Assessment of myocardial viability with 99mTc-sestamibi tomography before coronary bypass graft surgery: correlation with histopathology and postoperative improvement in cardiac function

Myocardial Viability Testing in the Management of Ischemic Heart Failure

Although major advances have occurred lately in medical therapy, ischemic heart failure remains an important cause of death and disability. Viable myocardium represents a cause of reversible ischemic left ventricular dysfunction. Coronary revascularization may improve left ventricular function and prognosis in patients with viable myocardium. Although patients with impaired left ventricular function and multi-vessel coronary artery disease benefit the most from revascularization, they are at high risk of complications related to revascularization procedure. An important element in selecting the patients for myocardial revascularization is the presence of the viable myocardium. Multiple imaging modalities can assess myocardial viability and predict functional improvement after revascularization, with dobutamine stress echocardiography, nuclear imaging tests and magnetic resonance imaging being the most frequently used. However, the role of myocardial viability testing in the management of patients with ischemic heart failure is still controversial due to the failure of randomized controlled trials of revascularization to reveal clear benefits of viability testing. This review summarizes the current knowledge regarding the concept of viable myocardium, depicts the role and tools for viability testing, discusses the research involving this topic and the controversies related to the utility of myocardial viability testing and provides a patient-centered approach for clinical practice.

Myocardial Scar But Not Ischemia Is Associated With Defibrillator Shocks and Sudden Cardiac Death in Stable Patients With Reduced Left Ventricular Ejection Fraction

OBJECTIVES

This study sought to investigate the association of myocardial scar and ischemia with major arrhythmic events (MAEs) in patients with left ventricular ejection fraction (LVEF) ≤35%.

BACKGROUND

Although myocardial scar is a known substrate for ventricular arrhythmias, the association of myocardial ischemia with ventricular arrhythmias in stable patients with left ventricular dysfunction is less clear.

METHODS

A total of 439 consecutive patients (median age, 70 years; 78% male; 55% with implantable cardioverter defibrillator [ICD]) referred for stress/rest positron emission tomography (PET) and resting LVEF ≤35% were included. Primary outcome was time-to-first MAE defined as sudden cardiac death, resuscitated sudden cardiac death, or appropriate ICD shocks for ventricular tachyarrhythmias ascertained by blinded adjudication of hospital records, Social Security Administration's Death Masterfile, National Death Index, and ICD vendor databases.

RESULTS

Ninety-one MAEs including 20 sudden cardiac deaths occurred in 75 (17%) patients during a median follow-up of 3.2 years. Transmural myocardial scar was strongly associated with MAEs beyond age, sex, cardiovascular risk factors, beta-blocker therapy, and resting LVEF (adjusted hazard ratio per 10% increase in scar, 1.48 [95% confidence interval: 1.22 to 1.80]; p < 0.001). However, non transmural scar/hibernation or markers of myocardial ischemia on PET including global or peri-infarct ischemia, coronary flow reserve, and resting or hyperemic myocardial blood flows were not associated with MAEs in univariable or multivariable analysis. These findings remained robust in subgroup analyses of patients with ICD (n = 223), with ischemic cardiomyopathy (n = 287), and in patients without revascularization after the PET scan (n = 365).

CONCLUSIONS

Myocardial scar but not ischemia was associated with appropriate ICD shocks and sudden cardiac death in patients with LVEF ≤35%. These findings have implications for risk-stratification of patients with left ventricular dysfunction who may benefit from ICD therapy.

Nuclear Image-Guided Approaches for Cardiac Resynchronization Therapy (CRT)

Cardiac resynchronization therapy (CRT) is a standard treatment for patients with heart failure. However, 30-40 % of the patients having CRT do not respond to CRT with improved clinical symptom and cardiac functions. It is important for CRT response that left ventricular (LV) lead is placed away from scar and at or near the site of the latest mechanical activation. Nuclear image-guided approaches for CRT have shown significant clinical value to assess LV myocardial viability and mechanical dyssynchrony, recommend the optimal LV lead position, and navigate the LV lead to the target coronary venous site. All these techniques, once validated and implemented, should impact the current clinical practice.

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.

Tc-99m SPECT sestamibi for the measurement of infarct size

There are a variety of approaches to assess the efficacy of reperfusion therapy, and myocardial protection, in acute myocardial infarction. This review summarizes the available evidence validating the use of technetium-99m sestamibi single-photon emission computed tomography (SPECT) for this purpose. Multiple lines of evidence have validated its clinical utility. SPECT sestamibi infarct size has been used as an endpoint in multiple randomized clinical trials. A smaller number of clinical trials have used both early and later imaging with SPECT sestamibi to assess myocardium at risk and myocardial salvage. SPECT sestamibi has a number of limitations which must be recognized. Nevertheless, SPECT sestamibi infarct size is a well-validated measurement with a long track record of performance as an endpoint in multicenter, randomized clinical trials.

Scintigraphic parameters with emphasis on perfusion appraisal in rest 99mTc-sestamibi SPECT in the recovery of myocardial function after thrombolytic therapy in patients with ST elevation myocardial infarction (STEMI)

Introduction: This study was performed to determine the clinical application of rest 99mTc-sestamibi in the assessment of viability and functional improvement of the left ventricle (LV) myocardium in the post-thrombolytic therapy of acute myocardial infarction (AMI). Material and methods: In 37 patients with AMI who received thrombolytic therapy, 2-dimensional (2D) echocardiography, as well as the resting redistribution of 99mTc-sestamibi, was investigated, both within 1 week and 3–5 months after AMI. The predictive capacity of the perfusion percentage for myocardial function recovery was evaluated. Also, the capacities of the possible variables in the prediction of recovery of myocardial function resulting from a change in LV ejection fraction (EF) were evaluated using stepwise multiple regression analysis. Results: Thirty-seven patients (30 men and 7 women; mean age: 58±14 years) with AMI were enrolled in the study. Redistribution was observed in 35 and 50 segments of the initial and follow-up scans, respectively. In addition, 146 segments with reverse redistribution (RR), both in the initial scan (118 segments) and the follow-up scan (86 segments), were also observed. An apparent difference in wall motion scores was seen between the initial and follow-up echocardiographs (p<0.001). Furthermore, using the optimal cut-off point of perfusion percentage in each image set, sensitivity as well as specificity and likelihood ratio (LR) for the improvement of regional wall motion after 3–5 months were defined. Conclusion: These data showed that redistribution and reverse redistribution of 99mTc-sestamibi post thrombolytic therapy can be used as a marker of viability to predict the recovery of segmental wall motion abnormality (stunning), as well as the improvement of segmental perfusion uptake. This study also demonstrates that the resting 99mTc-sestamibi SPECT can be used for an approximate assessment of LV function status and can predict the recovery of jeopardized myocardium function after thrombolytic therapy.

Cell therapy in patients with left ventricular dysfunction due to myocardial infarction

OBJECTIVES

The purpose of this study was to determine the impact of autologous transplantation of mononuclear bone marrow cells on myocardial function in patients with left ventricular (LV) dysfunction due to an acute myocardial infarction.

METHODS

The randomized study included 82 patients with a first acute myocardial infarction treated with a stent implantation. This presentation is a subanalysis of 47 patients with left ventricular dysfunction-EF (ejection fraction) <or= 40%. Group H patients (n = 17) received higher number (100,000,000) of cells; Group L patients (n = 13) received lower number (10,000,000) of cells. The patients of control Group C (n = 17) were not treated with cells. The Doppler tissue imaging and single photon emission computed tomography were performed before cell transplantation and 3 months later.

RESULTS

At 3 months of follow-up, the baseline EF of 35%, 36%, 35% in Groups H, L, and C increased by 6% (P < 0.01 vs. baseline), 5% (P < 0.01 vs. baseline), and 4% (P = NS vs. baseline), respectively, as assessed by single photon emission computed tomography (P = NS between groups). The baseline number of akinetic segments of 6.9, 7.0, and 6.2 in H, L, and C groups decreased by 1.7 (P < 0.01 vs. baseline), 1.5 (P < 0.01 vs. baseline), and 0.7 (P = NS vs. baseline, P = NS between groups), respectively, as demonstrated by echocardiography.

CONCLUSION

In our study, the statistically important effect of transplantation of mononuclear bone marrow cells on myocardial function was not found. Only an insignificant trend toward the improvement of global LV EF fraction was found at 3-month follow-up.

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.

Predictors of infarct size after primary coronary angioplasty in acute myocardial infarction from pooled analysis from four contemporary trials

Determinates of infarct size in patients with acute myocardial infarction (AMI) undergoing percutaneous coronary intervention (PCI) have been incompletely characterized, in part because of the limited sample size of previous studies. Databases therefore were pooled from 4 contemporary trials of primary or rescue PCI (EMERALD, COOL-MI, AMIHOT, and ICE-IT), in which the primary end point was infarct size assessed using technetium-99m sestamibi single-photon emission computed tomographic imaging, measured at the same core laboratory. Of 1,355 patients, infarct size was determined using technetium-99m sestamibi imaging in 1,199 patients (88.5%), at a mean time of 23 +/- 15 days. Median infarct size of the study population was 10% (interquartile range 0% to 23%; mean 14.9 +/- 16.1%). Using multiple linear regression analysis of 18 variables, left anterior descending infarct artery, baseline Thrombolysis In Myocardial Infarction grade 0/1 flow, male gender, and prolonged door-to-balloon time were powerful independent predictors of infarct size (all p <0.0001). Other independent correlates of infarct size were final Thrombolysis In Myocardial Infarction grade <3 flow (p = 0.0001), previous AMI (p = 0.005), symptom-onset-to-door time (p = 0.021), and rescue angioplasty (p = 0.026). In conclusion, anterior infarction, time to reperfusion, epicardial infarct artery patency before and after reperfusion, male gender, previous AMI, and failed thrombolytic therapy were important predictors of infarct size after angioplasty in patients with AMI assessed using technetium-99m sestamibi imaging and should be considered when planning future trials of investigational drugs or devices designed to enhance myocardial recovery.

Three-, 6-, and 12-month results of autologous transplantation of mononuclear bone marrow cells in patients with acute myocardial infarction

BACKGROUND

There are only few data on long-term effectiveness of the stem cell therapy.

AIM

We studied the time course of global and regional left ventricular function in patients with acute myocardial infarction within 1 year after the autologous mononuclear bone marrow cell transplantation.

METHODS

Sixty patients with a first acute myocardial infarction, who had been randomized into 3 groups, completed a 12-month protocol. Two groups were intracoronarily given bone marrow cells in either higher (10(8) cells, HD group, n=20) or lower (10(7) cells, LD group, n=20) doses. Twenty patients without cell transplantation served as a control (C) group. Doppler tissue imaging and the gated technetium-99m sestamibi single photon emission computed tomography were performed before cell transplantation and at 3, 6, and 12 months later.

RESULTS

The baseline peak systolic velocities of longitudinal contraction of the infarcted wall (S(infarct)) of 5.2 cm/s, 4.6 cm/s, and 4.4 cm/s in C, LD, and HD groups increased by 0.0 cm/s, 0.3 cm/s (p=NS vs. C group), and by 0.7 cm/s (p<0.05 vs. C group), respectively, at 3 months. At 12 months, however, the corresponding changes from baseline values of 0.1 cm/s, 0.2 cm/s, and 0.6 cm/s did not differ significantly (all p=NS). In contrast, the post-transplant improvements in the left ventricular ejection fraction by 6%, 7%, and 7% at months 3, 6, and 12, respectively, were preserved in HD group patients during the whole 12-month follow-up and remained significantly better as compared to controls.

CONCLUSIONS

In our study, the autologous mononuclear bone marrow cell transplantation provided sustained improvement in global left ventricular systolic function in patients with acute myocardial infarction. However, when evaluating regional systolic function of the infarcted wall, the short-term benefit was partially lost during the 12-month follow-up.

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.

Assessment of myocardial viability by radionuclide and echocardiographic techniques: is it simply a sensitivity and specificity issue?

PURPOSE OF REVIEW

The assessment of myocardial viability provides important information that may guide therapeutic decisions in patients with coronary artery disease and left ventricular dysfunction. This review describes methods for assessing myocardial viability using single-photon emission computed tomography, with an emphasis on how to optimize the detection of viable myocardium using current techniques. Relevant comparisons of radionuclide techniques with echocardiographic methods are also discussed.

RECENT FINDINGS

The basis for the assessment of myocardial viability using radionuclides is reviewed briefly. Radionuclide techniques provide important prognostic information that may affect the decision on if patients with coronary artery disease should be revascularized or treated medically. Data suggest that dobutamine stress echocardiography may underestimate viability in certain patients. Radionuclide techniques that assess both radiotracer uptake and ventricular function can provide a comprehensive approach to detect viable myocardium in most patients.

SUMMARY

The methods for assessing myocardial viability using single-photon emission computed tomography are accurate, reproducible, and widely available. Viability testing should be considered in patients with known coronary artery disease and left ventricular dysfunction. Further studies are warranted to assess the affect of viability assessment on clinical outcomes.

Do mechanical markers of myocardial ischaemia predict the transmural extent of myocardial infarction in man?

BACKGROUND

The present study aimed to explore the relationship between the transmural extent of myocardial necrosis and mechanical markers of myocardial ischaemia in man.

METHODS

A group of 40 patients with previous Q-wave myocardial infarction and a left ventricular ejection fraction (LVEF) of 27 +/- 11% was studied by cine and contrast-enhanced magnetic resonance imaging.

RESULTS

Necrotic areas of delayed contrast enhancement were present in every patient and involved 20 +/- 8% of left ventricular myocardium. In involved segments, the transmural extent of contrast enhancement varied from 5% to 100%, being on average 38 +/- 25% of the wall thickness. End-diastolic left ventricular wall thickness and systolic wall thickening were lower in contrast-enhanced segments than in the other segments (P < 0.001). Furthermore, although left ventricular wall thickness and systolic wall thickening decreased as the transmural extent of contrast enhancement increased, the correlations were weak (r = -0.382 and -0.45, respectively). Finally, a delayed contrast enhancement was present in 89% of akinetic and in 94% of dyskinetic segments; however, contrast enhancement was also present in 18% of the segments with normal wall motion and in 56% of hypokinetic segments.

CONCLUSIONS

Although mechanical markers of myocardial ischaemia substantially reflect the transmural extent of myocardial infarction, none of them can be considered as a substitute for the direct observation of necrotic tissue and its transmural extent, as provided by contrast-enhanced magnetic resonance imaging.

Contribution of 99mTc-sestamibi infusion SPECT to the characterization of fixed perfusion defects

In patients with coronary artery disease, the distinction between scar and viable myocardium by means of myocardial perfusion imaging (MPI) sometimes can be difficult because of the equivocal meaning of fixed perfusion defects. In this study we examined whether addition of a 99mTc-sestamibi infusion study to the standard MPI could provide extra information regarding the fixed defects. Thirty-seven patients underwent standard MPI and an extra SPECT study in which 99mTc-sestamibi was given as a prolonged constant infusion. Of 324 myocardial segments available for analysis, 134 had fixed or resting perfusion abnormalities on standard MPI studies, of which 25% (33/134) in 12 patients showed partial improvement in the perfusion pattern whereas in 6% (8/134) the improvement was very significant in infusion studies. In 19 patients who were also examined with dobutamine echocardiography, 13 showed concordance between echocardiography and infusion MPI. This study suggests that infusion MPI may provide complementary information to the conventional scintigraphy with regard to interpretation of standard myocardial perfusion scans with fixed defects.

Detection of hibernate myocardium by 99mTc sestamibi gated SPECT during low-dose dobutamine infusion plus nitrate in patients with first acute myocardial infarction

AIM

To investigate the role of Tc-MIBI gated SPECT imaging following the administration of low-dose dobutamine plus nitrate (LDD+nitrate) in the assessment of left ventricular function and the perfusion of hibernate myocardial tissue.

METHODS

The study group comprised 29 patients diagnosed as having acute myocardial infarction. In the first month post-infarction, Tc-MIBI gated SPECT imaging was performed in all patients at rest-dobutamine stress and LDD+nitrate. Ejection fraction, end diastolic volume (EDV), end systolic volume (ESV), stroke volume, volume, extent score, and reversibility score values were calculated.

RESULTS

The findings of Tc-MIBI gated SPECT imaging following the administration of LDD+nitrate and the rest Tc-MIBI gated SPECT findings revealed that while the levels of ejection fraction (P=0.004) and reversibility score (P=0.000) increased significantly, there was a significant decrease in EDV (P=0.001), ESV (P=0.001), volume (P=0.017), stroke volume (P=0.257) and extent score (P=0.039) values.

CONCLUSION

The use of Tc-MIBI gated SPECT concomitantly with the administration of LDD+nitrate is useful in the determination of myocardial hibernation in patients with left ventricular failure following acute myocardial infarction.

A randomized, double-blinded, placebo-controlled multicenter trial of adenosine as an adjunct to reperfusion in the treatment of acute myocardial infarction (AMISTAD-II)

OBJECTIVES

The purpose of this research was to determine the effect of intravenous adenosine on clinical outcomes and infarct size in ST-segment elevation myocardial infarction (STEMI) patients undergoing reperfusion therapy.

BACKGROUND

Previous small studies suggest that adenosine may reduce the size of an evolving infarction.

METHODS

Patients (n = 2,118) with evolving anterior STEMI receiving thrombolysis or primary angioplasty were randomized to a 3-h infusion of either adenosine 50 or 70 microg/kg/min or of placebo. The primary end point was new congestive heart failure (CHF) beginning >24 h after randomization, or the first re-hospitalization for CHF, or death from any cause within six months. Infarct size was measured in a subset of 243 patients by technetium-99m sestamibi tomography.

RESULTS

There was no difference in the primary end point between placebo (17.9%) and either the pooled adenosine dose groups (16.3%) or, separately, the 50-microg/kg/min dose and 70-microg/kg/min groups (16.5% vs. 16.1%, respectively, p = 0.43). The pooled adenosine group trended toward a smaller median infarct size compared with the placebo group, 17% versus 27% (p = 0.074). A dose-response relationship with final median infarct size was seen: 11% at the high dose (p = 0.023 vs. placebo) and 23% at the low dose (p = NS vs. placebo). Infarct size and occurrence of a primary end point were significantly related (p < 0.001).

CONCLUSIONS

Clinical outcomes in patients with STEMI undergoing reperfusion therapy were not significantly improved with adenosine, although infarct size was reduced with the 70-microg/kg/min adenosine infusion, a finding that correlated with fewer adverse clinical events. A larger study limited to the 70-microg/kg/min dose is, therefore, warranted.

Clinical decision-making and myocardial viability: current perspectives

Not all myocardium involved in a myocardial infarction is dead or irreversibly damaged. The balance between the amount of scar and live tissue, and the nature of the live tissue, determine the likelihood that contractile function will improve after revascularisation. This improvement (which defines viability) may be predicted with about 80% accuracy using several techniques. This review examines the determinants of functional recovery and how they may be integrated in making decisions regarding revascularisation.

The influence of myocardial blood flow and volume of distribution on late Gd-DTPA kinetics in ischemic heart failure

PURPOSE

To determine the mechanism of enhancement of contrast-enhanced MRI (ceMRI) in chronic ischemic myocardium. While ceMRI can identify scar tissue in chronic ischemic myocardium, the mechanism of enhancement is not completely understood.

MATERIALS AND METHODS

A total of 11 patients with ischemic heart failure (ejection fraction [EF] 28 +/- 9%) were imaged with ceMRI and positron emission tomography (PET) to measure myocardial blood flow (MBF). Longitudinal relaxation rate (T1) of blood, normal tissue, and scar tissue defined by ceMRI was determined before and two to 50 minutes after contrast (Look Locker technique), and the partition coefficient (lambda) and volume of distribution (VD) were calculated.

RESULTS

In scar and viable tissue, T1 was significantly different over the whole period after contrast, but not before contrast. However, T1 of scar and blood were similar five to 15 minutes post contrast, making the detection of subendocardial defects difficult. lambda reached an initial steady state in viable tissue, but was delayed (20 minutes) in scar tissue. VD in scar was double that of viable tissue (0.54 +/- 0.01 vs. 0.29 +/- 0.02, respectively) indicating an increased interstitial space. Contrast wash-in kinetics correlated moderately with MBF (r = -0.36), but well with the combination of MBF and VD (r = 0.59).

CONCLUSION

Late myocardial contrast kinetics depend on both MBF and VD; however the increased VD seems to be the main mechanism for the late enhancement effect.

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.

The quantification of infarct size

We sought to summarize the published evidence regarding the measurement of infarct size by serum markers, technetium-99m sestamibi single-photon emission computed tomography (SPECT) myocardial perfusion imaging, and magnetic resonance imaging. The measurement of infarct size is an attractive surrogate end point for the early assessment of new therapies for acute myocardial infarction. For each of these three approaches, we reviewed reports published in English providing the clinical validation for the measurement of infarct size and the relevant clinical trial experience. The measurement of infarct size by serum markers has multiple theoretical and practical limitations. The measurement of troponin is promising, but the available data validating this marker are limited. Sestamibi SPECT imaging has five separate lines of published evidence supporting its validity and has received extensive study in multicenter trials. Magnetic resonance imaging has great promise but has less clinical validation and no multicenter trial experience. Therefore, SPECT sestamibi imaging is currently the best available technique for the quantitation of infarct size to assess the incremental treatment benefit of new therapies in multicenter trials of acute myocardial infarction.

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.

Baseline/post-nitrate Tc-99m tetrofosmin mismatch for the assessment of myocardial viability in patients with severe left ventricular dysfunction: comparison with baseline Tc-99m tetrofosmin scintigraphy/FDG PET imaging

BACKGROUND

Positron emission tomography (PET) flow/metabolic mismatch is considered the nuclear medicine gold standard for the assessment of myocardial viability. The aim of this study was to investigate whether baseline/nitrate technetium 99m tetrofosmin single photon emission computed tomography (SPECT) mismatch may provide equivalent clinical information.

METHODS AND RESULTS

We studied 23 patients (aged 62 +/- 10 years, 19 men) with previous myocardial infarction (16 anterior, 4 inferior, and 3 anterior plus inferior) and postischemic heart failure (gated SPECT [G-SPECT] ejection fraction, 26% +/- 8%). All patients underwent Tc-99m tetrofosmin G-SPECT at rest and after nitrates (intravenous isosorbide dinitrate, 0.2 mg/mL, 10 mL/h) as well as a fluorine 18 fluoro-2-deoxy-d-glucose (FDG) PET scan. Regional wall motion analysis was performed with quantitative G-SPECT (QGS). Myocardial dysfunction was defined as a regional QGS score of 2 or greater. Regional perfusion was assessed by quantitative perfusion score (QPS) providing percent Tc-99m tetrofosmin uptake in a 20-segment model. Semiquantitative analysis of FDG uptake was performed by use of polar maps generated by Siemens ECAT HR + software. In areas with a perfusion rate lower than 80%, PET viability was identified by a normalized FDG percent uptake/baseline Tc-99m tetrofosmin percent uptake ratio greater than 1.2. We analyzed 460 segments; 298 (64%) were dysfunctional by QGS analysis. Of these, 170 were viable by PET imaging whereas 128 were nonviable. Regional Tc-99m tetrofosmin uptake was higher in viable than in nonviable segments both at rest (60% +/- 24% vs 42% +/- 12%, P <.01) and after nitrates (67% +/- 20% vs 41% +/- 18%, P <.01). According to receiver operating characteristic curve analysis, a cutoff value of 63% for resting as well as post-nitrate G-SPECT provided the highest diagnostic accuracy for the detection of myocardial viability (67% and 72% at rest and after nitrates, respectively). When the same algorithm used for the comparison with PET (normalized nitrate percent uptake/baseline percent uptake) was applied to G-SPECT, we obtained the highest agreement with PET (accuracy, 93%; sensitivity, 95%; specificity, 92%).

CONCLUSIONS

In patients with severe left ventricular dysfunction, perfusion data alone, both at rest and after nitrates, do not allow an accurate estimate of myocardial viability. In dysfunctioning segments, the analysis of rest/post-nitrate Tc-99m tetrofosmin mismatch provides results similar to those obtained by PET flow/metabolic mismatch.

MR imaging evaluation of myocardial viability in the setting of equivocal SPECT results with (99m)Tc sestamibi

PURPOSE

To determine if contrast material-enhanced magnetic resonance (MR) imaging is useful for assessment of myocardial viability in patients with equivocal stress-rest results from single photon emission computed tomographic (SPECT) examination with technetium 99m sestamibi.

MATERIALS AND METHODS

Twenty patients underwent stress-rest SPECT examinations with sestamibi. Results were considered equivocal for assessment of myocardial infarct on the basis of fixed perfusion defects that either had normal wall motion or exceeded any wall motion abnormalities. Patients then underwent (a). contrast-enhanced MR imaging for assessment of myocardial infarct and (b). cine MR imaging for assessment of wall motion. For image analyses, the left ventricle was divided into 14 segments. Wall motion and extent of infarct were assessed independently and compared.

RESULTS

Forty-one segments were equivocal for infarct at SPECT, and most (21 of 41 [51%]) involved the posterior or inferior wall. Infarct was confirmed with MR imaging in 10 of 41 (24%) equivocal segments in eight patients (40%). An additional 29 segments in eight patients had infarct at MR imaging that was not suspected at SPECT, including segments in three patients with no clinical history of myocardial infarct prior to imaging. All cases of infarct except one that were equivocal or undetected with sestamibi at SPECT were nontransmural at MR imaging, and most of the unsuspected subendocardial infarcts (15 of 28 [54%]) had no associated wall motion abnormalities.

CONCLUSION

Patients with radionuclide examination findings that are equivocal for infarct may benefit from contrast-enhanced MR imaging, particularly in the setting of nontransmural infarct.

Myocardial viability in chronic ischemic heart disease: comparison of contrast-enhanced magnetic resonance imaging with (18)F-fluorodeoxyglucose positron emission tomography

OBJECTIVES

We sought to compare contrast-enhanced magnetic resonance imaging (ceMRI) with nuclear metabolic imaging for the assessment of myocardial viability in patients with chronic ischemic heart disease and left ventricular (LV) dysfunction.

BACKGROUND

Contrast-enhanced MRI has been shown to identify scar tissue in ischemically damaged myocardium.

METHODS

Twenty-six patients with chronic coronary artery disease and LV dysfunction (mean ejection fraction 31 +/- 11%) underwent (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET), technetium-99m tetrofosmin single-photon emission computed tomography (SPECT), and ceMRI. In a 17-segment model, the segmental extent of hyperenhancement (SEH) by ceMRI, defined as the relative amount of contrast-enhanced tissue per myocardial segment, was compared with segmental FDG and tetrofosmin uptake by PET and SPECT.

RESULTS

In severely dysfunctional segments (n = 165), SEH was 9 +/- 14%, 33 +/- 25% (p < 0.05), and 80 +/- 23% (p < 0.05) in segments with normal metabolism/perfusion, metabolism/perfusion mismatch, and matched defects, respectively. Segmental glucose uptake by PET was inversely correlated to SEH (r = -0.86, p < 0.001). By receiver operator characteristic curve analysis, the area under the curve was 0.95 for the differentiation between viable and non-viable segments. At a cutoff value of 37%, SEH optimally differentiated viable from non-viable segments defined by PET. Using this threshold, the sensitivity and specificity of ceMRI to detect non-viable myocardium as defined by PET were 96% and 84%, respectively.

CONCLUSIONS

Contrast-enhanced MRI allows assessment of myocardial viability with a high accuracy, compared with FDG-PET, in patients with chronic ischemic heart disease and LV dysfunction.

Comparison of 99mTc-sestamibi-18F-fluorodeoxyglucose dual isotope simultaneous acquisition and rest-stress 99mTc-sestamibi single photon emission computed tomography for the assessment of myocardial viability

Dual isotope simultaneous acquisition single photon emission computed tomography (DISA SPECT) offers the advantage of obtaining information on myocardial perfusion using Tc-sestamibi ( Tc-MIBI) and metabolism using F-fluorodeoxyglucose ( F-FDG) in a single study. The prerequisite is that the Tc-MIBI images are not degraded by scattered 511 keV photons or poor count statistics due to the lower efficiency of the extra high energy (EHE) collimator. Therefore, we compared the registered Tc-MIBI uptake and image quality of DISA and single isotope acquisition. Furthermore, we investigated whether DISA yields additional information for the assessment of myocardial viability in comparison with rest-stress Tc-MIBI. Nineteen patients with known coronary artery disease and irreversible perfusion defects on previous rest-stress MIBI test studies were investigated. After oral glucose loading and simultaneous injection of 600 MBq of Tc-MIBI and 185 MBq of F-FDG at rest, DISA was performed using energy windows of 140 (+/-15%), 170 (+/-20%) and 511 keV (+/-15%). Planar 140 keV images were corrected for scatter by subtraction using the 170 keV window. The single and dual isotope Tc-MIBI images were both displayed in a polar map with 128 segments normalized to maximum counts. F-FDG and Tc-MIBI images were visually scored for a perfusion-metabolism mismatch pattern using nine regions per heart. There was an excellent correlation (r =0.93, P<0.0001) between the Tc-MIBI uptake detected in the single and dual isotope acquisition. The average difference between the dual and single isotope Tc-MIBI uptake was -1.2% (not significantly different from zero) and the coefficient of variation of the difference was 8.7%. Of the 79 regions with irreversible perfusion defects on previous rest-stress Tc-MIBI, six regions in five patients showed a perfusion-metabolism mismatch pattern. We conclude that DISA does not affect the quality of the Tc-MIBI images. Furthermore, F-FDG- Tc-MIBI DISA may show viability in a small but significant (7.6%, P<0.0034) number of regions with irreversible perfusion defects on rest-stress Tc-MIBI.

MR imaging of myocardial perfusion and viability

CMR is a rapidly developing new modality with applications in clinical cardiology for detection and assessment of myocardial ischemia and viability. CMR perfusion results for the detection of ischemia in comparison with stress echocardiography and scintigraphic techniques are reasonable, but all the studies reported to date have been conduced in selected patients. Larger studies in patient populations reflecting a broader spectrum of disease are necessary before perfusion CMR can be envisaged as a clinically reliable and robust diagnostic tool. Other CMR techniques provide a variety of novel methods of obtaining information on postischemic viability. Signs of viability that can be observed by CMR are the absence of late gadolinium-based contrast enhancement in a myocardial region involved in a recent infarct, any sign of wall thickening at rest (which is detectable with high accuracy by CMR), wall thickening after stimulation by low-dose dobutamine, and preserved wall thickness. Conversely, myocardial necrosis is characterized by signal enhancement of the infarct area after injection of Gd-DTPA, reduced wall thickness in chronic infarcts, and absence of a contractile reserve during dobutamine stimulation. Dobutamine CMR and late enhancement contrast-enhanced CMR predict contractile improvement after revascularization.

Optimal analysis of intravenous myocardial contrast echocardiography for predicting myocardial functional recovery in patients with acute myocardial infarction

OBJECTIVE

This study attempted to determine the optimal interpretation method of intravenous myocardial contrast echocardiography (MCE) for predicting myocardial functional recovery in patients with acute myocardial infarction.

BACKGROUND

Assessment of the myocardial contrast effect is subjective and there is currently no universal agreement on the pulsing interval (PI) for imaging.

METHODS

Twenty-nine patients underwent percutaneous transluminal coronary angioplasty (PTCA) 4.8 +/- 1.9 days after acute myocardial infarction and intravenous MCE before and 24 hours after PTCA by using intermittent harmonic angioimaging at a series of PIs of 4, 8, 12, and 16 cardiac cycles. Adequate contrast enhancement was defined by homogeneous (MCEhomo score) and heterogeneous patterns (MCEheter score), and by a combination of intensity threshold and computed planimetry (MCEcom score). Adequate contrast enhancement at a shorter PI defined a higher MCE score (1 vs 5). The regional wall motion in the risk area was assessed before PTCA and 2 months after PTCA to evaluate functional recovery.

RESULTS

A significant improvement after PTCA was noted in the MCEhomo score (3.2 +/- 1.7 vs 3.6 +/- 1.7, P =.008) and the MCEcom score (2.9 +/- 1.6 vs 3.3 +/- 1.5, P <.0001), but not in the MCEheter score (4.3 +/- 1.3 vs 4.5 +/- 1.1, P =.058). Twenty-four hours after PTCA, segments with functional recovery had a higher MCEheter score (4.9 +/- 0.5 vs 3.8 +/- 1.6, P =.002), MCEhomo score (4.2 +/- 1.4 vs 2.6 +/- 1.9, P <.0001), and MCEcom score (3.8 +/- 1.2 vs 2.1 +/- 1.4, P <.0001) than those without. For the prediction of function recovery, MCEheter generally had a higher sensitivity but a lower specificity and accuracy than did MCEhomo and MCEcom. MCEcom had the best accuracy (83%) with a sensitivity of 95% and specificity of 61% at a PI of 16 cardiac cycles.

CONCLUSION

Using a combination of intensity threshold and computed planimetry for interpreting myocardial contrast enhancement at a long PI can optimize the value of MCE in predicting functional recovery after PTCA in patients with acute myocardial infarction.

Myocardial hibernation in coronary artery disease

Coronary artery disease (CAD) is very prevalent in Western societies and is a leading cause of mortality and morbidity. Despite decreases in mortality rates from CAD over the past 30 years, ischemic heart failure remains an important problem because people with CAD are now living longer. Hibernating myocardium may be defined as reversible left ventricular dysfunction due to chronic CAD that shows improvement in function after revascularization. Many patients with ischemic cardiomyopathy have areas of hibernating myocardium, and thus can potentially show improvement in left ventricular regional and global function if they are revascularized. Whether hibernating myocardium represents an adaptive response to hypoperfusion in the face of chronic ischemia or whether it is a degenerative process is not entirely clear. Clearly, ultrastructural changes of de-differentiation are seen, and include loss of sarcomeres and the appearance of small mitochondria and glycogen accumulation. Although the mechanisms underlying the changes in morphology and depressed contractility, and the factors governing recovery of function are not clear, changes in adrenergic receptor density, cytokine upregulation, and the degree of fibrosis may all play a role. Identification of viability is commonly performed with dobutamine echocardiography or nuclear imaging. Because patients with extensive CAD and poor left ventricular systolic function are high-risk candidates for coronary bypass surgery, the preoperative identification of viability provides important prognostic information. Patients with viable myocardium who are treated with revascularization rather than medical therapy have better outcomes in terms of survival, left ventricular function, symptoms, and exercise capacity.

The histology of viable and hibernating myocardium in relation to imaging characteristics

OBJECTIVES

This study characterizes the histology of myocardium predicted to be hibernating using three different imaging techniques to explain the discordance among them.

BACKGROUND

Both radionuclide and functional imaging techniques were used to assess myocardial hibernation. The former have high sensitivity and the latter high specificity for predicting functional recovery.

METHODS

Nineteen patients underwent thallium-201 and 99m-technetium tetrofosmin myocardial perfusion imaging, and dobutamine magnetic resonance imaging (MRI), prior to coronary bypass grafting. Criteria for predicted hibernation for each technique were defined before operation. Postoperative criteria for scar and true hibernation were also defined. Biopsies were analyzed for myocyte volume fraction (MVF), glycogen deposition and pathologic cell features.

RESULTS

Thallium was most sensitive in predicting hibernation (88%) and MRI most specific (84%); and, although there was good agreement between thallium and tetrofosmin (85%), agreement between MRI and thallium (59%) or tetrofosmin (59%) was poor. For each technique, MVF was higher in segments predicted to be hibernating rather than scar (p < 0.05). The MVF was higher where both thallium and MRI predicted hibernation (0.77+/-0.07) than in segments predicted by thallium alone (0.69+/-0.13, p < 0.05). Proven hibernating segments had a higher MVF than scar (0.72+/-0.11 vs. 0.6+/-0.26, p < 0.05).

CONCLUSIONS

Preservation of myocyte fraction is an important determinant of functional recovery after revascularization. A higher myocyte fraction is required to maintain contractile reserve than to achieve significant tracer uptake. This explains the higher sensitivity of radionuclide imaging compared with dobutamine MRI in the identification of myocardial hibernation.

99mTc-Sestamibi SPECT is a useful technique for viability detection: results of a comparison with NH3/FDG PET

OBJECTIVE

Assessment of myocardial viability by 99mTc-Sestamibi Single Photon Emission Computerized Tomography (SPECT) has been suggested as a more readily available and cheaper alternative to Positron Emission Tomography (PET) with 13N-ammonia (NH3) and 18F-fluoro-deoxy-glucose (FDG). We hypothesized that a semi-quantitative evaluation by SPECT could delineate myocardial viability with an acceptable concordance to PET.

DESIGN

Fifty patients (age 57+/-7 years; ejection fraction 28 +/- 8%), with ischemic cardiomyopathy, underwent SPECT and PET imaging in random order. Viability by SPECT was defined as a defect size <50% of the segment area, or a defect representing > or =50% of the segment but with a mean activity > or =50% of peak activity. PET viability was defined as a perfusion score >2 and FDG score < or =2 (five-point scale, 0 = normal, 4 = absent activity).

RESULTS

By segmental comparison to PET. SPECT yielded a sensitivity and specificity of 87% and 82% for detection of viable myocardium. The positive and negative predictive values were 96% and 58%, respectively.

CONCLUSION

In patients with severe ischemic cardiomyopathy 99mTc-Sestamibi SPECT can delineate viable myocardium with an acceptable segmental concordance to NH3/FDG PET.

Relevance of 99mTc-MIBI rest uptake, ejection fraction and location of contractile abnormality in predicting myocardial recovery after revascularization

The aim of this study was to analyse the influence of rest technetium-99m-methoxy-isobutyl-isonitrile (99mTc-MIBI) uptake, left ventricular ejection fraction (EF) and dysfunctional location in the prediction of myocardial viability. Rest 99mTc-MIBI single photon emission computed tomography (SPECT) was analysed in 82 patients (59+/-9 years, 70 men, 12 women) with one or more segments showing severe hypokinesia, akinesia or dyskinesia who had undergone coronary revascularization. Before and within 3-6 months after the revascularization, gated blood pool scintigraphy was performed. In the post-revascularization control, contractile recovery was observed in 48.7% (155/318) of the segments with severe hypokinesia, akinesia or dyskinesia. Significant increases in sensitivity (53%, 72% and 91%, P<0.0001) and negative predictive value (62%, 68% and 79%, P = 0.01) were observed with decreasing rest uptake 99mTc-MIBI levels of 50%, 40% and 30%, respectively. The decrease in specificity was also significant (67%, 53% and 32%, P<0.0001). The negative predictive value was higher than the positive predictive value mainly in patients with EF < or = 0.35 and with anterior dysfunction. In logistic regression analysis, uptake levels and EF were independent variables that influenced sensitivity and specificity. The negative predictive value was influenced by EF and the positive predictive value only by dysfunctional location. This study suggests that the negative predictive value of 99mTc-MIBI SPECT is higher than the positive predictive value, mainly in patients with EF < or = 0.35, and that the rest uptake level, EF and dysfunctional location are factors that must be considered when results of 99mTc-MIBI SPECT are analysed.

Role of dobutamine echocardiography in detection of myocardial viability for predicting outcome after revascularization in ischemic cardiomyopathy

Coronary artery disease is the most common cause of heart failure in the Western world. Compared with medical therapy, surgical revascularization has been shown to improve survival rates in nonrandomized trials in patients with ischemic cardiomyopathy. However, perioperative mortality is high in this group of patients who do not demonstrate significant viable myocardium. Echocardiography during dobutamine infusion has been shown to reliably detect viable myocardium. Several studies have demonstrated its ability to provide high predictive value for recovery of both regional and global left ventricular function after revascularization. Indeed, nonrandomized studies also have indicated its value in predicting which patients with severe ischemic cardiomyopathy are likely to survive after revascularization. Dobutamine stress echocardiography has emerged as a safe and valuable technique for the assessment of myocardial viability and for the selection of patients for revascularization.

The identification of myocardial hibernation in patients with ischemic heart failure by echocardiography and radionuclide studies

Dobutamine echocardiography and myocardial radionuclide tomography are widely used to assess viability in patients with ischemic cardiomyopathy and left ventricular dysfunction. The main goal of viability evaluation has been the identification of reversible regional dysfunction in the attempt to identify patients in whom revascularization may determine an improvement of global left ventricular ejection fraction. In this application, echocardiographic and radionuclide techniques are used to characterize different pathophysiologic aspects of viable myocardium, ie, integrity of cell membrane and contractile reserve. This explains why the information of the 2 techniques are often divergent and why radionuclide techniques have the highest sensitivity but reduced specificity compared with echocardiography for predicting recovery of regional dysfunction. The identification of residual viable myocardium by either technique is strongly associated with adverse prognosis if the patients are not revascularized, and this substantially contributes to the decision-making process in individual patients. Although it has been assumed that prognostic advantages of revascularization are linked to an increase of ejection fraction, pathophysiologic and clinical observations challenge us with the possibility that benefits of revascularization may also ensue independently on the recovery of ejection fraction through alternative pathophysiologic mechanisms. Therefore, clinical application of viability tests should be evaluated against relevant endpoints, mainly represented by prolongation of life and improvement of life quality, and not by surrogate endpoints as represented by recovery of global ejection fraction. Future studies are needed to assess whether a more clinically oriented approach will provide a better selection of patient candidates for revascularization.