Review
Potential clinical applications of myocardial contrast echocardiography in evaluating myocardial perfusion in coronary artery disease

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Abstract

Myocardial contrast echocardiography (MCE) is a relatively new technique that uses microbubbles to produce myocardial opacification. Recent advances in echocardiography have resulted in improved detection of microbubbles within the myocardium allowing combined acquisition of function and perfusion data, thus making MCE suitable for bedside use. Regardless of the imaging modality chosen or the type of stress used, MCE detects changes developing in the coronary microcirculation, providing important information for the evaluation of severity of coronary artery disease and for the detection of viable myocardial tissue in acute or chronic coronary artery disease.

Introduction

Echocardiography is a highly suited method for the non-invasive assessment of myocardial function. It is widely accepted that disturbance of myocardial perfusion is one of the initial steps in the ischemic cascade followed by wall motion and thickening abnormalities. So far, the evaluation of regional myocardial systolic/diastolic function was used to provide information of paramount importance concerning the management of patients with ischemic cardiomyopathy, in the Echo Lab. Echocardiography comes into a new era since the evaluation of myocardial perfusion will soon be a reality. Through advances in contrast agents and ultrasound technology, it has been obviously realized that myocardial contrast echocardiography (MCE) is probably a new technique to delineate the spectrum of perfusion derangements on acute or chronic coronary disease.

MCE is a technique that uses microbubbles. These microbubbles remain entirely within the intravascular space and their presence in any myocardial region denotes the status of microvascular perfusion within that region. During the last few years a large number of research studies have been spent on this topic. Virtually, myocardial perfusion imaging, using contrast echo, is still a research rather than a clinical tool. In contrast to other echocardiographic methods, MCE has not been in clinical practice after two decades of experimental and clinical work on this field, according to a recent editorial of Paolo Voci [1]. It is known that 2D and Doppler echocardiography soon became “the prima donna” of echocardiography as there are many difficulties for MCE to be applied in clinical practice. For the interpretation of the MCE images, there is always the question: “Does every heterogeneity on myocardial imaging always reflect perfusion derangement?” Actually, there are many key issues concerning which technology should be applied combined with an appropriate contrast agent as well as which mode of intravenous infusion of contrast agents should be followed. Furthermore, MCE is the only technique in which the imaging modality may cause periodically a decline in the contrast agent concentration. On the contrary, in all other imaging modalities, such as positron emission tomography, magnetic resonance imaging, and computed tomography, this does not occur. Each of the aforementioned techniques has its specific dynamics and limitations, but it seems that only MCE has been implemented in routine diagnostic investigation, in bedside, even in an acute coronary event.

Section snippets

Basic principles of contrast echocardiography for the assessment of myocardial perfusion

The study of myocardial perfusion with echocardiography involves an intracoronary or intravascular injection of contrast agents that can scatter ultrasound [2]. The ultrasonic contrast agents are microbubbles that resonate when excited by diagnostic ultrasound frequencies producing an increasing ultrasound backscatter from the blood.

Detection of coronary artery disease

From the pathophysiological point of view, in the presence of epicardial coronary stenosis up to 85%, myocardial autoregulatory process represents the primary mechanism by which coronary flow remains constant at rest [14], [15], [16], [17]. Hence, arterioles dilate to such a degree that the decrease in arteriolar resistance balances the increase in transtenotic resistance, allowing blood flow to be maintained at normal resting levels [18]. During hyperemia however, the compartment with the

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