Assessment of myocardial viability in patients with chronic coronary artery disease. Rest-4-hour-24-hour 201Tl tomography versus dobutamine echocardiography

Myocardial Viability – An Important Decision Making Factor in the Treatment Protocol for Patients with Ischemic Heart Disease

Ischemic heart disease (IHD) affects > 110 million individuals worldwide and represents an important contributor to the rise in the prevalence of heart failure and the associated mortality and morbidity. Despite modern therapies, up to one-third of patients with acute myocardial infarction would develop heart failure. IHD is a pathologic condition of the myocardium resulting from the imbalance in a given moment between its oxygen demands and the actual perfusion. Acute and chronic forms of the disease may potentially lead to extensive and permanent damage of the cardiac muscle. From a clinical point of view, determination of the still viable extent of myocardium is crucial for the therapeutic protocol – since ischemia is the underlying cause, then revascularization should provide for a better prognosis. Different methods for evaluation of myocardial viability have been described – each one presenting some advantages over the others, being, in the same time, inferior in some respects. The review offers a relatively comprehensive overview of methods available for determining myocardial viability.

State of the Art: Imaging for Myocardial Viability: A Scientific Statement From the American Heart Association

A substantial proportion of patients with acute myocardial infarction develop clinical heart failure, which remains a common and major healthcare burden. It has been shown that in patients with chronic coronary artery disease, ischemic episodes lead to a global pattern of cardiomyocyte remodeling and dedifferentiation, hallmarked by myolysis, glycogen accumulation, and alteration of structural proteins. These changes, in conjunction with an impaired global coronary reserve, may eventually become irreversible and result in ischemic cardiomyopathy. Moreover, noninvasive imaging of myocardial scar and hibernation can inform the risk of sudden cardiac death. Therefore, it would be intuitive that imaging of myocardial viability is an essential tool for the proper use of invasive treatment strategies and patient prognostication. However, this notion has been challenged by large-scale clinical trials demonstrating that, in the modern era of improved guideline-directed medical therapies, imaging of myocardial viability failed to deliver effective guidance of coronary bypass surgery to a reduction of adverse cardiac outcomes. In addition, current available imaging technologies in this regard are numerous, and they target diverse surrogates of structural or tissue substrates of myocardial viability. In this document, we examine these issues in the current clinical context, collect current evidence of imaging technology by modality, and inform future directions.

Prognostic Value of Viable Myocardium in Patients with Non-Q-wave and Q-wave Myocardial Infarction

This study assessed the amount and prognostic value of myocardial viability in patients with non-Q-wave myocardial infarction (NQMI) and Q-wave myocardial infarction (QMI). A total of 175 patients with MI and an ejection fraction ≤ 45% underwent dobutamine stress echocardiography. On the basis of clinical criteria and myocardial viability, 110 patients were revascularized. The amount of viable myocardium and the clinical outcome were compared in the NQMI and QMI groups. Patients with NQMI exhibited a larger amount of viable myocardium compared with those with QMI. The mortality rate was 6% in patients with NQMI with viable myocardium and subsequent revascularization, 33% in patients with NQMI without viable myocardium or revascularization, 27% in patients with QMI with viable myocardium and subsequent revascularization, and 33% in patients with QMI without viable myocardium or revascularization. In conclusion, our data suggest that patients with NQMI and viable myocardium have the best prognosis after revascularization.

Late gadolinium enhancement magnetic resonance imaging for the assessment of myocardial infarction: comparison of image quality between single and double doses of contrast agents

To compare the image quality of late gadolinium enhancement (LGE) cardiac magnetic resonance imaging (CMR) using a single dose of gadolinium contrast agent versus the conventional double dose for assessing myocardial infarction. This retrospective study examined 37 patients with chronic myocardial infarction who underwent LGE CMR using both inversion recovery (IR)-turbo fast low-angle shot magnitude-reconstructed and phase-sensitive images with two different dosages of gadolinium contrast agent: a single dose of 0.1 mmol/kg gadolinium-DTPA in 17 patients and a double dose of 0.2 mmol/kg in 20 patients. The contrast-to-noise ratio (CNR) and visual conspicuity between infarct and normal myocardium (CNRinfarct-normal, conspicuityinfarct-normal) and between infarct and left ventricular cavity (CNRinfarct-LVC, conspicuityinfarct-LVC) were compared. Interobserver agreement for the maximal transmural extent of infarction was also evaluated. CNRinfarct-normal was significantly higher with double-dose gadolinium contrast agent (15.5 ± 20.7 vs. 40.4 ± 16.1 in magnitude images and 9.5 ± 2.8 vs. 11.2 ± 2.7 in phase-sensitive images, P < 0.001) while conspicuityinfarct-normal showed no significant difference between the two groups (P > 0.05). Both CNRinfarct-LVC (7.7 ± 10.7 vs. -6.6 ± 19.0 in magnitude images and 4.1 ± 2.3 vs. -0.4 ± 4.1 in phase-sensitive images, P < 0.05) and conspicuityinfarct-LVC were significantly better with single-dose gadolinium contrast. Interobserver agreement for assessing the transmural extent of infarction was moderate in both groups: 0.591 for single-dose and 0.472 for double-dose. LGE CMR using a single dose of gadolinium contrast agent showed significantly better contrast between infarcted myocardium and left ventricular cavity lumen without a significant decrease in visual contrast between infarcted myocardium and normal myocardium, compared to a double dose.

Advances in SPECT in evaluating coronary disease

Myocardial perfusion scintigraphy is the longest established of the functional imaging investigations for patients with known or suspected coronary artery disease. This article describes recent technical and clinical advances that are ensuring that the technique remains relevant some 40 years after its first introduction.

Cardiac MR for the assessment of myocardial viability

This article focuses on delayed contrast enhanced MRI (DE-MRI) to assess myocardial viability. We start by discussing previous literature that evaluated the potential importance of myocardial viability testing and follow up with the more recent Surgical Treatment for Heart Disease Trial (STICH) trial results. We then provide an overview of the basic concepts and technical aspects of the current DE-MRI technique and review the initial studies demonstrating that DE-MRI before coronary revascularization can predict functional improvement. Finally, we use DE-MRI as a paradigm to discuss physiological insights into viability assessment and examine common assumptions in the metrics used to evaluate viability techniques.

Twenty four hour imaging delay improves viability detection by Tl-201 myocardial perfusion scintigraphy

Objective

Since twenty-four-hour imaging by Tl-201 myocardial perfusion scintigraphy has been introduced as an effective additional procedure, the aim of this study was to compare this method's result with only rest redistribution procedure in the diagnosis of myocardial viability.

Methods

Thirty patients (Seven female, 23 male; mean: 59.8 ± 10.7, 55.8-63.8 years old) with diagnosis of coronary artery disease were involved in this study. All patients had anamnesis of previous myocardial infarction and/or total occlusion of any main artery in the coronary angiography. Myocardial perfusion scintigraphy with Tl-201 with rest four hour (early) redistribution and 24 hour delayed redistribution protocol were performed to all of the patients. The images were evaluated according to 17 segment basis by an experienced nuclear medicine physician and improvement of a segment by visual interpretation was considered as viable myocardial tissue.

Results

Viability was found at 52 segments in the early redistribution images and additional 18 segments in the 24 hour delayed redistribution images on segment basis in the evaluation of 510 segments of 30 patients. On per patient basis, among the 26 patients who had viable tissue, 14 (54%) had additional improvement in 24 hour delayed images. Three (12%) patients had viable tissue in only 24 hour delayed images.

Conclusion

Delayed imaging in Tl-201 MPS is a necessary application for the evaluation of viable tissue according to considerable number of patients with additional improvement in 24 hour images in our study, which is restricted to the patients with myocardial infarct.

Noninvasive assessment myocardial viability: current status and future directions

Observations of reversibility of cardiac contractile dysfunction in patients with coronary artery disease and ischemia were first made more than 40 years ago. Since that time a wealth of basic science and clinical data has been gathered exploring the mechanisms of this phenomenon of myocardial viability and relevance to clinical care of patients. Advances in cardiac imaging techniques have contributed greatly to knowledge in the area, first with thallium-201 imaging, then later with Tc-99m-based tracers for SPECT imaging and metabolic tracers used in conjunction with positron emission tomography (PET), most commonly F-18 FDG in conjunction with blood flow imaging with N-13 ammonia or Rb-82 Cl. In parallel, stress echocardiography has made great progress also. Over time observational studies in patients using these techniques accumulated and were later summarized in several meta-analyses. More recently, cardiac magnetic resonance imaging (CMR) has contributed further information in combination with either late gadolinium enhancement imaging or dobutamine stress. This review discusses the tracer and CMR imaging techniques, the pooled observational data, the results of clinical trials, and ongoing investigation in the field. It also examines some of the current challenges and issues for researchers and explores the emerging potential of combined PET/CMR imaging for myocardial viability.

Multimodality imaging in the assessment of myocardial viability

The prevalence of heart failure due to coronary artery disease continues to increase, and it portends a worse prognosis than non-ischemic cardiomyopathy. Revascularization improves prognosis in these high-risk patients who have evidence of viability; therefore, optimal assessment of myocardial viability remains essential. Multiple imaging modalities exist for differentiating viable myocardium from scar in territories with contractile dysfunction. Given the multiple modalities available, choosing the best modality for a specific patient can be a daunting task. In this review, the physiology of myocardial hibernation and stunning will be reviewed. All the current methods available for assessing viability including echocardiography, cardiac magnetic resonance imaging, nuclear imaging with single photon emission tomography and positron emission tomography imaging and cardiac computed tomography will be reviewed. The effectiveness of the various techniques will be compared, and the limitations of the current literature will be discussed.

Twenty-four-hour thallium-201 imaging enhances the detection of myocardial ischemia and viability after myocardial infarction: a comparison study with echocardiography follow-up

BACKGROUND

To explore the value of 24 hour late Tl-201 imaging for detection of myocardial ischemia/viability after myocardial infarction.

MATERIALS AND METHODS

Thirty-eighty patients with myocardial infarction underwent immediate, 3 hour redistribution and 24-hour late imaging after intravenous injection of 5 mCi Tl-201. Image quality analysis was performed using a 4-grade model. The immediate/redistribution, redistribution/late, and immediate/late Tl-201 images were analyzed double-blinded. The capability of detection of myocardial ischemia/viability was compared between the 3 hour redistribution and the 24-hour late imaging. Thirty-two patients underwent coronary angiography and successful revascularization of stenotic coronary arteries. The relationship between the severity of coronary artery stenosis and the time to completed redistribution of myocardial perfusion defects after resting injection of Tl-201 was investigated. The sensitivity, specificity, and accuracy for predicting an improvement in function post revascularization were compared between the 24-hour late imaging and the 3-hour redistribution imaging by way of a follow-up echocardiography.

RESULTS

Three hour redistribution and 24-hour late imaging showed no significant differences in image quality according to the 4-grade model (P = 0.3580). Of 194 abnormal segments based on immediate Tl-201 imaging, redistribution imaging showed 60 reversible segments, taking up 31% (60/94), and late imaging showed 86 reversible segments, taking up 44% (86/194), with a significant difference (P = 0.0064). Of 128 severely abnormal segments, redistribution imaging showed 32 reversible segments, taking up 25% (32/128), and late imaging showed 48 reversible segments, taking up 38% (48/128), with a significant difference (P = 0.0310). Of 66 mildly abnormal segments, redistribution imaging showed 28 reversible segments, taking up 42% (28/66), and late imaging showed 38 reversible segments, taking up 58% (38/66), with no significant difference. Twenty-four hour late imaging showed an additional 30 reversible segments, taking up 22% (30/134) among 134 abnormal segments based on the immediate Tl-201 imaging, which did not improve on 3-hour redistribution imaging. The coronary arteries supplying the reversible segments detected by the 24-hour late imaging were more severe in diameter stenosis than those supplying the reversible segments detected by the 3-hour redistribution imaging. The sensitivity, specificity, and accuracy for predicting the functional improvement after the revascularization were 93% and 83%, 80% and 78%, 86% and 78%, respectively, by the 24-hour late imaging and the 3-hour redistribution imaging correspondingly, with the former being superior to the latter on the basis of the evaluation results of 9.90 +/- 3.62 months of follow-up echocardiography (chi = 10.8655, P = 0.0010).

CONCLUSION

Twenty-four hour late Tl-201 imaging, with satisfactory image quality, enhances the detection of myocardial ischemia/viability after myocardial infarction.

Rest-redistribution 201-Thallium single photon emission computed tomography predicts myocardial infarction and cardiac death in patients with ischemic left ventricular dysfunction

The prognostic role of rest-redistribution 201-Thallium imaging has not been extensively investigated in patients with left ventricular ischemic dysfunction.

OBJECTIVE

The aim of this study was to evaluate the ability of rest-redistribution 201-Thallium single photon emission computed tomography to predict cardiac death and occurrence of acute myocardial infarction in patients with ischemic mild-to-moderate left ventricular dysfunction.

METHODS

One-hundred and twenty-six patients with chronic coronary artery disease and mean left ventricular ejection fraction 39 +/- 11% were followed-up for 30 +/- 17 months after a rest-redistribution 201-Thallium imaging single photon emission computed tomography. Cardiac death and acute myocardial infarction were considered as major cardiac events.

RESULTS

During the follow up, 11 (9%) cardiac deaths and 9 (7%) acute myocardial infarctions occurred. The only variable showing significant difference between patients with and without events was the number of severe irreversible defects (1.7 +/- 1.9 versus 0.9 +/- 1.2, respectively; P = 0.02). By Kaplan-Meier analysis, the presence of three or less, or more than three severe defects was selected as the best cutoff to identify patients with longer event-free survival from cardiac death or acute myocardial infarction (log rank 19.84; P < 0.0001). When only cardiac death was considered as clinical event, the presence of at least two severe defects best separated patients who died from those who survived (log rank 8.68; P = 0.0032).

CONCLUSION

Rest-redistribution 201-Thallium single photon emission computed tomography provides prognostic information in coronary patients with mild-to-moderate left ventricular dysfunction. The number of severe irreversible defects per patient is a powerful predictor of prognosis.

Integrated imaging of cardiac anatomy, physiology, and viability

Technologic developments in imaging will have a significant impact on cardiac imaging over the next decade. These advances will permit more detailed assessment of cardiac anatomy, complex assessment of cardiac physiology, and integration of anatomic and physiologic data. The distinction between anatomic and physiologic imaging is important. For assessing patients with known or suspected coronary artery disease, physiologic and anatomic imaging data are complementary. The strength of anatomic imaging rests in its ability to detect the presence of disease, whereas physiologic imaging techniques assess the impact of disease, such as whether a coronary atherosclerotic lesion limits myocardial blood flow. Research indicates that physiologic data are more prognostically important than anatomic data, but both may be important in patient management decisions. Integrated cardiac imaging is an evolving field, with many potential indications. These include assessment of coronary stenosis, myocardial viability, anatomic and physiologic characterization of atherosclerotic plaque, and advanced molecular imaging.

The assessment of myocardial viability and hibernation using resting thallium imaging

Rest-redistribution thallium-201 imaging is widely used to assess recovery of regional systolic dysfunction in patients with chronic coronary artery disease. In several studies, this technique has demonstrated very high sensitivity but reduced specificity, as reported in general for radionuclide imaging. In clinical terms, this implicates that many dysfunctional territories will not recover after revascularization despite a substantial amount of tracer uptake. Yet, the amount of tracer uptake in a given myocardial segment, although not perfect, remains the best indicator for predicting reversible dysfunction. In fact, the occurrence of redistribution after rest injection is not very common and it does not substantially contribute to the accuracy of the test. However, it is still undetermined whether the presence of redistribution is relevant for prognostic implications.

Stress echocardiography expert consensus statement: European Association of Echocardiography (EAE) (a registered branch of the ESC)

Stress echocardiography is the combination of 2D echocardiography with a physical, pharmacological or electrical stress. The diagnostic end point for the detection of myocardial ischemia is the induction of a transient worsening in regional function during stress. Stress echocardiography provides similar diagnostic and prognostic accuracy as radionuclide stress perfusion imaging, but at a substantially lower cost, without environmental impact, and with no biohazards for the patient and the physician. Among different stresses of comparable diagnostic and prognostic accuracy, semisupine exercise is the most used, dobutamine the best test for viability, and dipyridamole the safest and simplest pharmacological stress and the most suitable for combined wall motion coronary flow reserve assessment. The additional clinical benefit of myocardial perfusion contrast echocardiography and myocardial velocity imaging has been inconsistent to date, whereas the potential of adding - coronary flow reserve evaluation of left anterior descending coronary artery by transthoracic Doppler echocardiography adds another potentially important dimension to stress echocardiography. New emerging fields of application taking advantage from the versatility of the technique are Doppler stress echo in valvular heart disease and in dilated cardiomyopathy. In spite of its dependence upon operator's training, stress echocardiography is today the best (most cost-effective and risk-effective) possible imaging choice to achieve the still elusive target of sustainable cardiac imaging in the field of noninvasive diagnosis of coronary artery disease.

MRI for the assessment of myocardial viability

Accurate distinction between viable and infarcted myocardium is important for assessment of patients who have cardiac dysfunction. Through the technique of delayed-enhancement MRI (DE-MRI), viable and infarcted myocardium can be simultaneously identified in a manner that closely correlates with histopathology findings. This article provides an overview of experimental data establishing the physiologic basis of DE-MRI-evidenced hyperenhancement as a tissue-specific marker of myocardial infarction. Clinical data concerning the utility of transmural extent of hyperenhancement for predicting response to medical and revascularization therapy are reviewed. Studies directly comparing DE-MRI to other viability imaging techniques are presented, and emerging applications for DE-MRI are discussed.

Correlation between delayed-enhancement magnetic resonance and nitrate myocardial Tc-99m tetrofosmin scintigraphy in myocardial infarction: a case report

Introduction

Delayed-enhancement magnetic resonance imaging (DE-MRI) has been recently proposed as an alternative tool in identifying myocardial viability and transmural distribution of necrosis in the myocardium.

Case presentation

We describe a case of a 71-year-old man admitted for ischemic-like chest pain in which DE-MRI and post-nitrate ^99mTc-tetrofosmin myocardial scintigraphy equally contributed to the diagnosis of previous lateral myocardial infarction.

Conclusion

In this patient with coronary artery disease, the absence of uptake of tracer at myocardial scintigraphy appeared to be closely correlated to DE-MRI data. Cardiologists can use SPECT or DE-MRI to obtain similar information about myocardial viability.

Polymorphisms in Adenosine Receptor Genes are Associated with Infarct Size in Patients with Ischemic Cardiomyopathy

The goal of this experiment was to identify the presence of genetic variants in the adenosine receptor genes and assess their relationship to infarct size in a population of patients with ischemic cardiomyopathy. Adenosine receptors play an important role in protecting the heart during ischemia and in mediating the effects of ischemic preconditioning. We sequenced DNA samples from 273 individuals with ischemic cardiomyopathy and from 203 normal controls to identify the presence of genetic variants in the adenosine receptor genes. Subsequently, we analyzed the relationship between the identified genetic variants and infarct size, left ventricular size, and left ventricular function. Three variants in the 3'-untranslated region of the A(1)-adenosine gene (nt 1689 C/A, nt 2206 Tdel, nt 2683del36) and an informative polymorphism in the coding region of the A3-adenosine gene (nt 1509 A/C I248L) were associated with changes in infarct size. These results suggest that genetic variants in the adenosine receptor genes may predict the heart's response to ischemia or injury and might also influence an individual's response to adenosine therapy.

Acute Myocardial Infarction Early Viability Assessment by 64-Slice Computed Tomography Immediately After Coronary Angiography

OBJECTIVES

Early evaluation of myocardial viability in acute myocardial infarction is useful to guide therapy. Therefore, we assessed 64-slice computed tomography (CT) immediately after coronary angiography in this setting.

BACKGROUND

Recent preliminary studies have shown the promising usefulness of late hyperenhancement multislice computed tomography (MSCT) for non-viability assessment.

METHODS

Thirty-six patients admitted for a first acute myocardial infarction had a coronary angiogram early after admission followed by 64-slice CT without iodine reinjection. The 16 segments of the left ventricle depicted by the American Society of Echocardiography were graded: no, subendocardial, or transmural hyperenhancement. No or subendocardial hyperenhancement were expected to reflect viability. Two to 4 weeks later, the same segments' contractility was evaluated at rest. Low-dose dobutamine echocardiography was performed in case of akinetic segment at rest.

RESULTS

Mean delay between coronary angiography and MSCT was 24 +/- 11 min (range 7 to 51 min). We compared 576 segments evaluated by each method. Agreement was noted for 560 segments (97%) and disagreement for 16 segments (3%). Thus, 64-slice CT after coronary angiography for an acute myocardial infarction had 98% sensitivity, 94% specificity, 97% accuracy, and 99% positive and 79% negative predictive values for detecting viable myocardial segments at a very early stage of an acute myocardial infarction. On a per-patient analysis, sensitivity, specificity, accuracy, and positive and negative predictive values were 92%, 100%, 94%, and 100% and 85%, respectively.

CONCLUSIONS

A 64-slice CT after coronary angiography for an acute myocardial infarction is a promising method for early evaluation of viable myocardium.

MRI for the Assessment of Myocardial Viability

Accurate distinction between viable and infarcted myocardium is important for assessment of patients who have cardiac dysfunction. Through the technique of delayed-enhancement MRI (DE-MRI), viable and infarcted myocardium can be simultaneously identified in a manner that closely correlates with histopathology findings. This article provides an overview of experimental data establishing the physiologic basis of DE-MRI-evidenced hyperenhancement as a tissue-specific marker of myocardial infarction. Clinical data concerning the utility of transmural extent of hyperenhancement for predicting response to medical and revascularization therapy are reviewed. Studies directly comparing DE-MRI to other viability imaging techniques are presented, and emerging applications for DE-MRI are discussed.

Prognostic role of single-photon emission computed tomography (SPECT) imaging in myocardial viability

PURPOSE OF REVIEW

Cardiac imaging is evolving rapidly. Appropriate use of this technology could reduce morbidity and mortality, but inappropriate use could have a significant financial burden. Single-photon emission computed tomography imaging is widely available. This review summarizes the clinical utility and limitations of the prognostic role of single-photon emission computed tomography imaging for myocardial viability in patients with coronary artery disease and left-ventricular dysfunction.

RECENT FINDINGS

201Tl single-photon emission computed tomography, 99mTc single-photon emission computed tomography with sestamibi or tetrofosmin, and 18F-fluorodeoxyglucose single-photon emission computed tomography are validated tools for assessing myocardial viability. These techniques have a very similar predictive value in determining regional and global response to revascularization. 201Tl single-photon emission computed tomography viability studies are predictive of reverse left-ventricular remodeling, symptom improvement, and patient outcome after revascularization. Combination imaging with dual-isotope simultaneous acquisition single-photon emission computed tomography or positron-emission tomography/single-photon emission computed tomography may improve the positive and negative predictive values of single-photon emission computed tomography-based viability studies.

SUMMARY

Single-photon emission computed tomography-based myocardial viability testing is an important diagnostic modality due to widespread availability and reasonably good sensitivity and specificity for detecting viable myocardium and predicting clinical and functional responses to revascularization. In the future single-photon emission computed tomography viability techniques may have a prognostic role in predicting responses to cardiac resynchronization therapy and evaluating myocardial stem-cell transplantation.

Direct epicardial mapping can differentiate hibernating from scarred myocardium: a validation study with 18F-FDG-PET

AIM

This study investigated the value of epicardial mapping immediately before CABG in the differentiation of hibernating from scarred myocardium in correlation to the noninvasive gold standard (18)F-FDG PET.

METHODS AND RESULTS

In 35 patients with CAD, myocardial perfusion ((99m)Tc-Tetrofosmin-SPECT), viability ((18)F-FDG-PET), and function (LVangiography) were assessed before CABG. 102 bipolar epicardial electrograms per patient (n = 3570 electrograms) were recorded simultaneously with a ventricular jacket array. Based on the scintigraphic and LV angiographic data at the site of each electrode with good myocardial contact (n = 1963), segments (n = 492, 14.1 +/- 5.6 per patient; mean +/- SD) were classified into three groups: hibernating (n = 139), scarred (n = 104), and control (n = 249). Regional mean bipolar voltage values were calculated for Receiver Operating Characteristic (ROC) analysis. Mean bipolar voltage was significantly lower in scarred when compared to hibernating myocardium. ROC curve analysis (area under the curve of 0.92 +/- 0.47, mean +/- SE) for mean bipolar voltage to discriminate between hibernating and scarred myocardium revealed a sensitivity of 94% with a specificity of 83% at a cut-off value of 8.75 mV.

CONCLUSION

Hibernating myocardium can be differentiated correctly from scarred myocardium by direct epicardial mapping. In the future, hibernating myocardium may be detectable by body surface mapping techniques using inverse solutions.

Use of cardiac magnetic resonance to assess viability

The accurate differentiation of viable and nonviable myocardium is crucial for therapy planning in patients with coronary artery disease and left ventricular dysfunction. Traditional techniques such as echocardiography, positron emission tomography, single photon emission computed tomography, and dobutamine echocardiography have established roles. Cardiac MRI (CMR) is a rapidly emerging new modality that is used at an increasing number of medical centers in Europe and the United States. This review describes the role of CMR for the assessment of myocardial viability in the setting of acute and chronic ischemic ventricular dysfunction.

Strain Rate Dobutamine Echocardiography for Prediction of Recovery After Revascularization in Patients With Ischemic Left Ventricular Dysfunction

BACKGROUND

The purpose of the present study was to assess the accuracy of quantitative segmental analysis by strain rate imaging (SRI) technique during dobutamine test for detecting myocardial recovery after revascularization in patients with chronic ischemic regional left ventricular (LV) dysfunction and compare results with those of 2-dimensional echocardiography (2D) and tissue Doppler imaging (TDI) as well as rest-4 hours-24 hours redistribution thallium SPECT (Tl SPECT).

METHODS AND RESULTS

Forty-one patients with chronic ischemic regional LV dysfunction (EF 29 +/- 8%) underwent dobutamine 2D/TDI/SRI and Tl SPECT before and after myocardial revascularization. The sensitivity, specificity, and accuracy for the recovery of regional LV function were 73%, 81%, and 77% for dobutamine 2D; 77%, 82%, and 80% for dobutamine TDI; 86%, 88%, and 85% for dobutamine SRI; and 94%, 76%, and 84% for Tl tomography. The area under the ROC curve (AUC), which reflects the overall performance for the prediction of recovery, was 0.79 for systolic-SR, 0.81 for Tl SPECT, 0.83 for postsystolic strain, and 0.87 for isovolumic-SR. If both systolic and postsystolic SRI indexes were combined with Tl SPECT, the AUC was improved to 0.94.

CONCLUSIONS

Dobutamine SRI is more accurate than TDI in identifying hibernating myocardium. Systo-diastolic values obtained using dobutamine SRI echocardiography and values derived from nuclear perfusion techniques may be complementary in assessing myocardial viability.

Twenty-four-hour thallium-201 late redistribution imaging enhances the detection of myocardial viability after myocardial infarction

BACKGROUND

Thallium-201 (201Tl) myocardial perfusion imaging has been widely used for evaluation of myocardial ischemia/viability after myocardial infarction. The 3- to 4-h early redistribution imaging has underestimated a considerable part of viable myocardium, while the 24-h late redistribution imaging may enhance the detection of myocardial ischemia/viability, but remains controversial.

METHODS

Thirty-eighty patients with myocardial infarction underwent the initial, 3-h, and 24-h redistribution imaging after intravenous injection of 148-185 MBq 201Tl. Image quality analysis was performed using a four-grade model: excellent, good, moderate, and poor. The initial and 3-h images, the initial and 24-h images, and the 3- and 24-h images were compared double-blinded.

RESULTS

The 3- and 24-h images showed no significant differences in image quality according to the four-grade model (P=.3580). Out of the 194 abnormal segments based on the initial imaging, 60 (31%) segments improved by at least one grade on the 3-h imaging, while 86 (44%) segments improved by at least one grade on the 24-h imaging. The 24-h late imaging detected more viable myocardium than the 3-h imaging did, with a significant difference (chi2=7.4235, P=.0064). There were 164 abnormal segments on the 3-h imaging, with an average 30% (48) segments improved by at least one grade on the 24-h imaging. There were 134 initial abnormal segments without any improvement on the 3-h imaging. Out of these segments, the 24-h late redistribution imaging detected additional redistribution in 30 segments, taking up 22%. The mean global score on the 3-h imaging significantly decreased compared to that on the initial imaging (t=5.71, P<.0001), and the mean global score on the 24-h imaging further decreased significantly compared to that on the 3-h imaging (t=6.28, P<.0001).

CONCLUSIONS

Twenty-four-hour late 201Tl imaging, with satisfactory image quality, enhances the detection of myocardial viability after myocardial infarction.

Prediction of functional improvement of ischemic myocardium with (123I-BMIPP SPECT and 99mTc-tetrofosmin SPECT imaging: a study of patients with large acute myocardial infarction and receiving revascularization therapy

BACKGROUND

(18)F-fluorodeoxyglucose (FDG) positron-emission tomography (PET) is assumed to be the most useful method of evaluating the viability of the myocardium, but its use is limited by the need for a cyclotron. In the present study, the ability of a combination of (99m)Tc-tetrofosmin (TF) and (123)I-beta-methyliodophenyl pentadecanoic acid (BMIPP) single-photon emission computed tomography (SPECT), a combination of (18)F-FDG PET and (123)I-BMIPP SPECT, and a combination of (18)F-FDG PET and (99m)Tc-TF SPECT were compared to predict functional improvement of ischemic myocardium after a large acute myocardial infarction (AMI).

METHODS AND RESULTS

Ten patients with large AMI were studied by (99m)Tc-TF SPECT, (123)I-BMIPP SPECT and (18)F-FDG PET within 3 weeks. Six months later, (99m)Tc-TF imaging was performed. All patients underwent successful revascularization, and had no restenosis. Regional tracer uptake was scored using a 4-point scale in 20 segments of the SPECT and PET images. When the defect score of (123)I-BMIPP SPECT exceeded the defect score of (99m)Tc-TF SPECT or (18)F-FDG PET by 1 point or more, and when the defect score of (99m)Tc-TF SPECT exceeded the defect score of (18)F-FDG PET by 1 point or more, the segment was considered to show mismatching. When the defect score was the same in 2 tracers, the segment was considered to show matching. (99m)Tc-TF imaging at 3 weeks and 6 months used quantitative gated SPECT (QGS) to score wall motion using a 6-point scale (-1= dyskinesis, 0= akinesis, 1= severe hypokinesis, 2= moderate hypokinesis, 3= mild hypokinesis, and 4= normokinesis). The sensitivity of the combination of (123)I-BMIPP and (99m)Tc-TF imaging in predicting functional improvement was 61%, that of (18)F-FDG PET and (123)I-BMIPP SPECT was 94%, and that of (18)F-FDG PET and (99m)Tc-TF SPECT was 76%. The specificity of the combination of (123)I-BMIPP and (99m)Tc-TF imaging in predicting functional improvement was 83%, that of (18)F-FDG PET and (123)I-BMIPP SPECT was 40%, and that of (18)F-FDG PET and (99m)Tc-TF SPECT was 49%. The accuracy of the combination of (123)I-BMIPP and (99m)Tc-TF imaging in predicting functional improvement was 70%, that of (18)F-FDG PET and (123)I-BMIPP SPECT was 71%, and that of (18)F-FDG PET and (99m)Tc-TF SPECT was 63%.

CONCLUSION

The combination of (123)I-BMIPP and (99m)Tc-TF imaging is a practical modality for predicting the functional improvement of ischemic myocardium after a large AMI.

Late gadolinium-enhanced magnetic resonance imaging in acute and chronic myocardial infarction

OBJECTIVES

We sought to determine serial changes of enhanced and nonenhanced tissue on late gadolinium-enhanced cardiac magnetic resonance (CMR) imaging in patients with a myocardial infarction (MI) and to assess whether thickness of nonenhanced myocardium can improve the detection of preserved contractile function in the chronic state.

BACKGROUND

Previous studies demonstrated that enhancement on late gadolinium-enhanced CMR images indicates myocardial necrosis, and nonenhancement shows the presence of viable myocardium.

METHODS

The CMR studies were performed within one week (scan 1) and more than five months (scan 2) after the onset of MI in 18 patients. The area and mean thickness of enhanced tissue and nonenhanced myocardium were measured by using a 30-segment model. Systolic wall thickening on cine CMR at scan 2 was assessed for evaluating regional contractile function.

RESULTS

The amount of enhanced tissue significantly decreased from scan 1 to 2 (22.1 +/- 14.0 ml vs. 15.0 +/- 9.3 ml, p < 0.001). The averaged thickness of nonenhanced myocardium in the infarct segments significantly increased from scan 1 to 2 (5.2 +/- 3.0 mm vs. 6.6 +/- 3.2 mm, p < 0.001). Receiver operating characteristic analysis demonstrated that the measurement of thickness of nonenhanced myocardium, compared with measurement of percent transmural enhancement, had better diagnostic accuracy for predicting improved systolic wall thickening form scan 1 to 2 in dysfunctional segments (Az 0.650 vs. 0.594, p < 0.05).

CONCLUSIONS

The amounts of enhanced tissue and nonenhanced myocardium significantly altered from the acute to chronic state in MI patients. The diagnostic performance of CMR imaging for detection of preserved contractile function can be significantly improved by measuring thickness of nonenhanced myocardium in MI patients.

The low oxygen-carrying capacity of Krebs buffer causes a doubling in ventricular wall thickness in the isolated heart

The buffer-perfused Langendorff heart is significantly vasodilated compared with the in vivo heart. In this study, we employed ultrasound to determine if this vasodilation translated into changes in left ventricular wall thickness (LVWT), and if this effect persisted when these hearts were switched to the "working" mode. To investigate the effects of perfusion pressure, vascular tone, and oxygen availability on cardiac dimensions, we perfused hearts (from male Wistar rats) in the Langendorff mode at 80, 60, and 40 cm H2O pressure, and infused further groups of hearts with either the vasoconstrictor endothelin-1 (ET-1) or the blood substitute FC-43. Buffer perfusion induced a doubling in diastolic LVWT compared with the same hearts in vivo (5.4 ± 0.2 mm vs. 2.6 ± 0.2 mm, p < 0.05) that was not reversed by switching hearts to "working" mode. Perfusion pressures of 60 and 40 cm H2O resulted in an increase in diastolic LVWT. ET-1 infusion caused a dose-dependent decrease in diastolic LVWT (6.6 ± 0.4 to 4.8 ± 0.4 mm at a concentration of 10–9 mol/L, p < 0.05), with a concurrent decrease in coronary flow. FC-43 decreased diastolic LVWT from 6.7 ± 0.5 to 3.8 ± 0.7 mm (p < 0.05), with coronary flow falling from 16.1 ± 0.4 to 8.1 ± 0.4 mL/min (p < 0.05). We conclude that the increased diastolic LVWT observed in buffer-perfused hearts is due to vasodilation induced by the low oxygen-carrying capacity of buffer compared with blood in vivo, and that the inotropic effect of ET-1 in the Langendorff heart may be the result of a reversal of this wall thickening. The implications of these findings are discussed.Key words: ultrasound, endothelin, ventricular wall thickness, vasodilation.

Myocardial Viability: Nuclear Assessment

There are an estimated 5 million patients with congestive heart failure (CHF) in the United States. The long-term outcome in these patients is poor with a 5-year mortality of 70%. There is evidence suggesting that revascularization in patients with viable myocardium can result in reduced event rate in these patients. The presence of viable myocardium best identifies patients who will improve with revascularization. Noninvasive imaging with radionuclide tracers has been used extensively to identify the presence and extent of viable myocardium. We have summarized the role of radionuclide myocardial perfusion and function evaluation in assessment of viable myocardium in this review.

Viable Myocardium: How Much Is Enough? A Comparison of Viability by Comparative Imaging Techniques to Assess the Quantity and Functionality of Ischemic Myocardium

Left ventricular systolic dysfunction is mainly a result of coronary artery disease (CAD). Decrease in myocardial contractility results as a response to a chronic hypoperfusion state that produces a change in cardiac myocyte metabolism, resulting in a perfusion-contraction mismatch in which function is sacrificed for survival. If revascularization is performed in a timely fashion, metabolism can be restored leading to recovery of function. Through the use of noninvasive imaging modalities, assessing myocardial viability can be easily performed and will aid in selecting those patients who will benefit from revascularization. Viable myocardium can be identified by nuclear modalities that have a high sensitivity but a lower specificity, such as thallium-201 single photon emission computed tomography and positron emission tomography (PET); or by the use of dobutamine stress echocardiogram (DSE), which has a decreased sensitivity but a better specificity. A modality that is increasingly being used with an overall good sensitivity and specificity is contrast-enhanced magnetic resonance imaging. The purpose of this review is to explore the amount of myocardial viability that is relevant to pursue revascularization, since as myocardial function improves there is a decrease in morbidity and mortality from heart failure and arrhythmias.

Assessment of Myocardial Viability with Dobutamine Stress Echocardiography in Patients with Ischemic Left Ventricular Dysfunction

The noninvasive assessment of myocardial viability has proved clinically useful for distinguishing hibernating and/or stunned myocardium from irreversibly injured myocardium in patients with chronic ischemic heart disease or recent myocardial infarction, with marked regional and/or global left ventricular (LV) dysfunction. Noninvasive techniques utilized for the detection of viability in asynergic myocardial regions include positron emission tomographic imaging of residual metabolic activity, single photon emission tomography (SPECT) of radioisotope uptake with thallium-201, low-dose dobutamine echocardiography assessment of inotropic reserve and myocardial contrast echocardiography for evaluation of microvascular integrity. Of these techniques, dobutamine stress echocardiography is a safe, widely available and relatively inexpensive modality for the identification of myocardial viability for risk stratification and prognosis. Low-dose dobutamine response can accurately predict improvement of dysfunctional yet viable myocardial regions, and thus identify a subset of patients whose LV function will improve following successful coronary revascularization.

The accuracy of electrocardiographic Q waves for the detection of prior myocardial infarction as assessed by a novel standard of reference

BACKGROUND

The electrocardiogram (ECG) is valuable for the identification of prior myocardial infarction (MI) in individuals participating in epidemiologic studies or undergoing screening examinations. Although the Minnesota Code, a set of criteria for the interpretation of ECGs in such situations, is commonly used to identify MI in these settings, its accuracy is incompletely understood.

HYPOTHESIS

We sought to test the accuracy of the Minnesota Code Q and QS criteria for MI against a new standard of reference, the presence of a perfusion defect on a resting myocardial scintigraphic image.

METHODS

The resting myocardial scintigrams of all patients studied in our nuclear cardiology laboratory during 7 consecutive months were screened for the presence of perfusion defects. For each patient with such a defect, two individuals examined on the same day, who had no perfusion defect, were selected as controls. Electrocardiograms recorded within 30 days of the scintigraphy were read blindly by two of the authors using the Minnesota Code criteria for Q or QS waves indicative of MI.

RESULTS

For 214 patients selected on the basis of their scintigraphic findings, a satisfactory ECG recorded within a month of the scintigraphy was also available. The overall sensitivity of the Q or QS criteria was 0.58 and the specificity was 0.75. As might be expected when only the most stringent criteria were applied, sensitivity was least and the specificity best.

CONCLUSIONS

As in previous studies, in which necropsy material served as the standard of reference, sensitivity of the Q and QS criteria contained in the Minnesota Code is relatively modest and specificity is reasonable but not outstanding.

The predictive value of 201Tl rest-redistribution and 18F-fluorodeoxyglucose SPECT for wall motion recovery after recent reperfused myocardial infarction

201Tl and 18F-FDG are useful for acute myocardial infarction (MI) assessment. The goal of this study was to compare their predictive value for wall motion recovery in the culprit area after a recent reperfused MI using SPECT technique.

METHODS

Forty-one patients (mean age: 56 +/- 12 years) were included, 81% of them male; all were studied within 1-24 days post MI. They underwent angioplasty in 27 cases (12 primary); bypass grafting in 10 cases and successful thrombolysis in 4. SPECT 201Tl injected at rest and redistribution (R-R) and also 18F-FDG, were performed on different days. Processed tomograms were interpreted blinded to clinical or angiographic data. Segmental wall motion assessed with echocardiography at baseline was compared with the 3 month follow up.

RESULTS

Sensitivity [Confidence Interval] for 201Tl R-R was 74.6% [60.5-84.5], for FDG it was 82.1% [70.8-90.4]; specificities were 73% [64.3-80.5] and 54.8% [45.6-63.7], respectively. 18F-FDG tended to be more sensitive than 201Tl R-R, but the latter was more specific (p < 0.0004). Both 201Tl RR and 18F-FDG presented high negative predictive value (p: ns).

CONCLUSION

In recent MI, SPECT 201Tl R-R is a valuable and widely available technique for viability detection, with similar sensitivity and significant better specificity than SPECT 18F-FDG.

Impact of scar thickness on the assessment of viability using dobutamine echocardiography and thallium single-photon emission computed tomography

OBJECTIVES

We sought to determine whether the transmural extent of scar (TES) explains discordances between dobutamine echocardiography (DbE) and thallium single-photon emission computed tomography (Tl-SPECT) in the detection of viable myocardium (VM).

BACKGROUND

Discrepancies between DbE and Tl-SPECT are often attributed to differences between contractile reserve and membrane integrity, but may also reflect a disproportionate influence of nontransmural scar on thickening at DbE.

METHODS

Sixty patients (age 62 +/- 12 years; 10 women and 50 men) with postinfarction left ventricular dysfunction underwent standard rest-late redistribution Tl-SPECT and DbE. Viable myocardium was identified when dysfunctional segments showed Tl activity >60% on the late-redistribution image or by low-dose augmentation at DbE. Contrast-enhanced magnetic resonance imaging (ceMRI) was used to divide TES into five groups: 0%, <25%, 26% to 50%, 51% to 75%, and >75% of the wall thickness replaced by scar.

RESULTS

As TES increased, both the mean Tl uptake and change in wall motion score decreased significantly (both p < 0.001). However, the presence of subendocardial scar was insufficient to prevent thickening; >50% of segments still showed contractile function with TES of 25% to 75%, although residual function was uncommon with TES >75%. The relationship of both tests to increasing TES was similar, but Tl-SPECT identified VM more frequently than DbE in all groups. Among segments without scar or with small amounts of scar (<25% TES), >50% were viable by SPECT.

CONCLUSIONS

Both contractile reserve and perfusion are sensitive to the extent of scar. However, contractile reserve may be impaired in the face of no or minor scar, and thickening may still occur with extensive scar.

Additive value of low-dose dobutamine to technetium-99m sestamibi-gated single-photon emission computed tomography for prediction of wall motion improvement in patients undergoing coronary artery bypass graft

BACKGROUND

The two most useful methods for myocardial viability assessment are perfusion imaging and dobutamine echocardiography.

HYPOTHESIS

The present study investigated the additive value of a new method, dobutamine technetium 99m (99mTc)-sestamibi-gated single-photon emission computed tomography (SPECT), which combines these two modalities, to the prediction of wall motion improvement after revascularization.

METHODS

Fifty-five consecutive patients with ischemic cardiomyopathy, who were referred for viability evaluation, underwent resting and dobutamine (dose, 5-10 microkg/kg/min) gated SPECT with 99mTc-sestamibi. Of these patients, 36 underwent coronary artery bypass graft (CABG) within 1 month of the study and 32 had repeat resting gated SPECT within 1 year. Global and regional wall motion, wall thickness, and perfusion were simultaneously analyzed at rest and after dobutamine using the 20-segment model; the sestamibi uptake and wall motion response to dobutamine of each segment were rated quantitatively. Based on these findings, the segments were categorized as normal, viable, or nonviable. The predictive values for wall motion improvement were assessed by perfusion, using cutoffs of 50 and 60% of sestamibi uptake, and thereafter by the addition of dobutamine response in the segments that were rated nonviable.

RESULTS

Of the 1,080 myocardial segments studied, 906 (84%) had abnormal wall motion and were analyzed for viability. Concordance between perfusion and wall motion response to dobutamine was 60% with the 50% cutoff of sestamibi uptake, and increased to 65% with the 60% sestamibi cutoff (p < 0.04). The respective predictive values of wall motion improvement using the 50 and 60% cutoff points were as follows: sensitivity 93 and 70%, respectively, (p < 0.01); specificity 59 and 86% (p < 0.001), respectively; accuracy 77% for both. The addition of the wall motion response to dobutamine to the assessment of the nonviable segments by perfusion (60% cutoff) increased the sensitivity from 70 to 85% (p = 0.001) and the negative predictive value from 70 to 81% (p = 0.009); the positive predictive value remained high (86 vs. 82%). No additive value of wall motion response to dobutamine was demonstrated for nonviable segments by perfusion with a 50% cutoff.

CONCLUSION

Dobutamine sestamibi-gated SPECT is a feasible method for the analysis of myocardial perfusion, function, and contractile reserve of individual myocardial segments in patients with ischemic cardiomyopathy. Viability assessment based on a threshold of 60% uptake of sestamibi, with the addition of the wall motion response to dobutamine in the nonviable segments, seems to yield better predictive values for wall motion improvement after CABG.

Ischemic and viable myocardium in patients with Non–Q-Wave or Q-Wave myocardial infarction and left ventricular dysfunction

OBJECTIVES

We investigated whether patients with non-Q-wave myocardial infarction (NQMI) have more ischemic viable myocardium (IVM) than patients with Q-wave myocardial infarction (QMI).

BACKGROUND

Non-Q-wave myocardial infarction is associated with higher incidences of cardiac events than QMI, suggesting more myocardium at risk in NQMI.

METHODS

To identify myocardial ischemia, hibernation, and scar, the resting and stress (82)rubidium perfusion and F-18 fluorodeoxyglucose metabolic positron emission tomographic imaging (PET) was performed in 64 consecutive patients with NQMI (n = 21) or QMI (n = 43). Echocardiography was performed for assessment of left ventricular function and wall motion index (WMI). The relationships between PET, echocardiographic, and electrocardiographic findings were analyzed.

RESULTS

There were no significant differences in left ventricular ejection fraction (LVEF) between NQMI and QMI groups (28 +/- 10% vs. 25 +/- 11%, p > 0.05). Ischemic and viable myocardium was more common in NQMI than in QMI (91% vs. 61%, p < 0.05). The total amount of IVM was significantly higher in NQMI than in QMI (6.5 +/- 5.2 vs. 2.9 +/- 2.8 segments, p < 0.001). Neither the number of Q waves, residual ST-segment depression of >or=0.5 mm or elevation of >or=1 mm, nor LVEF and WMI were significant predictors for IVM. Wall motion index correlated with scar segments (r = 0.54, p < 0.001) and LVEF (r = -0.67, p < 0.001).

CONCLUSIONS

Ischemic and viable myocardium is common in patients with NQMI and left ventricular dysfunction, suggesting that aggressive approaches should be taken to salvage the myocardium at risk in such patients.