Comparison of sestamibi, thallium, echocardiography and PET for the detection of hibernating myocardium

Updated knowledge and practical implementations of stress echocardiography in ischemic and non-ischemic cardiac diseases: an expert consensus of the Working Group of Echocardiography of the Hellenic Society of Cardiology

Stress echocardiography (SE) is a well-established and valid technique, widely-used for the diagnostic evaluation of patients with ischemic and non-ischemic cardiac diseases. This statement of the Echocardiography Working Group of the Hellenic Society of Cardiology summarizes the consensus of the writing group regarding the applications of SE, based on the expertise of their members and on a critical review of current medical literature. The main objectives of the consensus document include a comprehensive review of SE methodology and training, focusing on the preparation, the protocols used and the analysis of the SE images and an updated, evidence-based knowledge about SE applications on ischemic and non-ischemic heart diseases, such as in cardiomyopathies, heart failure and valvular heart disease.

Practical Implications of Myocardial Viability Studies

Many non-invasive methods, such as imaging tests, have been developed aiming to add a contribution to existing studies in estimating patients’ prognosis after myocardial injury. This prognosis is proportional to myocardial viability, which is evaluated in coronary artery disease and left ventricular dysfunction patients only.

While myocardial viability represents the likelihood of a dysfunctional muscle (resulting from decreased oxygen supply for coronary artery obstruction), hibernation represents post-interventional functional recovery itself.

This article proposes a review of pathophysiological basis of viability, diagnostic methods, prognosis and future perspectives of myocardial viability. An electronic bibliographic search for articles was performed in PubMed, Lilacs, Cochrane and Scielo databases, according to pre-established criteria.

The studies showed the ability of many imaging techniques in detecting viable tissues in dysfunctional areas of left ventricle resulting from coronary artery injuries. These techniques can identify patients who may benefit from myocardial revascularization and indicate the most appropriate treatment.

Quantification of diagnostic accuracy using nitrate enhanced Tc-99m sestamibi gated myocardial SPECT in assessing myocardial viability: prospective analysis

The aim of this prospective study was to assess myocardial viability with nitrate-enhanced Tc-99m sestamibi gated single-photon emission computed tomography in patients with known coronary artery disease. We enrolled 48 consecutive patients (39 men, 9 women) aged 24–82 years, with coronary artery disease and history of myocardial infarction. A Tc-99m sestamibi study was conducted at rest as baseline, followed by a nitrate-enhanced study the next day. Of 960 segments analyzed, 244 of 480 in the left anterior descending coronary artery territory showed viability on the baseline study, and 276 were viable according to the nitrate-enhanced study. Similarly, of 192 right coronary segments analyzed, 148 showed viability on the baseline study compared to 153 on the nitrate study. Of 288 left circumflex territory segments analyzed, 206 showed viability on the baseline study compared to 241 on the nitrate study. The overall improvement of viability with the nitrate study was 12.04%. On the gated studies, the overall improvement with nitrate was 2.02%. The gated study also allowed grading of wall motion and thickness. It was concluded that nitrate-augmented Tc-99m sestamibi myocardial imaging significantly improved the detection of hibernating myocardium, with gated images further improving the accuracy of detection in borderline cases.

PET imaging of cardiac hypoxia: opportunities and challenges

Myocardial hypoxia is a major factor in the pathology of cardiac ischemia and myocardial infarction. Hypoxia also occurs in microvascular disease and cardiac hypertrophy, and is thought to be a prime determinant of the progression to heart failure, as well as the driving force for compensatory angiogenesis. The non-invasive delineation and quantification of hypoxia in cardiac tissue therefore has the potential to be an invaluable experimental, diagnostic and prognostic biomarker for applications in cardiology. However, at this time there are no validated methodologies sufficiently sensitive or reliable for clinical use. PET imaging provides real-time spatial information on the biodistribution of injected radiolabeled tracer molecules. Its inherent high sensitivity allows quantitative imaging of these tracers, even when injected at sub-pharmacological (≥pM) concentrations, allowing the non-invasive investigation of biological systems without perturbing them. PET is therefore an attractive approach for the delineation and quantification of cardiac hypoxia and ischemia. In this review we discuss the key concepts which must be considered when imaging hypoxia in the heart. We summarize the PET tracers which are currently available, and we look forward to the next generation of hypoxia-specific PET imaging agents currently being developed. We describe their potential advantages and shortcomings compared to existing imaging approaches, and what is needed in terms of validation and characterization before these agents can be exploited clinically.

Validation of the calculation of the clearance rate constant (k(mono)) of [(11)C]acetate using parametric k(mono) image for myocardial oxidative metabolism

INTRODUCTION

The purpose of this study was to validate the calculation of myocardial oxidative metabolism rate using a parametric clearance rate constant (k(mono)) image.

METHODS

Fifteen subjects (seven volunteers, eight patients) were studied. Dynamic PET was acquired after intravenous injection of 700 MBq of [(11)C]acetate. The clearance rate constant of [(11)C]acetate (k(mono)) was calculated pixel by pixel to generate the parametric k(mono) image. The k(mono) values from this image and those calculated from the dynamic image were compared in the same regions of interest (ROIs).

RESULTS

Two different methods showed an excellent correlation except in the very low range. Regression equations were y=0.99x+0.0034 (r(2)=0.86, P<.001) and y=1.16x-0.0077 (r(2)=0.87, P<.001) in normal volunteer and patient groups, respectively, and y=1.07x-0.0019 (r(2)=0.87, P<.001) when combined.

CONCLUSIONS

Both methods exhibited similar values of k(mono). Parametric k(mono) image may result in better visual understanding of regional myocardial oxidative metabolism.

F-18-fluorodeoxyglucose positron emission tomography imaging-assisted management of patients with severe left ventricular dysfunction and suspected coronary disease: a randomized, controlled trial (PARR-2)

OBJECTIVES

We conducted a randomized trial to assess the effectiveness of F-18-fluorodeoxyglucose (FDG) positron emission tomography (PET)-assisted management in patients with severe ventricular dysfunction and suspected coronary disease.

BACKGROUND

Such patients may benefit from revascularization, but have significant perioperative morbidity and mortality. F-18-fluorodeoxyglucose PET can detect viable myocardium that might recover after revascularization.

METHODS

Included were patients with severe left ventricular (LV) dysfunction and suspected coronary disease being considered for revascularization, heart failure, or transplantation work-ups or in whom PET was considered potentially useful. Patients were stratified according to recent angiography or not, then randomized to management assisted by FDG PET (n = 218) or standard care (n = 212). The primary outcome was the composite of cardiac death, myocardial infarction, or recurrent hospital stay for cardiac cause, within 1 year.

RESULTS

At 1 year, the cumulative proportion of patients who had experienced the composite event was 30% (PET arm) versus 36% (standard arm) (relative risk 0.82, 95% confidence interval [CI] 0.59 to 1.14; p = 0.16). The hazard ratio (HR) for the composite outcome, PET versus standard care, was 0.78 (95% CI 0.58 to 1.1; p = 0.15); for patients that adhered to PET recommendations for revascularization, revascularization work-up, or neither, HR = 0.62 (95% CI 0.42 to 0.93; p = 0.019); in those without recent angiography, for cardiac death, HR = 0.4 (95% CI 0.17 to 0.96; p = 0.035).

CONCLUSIONS

This study did not demonstrate a significant reduction in cardiac events in patients with LV dysfunction and suspected coronary disease for FDG PET-assisted management versus standard care. In those who adhered to PET recommendations and in patients without recent angiography, significant benefits were observed. The utility of FDG PET is best realized in this subpopulation and when adherence to recommendations can be achieved.

Metabolic imaging using PET

INTRODUCTION

There is growing evidence that myocardial metabolism plays a key role not only in ischaemic heart disease but also in a variety of diseases which involve myocardium globally, such as heart failure and diabetes mellitus. Understanding myocardial metabolism in such diseases helps to elucidate the pathophysiology and assists in making therapeutic decisions.

MEASUREMENT

As well as providing information on regional changes, PET can deliver quantitative information about both regional and global changes in metabolism. This capability of quantitative measurement is one of the major advantages of PET along with physiological positron tracers, especially relevant in evaluating diseases which involve the whole myocardium.

DISCUSSION

This review discusses major PET tracers for metabolic imaging and their clinical applications and contributions to research regarding ischaemic heart disease and other diseases such as heart failure and diabetic heart disease. Future applications of positron metabolic tracers for the detection of vulnerable plaque are also highlighted briefly.

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.