Real-time assessment of myocardial perfusion and wall motion during bicycle and treadmill exercise echocardiography: comparison with single photon emission computed tomography

Contrast Echocardiography for Assessing Myocardial Perfusion

PURPOSE OF REVIEW

Improvements in ultrasound methods for detecting microbubble ultrasound enhancing agents have led to an increase in the use of perfusion imaging with myocardial contrast echocardiography (MCE). This technique is now beginning to play an important role in specific clinical scenarios, which is the focus of this review.

RECENT FINDINGS

MCE was originally conceived as a technique for detecting resting perfusion abnormalities related to ischemia at rest or during stress from coronary artery disease. More recently, MCE has increasingly been used in circumstances where the technique's ability to provide rapid, quantitative, or bedside assessment of perfusion is advantageous. Quantitative MCE is also increasingly being used as a research technique for evaluating pathobiology and therapy that involve changes in the myocardial microcirculation. While MCE was developed and validated decades ago, it is only now beginning to be used by an increasing number of clinicians due to improvements in imaging technology and recognition of specific situations where the technique is impactful.

The Use of Stress Cardiovascular Imaging in Pediatric Population

Although not frequent in the pediatric population, ischemia could occur in children due to several congenital and acquired disease. Stress imaging is key for the non-invasive evaluation of myocardial abnormalities and perfusion defect in this clinical setting. Moreover, beyond ischemia assessment, it can provide complementary diagnostic and prognostic information in valvular heart disease and cardiomyopathies. When performed using cardiovascular magnetic resonance, it could detect, in addition, myocardial fibrosis and infarction, increasing the diagnostic yield. Several imaging modalities are currently available for the evaluation of stress myocardial perfusion. Advances in technologies have also increased the feasibility, safety and availability of these modalities in the pediatric age group. However, despite the established role of stress imaging and its increasing use in daily clinical practice, there are currently no specific guidelines, and little data are available in the literature on this topic. The aim of this review is to summarize the most recent evidence on pediatric stress imaging and its clinical application with a focus on the advantages and limitations of each imaging modality currently available.

Review of ultrasound contrast agents in current clinical practice with special focus on DEFINITY® in cardiac imaging

Echocardiography is the most widely used noninvasive modality to evaluate the structure and function of the cardiac muscle in daily practice. However, up to 15-20% of echocardiograms are considered suboptimal. To enable accurate assessment of cardiac function and wall motion abnormality, the use of ultrasound microbubble contrast has shown substantial benefits in cases of salvaging nondiagnostic studies and enhancing the diagnostic accuracy in daily practice. DEFINITY^® is a perflutren based, lipid shelled microbubble contrast agent, which is US FDA approved for left ventricular opacification. The basis of ultrasound microbubbles, its development, and the clinical role of DEFINITY (characteristics, indications and case examples, side effect profile and existing evidence) is the subject of discussion in this review.

Is 3D Dobutamine stress echocardiography ready for prime time? Diagnostic and prognostic implications

Aims

Compare the diagnostic accuracy and prognostic value of echo contrast enhanced 2D and 3D Dobutamine stress echocardiography (DSE).

Methods and results

We included 718 patients indicated for DSE. All had standard 2D, and contrast enhanced left ventricular opacification (LVO) for 2D and 3D acquisitions at rest and peak stress. Chi-square test was done to assess relationship between DSE result and early revascularization. Kaplan–Meier plots with Logistic regression analysis predicted late major adverse cardiovascular events (MACE) at a maximum follow-up of 84 months. The mean age was 63 ± 13 years (61% males) and follow-up was obtained in 692/718 (96.4%) patients. Only 32% had excellent baseline image quality. The DSE was abnormal in 19.4% patients on 2D, in 17.1% on 2D-LVO and in 19.1% on 3D-LVO. Early revascularization was performed in, respectively, 32.8%, 45.8%, and in 48.5% of stress-positive 2D, 2D-LVO, and 3D-LVO studies. After excluding the 66 patients receiving early revascularization 68/626 (10.9%) had MACE at a maximum follow-up of 84 months. Kaplan–Meier plots showed that stress-positive 2D-LVO and 3D-LVO studies not receiving early revascularization when assessed separately and combined had significantly worse outcomes for MACE compared with stress-negative patients (OR 3.69; 95% CI: 1.54–8.87; P = 0.011, OR 4.54; 95% CI: 1.72–12.93; P = 0.008, and OR 7.07, 95% CI: 1.62–25.16; P = 0.001, respectively).

Conclusion

Combined use of 2D- and 3D-LVO DSE is ready for prime time considering the feasibility, improved diagnostic accuracy and prognostic value.

Clinical practice of contrast echocardiography: recommendation by the European Association of Cardiovascular Imaging (EACVI) 2017

Contrast echocardiography is widely used in cardiology. It is applied to improve image quality, reader confidence and reproducibility both for assessing left ventricular (LV) structure and function at rest and for assessing global and regional function in stress echocardiography. The use of contrast in echocardiography has now extended beyond cardiac structure and function assessment to evaluation of perfusion both of the myocardium and of the intracardiac structures. Safety of contrast agents have now been addressed in large patient population and these studies clearly established its excellent safety profile. This document, based on clinical trials, randomized and multicentre studies and published clinical experience, has established clear recommendations for the use of contrast in various clinical conditions with evidence-based protocols.

Comparison of Fractional Flow Reserve Assessment With Demand Stress Myocardial Contrast Echocardiography in Angiographically Intermediate Coronary Stenoses

Background—

Real-time myocardial contrast echocardiography (RTMCE) directly measures capillary flow (CBF), which in turn is a major regulator of coronary flow and resistance during demand or hyperemic stress. Although fractional flow reserve (FFR) was developed to assess the physiological relevance of an epicardial stenosis, it assumes maximal microvascular vasodilation and minimal resistance during vasodilator stress. Therefore, we sought to determine the relationship between CBF assessed with RTMCE during stress echocardiography and FFR in intermediate coronary lesions.

Methods and Results—

Sixty-seven vessels with 50% to 80% diameter stenoses by quantitative coronary angiography in 58 consecutive patients were examined with FFR and RTMCE (mean age, 60±13 years). RTMCE was performed using an incremental dobutamine (n=32) or exercise (n=26) stress protocol, and myocardial perfusion was assessed using a continuous infusion of ultrasound contrast. The presence or absence of inducible perfusion defects and wall motion abnormalities were correlated with FFR. Mean percent diameter stenosis was 60±9%. Eighteen stenoses (27%) had an FFR ≤ 0.8. Although 17 of the 18 stenoses that were FFR+ had abnormal CBF during RTMCE, 28 of the 49 stenoses (57%) that were FFR had abnormal CBF, and 24 (49%) had abnormal wall motion in the corresponding coronary artery territory during stress echocardiography.

Conclusions—

In a significant percentage of intermediate stenoses with normal FFR values, CBF during demand stress is reduced, resulting in myocardial ischemia.

Differences in patient outcomes after conventional versus real time perfusion stress echocardiography in men versus women: a prospective randomised trial

OBJECTIVE

The purpose of our study was to determine whether sex affects the predictive value of perfusion and wall motion imaging obtained with real time myocardial contrast echocardiography (RTMCE) when compared with conventional stress echocardiography (CSE).

METHODS

We prospectively enrolled 1649 age-matched men and women with intermediate pretest probability of coronary artery disease (CAD) undergoing stress echocardiography for suspicion of CAD. Patients with known CAD were excluded. Those who consented to participate in the study were randomised to undergo either CSE or RTMCE. Events were defined as death, non-fatal myocardial infarction (MI) and need for revascularisation.

RESULTS

Median follow-up was 2.6 years (927 women, 722 men). Mean age was 58±13 years in both sexes. There were a total of 62 deaths, 12 MIs and 85 revascularisations with a 2-year event rate of 3.5% (95% CI 2.7% to 4.7%). Male sex was a significant independent predictor of adverse outcome (death, non-fatal MI) in both CSE and RTMCE (CSE HR 2.07, 95% CI 1.07 to 4.02, RTMCE HR 2.14; 95% CI 1.04 to 4.33). Higher 2-year event rates were noted in men in comparison with women after a normal CSE (men 5.4%, women 1.6%, p=0.02), but not after a normal RTMCE (men 5.8%, women 3.7%, p=0.41). Event rates were also significantly higher in men after an abnormal RTMCE (men 34.8%, women 16.4%, p=0.02) but no difference in outcome between sexes was observed after an abnormal CSE (men 17.8%, women 18.6%, p=0.90).

CONCLUSIONS

The addition of perfusion imaging with RTMCE improves the predictive value of stress echocardiography in men with no known CAD, but does not improve the predictive value in age-matched women.

Current status of stress echocardiography: is it a required procedure for every sonographer?

BACKGROUND

Stress echocardiography is a versatile modality in the clinical cardiology. In its earlier days, its sole indication was restricted to diagnosing coronary artery disease. However, in response to the rapid development of ultrasound technology and analysis software, the indications have now evolved with expansion to several fields of cardiovascular disease.

METHODS

I reviewed previous stress echocardiography publications, and discussed the current status of stress echocardiography in routine clinical setting.

RESULTS

Although its portability and online assessment make possible for immediate diagnosis even at the bedside, establishment of an appropriate procedure and an accurate assessment require some experience. Other imaging competitors, such as multidetector computed tomography and cardiac magnetic resonance are gradually replacing the role of stress echocardiography in some fields. However, stress echocardiography has a potential for other new fields, including valvular heart disease and congestive heart failure.

CONCLUSION

Although primary indication of stress echocardiography for coronary artery disease seems to be not relevant especially in Japan, novel indication of stress echocardiography in other field of cardiovascular disease is rapidly expanding in conjunction with the advent of new technology. Stress echocardiography is not a tool for limited researchers, but rather a fundamental routine method of choice for every sonographer.

A primer on the methods and applications for contrast echocardiography in clinical imaging

Contrast echocardiography is broadly described as a variety of techniques whereby the blood pool on cardiac ultrasound is enhanced with encapsulated gas-filled microbubbles or other acoustically active nano- or microparticles. The development of this technology has occurred primarily in response to the need improve current diagnostic applications of echocardiography such as the need to better define left ventricular cavity volumes, regional wall motion, or the presence or absence of masses and thrombi. A secondary reason for the development of contrast echocardiography has been to expand the capabilities of echocardiography. These new applications include myocardial perfusion imaging for detection of ischemia and viability, perfusion imaging of masses/tumors, and molecular imaging. The ability to fill all of these current and future clinical roles has been predicated on the ability to produce robust contrast signal which, in turn, has relied on technical innovation with regards to the microbubble contrast agents and the ultrasound imaging paradigms. In this review, we will discuss the basics of contrast echocardiography including the composition of microbubble contrast agents, the unique imaging methods used to optimize contrast signal-to-noise ratio, and the clinical applications of contrast echocardiography that have made a clinical impact.

Imagify™ (perflubutane polymer microspheres) injectable suspension for the assessment of coronary artery disease

Myocardial contrast echocardiography is a rapidly evolving technique for the assessment of myocardial perfusion. Many studies have indicated their ability to detect flow-limiting coronary artery disease. Imagify (perflubutane polymer microspheres) injectable suspension, also known as AI-700, is a new ultrasound contrast agent that satisfies all the characteristics of an ideal agent for the assessment of myocardial perfusion. Preliminary studies with Imagify indicate that it is comparable with radionuclide perfusion techniques (presently the most widely used imaging technique to assess coronary artery disease) without the disadvantages of radiation and lack of availability at the bedside. This article provides an overview of Imagify, a new ultrasound contrast agent.

The value of quantitative real-time myocardial contrast echocardiography for detection of angiographically significant coronary artery disease

BACKGROUND

Real-time (RT) myocardial contrast echocardiography (MCE) is a novel method for the assessment of regional myocardial perfusion. We sought to evaluate the feasibility and diagnostic accuracy of quantitative RT-MCE in predicting significant coronary stenosis, with reference to quantitative coronary angiography.

HYPOTHESIS

RT-MCE can identify anatomically significant coronary artery stenosis in selected patients. RT-MCE is probably an effective method for detection of angiographically significant coronary artery stenosis.

METHODS

Thirty-five patients (mean age, 59.94 ± 10.63 years; 25 males) scheduled for coronary angiography underwent RT-MCE at rest, and shortly afterward underwent gated single-photon emission computed tomography (gated-SPECT). Coronary angiography was performed within 1 week after RT-MCE in all patients. The observing indexes included the images of RT-MCE that were analyzed quantitatively from microbubble replenishment curves for myocardial perfusion by using the Q-Lab software. The sensitivity and specificity of RT-MCE for quantitative detection of coronary artery disease (CAD) were obtained. The receiver operator characteristic (ROC) curves were used to assess the differences of accuracy in ischemic segments with A, β and A × β respectively. The sensitivity and specificity of gated-SPECT and RT-MCE for assessment of CAD were calculated using a 4-score method.

RESULTS

A total of 513 segments among 595 segments in 35 patients were obtained. The cutoffs for A, β and A × β were 4.58, 0.64, and 2.73, and the sensitivity and specificity of quantitative RT-MCE for detection of CAD were 86.0%, 80.2%, 88.9%, and 84.1%, 64.6%, 79.9%, respectively. Meanwhile, the sensitivity and specificity of semiquantitative analysis for assessment of CAD were 66.7% and 61.8%. The ROC curve area of A and A × β was 0.91 and 0.90 in the middle segments. The ROC area of A was 0.52 in the base segments. The sensitivity and specificity of gated-SPECT for assessment of CAD were 84.8% and 82.7%, respectively. The sensitivity of multi-indexes RT-MCE increased. The sensitivity was 89.1%, 90.4%, and 96.3% by A + β, A + A × β, and β + A × β.

CONCLUSIONS

Quantitative RT-MCE is an effective method for the detection of coronary artery stenosis. Quantitative RT-MCE is segmented for assessment to ischemic myocardium. RT-MCE with multi-indexes has a valuable application for assessment of CAD surpassing SPECT.

Patient outcome following 2 different stress imaging approaches: a prospective randomized comparison

OBJECTIVES

The study sought to prospectively compare patient outcome after stress real-time myocardial contrast echocardiography (RTMCE) versus conventional stress echo (CSE), where contrast is used to optimize wall motion (WM) analysis.

BACKGROUND

Myocardial perfusion imaging with RTMCE may improve the detection of coronary artery disease (CAD), and predict patient outcome.

METHODS

Patients with intermediate to high pre-test probability referred for dobutamine or exercise stress echocardiography were prospectively randomized to either RTMCE or CSE. Definity contrast was used for CSE only when endocardial border delineation was inadequate (63% of studies). Studies were interpreted by either an experienced contrast reviewer (R1; n = 1257), or 4 Level 3 echocardiographers (R2) with basic contrast training (n = 806). Death, nonfatal myocardial infarction (MI), and revascularizations were recorded at follow-up.

RESULTS

Follow-up was available in 2,014 patients (median 2.6 years). Mean age was 59 ± 13 years (53% women). An abnormal RTMCE was more frequently observed than an abnormal CSE (p < 0.001), and more frequently resulted in revascularization (p = 0.004). Resting WM abnormalities were also more frequently seen with RTMCE (p < 0.01), and were an independent predictor of death/nonfatal MI (p = 0.005) for RTMCE, but not CSE. The predictive value of a positive study, whether with CSE or RTMCE, was significant for both R1 and R2 reviewers in predicting the combined endpoint, but R1 was better than R2 at predicting patients at risk for death or nonfatal MI.

CONCLUSIONS

Perfusion imaging with RTMCE improves the detection of CAD during stress echocardiography, and identifies those more likely to undergo revascularization following an abnormal study.

Computed tomography coronary angiography and invasive coronary angiography demonstrate high correlation for area stenosis quantification in noncalcified and mixed plaques

We compared the variance of area and diameter significant stenosis measurement between quantitative computed tomography coronary angiography (QCTA) and quantitative invasive coronary angiography (QCA). Fifty patients presenting 65 significant coronary artery stenoses (≥70% area stenosis) in QCTA and QCA were included. Spearman's rank correlation revealed that area stenosis measurement by QCTA and QCA yields higher correlation than diameter stenosis and is highest for noncalcified and mixed lesions.

Myocardial viability imaging: does it still have a role in patient selection prior to coronary revascularisation?

Patients with severe left ventricular (LV) dysfunction and multi-vessel coronary artery disease (CAD) are at high risk during revascularisation, however they are also likely to derive the most benefit. Historically, the detection of dysfunctional but potentially viable myocardium ('stunned or hibernating myocardium') has been central to the decision-making regarding revascularisation. A number of recent studies have challenged this paradigm, questioning the role of viability testing in this population. In this review, we will examine the position of viability testing and how it is best incorporated in the modern era of coronary revascularisation. We will outline the role of currently available imaging modalities in viability assessment. Myocardial viability testing will continue to play a role in revascularisation decisions, although larger randomised trials with clinical outcome end-points are needed to further define its role.

Imaging techniques in coronary atherosclerotic disease: dobutamine stress echocardiography--evidence and perspectives

Dobutamine stress echocardiography is the most widely disseminated noninvasive technique for the assessment of coronary artery disease. Its results are important for clinical decisions. It is a versatile technique with high sensitivity and specificity for detecting viable myocardium at jeopardy. More recently, strain rate imaging has been applied to stress echocardiography. This approach relies on tissue Doppler or two-dimensional strain imaging to quantify myocardial deformation. The application of contrast echocardiographic techniques to stress echocardiography enables left ventricular opacification for border enhancement and myocardial perfusion imaging. Thus, this application is not limited to stress echocardiography, but has utility whenever image quality adversely affects wall motion assessment. Recently, three-dimensional stress echocardiography imaging has been proposed as an alternative approach to assess myocardial ischemia.

Myocardial perfusion imaging with contrast ultrasound

This report reviews the development and clinical application of myocardial perfusion imaging with myocardial contrast echocardiography (MCE). This includes the development of microbubble formulations that permit the detection of left ventricular contrast from venous injection and the imaging techniques that have been invented to detect the transit of these microbubbles through the microcirculation. The methods used to quantify myocardial perfusion during a continuous infusion of microbubbles are described. A review of the clinical studies that have examined the clinical utility of myocardial perfusion imaging with MCE during rest and stress echocardiography is then presented. The limitations of MCE are also discussed.

Customized exercise echocardiography: beyond detection of coronary artery disease

Exercise echocardiography has been established as a reliable diagnostic tool for assessment of myocardial ischemia. However, more recent advances in its technique have expanded its routine clinical use to include quantification of exercise-induced diastolic dysfunction, exercise-induced pulmonary hypertension, and dynamic assessment of mitral and aortic valve function. The indications for exercise echocardiography have increased to include cardiac symptoms such as exertional dyspnea, fatigue, and limited exercise capacity. In light of its expanded capability for evaluating cardiovascular function, we believe that exercise echocardiography should be utilized in a new paradigm of personalized cardiology, in which we regularly investigate individual patient symptoms for endpoints beyond critical myocardial ischemia, for example, exercise-induced pulmonary hypertension. We refer to this refocused use of exercise echocardiography as "customized exercise echocardiography." In this review article, we present current scientific evidence to support our proposed role and discuss the logistical requirements for proper test performance of customized exercise echocardiography.

Impact of previous myocardial infarction on the incremental value of myocardial contrast to two-dimensional supine bicycle stress echocardiography in evaluation of coronary artery disease

BACKGROUND

If compared to two-dimensional echocardiography (2DE), myocardial contrast echocardiography (MCE) improves detection of coronary artery disease (CAD) during pharmacological stress, but data on MCE vs. 2DE during supine bicycle stress is limited. Although previous myocardial infarction (MI) influences sensitivity of 2DE, its effect on MCE has not been evaluated.

OBJECTIVES

The study sought to determine the incremental benefit of MCE over 2DE for evaluation of CAD during supine bicycle stress and to assess the impact of previous MI on diagnostic values of both methods.

METHODS

We studied 103 consecutive patients scheduled for coronary angiography. Prior to coronary angiography, all patients underwent supine bicycle stress. 2DE and MCE were performed during this stress test. The diagnosis of obstructive CAD (> or =50% stenosis) was based on the presence of inducible wall motion and perfusion abnormalities.

RESULTS

Quantitative coronary angiography revealed > or =50% stenosis in 53 of 77 patients without previous MI and in 21 of 26 patients with previous MI. If compared to 2DE, MCE was more sensitive (68% vs. 86%; p<0.001) and more accurate (73% vs. 86%; p < 0.001) to detect > or =50% stenosis. In patients without previous MI, 2DE and MCE yielded sensitivity of 65% and 85% (p < 0.01) and accuracy of 71% and 85% (p < 0.01), whereas in patients with previous MI sensitivity was 79% and 90% (p=NS) and accuracy 79% and 88% (p = NS), respectively.

CONCLUSIONS

MCE enhances sensitivity and accuracy of 2DE in detection of obstructive CAD during supine bicycle stress. The incremental benefit of MCE is especially present in patients without previous MI.

Echocardiography in 2009: the future of clinical diagnosis

Over the past 10 years we have observed a tremendous expansion on cardiovascular imaging with breathtaking images observing all aspects of the cardiac anatomy and functions. So much so that each imaging modality has grown to the point that one single individual cannot possess all the required expertise for its optimal use and the need for subspecialization in the various imaging modalities is crucial. Echocardiography has surprised many for its ability to adapt in the ever increasing demand and the discovery of the many new modalities. These include 3D and deformation imaging, as well as contrast utilization during the studies, which will continue to put echocardiography in a league of its own in terms of patients management. Some basic descriptions of the various modalities are summarized and their contribution to a number of clinical scenarios, today and in the future, are explored.

Prognostic value of dipyridamole stress myocardial contrast echocardiography: comparison with single photon emission computed tomography

BACKGROUND

Dipyridamole stress myocardial contrast echocardiography (MCE) can be used to detect coronary artery disease (CAD). Because it measures myocardial blood flow velocity in addition to measuring myocardial blood volume, it was hypothesized that it should have greater prognostic utility than single photon-emission computed tomography (SPECT), which measures only myocardial blood volume. Because blood flow mismatch precedes wall thickening (WT) abnormalities during demand ischemia, it was also postulated that perfusion on MCE would be superior to WT abnormalities on echocardiography for this purpose.

METHODS

The incidence of nonfatal myocardial infarction and cardiac death was determined in 261 patients with known or suspected CAD over a mean follow-up period of 14 months who underwent simultaneous dipyridamole stress MCE and 99mTc-sestamibi SPECT. Comparisons of survival curves were conducted with stratified (and unstratified) log-rank tests.

RESULTS

Abnormal results on MCE were found to be the best predictor of an adverse outcome (odds ratio, 23; 95% confidence interval, 6-201; P<.0001) and provided incremental prognostic value over clinical variables (age>60 years, the presence of >or=3 cardiac risk factors, known peripheral vascular disease, prior myocardial infarction, and left ventricular systolic function), inducible WT abnormalities, and SPECT. Prognoses were worst in patients who had both abnormal results on MCE and inducible WT abnormalities and best in those who had neither. Patients with abnormal results on MCE but no inducible WT abnormalities had intermediate outcomes.

CONCLUSION

In patients with known or suspected CAD undergoing dipyridamole stress, MCE provides powerful prognostic information that is superior to clinical variables, electrocardiography, left ventricular systolic function, WT analysis, and SPECT. MCE may therefore serve as a method of choice for myocardial perfusion assessment in patients with known or suspected CAD. Larger studies are needed to confirm these findings.

American Society of Echocardiography Consensus Statement on the Clinical Applications of Ultrasonic Contrast Agents in Echocardiography

ACCREDITATION STATEMENT: The American Society of Echocardiography (ASE) is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians. The ASE designates this educational activity for a maximum of 1 AMA PRA Category 1 Credit.trade mark Physicians should only claim credit commensurate with the extent of their participation in the activity. The American Registry of Diagnostic Medical Sonographers and Cardiovascular Credentialing International recognize the ASE's certificates and have agreed to honor the credit hours toward their registry requirements for sonographers. The ASE is committed to resolving all conflict-of-interest issues, and its mandate is to retain only those speakers with financial interests that can be reconciled with the goals and educational integrity of the educational program. Disclosure of faculty and commercial support sponsor relationships, if any, have been indicated.

TARGET AUDIENCE

This activity is designed for all cardiovascular physicians, cardiac sonographers, and nurses with a primary interest and knowledge base in the field of echocardiography; in addition, residents, researchers, clinicians, sonographers, and other medical professionals having a specific interest in contrast echocardiography may be included.

OBJECTIVES

Upon completing this activity, participants will be able to: 1. Demonstrate an increased knowledge of the applications for contrast echocardiography and their impact on cardiac diagnosis. 2. Differentiate the available ultrasound contrast agents and ultrasound equipment imaging features to optimize their use. 3. Recognize the indications, benefits, and safety of ultrasound contrast agents, acknowledging the recent labeling changes by the US Food and Drug Administration (FDA) regarding contrast agent use and safety information. 4. Identify specific patient populations that represent potential candidates for the use of contrast agents, to enable cost-effective clinical diagnosis. 5. Incorporate effective teamwork strategies for the implementation of contrast agents in the echocardiography laboratory and establish guidelines for contrast use. 6. Use contrast enhancement for endocardial border delineation and left ventricular opacification in rest and stress echocardiography and unique patient care environments in which echocardiographic image acquisition is frequently challenging, including intensive care units (ICUs) and emergency departments. 7. Effectively use contrast echocardiography for the diagnosis of intracardiac and extracardiac abnormalities, including the identification of complications of acute myocardial infarction. 8. Assess the common pitfalls in contrast imaging and use stepwise, guideline-based contrast equipment setup and contrast agent administration techniques to optimize image acquisition.

Accelerated stress real-time myocardial contrast echocardiography for the detection of coronary artery disease: comparison with 99mTc single photon emission computed tomography

OBJECTIVE

The aims of this prospective study were to compare the diagnostic value of accelerated vasodilator stress real-time myocardial contrast echocardiography (MCE) and single photon emission computed tomography (SPECT) against coronary angiography and to evaluate whether the addition of MCE perfusion data improves the diagnostic accuracy of stress echocardiography.

METHODS

A total of 103 patients with suspected or known stable coronary artery disease (CAD) underwent SPECT and accelerated high-dose dipyridamole (0.84 mg/kg intravenously for 4 minutes) atropine (up to 1 mg intravenously) stress real-time qualitative MCE. The presence of CAD was detected by coronary angiography.

RESULTS

CAD defined as >or= 70% stenosis was detected in 77% of patients, whereas 86% of patients had CAD defined as >or= 50% stenosis. In a territory-by-territory analysis, the concordance between MCE and SPECT in detecting perfusion defects varied from 72.8% (kappa = 0.386) to 89.3% (kappa = 0.642). There were no significant differences between MCE and SPECT in sensitivity, specificity, and diagnostic accuracy for identifying patients with CAD. Combining MCE and wall motion abnormality analysis significantly improved the sensitivity of the test compared with wall motion abnormality analysis alone.

CONCLUSIONS

Accelerated vasodilator stress real-time MCE yields a good concordance with SPECT in detection of perfusion defects and a similar diagnostic value for the detection of CAD. The addition of MCE perfusion data improves the diagnostic value of stress echocardiography.

Contrast echocardiography: evidence for clinical use

The failure of echocardiography to give diagnostically useful information in a significant proportion of patients has led to the development of specific contrast agents to enhance imaging. Suitable contrast media must have the ability to modify ultrasound characteristics, be capable of crossing the pulmonary capillary bed, show stability over the duration of a procedure, offer low blood solubility with low toxicity and be rapidly eliminated. The current generation of ultrasound contrast agents comprises microbubbles of a high molecular-weight gas encapsulated in a shell of phospholipid or protein. A review of the clinical evidence shows that these agents are clinically effective in enhancing echocardiographic imaging. They enable the rescue of failed procedures, often sparing patients from invasive tests, but appear not to add to the burden of side effects. Indeed, the benefits of using contrast agents in stress echocardiography have been recommended in recently published American Society of Echocardiography guidelines. Myocardial contrast echocardiography has now developed to the stage where assessment of myocardial perfusion for the detection of coronary artery disease is possible with the same diagnostic accuracy as radionuclide imaging. However, in comparison with the latter technique, it is less expensive, is more portable, and avoids the use of ionizing radiation. It is precisely the ability of myocardial contrast echocardiography to simultaneously assess function and perfusion at the bedside that has given it a unique role in clinical practice. This review provides an overview of the clinical evidence supporting the efficacy of contrast echocardiography in the assessment of myocardial structure, function, and perfusion.

Real-time myocardial contrast echocardiography for assessing perfusion and function in healthy and infarcted wistar rats

Real-time myocardial contrast echocardiography (MCE) is a noninvasive perfusion imaging method, whereas technical and resolution problems impair its application in small animals. Hence, we investigated the feasibility of MCE in experimental cardiovascular set-ups involving healthy and infarcted myocardium in rats. Twenty-five male Wistar rats were examined under volatile anesthesia (2.5% isoflurane) with high-resolution conventional 2-D echocardiography (2DE) and real-time MCE (Sonos 7,500 with 15MHz-transducer, Philips Medical Systems, Andover, MA, USA) in short-axis view. Contrast agent (SonoVue, Bracco, Milan, Italy) was infused as a bolus into a sublingual vein. Background-subtracted contrast signal intensity (SI) was measured off-line in six end-systolic segments and fitted to an exponential curve (gamma variate). Derived peak SI was subsequently calculated and compared with wall motion and common functional measured quantities (left ventricular end-diastolic diameter [LVEDD], area shortening [AS]). Recordings were performed before and 14 days after left anterior descending (LAD) ligature. Infarction induced anterior wall motion abnormalities (WMA) in all animals (16 akinetic, 9 hypokinetic), increased LVEDD (9.1 +/- 0.6 vs. 7.9 +/- 0.6 mm, p < 0.001), reduced AS (36.1 +/- 10.0 vs. 59.5 +/- 4.1%, p < 0.001) and reduced anterior segmental SI (0.4 +/- 0.4 dB akinetic / 1.7 +/- 1.7 dB hypokinetic vs. 15.8 +/- 10.9 dB preinfarct, p < 0.001 / p < 0.001). Segmental SI in normokinetic segments remained unchanged. Area at risk (perfusion defect) correlated well with WMA (r = 0.838). These data confirmed high-resolution real-time MCE as a rational tool for assessing myocardial perfusion of Wistar rats. It may therefore be a useful diagnostic tool for in-vivo cardiovascular research in small animals.

Real Time Myocardial Contrast Echocardiography During Supine Bicycle Stress and Continuous Infusion of Contrast Agent. Cutoff Values for Myocardial Contrast Replenishment Discriminating Abnormal Myocardial Perfusion

BACKGROUND

Myocardial contrast echocardiography (MCE) is a new imaging modality for diagnosing coronary artery disease (CAD).

OBJECTIVE

The aim of our study was to evaluate feasibility of qualitative myocardial contrast replenishment (RP) assessment during supine bicycle stress MCE and find out cutoff values for such analysis, which could allow accurate detection of CAD.

METHODS

Forty-four consecutive patients, scheduled for coronary angiography (CA) underwent supine bicycle stress two-dimensional echocardiography (2DE). During the same session, MCE was performed at peak stress and post stress. Ultrasound contrast agent (SonoVue) was administered in continuous mode using an infusion pump (BR-INF 100, Bracco Research). Seventeen-segment model of left ventricle was used in analysis. MCE was assessed off-line in terms of myocardial contrast opacification and RP. RP was evaluated on the basis of the number of cardiac cycles required to refill the segment with contrast after its prior destruction with high-power frames. Determination of cutoff values for RP assessment was performed by means of reference intervals and receiver operating characteristic analysis. Quantitative CA was carried out using CAAS system.

RESULTS

MCE could be assessed in 42 patients. CA revealed CAD in 25 patients. Calculated cutoff values for RP-analysis (peak-stress RP >3 cardiac cycles and difference between peak stress and post stress RP >0 cardiac cycles) provided sensitive (88%) and accurate (88%) detection of CAD. Sensitivity and accuracy of 2DE were 76% and 79%, respectively.

CONCLUSIONS

Qualitative RP-analysis based on the number of cardiac cycles required to refill myocardium with contrast is feasible during supine bicycle stress MCE and enables accurate detection of CAD.

Evaluation of Blood Flow Reserve in Left Anterior Descending Coronary Artery Territory by Quantitative Myocardial Contrast and Doppler Echocardiography

We sought to compare the feasibility and accuracy of myocardial blood flow reserve (MBFR) measured by quantitative real-time myocardial contrast echocardiography with those of coronary flow velocity reserve (CFVR) obtained by transthoracic Doppler echocardiography for detecting left anterior descending coronary artery (LAD) stenosis. We studied 71 patients who underwent adenosine stress contrast echocardiography, transthoracic Doppler echocardiography, and quantitative coronary angiography within 1 month. An index of myocardial blood flow (A x beta) was determined by quantification of peak plateau acoustic intensity (A) and microbubble replenishment velocity (beta) by contrast echocardiography. Feasibilities of qualitative analysis of myocardial perfusion, and CFVR and MBFR measurements were 98%, 83%, and 94%, respectively. Patients with LAD stenosis had lower CFVR (1.1 +/- 0.4 vs 2.7 +/- 0.8, P < .001), MBFR (1.2 +/- 0.5 vs 2.5 +/- 0.8, P < .001), and beta reserve (1.1 +/- 0.5 vs 2.4 +/- 0.6, P < .001) than those without lesion. Sensitivities, specificities, and accuracies for detecting LAD stenosis were 64%, 93%, and 80% for qualitative analysis of myocardial perfusion; 92%, 94%, and 93% for CFVR; 84%, 87%, and 86% for MBFR; and 80%, 97%, and 89% for beta reserve. In this selected study population, CFVR was the best index for detecting LAD stenosis (odds ratio = 1.78, 95% confidence interval = 1.28-2.47).

Contrast echocardiography

Myocardial contrast echocardiography (MCE) is a noninvasive imaging technique that relies on the ultrasound detection of microbubble contrast agents. These agents are confined to the intravascular space thereby producing signal enhancement from the blood pool. This review encompasses many of the key concepts regarding the clinical application of MCE. The first section focuses on the composition, safety, and biokinetics of ultrasound contrast agents. Then we discuss new ultrasound imaging methodology that has been developed to enhance detection of contrast agent and to assess perfusion at the tissue level. Next, the clinical applications of contrast ultrasound are reviewed. These include enhancement of the cardiac chambers for better assessment of cardiac function and masses, myocardial perfusion imaging for the detection of coronary artery disease, and the assessment of myocardial viability and microvascular reflow. Finally, we discuss some of the future applications for MCE, which include molecular imaging of disease and drug/gene delivery. The overall aim of the review is to update the clinician on state-of-the-art MCE and how it can be applied in patients with cardiovascular disease.

Myocardial Contrast Echocardiography Evolving as a Clinically Feasible Technique for Accurate, Rapid, and Safe Assessment of Myocardial Perfusion

Intravenous myocardial contrast echocardiography (MCE) is a recently developed technique for assessment of myocardial perfusion. Up to now, many studies have demonstrated that the sensitivity and specificity of qualitative assessment of myocardial perfusion by MCE in patients with acute and chronic ischemic heart disease are comparable with other techniques such as cardiac scintigraphy and dobutamine stress echocardiography. Furthermore, quantitative parameters of myocardial perfusion derived from MCE correlate well with the current clinical standard for this purpose, positron emission tomography. Myocardial contrast echocardiography provides a promising and valuable tool for assessment of myocardial perfusion. Although MCE has been primarily performed for medical research, its implementation in routine clinical care is evolving. This article is intended to give an overview of the current status of MCE.

Comparison of myocardial contrast echocardiography with SPECT in the evaluation of coronary artery disease in asymptomatic patients with LBBB

OBJECTIVE

The non-invasive assessment of coronary artery disease (CAD) in patients with left bundle branch block (LBBB) is troublesome. In this study, we investigated the diagnostic accuracy of myocardial contrast echocardiography (MCE) with adenosine to detect CAD in asymptomatic patients with LBBB, and we compared it with single photon emission computed tomography (SPECT) with adenosine.

METHODS

Forty-seven patients with LBBB, and no previously documented CAD, initially underwent SPECT imaging and 1-3 days later MCE. Coronary arteriography was performed within 1 week from the latter procedure.

RESULTS

The overall sensitivity, specificity, positive predictive value, negative predictive value, diagnostic accuracy, and kappa index of concordance of SPECT were 73%, 72%, 44%, 90%, 72%, and 0.37+/-0.13, respectively, whereas those of MCE were 91%, 92%, 77%, 97%, 92%, and 0.77+/-0.1, respectively (p<0.05 for all comparisons). Significant CAD was present in 11 patients (23%). Left anterior descending coronary artery was involved in 8 patients, left circumflex artery in 2 patients, and right coronary artery in 4 patients. Concerning the left anterior descending artery disease detection, SPECT had a sensitivity of 75%, a specificity of 79%, a positive predictive value of 43%, a negative predictive value of 94%, and a diagnostic accuracy of 79%. The respective values of MCE were 100% for all of the above variables.

CONCLUSIONS

MCE with adenosine has a higher global diagnostic accuracy compared to SPECT for the detection of CAD in patients with LBBB, mainly due to the poor specificity of SPECT concerning perfusion defects detection in the left anterior descending artery territory.

Noninvasive cardiac imaging in the evaluation of suspected acute coronary syndromes

Optimal management of patients presenting with chest pain to the emergency department is a major challenge, both in terms of a diagnostic dilemma and consumption of resources. The triage of such patients can be aided vastly by the appropriate use of noninvasive imaging. Noninvasive imaging modalities such as echocardiogram, radionuclide perfusion studies, positron emission tomography, cardiac magnetic resonance imaging and computed tomography have all been demonstrated to have favorable diagnostic and prognostic value, with an enhanced sensitivity to detect acute ischemia. A normal noninvasive evaluation in the appropriate clinical setting presents a strong argument against acute ischemia as an etiology of the chest pain. Randomized trials of both rest and stress imaging in the emergency department have confirmed a reduction in unnecessary hospitalizations and cost savings without compromising the safety of the patient. Cardiac magnetic resonance and computed tomography would provide an insight into subendocardial ischemia, the detection of which has previously been difficult, using single-photon emission tomography and echocardiography. In this review, novel hot-spot imaging modalities are discussed including infarct-avid imaging agents and ischemia-avid imaging agents, thus elucidating the pathophysiology of reperfusion-induced cell death. These agents represent work in evolution and are likely to be used routinely in the future as understanding of coronary syndromes and coronary artery disease becomes clearer.

Detection of coronary artery disease using real-time myocardial contrast echocardiography: a comparison with dual-isotope resting thallium-201/stress technectium-99m sestamibi single-photon emission computed tomography

Real-time myocardial contrast echocardiography (MCE) has the potential to evaluate myocardial perfusion and wall motion (WM) simultaneously. The purposes of this study were to correlate the diagnostic value of MCE with radionuclide single-photon emission computed tomography (SPECT), and to assess the sensitivity and specificity of real-time MCE in detecting coronary artery disease (CAD). Seventy patients with clinically suspected CAD underwent MCE and SPECT at baseline and after dipyridamole infusion. Segmental perfusion with MCE using low mechanical index after 0.3-0.4-ml bolus injections of perfluorocarbon exposed sonicated dextrose albumin solution was performed. All patients had a dual-isotope (rest thallium-201, stress sestamibi) study performed both at baseline and after dipyridamole infusion, and 40 patients had subsequent quantitative coronary angiography. Abnormalities were noted in 27 patients (38.6%) by MCE, in 29 patients (41.4%) by WM analysis, and in 30 patients (42.9%) by SPECT imaging. When MCE and WM analysis were combined, the agreement with SPECT imaging improved from 75.7% (Kappa = 0.50) to 82.0% (Kappa = 0.62). In 40 patients (120 territories) who underwent coronary angiography, good perfusion concordance was achieved for the left anterior descending and left circumflex arteries, and was fair for the right coronary arteries. Compared with quantitative angiography, there was no difference in sensitivity, specificity, and accuracy in detecting significant CAD among the three modalities. The combination of MCE and WM had a better sensitivity (84%), specificity (93.3%), and accuracy (87.5%) than the MCE and WM analysis alone. However, the difference did not reach statistical significance. Real-time MCE has a good agreement with SPECT imaging for detecting CAD. The combination of MCE and WM appears to have higher sensitivity, specificity, and accuracy in detecting CAD than either technique alone.