Evaluation of Coronary Flow Reserve After Myocardial Ischemia Reperfusion in Rats

Summary

Coronary flow reserve (CFR), is defined as the ratio of maximal coronary blood flow to the resting coronary blood flow. We present a protocol for evaluating CFR in rats via ultrasound, which offers the opportunity to predict cardiovascular risk factors in the absence of obstructive coronary disease.

Abstract

Coronary artery disease is the leading cause of death worldwide. After an acute myocardial infarction, early and successful myocardial intervention via recanalization of the coronary artery is the most effective strategy for reducing the size of ischemic myocardium. The coronary microvasculature cannot be visualized and imaged in vivo, but there are several invasive and noninvasive techniques that can be used to assess parameters which depend directly on coronary microvascular function. The endothelial function after ischemia reperfusion can be assessed also at the level of the coronary circulation via the coronary flow reserve (CFR). In this study, peak velocity of left anterior descending (LAD) coronary arteries was measured in rats in vivo via Transthoracic Doppler Echocardiography during resting and stress challenge (induced by Dobutamine). A normal heart can increase its coronary blood flow up to four times above the resting values during stress induction. Following ischemia reperfusion, we found a significantly diminished CFR, which can be used as a marker of coronary microvascular dysfunction. CFR has opened a window on the importance of microvascular dysfunction and has been shown to predict cardiovascular risk independent of whether the severe obstructive disease is present.

Introduction

Myocardial ischemia reperfusion (IR) is a condition where blood supply is restricted to the heart followed by the restoration of perfusion and simultaneous reoxygenation¹. Occlusion of coronary arteries can be caused by an embolus or cholesterol plaque rupture, which results in a severe imbalance of metabolic supply and demand, causing tissue hypoxia. Salvage of jeopardized myocardium, improve left ventricular function, and enhance survival in patients with acute myocardial infarction have been observed by the reperfusion therapy. However, after recanalization of the coronary artery, functional abnormalities of small coronary vessels may occur<....

Protocol

All procedures were performed in accordance with protocols approved by the University of Louisville Institutional Animal Care and Use Committee (IACUC-approved protocol 18223) and the NIH Guide for the Care and Use of Laboratory Animals¹¹.

1. Animals

1. Use 4-month-old female Fisher 344 rats (BW~150-180 g) for the study.

2. Ultrasound Imaging before IR surgery

1. Anesthetize the rat with isoflurane - induction chamber at 5% with 1.5–2.0 L/min O₂ flow followed by 1.5–2.0% with 1.5–2.0 L/min O₂ flow. This anesthesia is maintain....

Results

For this study, we used 12 female Fisher 344 rats. We performed a stress test with Dobutamine and measured LAD coronary artery velocity before and 72 hours after the IR surgery. Before the IR surgery, resting LAD coronary artery velocity was measured as 423 ± 59 mm/s, which was increased after Dobutamine infusion (1005 ± 77mm/s) (Figure 3A). After 72 h of ischemia reperfusion, resting LAD coronary artery velocity was significantly higher compared to the resti.......

Discussion

The major findings from the present study are that IR increases the resting LAD coronary artery velocity and impairs CFR, even in the absence of any residual angiographic stenosis.

Understanding the coronary physiology is an essential part of the clinical decision-making for cardiologists to treat coronary artery disease. CFR is one of the important functional parameters in understanding the pathophysiology of coronary microcirculation^7,13

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
10 mL syringe	BD Syringe	302995
250S 13–24 MHz linear probe	FUJIFILM VisualSonics Inc
Dobutamine hydrochloride	Sigma	D0676-10mg
Isoflurane	RRC	27376
Legato 100 Syringe pump	KD Scientific	788100
Vevo 3100	FUJIFILM VisualSonics Inc
Winged infusion set, 27G x 1/2",	Medline.com	TMOSV27ELZ