocol was applied before, during, and after the intervention, and the results were compared with those of a sham operated group (n = 7). After 5 weeks, programmed stimulation and high-resolution mapping were performed on isolated and perfused hearts using the Langendorff technique. The infarct size determined by 2,3,5-triphenyltetrazolium chloride inside of the area at risk (thioflavin-S) was then determined. The area at risk was similar in both groups (54.33% (experimental infarct group) vs. 58.59% (sham group), ns). The infarct size was 73.16% as a percentage of the risk area. The experimental infarct group had a higher inducibility of ventricular arrhythmias (100% vs. 43% in the sham group, p = 0.009). A reproducible chronic experimental model of myocardial infarction is presented in which the extent and characteristics of the lesions enable the study of the vulnerability to develop ventricular arrhythmias because of the remodeling process that occurs during cardiac tissue repair.

Monitoring reperfused myocardial infarction with delayed left ventricular systolic dysfunction in rabbits by longitudinal imaging

Background

An experimental imaging platform for longitudinal monitoring and evaluation of cardiac morphology-function changes has been long desired. We sought to establish such a platform by using a rabbit model of reperfused myocardial infarction (MI) that develops chronic left ventricle systolic dysfunction (LVSD) within 7 weeks.

Methods

Fifty-five New Zeeland white (NZW) rabbits received sham-operated or 60-min left circumflex coronary artery (LCx) ligation followed by reperfusion. Cardiac magnetic resonance imaging (cMRI), transthoracic echocardiography (echo), and blood samples were collected at baseline, in acute (48 hours or 1 week) and chronic (7 weeks) stage subsequent to MI for in vivo assessment of infarct size, cardiac morphology, LV function, and myocardial enzymes. Seven weeks post MI, animals were sacrificed and heart tissues were processed for histopathological staining.

Results

The success rate of surgical operation was 87.27%. The animal mortality rates were 12.7% and 3.6% both in acute and chronic stage separately. Serum levels of the myocardial enzyme cardiac Troponin T (cTnT) were significantly increased in MI rabbits as compared with sham animals after 4 hours of operation (P<0.05). According to cardiac morphology and function changes, 4 groups could be distinguished: sham rabbits (n=12), and MI rabbits with no (MI_NO_LVSD; n=10), moderate (MI_M_LVSD; n=9) and severe (MI_S_LVSD; n=15) LVSD. No significant differences in cardiac function or wall thickening between sham and MI_NO_LVSD rabbits were observed at both stages using both cMRI and echo methods. cMRI data showed that MI_M_LVSD rabbits exhibited a reduction of ejection fraction (EF) and an increase in end-systolic volume (ESV) at the acute phase, while at the chronic stage these parameters did not change further. Moreover, in MI_S_LVSD animals, these observations were more striking at the acute stage followed by a further decline in EF and increase in ESV at the chronic stage. Lateral wall thickening determined by cMRI was significantly decreased in MI_M_LVSD versus MI_NO_LVSD animals at both stages (P<0.05). As for MI_S_LVSD versus MI_M_LVSD rabbits, the thickening of anterior, inferior and lateral walls was significantly more decreased at both stages (P<0.05). Echo confirmed the findings of cMRI. Furthermore, these in vivo outcomes including those from vivid cine cMRI could be supported by exactly matched ex vivo histomorphological evidences.

Conclusions

Our findings indicate that chronic LVSD developed over time after surgery-induced MI in rabbits can be longitudinally evaluated using non-invasive imaging techniques and confirmed by the entire-heart-slice histomorphology. This experimental LVSD platform in rabbits may interest researchers in the field of experimental cardiology and help strengthen drug development and translational research for the management of cardiovascular diseases.