Preoperative positron emission tomographic viability assessment and perioperative and postoperative risk in patients with advanced ischemic heart disease

Myocardial Viability Testing by Positron Emission Tomography: Basic Concepts, Mini-Review of the Literature and Experience From a Tertiary PET Center

Ischemic heart disease ranges in severity from slightly reduced myocardial perfusion with preserved contractile function to chronic occlusion of coronary arteries with myocardial cells replaced by acontractile scar tissue-ischemic heart failure (iHF). Progression towards scar tissue is thought to involve a period in which the myocardial cells are acontractile but still viable despite severely reduced perfusion. This state of reduced myocardial function that can be reversed by revascularization is termed "hibernation." The concept of hibernating myocardium in iHF has prompted an increasing amount of requests for preoperative patient workup, but while the concept of viability is widely agreed upon, no consensus on clinical testing of hibernation has been established. Therefore, a variety of imaging methods have been used to assess hibernation including morphology based (MRI and ultrasound), perfusion based (MRI, SPECT, or PET) and/or methods to assess myocardial metabolism (PET). Regrettably, the heterogeneous body of literature on the subject has resulted in few robust prospective clinical trials designed to assess the impact of preoperative viability testing prior to revascularization. However, the PARR-2 trial and sub-studies has indicated that >5% hibernating myocardium favors revascularization over optimized medical therapy. In this paper, we review the basic concepts and current evidence for using PET to assess myocardial hibernation and discuss the various methodologies used to process the perfusion/metabolism PET images. Finally, we present our experience in conducting PET viability testing in a tertiary referral center.

Functional and metabolic improvement after coronary intervention for non-viable myocardium detected by 18F fluorodeoxyglucose positron emission tomography

We report a case of a 64-year-old man suspected of myocardial infarction two months previously. Coronary angiography revealed total occlusion of the left anterior descending (LAD), and left ventriculography (LVG) showed remarkably reduced cardiac function and anterior dyskinesis. Electrocardiogram-gated thallium-201 Single Photon Emission Tomography (TL-SPECT) and ¹⁸F fluorodeoxyglucose positron emission tomography (FDG) were performed separately, and revealed large anterior myocardial infarction with markedly reduced tracer uptake, suggestive of non-viable myocardium. Percutaneous coronary intervention (PCI) was performed and stent was implanted successfully. Six months after PCI, LVG showed remarkable recovery in global function. Significant wall motion improvement and recovered glucose metabolism were observed in the infarcted myocardium despite having previously been diagnosed as lacking viability. <Learning Objectives: In patients with left ventricular dysfunction, revascularized myocardium can contribute to improve cardiac function and prognosis. This evidence was established for old, or chronic status of myocardial infarction which is defined as over one month from onset of acute myocardial infarction. In this case report, we suggest that it can be premature to determine myocardial viability using FDG for the patient with under pre-chronic status after myocardial infarction due to underestimation on myocardial FDG uptake.>.

Multimodality imaging assessment of mitral valve anatomy in planning for mitral valve repair in secondary mitral regurgitation

Secondary mitral regurgitation (MR) is frequent valvular heart disease and conveys worse prognostic. Therapeutic surgical or percutaneous options are available in the context of severe symptomatic secondary MR, but the best approach to treat these patients remains unclear, given the lack of clear clinical evidence of benefit. A comprehensive evaluation of the mitral valve apparatus and the left ventricle (LV) has the ability to clearly define and characterize the disease, and thus determine the best option for the patient to improve its clinical outcomes, as well as quality of life and symptoms. The current report reviews the mitral valve (MV) anatomy, the underlying mechanisms associated with secondary MR, the related therapeutic options available, and finally the usefulness of a multimodality imaging approach for the planning of surgical or percutaneous mitral valve intervention.

Imaging Techniques for the Assessment of Myocardial Perfusion

One of the most significant causes of heart failure is coronary heart disease and subsequent left ventricular dysfunction. The prognosis and perioperative mortality are influenced by left ventricular function, which is also an important predictor marker following revascularization. The evaluation of myocardial perfusion is of utmost importance in patients who present several symptoms before choosing cardiac catheterization as treatment. The evaluation of myocardial perfusion and myocardial viability leads to superior diagnostic and treatment algorithms, thus resulting in an important improvement in the outcomes of patients with coronary artery disease. Color Doppler myocardial imaging, single-photon emission computed tomography (SPECT), contrast perfusion echocardiography, positron emission computed tomography (PET) and magnetic resonance imaging (MRI) are currently used methods for assessing myocardial perfusion. This review aims to summarize the benefits and disadvantages of each of these techniques.

Role of PET-CT in the assessment of myocardial viability in patients with left ventricular dysfunction

AIM

Role of PET-CT in assessment of myocardial viability in patients with LV dysfunction.

METHODS

This prospective study included 120 patients with LV dysfunction who underwent 99mTechnetium-Sestamibi myocardial perfusion SPECT-CT and 18FFDG cardiac PET-CT. They also underwent serial echocardiography and coronary angiography along with myocardial perfusion and FDG PET study.

RESULTS

Thirty-three patients had single vessel disease, 48 had triple vessel disease, and rest had double vessel disease. Among 786 segments, matched defects were seen in 432 (55%) and mismatched defects in 354 (45%) segments. 78 patients were surgically managed, and 42 were medically managed. The change in LVEF after surgical management was statistically significant compared to medical management.

CONCLUSION

Viability assessment should be performed in patients who present after 12h of acute myocardial infarction or with LV dysfunction due to ischemic heart disease to decide upon appropriate surgical management.

Mid-term results of coronary bypass graft surgery in patients with ischaemic left ventricular systolic dysfunction and no detected myocardial viability

OBJECTIVES

There are concerns about effects of surgical revascularization on patients with ischaemic systolic dysfunction when no signs of myocardial viability have been detected by nuclear imaging preoperatively. We reviewed our data to determine the efficacy of coronary bypass graft in this special patient cohort.

METHODS

A retrospective review with prospectively collected clinical data was conducted on 87 consecutive patients between 2000 and 2012 whose left ventricular ejection fraction was less than 40%. All patients received positron emission tomography examination before undergoing coronary artery bypass graft and showed no signs of myocardial viability. Improvements in ejection fraction, postoperative re-examination of myocardial viability by nuclear imaging and freedom from major cardiac events were observed. Survival was calculated using Kaplan-Meier analysis.

RESULTS

The 30-day mortality rate was 7%. Ejection fraction improvement (defined as over 5%) was observed in 13 (16%) patients within 6 months postoperatively. Ejection fraction improvement was observed in 46 (58%) patients by the end of the first year and 50 (63%) patients by the second year. It was noted that 25 (32%) and 43 (54%) patients progressed to heart functional class I or II at 1 and 5 years, respectively. Positron emission tomography examination showed enhanced myocardial viability in the non-viable ventricular wall segment in 53 (67%) patients at 1 year. Freedom from major adverse cardiac events was observed in 56 (71%) patients at 1 year and 47 (60%) patients at 5 years. Survival rates were 82 and 66% at 1 and 5 years, respectively.

CONCLUSIONS

Coronary artery bypass graft proved to be a positive choice of treatment for patients with severe ischaemic systolic dysfunction when there was no viable myocardium detected through nuclear imaging.

Myocardial viability as integral part of the diagnostic and therapeutic approach to ischemic heart failure

Chronic heart failure is a major public-health problem with a high prevalence, complex treatment, and high mortality. A careful and comprehensive analysis is needed to provide optimal (and personalized) therapy to heart failure patients. The main 4 non-invasive imaging techniques (echocardiography, magnetic resonance imaging, multi-detector-computed tomography, and nuclear imaging) provide information on cardiovascular anatomy and function, which form the basis of the assessment of the pathophysiology underlying heart failure. The selection of imaging modalities depends on the information that is needed for the clinical management of the patients: (1) underlying etiology (ischemic vs non-ischemic); (2) in ischemic patients, need for revascularization should be evaluated (myocardial ischemia/viability?); (3) left ventricular function and shape assessment; (4) presence of significant secondary mitral regurgitation; (5) device therapy with cardiac resynchronization therapy and/or implantable cardiac defibrillator (risk of sudden cardiac death). This review is dedicated to assessment of myocardial viability, however "isolated assessment of myocardial viability" may be clinically not meaningful and should be considered among all those different variables. This complete information will enable personalized treatment of the patient with ischemic heart failure.

Serial dual single-photon emission computed tomography of thallium-201 and iodine-123 beta-methyliodophenyl pentadecanoic acid scintigraphy can predict functional recovery of patients with coronary artery disease after coronary artery bypass graft surgery

BACKGROUND

A mismatch between thallium-201 ((201)Tl) and iodine-123 ((123)I)-beta-methyl iodophenyl pentadecanoic acid (BMIPP) dual single-photon emission computed tomography (SPECT) reflects a dysfunctional but viable myocardium, such as stunned or hibernating myocardium, in patients with coronary artery disease (CAD). However, the cardiac function does not always improve after revascularization. The present study aimed to determine whether serial (201)Tl and (123)I-BMIPP dual SPECT can predict improvements in cardiac function after coronary artery bypass graft surgery (CABG) in patients with CAD.

MATERIALS AND METHODS

The study included 98 patients with CAD requiring CABG and having a left ventricular ejection fraction (LVEF) less than 50%. The total defect score (TDS) was calculated from (201)Tl and (123)I-BMIPP dual-SPECT images acquired before and 3 weeks after CABG. The LVEF, left ventricular end-diastolic volume index, and end-systolic volume index were determined by means of contrast left ventriculography before and 6 months after CABG.

RESULTS

After 6 months, LVEF improved by 5% or more in 62 patients (group A) but did not improve in the remaining 36 patients (group B). Baseline Tl-TDS was significantly lower (9.1±4.6 vs. 14.6±6.5, P<0.001), and the mismatch score (BMIPP-TDS-Tl-TDS) was significantly higher (6.9±4.2 vs. 4.2±3.9, P=0.002) in group A than in group B. The extent of change in BMIPP-TDS 3 weeks after CABG compared with that before (delta-BMIPP-TDS) was significantly greater in group A than in group B (-5.9±3.0 vs. 2.8±4.3, P<0.001). Stepwise multivariate analysis selected delta-BMIPP-TDS as a significant independent predictor of improvement in LVEF at 6 months after CABG (multivariate β-coefficient=-0.718, P<0.001). The degree of change in LVEF 6 months after CABG compared with that before significantly and negatively correlated with delta-BMIPP-TDS (r=-0.631, P<0.001).

CONCLUSION

The delta-BMIPP-TDS evaluated by serial (201)Tl and (123)I-BMIPP dual SPECT can predict improvements in cardiac function during the chronic phase of CAD.

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.

Intracardiac acoustic radiation force impulse (ARFI) and shear wave imaging in pigs with focal infarctions

Four pigs, three with focal infarctions in the apical intraventricular septum (IVS) and/or left ventricular free wall (LVFW), were imaged with an intracardiac echocardiography (ICE) transducer. Custom beam sequences were used to excite the myocardium with focused acoustic radiation force (ARF) impulses and image the subsequent tissue response. Tissue displacement in response to the ARF excitation was calculated with a phase-based estimator, and transverse wave magnitude and velocity were each estimated at every depth. The excitation sequence was repeated rapidly, either in the same location to generate 40 Hz M-modes at a single steering angle, or with a modulated steering angle to synthesize 2-D displacement magnitude and shear wave velocity images at 17 points in the cardiac cycle. Both types of images were acquired from various views in the right and left ventricles, in and out of infarcted regions. In all animals, acoustic radiation force impulse (ARFI) and shear wave elasticity imaging (SWEI) estimates indicated diastolic relaxation and systolic contraction in noninfarcted tissues. The M-mode sequences showed high beat-to-beat spatio-temporal repeatability of the measurements for each imaging plane. In views of noninfarcted tissue in the diseased animals, no significant elastic remodeling was indicated when compared with the control. Where available, views of infarcted tissue were compared with similar views from the control animal. In views of the LVFW, the infarcted tissue presented as stiff and non-contractile compared with the control. In a view of the IVS, no significant difference was seen between infarcted and healthy tissue, whereas in another view, a heterogeneous infarction was seen to be presenting itself as non-contractile in systole.

Decision making and results of coronary artery bypass grafting for patients with poor left ventricular function

BACKGROUND

The aim of this study is to determine the results of coronary artery bypass surgery in patients with a low ejection fraction. Between January 2007 and January 2011, 3556 consecutive patients who underwent coronary artery bypass grafting at the Cardiovascular Surgery Clinic at Sifa University Hospital, Izmir, Turkey, were analyzed retrospectively.

METHODS

The patients were divided into 2 groups. Patients undergoing isolated first-time elective coronary bypass surgery were classified according to their preoperative ejection fraction; Patients in Group I had an ejection fraction between 20% and 35% with poor left ventricular function (n = 1246; 695 men and 551 women; mean age, 62.25 ± 5.72 years, range, 47-78 years). Control patients in Group II underwent elective coronary artery bypass grafting at the same time and had left ventricular ejection fraction between 36% and 49% (n = 2310; 1211 men and 1099 women; mean age, 61.83 ± 8.12 years, range, 41-81 years). The mean follow-up time for all patients was 24 ± 9.4 months (range, 12-48 months). Patients were followed postoperatively at the end of the first month and every 6 months. The left ventricular ejection fraction was assessed by transthoracic echocardiography.

RESULTS

The mean number of distal anastomoses, myocardial infarction, and mean age was not significantly different between the 2 groups; however, cross-clamp time was longer in Group I. Patient recovery time was significantly longer in Group I. Morbidity (14.5% in Group I versus 7.4% in Group II, P < .005) and mortality (1.76% versus 0.30%, P < .005) were higher in Group I. During late follow-up, the 2-year survival rate (85.1% versus 94.5%) and 2-year event-free rate (77.6% versus 86.9%) were significantly lower in Group I when compared to Group II. Postoperative left ventricular ejection fraction values were significantly superior in Group I compared to Group II.

CONCLUSION

Coronary artery bypass grafting can be safely performed in patients with low ejection fraction with minimal postoperative morbidity and mortality. The viable myocardium could be reliably determined by positron emission tomography. Low ejection fraction patients could greatly benefit from coronary bypass surgery regarding postoperative ejection fraction, increased long-term survival, improvement in New York Heart Association classification, and higher quality of life.

Cardiac stem cells in patients with ischemic cardiomyopathy: discovery, translation, and clinical investigation

The increasing prevalence of heart failure, in the US and worldwide, poses a significant burden to patients, practitioners, and healthcare systems. Hence, there is a pressing need for alternative therapies to enhance the current treatment armamentarium. Accordingly, when considering heart failure of ischemic etiology, an intervention designed to regenerate the attending loss of myocardium could potentially result in improved cardiac function, functional status, and quality of life. Significant strides have been made by investigators in the study of stem cell therapy for cardiac repair; recently with cardiac-derived progenitor cells. These cells include cardiospheres, cardiosphere-derived cells, and c-kit positive cardiac stem cells. Herein, a review of both preclinical studies and phase I clinical trials of these cell types is presented. A detailed account of in vitro characterization, in vivo bioactivity, and safety and efficacy in humans is outlined. Thus far, encouraging results have been realized, although larger studies have yet to be undertaken.

Assessment of myocardial perfusion and viability by positron emission tomography

An important evolution has taken place recently in the field of cardiovascular Positron Emission Tomography (PET) imaging. Being originally a highly versatile research tool that has contributed significantly to advance our understanding of cardiovascular physiology and pathophysiology, PET has gradually been incorporated into the clinical cardiac imaging portfolio contributing to diagnosis and management of patients investigated for coronary artery disease (CAD). PET myocardial perfusion imaging (MPI) has an average sensitivity and specificity around 90% for the detection of angiographically significant CAD and it is also a very accurate technique for prognostication of patients with suspected or known CAD. In clinical practice, Rubidium-82 ((82)Rb) is the most widely used radiopharmaceutical for MPI that affords also accurate and reproducible quantification in absolute terms (ml/min/g) comparable to that obtained by cyclotron produced tracers such as Nitrogen-13 ammonia ((13)N-ammonia) and Oxygen-15 labeled water ((15)O-water). Quantification increases sensitivity for detection of multivessel CAD and it may also be helpful for detection of early stages of atherosclerosis or microvascular dysfunction. PET imaging combining perfusion with myocardial metabolism using (18)F-Fluorodeoxyglucose ((18)F FDG), a glucose analog, is an accurate standard for assessment of myocardial hibernation and risk stratification of patients with left ventricular dysfunction of ischemic etiology. It is helpful for guiding management decisions regarding revascularization or medical treatment and predicting improvement of symptoms, exercise capacity and quality of life post-revascularization. The strengths of PET can be increased further with the introduction of hybrid scanners, which combine PET with computed tomography (PET/CT) or with magnetic resonance imaging (PET/MRI) offering integrated morphological, biological and physiological information and hence, comprehensive evaluation of the consequences of atherosclerosis in the coronary arteries and the myocardium.

Layer-specific analysis of myocardial deformation for assessment of infarct transmurality: comparison of strain-encoded cardiovascular magnetic resonance with 2D speckle tracking echocardiography

AIMS

Separate analysis of endocardial and epicardial myocardial layer deformation has become possible using strain-encoded cardiovascular magnetic resonance (SENC) and 2D-dimensional speckle tracking echocardiography (Echo). This study evaluated and compared both modalities for the assessment of infarct transmurality as defined by late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR).

METHODS AND RESULTS

In 29 patients (age 62.4 ± 11.7 years, 23 male) with ischaemic cardiomyopathy, SENC using 1.5 T CMR and Echo were performed. Peak circumferential systolic strain of the endocardial and the epicardial layer of 304 myocardial segments was assessed by SENC and by Echo. The segmental transmurality of myocardial infarction was determined as relative amount of LGE (0%: no infarction; 1-50%: non-transmural infarction; 51-100%: transmural infarction). Endocardial and epicardial strain defined by SENC and by Echo differed significantly between segments of different infarct transmurality determined by CMR. Endocardial layer circumferential strain analysis by Echo and by SENC allowed distinction of segments with non-transmural infarction from non-infarcted segments with similar accuracy [area under the curve (AUC) 0.699 vs. 0.649, respectively, P = 0.239]. Epicardial layer circumferential strain analysis by Echo and by SENC allowed distinction of transmural from non-transmural myocardial infarction defined by LGE CMR with similar accuracy (AUC 0.721 vs. 0.664, respectively, P = 0.401). Endocardial strain by SENC correlated moderately with endocardial strain by Echo (r = 0.50; standard error of estimate = 5.2%).

CONCLUSION

Layer-specific analysis of myocardial deformation by Echo and by SENC allows discrimination between different transmurality categories of myocardial infarction with similar accuracy. However, accuracy of both methods is non-optimal, indicating that further tools for improvement should be evaluated in the future.

Gadobutrol for magnetic resonance imaging of chronic myocardial infarction: intraindividual comparison with gadopentetate dimeglumine

OBJECTIVES

To compare 0.15 mmol/kg gadobutrol with 0.20 mmol/kg gadopentetate dimeglumine with regard to late gadolinium enhancement (LGE) of infarcted myocardium at magnetic resonance (MR) imaging.

MATERIALS AND METHODS

Twenty patients with history of chronic myocardial infarction underwent 2 cardiac MR examinations at 1.5 Tesla. For the evaluation of myocardial infarction, late gadolinium enhancement (LGE) imaging was performed with an inversion recovery-prepared gradient-echo sequence 15 minutes after administration of either gadobutrol (r1 = 5.2 mmol(-1)s(-1)) or gadopentetate dimeglumine (r1 = 4.1 mmol(-1)s(-1)). The dose of the contrast agents was adjusted based on the relaxivity of both contrast agents. Hence, gadobutrol and gadopentetate dimeglumine were administered at 0.15 mmol/kg and 0.20 mmol/kg, respectively. Contrast-to-noise ratios (CNR) between infarcted myocardium and remote myocardium (CNR remote) and between infarcted myocardium and left ventricular lumen (CNR lumen) were assessed by 2 independent readers. Additionally, infarct size was assessed semiautomatically by using a threshold of 5 standard deviations above the mean signal intensity of remote myocardium.

RESULTS

Subendocardial or transmural LGE was present in 16 of 20 (80%) patients. The optimal inversion time for LGE imaging did not differ significantly between gadobutrol and gadopentetate dimeglumine (275 ± 21 milliseconds [range, 240-320 milliseconds] and 282 ± 23 milliseconds [range, 240-330 milliseconds], respectively; P = 0.32). The CNR remote after administration of gadobutrol (40.0 ± 4.6; 95% confidence interval [CI]: 30.3; 49.7) and gadopentetate dimeglumine (40.6 ± 4.6; 95% CI: 30.9; 50.3) did not show significant differences (P = 0.90), whereas gadobutrol yielded a significantly higher CNR lumen (6.2 ± 3.6; 95% CI: -1.5; 13.9) compared with gadopentetate dimeglumine (0.8 ± 3.6; 95% CI: -6.9; 8.5). Infarct size after administration of gadobutrol (23.7 ± 4.7 mL; 95% CI: 13.6; 33.7) and gadopentetate dimeglumine (23.7 ± 4.7 mL;95% CI: 13.7; 33.8) was not statistically different (P = 0.94). There was an excellent correlation between gadobutrol- and gadopentetate dimeglumine-enhanced assessment of infarct size (Spearman r = 0.99 and r = 0.97 for reader 1 and 2, respectively).

CONCLUSION

This pilot study shows that 0.15 mmol/kg gadobutrol is an effective contrast agent for LGE imaging with better delineation of infarcted myocardium from left ventricular lumen than 0.20 mmol/kg gadopentetate dimeglumine.

Evaluation of myocardial viability with cardiac magnetic resonance imaging

Assessment of myocardial viability is of clinical and scientific significance. Traditionally, the detection of myocardial viability (either stunning or hibernation) has been used in aiding diagnosis before revascularization, especially in high-risk patients. There is a considerable body of observational evidence showing substantial improvement after revascularization in patients with significant left ventricular dysfunction and myocardial viability. Recent randomized evidence has questioned the benefit of viability testing but must be interpreted with caution. Dobutamine stress echocardiography, nuclear imaging, and cardiovascular magnetic resonance are the mainstays of viability testing and provide information on contractile function, cellular metabolism, and myocardial fibrosis, respectively. Larger, multicenter trials with outcome data are needed to define the nature of viability testing and, particularly, cardiovascular magnetic resonance in moderate-to-severe ischemic cardiomyopathy.

PET and PET/CT in cardiovascular disease

The present review provides an overview of the role of cardiac positron emission tomography in the diagnosis and management of cardiovascular disease. It expands on the relative advantages and disadvantages over other imaging modalities as well as the available evidence supporting its value in the diagnosis and management of patients with coronary artery disease, the assessment of myocardial viability, and evaluation of the cardiac sympathetic nervous system. Furthermore, the recent developments, such as the implementation of high-end computed tomography devices to form hybrid systems, and the advances of molecular imaging probes in experimental applications are briefly discussed.

Radionuclide Imaging of Viable Myocardium: Is it Underutilized?

Coronary artery disease is the major cause of heart failure in North America. Viability assessment is important as it aims to identify patients who stand to benefit from coronary revascularization. Radionuclide modalities currently used in the assessment of viability include (201)Tl SPECT, (99m)Tc-based SPECT imaging, and (18)F-fluorodexoyglucose ((18)F-FDG)-PET imaging. Different advances have been made in the last year to improve the sensitivity and specificity of these modalities. In addition, the optimum amount of viable (yet dysfunctional) myocardium is important to identify in patients, as a risk-benefit ratio must be considered. Patients with predominantly viable/hibernating myocardium can benefit from revascularization from a mortality and morbidity standpoint. However, in patients with minimal viability (predominantly scarred myocardium), revascularization risk may certainly be too high to justify revascularization without expected benefit. Understanding different radionuclide modalities and new developments in the assessment of viability in ischemic heart failure patients is the focus of this discussion.

Myocardial perfusion reserve after a PET-driven revascularization procedure: a strong prognostic factor

Not all patients treated on the basis of PET-proven viability benefit from revascularization. Myocardial perfusion reserve (MPR) predicts survival in patients not undergoing revascularization. In the present study, we investigated whether MPR is related to survival in ischemic heart disease (IHD) patients after a PET-driven intervention.

METHODS

Between 1995 and 2003, 119 consecutive patients with chronic IHD underwent a PET-driven revascularization procedure based on ischemia-viability assessment with PET. Patients were followed for all-cause mortality and major cardiovascular events.

RESULTS

One hundred nineteen patients underwent a PET-driven revascularization procedure (67 percutaneous coronary interventions, 52 coronary artery bypass grafts) because of angina complaints. The mean age was 67 ± 11 y (96 men, 23 women); global left ventricle MPR was 1.54 ± 0.43. MPR intertertile boundaries were 1.34 and 1.67. Significantly more cardiac deaths were observed in the lowest and middle MPR tertiles than in the highest tertile. The age- and sex-corrected hazard ratio for the middle tertile was 8.3 (95% confidence interval, 1.02-68.3) and for the lowest tertile 23.6 (95% confidence interval, 3.1-179) (P = 0.002). After left ventricular ejection fraction (LVEF) and viability were added to the model, MPR remained significant, with hazard ratios of 6.5 (0.8-54.4) and 18.5 (2.3-145.5) (P = 0.004), whereas neither LVEF nor viability reached significance in this model. Comparable results were found for major adverse cardiac events, with hazard ratios of 3.15 (0.82-12.0) and 8.24 (2.36-28.8) (P = 0.002).

CONCLUSION

Patients with IHD revascularized on the basis of PET viability assessment who have a low MPR are at risk for cardiac death and subsequent cardiac events. MPR is a more sensitive predictor for cardiac death than LVEF and extent of viability.

Quantification of myocardial viability distribution with Gd(DTPA) bolus-enhanced, signal intensity-based percent infarct mapping

INTRODUCTION

A substantial, common shortcoming of the currently used semiautomated techniques for the quantification of myocardial infarct with delayed enhancement magnetic resonance imaging is the assumption that the whole myocardial slab that corresponds to the hyperenhanced tomographic area is 100% nonviable. This assumption is, however, incorrect. To resolve this conflict, we have recently proposed the signal intensity percent-infarct mapping method and validated it in an ex vivo, canine experiment. The purpose of the current study has been the validation of the signal intensity percent-infarct mapping method in vivo, using a porcine model of reperfused myocardial infarct.

METHODS

In swines (n=6), reperfused myocardial infarct was generated occluding for 90 min by an angioplasty balloon either the left anterior descending or the left circumflex coronary artery. To obtain DE images, Gd(DTPA) enhanced inversion-recovery fast gradient-echo acquisitions were carried out on day 28 after myocardial infarction. Scanning started 15 min after intravenous injection of 0.2 mmol/kg Gd(DTPA). At the end of the MRI session, the animal was sacrificed and 2,3,5-triphenyltetrazolium chloride staining was used to validate the existence and to determine the accurate size of the myocardial infarct. Tissue samples were taken and stained with hematoxylin-eosin and Masson's trichrome for histological assessment of the infarct and the periinfarct zone. The signal intensity percent-infarct mapping data were compared with corresponding data from the delayed enhancement images analyzed with SI(remote+2S.D.) thresholding, and with corresponding triphenyltetrazolium-chloride staining data using Friedman's repeated measure analysis of variance on ranks.

RESULTS

The infarct volume determined by the triphenyltetrazolium chloride, SI(remote+2S.D.) and signal intensity percent-infarct mapping methods was 3.04 ml [2.74, 3.45], 13.62 ml [9.06, 18.45] and 4.27 ml [3.45, 6.33], respectively. Median infarct volume determined by SI(remote+2S.D.) significantly differed from that determined by triphenyltetrazolium chloride (P<.05). The Bland-Altman overall bias was 12.49% of the volume of the left ventricle. Median infarct volume determined by signal intensity percent-infarct mapping, however, did not differ significantly (NS) from that obtained by triphenyltetrazolium chloride. Signal intensity percent-infarct mapping yielded only a 1.99% Bland-Altman overall bias of the left ventricular volume.

CONCLUSIONS

This in vivo study in the porcine reperfused myocardial infarct model demonstrates that signal intensity percent-infarct mapping is a highly accurate method for the determination of the extent of myocardial infarct. MRI images for signal intensity percent-infarct mapping are obtained with the pulse sequence of conventional delayed enhancement imaging and are acquired within clinically acceptable scanning time. This makes signal intensity percent-infarct mapping a practical method for clinical implementation.

18F-FDG PET imaging of myocardial viability in an experienced center with access to 18F-FDG and integration with clinical management teams: the Ottawa-FIVE substudy of the PARR 2 trial

(18)F-FDG PET may assist decision making in ischemic cardiomyopathy. The PET and Recovery Following Revascularization (PARR 2) trial demonstrated a trend toward beneficial outcomes with PET-assisted management. The substudy of PARR 2 that we call Ottawa-FIVE, described here, was a post hoc analysis to determine the benefit of PET in a center with experience, ready access to (18)F-FDG, and integration with clinical teams.

METHODS

Included were patients with left ventricular dysfunction and suspected coronary artery disease being considered for revascularization. The patients had been randomized in PARR 2 to PET-assisted management (group 1) or standard care (group 2) and had been enrolled in Ottawa after August 1, 2002 (the date that on-site (18)F-FDG was initiated) (n = 111). The primary outcome was the composite endpoint of cardiac death, myocardial infarction, or cardiac rehospitalization within 1 y. Data were compared with the rest of PARR 2 (PET-assisted management [group 3] or standard care [group 4]).

RESULTS

In the Ottawa-FIVE subgroup of PARR 2, the cumulative proportion of patients experiencing the composite event was 19% (group 1), versus 41% (group 2). Multivariable Cox proportional hazards regression showed a benefit for the PET-assisted strategy (hazard ratio, 0.34; 95% confidence interval, 0.16-0.72; P = 0.005). Compared with other patients in PARR 2, Ottawa-FIVE patients had a lower ejection fraction (25% +/- 7% vs. 27% +/- 8%, P = 0.04), were more often female (24% vs. 13%, P = 0.006), tended to be older (64 +/- 10 y vs. 62 +/- 10 y, P = 0.07), and had less previous coronary artery bypass grafting (13% vs. 21%, P = 0.07). For patients in the rest of PARR 2, there was no significant difference in events between groups 3 and 4. The observed effect of (18)F-FDG PET-assisted management in the 4 groups in the context of adjusted survival curves demonstrated a significant interaction (P = 0.016). Comparisons of the 2 arms in Ottawa-FIVE to the 2 arms in the rest of PARR 2 demonstrated a trend toward significance (standard care, P = 0.145; PET-assisted management, P = 0.057).

CONCLUSION

In this post hoc group analysis, a significant reduction in cardiac events was observed in patients with (18)F-FDG PET-assisted management, compared with patients who received standard care. The results suggest that outcome may be benefited using (18)F-FDG PET in an experienced center with ready access to (18)F-FDG and integration with imaging, heart failure, and revascularization teams.

Impact of preoperative positron emission tomography in patients with severely impaired LV-function undergoing surgical revascularization

In patients with ischemic cardiomyopathy, coronary artery bypass grafting (CABG) offers an important therapeutic option but is still associated with high perioperative mortality. Although previous studies suggest a benefit from revascularization for patients with defined viability by a non-invasive technique, the role of viability assessment to determine suitability for revascularization in patients with ischemic cardiomyopathy has not yet been defined. This study evaluates the hypothesis that the use of PET imaging in the decision-making process for CABG will improve postoperative patient survival. We reviewed 476 patients with ischemic cardiomyopathy (LV ejection fraction ≤0.35) who were considered candidates for CABG between 1994 and 2004 on the basis of clinical presentation and angiographic data. In a Standard Care Group, 298 patients underwent CABG. In a second PET-assisted management group of 178 patients, 152 patients underwent CABG (PET-CABG) and 26 patients were excluded from CABG because of lack of viability (PET-Alternatives). Primary endpoint was postoperative survival. There were two in hospital deaths in the PET-CABG (1.3%) and 30 (10.1%) in the Standard Care Group (P = 0.018). The survival rate after 1, 5 and 9.3 years was 92.0, 73.3 and 54.2% in the PET-CABG and 88.9, 62.2 and 35.5% in the Standard Care Group, respectively (P = 0.005). Cox-regression analysis revealed a significant influence on long-term survival of patient selection by viability assessment via PET (P = 0.008), of LV-function (P = 0.017), and age >70 (P = 0.016). Preoperative assessment of myocardial viability via PET identifies patients, who will benefit most from CABG.

PET and MRI in cardiac imaging: from validation studies to integrated applications

INTRODUCTION

Positron emission tomography (PET) is the gold standard for non-invasive assessment of myocardial viability and allows accurate detection of coronary artery disease by assessment of myocardial perfusion. Magnetic resonance imaging (MRI) provides high resolution anatomical images that allow accurate evaluation of ventricular structure and function together with detection of myocardial infarction.

OBJECTIVE

Potential hybrid PET/MR tomography may potentially facilitate the combination of information from these imaging modalities in cardiology. Furthermore, the combination of anatomical MRI images with the high sensitivity of PET for detecting molecular targets may extent the application of these modalities to the characterization of atherosclerotic plaques and to the evaluation of angiogenetic or stem cell therapies, for example.

DISCUSSION

This article reviews studies using MRI and PET in parallel to compare their performance in cardiac applications together with the potential benefits and applications provided by hybrid PET/MRI systems.

Prognostic performance of quantitative PET tools for stratification of patients with ischemic cardiomyopathy undergoing myocardial viability assessment

OBJECTIVES

This study was performed to determine the prognostic performance of quantitative PET tools in the stratification of patients with ischemic cardiomyopathy undergoing myocardial viability assessment.

METHODS

We applied four different quantitative tools to 104 consecutive patients with coronary artery disease and previous myocardial infarction who had undergone rest Rb/gated F-fluorodeoxyglucose (FDG) PET, to assess myocardial viability for potential revascularization. One of these tools was based on the FDG study alone and the other three tools assessed the extent of match/mismatch defects using FDG in comparison with a perfusion reference database. The four quantitative tools used in this research to define viability were (i) FDG alone, which calculates the percentage of left ventricular myocardium (LVM) that is above the 50% of the maximum LVM FDG counts, (ii) low flow match/mismatch, which determines the area with a 5% increase in normalized FDG counts in relation to defined resting perfusion defects as compared with a reference database, (iii) all regions match/mismatch, which computes the area with a 10% increase in normalized FDG counts in relation to the left ventricle resting perfusion distribution, and (iv) percentage max FDG match/mismatch, which defines the area with FDG uptake greater than 60% of the maximum LVM FDG counts within defined perfusion defects as determined by the reference database. The primary endpoint for this analysis was cardiac death.

RESULTS

During the follow-up period (22+/-14 months), 19 patients (18%) died; in 17 of these the cause of death was cardiac. Using univariate analysis, none of the methods were predictive of cardiac death. Receiver operating characteristic analysis defined the optimal thresholds for the extent of myocardial viability for the four tools in the prediction of cardiac death: FDG alone=20%, low flow match/mismatch=15%, all regions match/mismatch=35%, and percentage max FDG match/mismatch=20%. A censored survival analysis using a Kaplan-Meier method showed a statistically significant difference between patients with cardiac death and those with no cardiac death using only the low flow match/mismatch (hazard ratio=0.29, P=0.01) and percentage max FDG match/mismatch criteria (hazard ratio=0.23, P=0.005) tools.

CONCLUSION

The low flow match/mismatch and percentage max FDG match/mismatch quantitative PET tools are useful for prognostic stratification of patients with ischemic cardiomyopathy undergoing myocardial viability assessment.

[Assessment of myocardial viability in postinfarction and indications of revascularization]

Following myocardial infarction, it is indispensable to investigate the viability of the myocardium when signs of left ventricular dysfunction are predominant, so as to distinguish between permanent ventricular dysfunction and dysfunction that can be improved with treatment. Several imaging techniques are capable of detecting viable hibernating myocardium; each addresses a specific aspect of the problem. Stress echocardiography and nuclear imaging techniques remain the most widely used even though new techniques like MRI may be better for detecting myocardial viability. Remote myocardial revascularization can lead to regression of the remodeling of the left ventricle, which occurs after infarction causing latent or patent cardiac failure, and thus to recovery of left ventricular function. It is therefore indicated, in association with optimal medical treatment, in patients selected by viability explorations. The best revascularization method (angioplasty or surgery) should be proposed according to scientific knowledge, the comorbidities, and the patient's choice.

Identification of hibernating myocardium with myocardial contrast echocardiography

Very little is known about the accuracy of intravenous myocardial contrast echocadiography (MCE) in the detection of myocardial hibernation. There are also currently no data on the comparison of MCE to late gadolinium-enhanced magnetic resonance (LGE-MR) in this clinical setting. The aim of this pilot study was to predict recovery of regional function in patients with ischemic LV dysfunction undergoing bypass surgery and to compare the accuracy of MCE with LGE-MR in this clinical setting. The sensitivity of preserved myocardial perfusion during MCE for segmental function recovery (hibernating myocardium) of akinetic segments was 78% and was similar to LGE-MR (87%, p--NS). Specificity of MCE was higher than for LGE-CMR (72%, and 52%, respectively; p<0.01). This pilot study has showed good diagnostic accuracy of MCE for prediction of function recovery after bypass surgery, which is comparable to "gold standard" in assessing myocardial viability--LGE-MR.