Value of metabolic imaging with positron emission tomography for evaluating prognosis in patients with coronary artery disease and left ventricular dysfunction

Functional and Metabolic Imaging in Heart Failure with Preserved Ejection Fraction: Promises, Challenges, and Clinical Utility

Heart failure with preserved ejection fraction (HFpEF) is recognised as an increasingly prevalent, morbid and burdensome condition with a poor outlook. Recent advances in both the understanding of HFpEF and the technological ability to image cardiac function and metabolism in humans have simultaneously shone a light on the molecular basis of this complex condition of diastolic dysfunction, and the inflammatory and metabolic changes that are associated with it, typically in the context of a complex patient. This review both makes the case for an integrated assessment of the condition, and highlights that metabolic alteration may be a measurable outcome for novel targeted forms of medical therapy. It furthermore highlights how recent technological advancements and advanced medical imaging techniques have enabled the characterisation of the metabolism and function of HFpEF within patients, at rest and during exercise.

Complications of Vascular Disease

Vascular diseases and their sequelae increase perioperative risk for noncardiac surgical patients. In this review, the authors discuss vascular diseases, their epidemiology and pathophysiology, risk stratification, and management strategies to reduce adverse perioperative outcomes.

Controversy: Critical Review of the Stich Trial and Assessment of Viability. “Back to the Future” Or Maybe Not

The management of patients with coronary artery disease and heart failure has been debated for years. In the 1980’s Braunwald coined the words “viability” and “stunning”. Multiple trials have been done since then. Since the early eighties coronary bypass grafting was considered as gold standard for patients with impaired left ventricular fraction and coronary artery disease. Since then, nuclear imaging studies have been used to evaluate the “viability” of the impaired areas and to decide if revascularisation would be reasonable. Beginning with the CASS study and ending with the more recent STICH study we aim to provide a “bird’s eye view” of the pros and cons for revascularisation. In addition, we aim to shed some light on the daily advancements in medical management, including devices and not just medication. We therefore chose the title “Back to the future” or maybe not.

A Striking Case of Perfusion-Metabolism "Flip-Flop" in a Patient With Left Anterior Descending Artery Total Occlusion

ABSTRACT

A 57-year-old man diagnosed with left anterior descending artery chronic total occlusion underwent rest gated 99mTc-MIBI scan showing moderately to markedly decreased perfusion with abnormal wall motion in the apex, anterior, anteroseptal, and apical anterolateral walls. 18F-FDG PET showed a "flip-flop" phenomenon with markedly increased FDG uptake in the hypoperfused regions and absent/markedly decreased uptake in the normally perfused, normokinetic myocardium, presumably due to the predominant use of free fatty acids under normoxic conditions. After coronary artery bypass grafting, left ventricular motion normalized except for surgery-related paradoxical septal motion and the left ventricular ejection fraction improved from 52% to 68%.

Multimodality imaging of myocardial viability: an expert consensus document from the European Association of Cardiovascular Imaging (EACVI)

In clinical decision making, myocardial viability is defined as myocardium in acute or chronic coronary artery disease and other conditions with contractile dysfunction but maintained metabolic and electrical function, having the potential to improve dysfunction upon revascularization or other therapy. Several pathophysiological conditions may coexist to explain this phenomenon. Cardiac imaging may allow identification of myocardial viability through different principles, with the purpose of prediction of therapeutic response and selection for treatment. This expert consensus document reviews current insight into the underlying pathophysiology and available methods for assessing viability. In particular the document reviews contemporary viability imaging techniques, including stress echocardiography, single photon emission computed tomography, positron emission tomography, cardiovascular magnetic resonance, and computed tomography and provides clinical recommendations for how to standardize these methods in terms of acquisition and interpretation. Finally, it presents clinical scenarios where viability assessment is clinically useful.

Rescue Protocol to Improve the Image Quality of 18F-FDG PET/CT Myocardial Metabolic Imaging

PURPOSE

18F-FDG PET myocardial metabolic imaging is used to estimate myocardial viability. However, poor image quality can affect the accurate quantification of viable myocardium. We assessed the feasibility of a rescue protocol that reinjected low-dose 18F-FDG with simultaneous 1 to 2 U of insulin injection and oral administration of 10 g of glucose to improve the image quality of 18F-FDG PET myocardial metabolic imaging.

PATIENTS AND METHODS

Fifty-one consecutive patients with poor quality to uninterpretable 18F-FDG PET/CT myocardial metabolic images received the rescue protocol immediately after the initial image acquisition. The postrescue image acquisition was performed 1 hour later. The rescue image quality was compared with the initial image. The qualitative visual estimation of the images was graded as follows: grade 0, homogeneous, minimal uptake; grade 1, predominantly minimal or mild uptake; grade 2, moderate uptake; and grade 3, good uptake. The myocardium-to-blood pool activity ratio (M/B) was measured to assess the image quality quantitatively.

RESULTS

The grades of 0 to 3 were observed in 24 (47%), 27 (53%), 0 (0%), and 0 (0%) patients, respectively, for the initial imaging, and in 0 (0%), 3 (5.9%), 4 (7.8%), and 44 (86.3%) patients for the rescue imaging (P < 0.001). The rescue M/B was significantly higher than the initial M/B (3.4 ± 1.4 vs 1.6 ± 0.6, respectively; P < 0.001).

CONCLUSIONS

The rescue protocol successfully and rapidly improved the quality of myocardial 18F-FDG metabolic imaging.

CoQ10 enhances PGC1α and increases expression of mitochondrial antioxidant proteins in chronically ischemic swine myocardium

Background

Expression of mitochondrial proteins is reduced within hibernating myocardium (HM). It is unclear whether dietary supplementation with CoQ₁₀ can increase expression of mitochondrial electron transport chain (ETC) and antioxidant proteins within this tissue. In a swine model of HM, we tested whether dietary administration of CoQ₁₀ for four weeks enhances the expression of ETC and antioxidant proteins within the mitochondria via increased PGC1α signaling.

Methods

12 swine were instrumented with a fixed constrictor around the LAD artery to induce gradual stenosis. At three months, transthoracic ECHO was performed to confirm the presence of a wall motion abnormality in the anterior wall. Animals were then randomly assigned to receive daily dietary supplements of either CoQ₁₀ (10 mg/kg/day) or placebo for four weeks. At this time, animals underwent a final ECHO and terminal procedure. Expression of nuclear-bound PGC1α (Western blots) and mitochondrial proteins (Tandem Mass Tag) were determined.

Results

Mitochondrial and nuclear membranes were isolated from the LAD region. Nuclear-bound PGC1α levels were > 200-fold higher with administration of four weeks of CoQ₁₀ treatment (p = 0.016). Expression of ETC proteins was increased in those animals that received CoQ₁₀. Compared with mitochondria in the LAD region from placebo-treated pigs, CoQ₁₀-treated pigs had higher levels of Complex I (p = 0.03), Complex IV (p = 0.04) and Complex V (p = 0.028) peptides.

Conclusions

Four weeks of dietary CoQ₁₀ in HM pigs enhances active, nuclear-bound PGC1α and increases the expression of ETC proteins within mitochondria of HM tissue.

Impact of hibernating and viable myocardium on improvement in perfusion and left ventricular ejection fraction after coronary artery bypass graft

OBJECTIVES

The association between the extent and degree of perfusion-metabolism mismatch and improvement in perfusion and left ventricular ejection fraction (LVEF) after revascularization was assessed. The secondary aim was to identify the best precoronary artery bypass graft surgery (pre-CABG) PET parameter, if any, to predict the improvement in the perfusion and LVEF after CABG.

METHODS AND RESULTS

Overal, 31 patients (mean age: 58+8.3 years) with ischemic left ventricle dysfunction underwent NH3 and F-FDG PET for the assessment of myocardial viability. CABG was performed in these patients and after a mean interval of 3 months, NH3 PET was repeated. The percentages of viable myocardium (VM), hibernating myocardium, degree of mismatch, and LVEF in pre-CABG PET were calculated. These were compared, the median [INCREMENT]LVEF and percent increase in perfusion being 5 (interquartile range: 3-9) and 78.7 (interquartile range: 51.3-100), respectively. No significant association was observed between the severity or extent of perfusion defect/mismatch and improvement in perfusion or LVEF after CABG. Patients with at least 65% VM predicted a 5-unit increase in LVEF at 88.9% sensitivity (P=0.1).

CONCLUSION

There was no significant relation between the severity and extent of perfusion-metabolism mismatch with improvement in perfusion and LVEF after CABG. After CABG for ischemic left ventricle dysfunction, VM shows a tendency toward better improvement in LVEF.

Cardiac PET/MRI-an update

It is now about 8 years since the first whole-body integrated PET/MRI has been installed. First, reports on technical characteristics and system performance were published. Early after, reports on the first use of PET/MRI in oncological patients were released. Interestingly, the first article on the application in cardiology was a review article, which was published before the first original article was put out. Since then, researchers have gained a lot experience with the PET/MRI in various cardiovascular diseases and an increasing number on auspicious indications is appearing. In this review article, we give an overview on technical updates within these last years with potential impact on cardiac imaging and summarize those scenarios where PET/MRI plays a pivotal role in cardiovascular medicine.

Right ventricle performances with echocardiography and 99mTc myocardial perfusion imaging in pulmonary arterial hypertension patients

Right heart catheterization is commonly used to measure right ventricle hemodynamic parameters and is the gold standard for pulmonary arterial hypertension diagnosis; however, it is not suitable for patients' long-term follow-up. Non-invasive echocardiography and nuclear medicine have been applied to measure right ventricle anatomy and function, but the guidelines for the usefulness of clinical parameters remain to be established. The goal of this study is to identify reliable clinical parameters of right ventricle function in pulmonary arterial hypertension patients and analyze the relationship of these clinical parameters with the disease severity of pulmonary arterial hypertension. In this study, 23 normal subjects and 23 pulmonary arterial hypertension patients were recruited from January 2015 to March 2016. Pulmonary arterial hypertension patients were classified into moderate and severe pulmonary arterial hypertension groups according to their mean pulmonary arterial pressure levels. All the subjects were subjected to physical examination, chest X-ray, 12-lead electrocardiogram, right heart catheterization, two-dimensional echocardiography, and technetium 99m (^99mTc) myocardial perfusion imaging. Compared to normal subjects, the right heart catheterization indexes including right ventricle systolic pressure, right ventricle end diastolic pressure, pulmonary artery systolic pressure, pulmonary artery diastolic pressure, pulmonary vascular resistance, and right ventricle end systolic pressure increased in pulmonary arterial hypertension patients and were correlated with mean pulmonary arterial pressure levels. Echocardiography parameters, including tricuspid regurgitation peak velocity, tricuspid regurgitation pressure gradient, tricuspid annular plane systolic excursion and fractional area, right ventricle-myocardial performance index, were significantly associated with the mean pulmonary arterial pressure levels in pulmonary arterial hypertension patients. Furthermore, myocardial perfusion imaging was not observed in the normal subjects but in pulmonary arterial hypertension patients, especially severe pulmonary arterial hypertension subgroup, and showed potential diagnostic properties for pulmonary arterial hypertension. In conclusion, mean pulmonary arterial pressure levels are correlated with several right heart catheterization and echocardiography markers in pulmonary arterial hypertension patients; echocardiography and ^99mTc myocardial perfusion can be used to evaluate right ventricle performance in pulmonary arterial hypertension patients. Impact statement In this study, we analyzed the clinical parameters for evaluating RV function, including right ventricle catheterization (RHC), echocardiography, and technetium 99m (^99mTc) myocardial perfusion imaging (MPI) in normal Asian subjects and PAH patients ( n = 23 for each group). Our results demonstrated that six RHC indexes, four echocardiography indexes and MPI index were significantly altered in PAH patients and correlated with the levels of mean pulmonary arterial pressure. Importantly, we evaluated the diagnostic performance of MPI and found that MPI has a strong diagnostic accuracy in PAH patients. The findings from this study will be of interest to clinical investigators who make diagnosis and therapeutic strategies for PAH patients.

Surgical Swine Model of Chronic Cardiac Ischemia Treated by Off-Pump Coronary Artery Bypass Graft Surgery

Chronic cardiac ischemia that impairs cardiac function, but does not result in infarct, is termed hibernating myocardium (HM). A large clinical subset of coronary artery disease (CAD) patients have HM, which in addition to causing impaired function, puts them at higher risk for arrhythmia and future cardiac events. The standard treatment for this condition is revascularization, but this has been shown to be an imperfect therapy. The majority of pre-clinical cardiac research focuses on infarct models of cardiac ischemia, leaving this subset of chronic ischemia patients largely underserved. To address this gap in research, we have developed a well-characterized and highly reproducible model of hibernating myocardium in swine, as swine are ideal translational models for human heart disease. In addition to creating this unique disease model, we have optimized a clinically relevant treatment model of coronary artery bypass surgery in swine. This allows us to accurately study the effects of bypass surgery on heart disease, as well as investigate additional or alternate therapies. This model surgically induces single vessel stenosis by implanting a constrictor on the left anterior descending (LAD) artery in a young pig. As the pig grows, the constrictor creates a gradual stenosis, resulting in chronic ischemia with impaired regional function, but preserving tissue viability. Following the establishment of the hibernating myocardium phenotype, we perform off-pump coronary artery bypass graft surgery to revascularize the ischemic region, mimicking the gold-standard treatment for patients in the clinic.

N-Terminal Pro B-Type Natriuretic Peptide and High-Sensitivity Cardiac Troponin T Levels Are Related to the Extent of Hibernating Myocardium in Patients With Ischemic Heart Failure

BACKGROUND

Increased N-terminal pro b-type natriuretic peptide (NT-proBNP) and high-sensitivity cardiac troponin T (hs-cTnT) can identify patients with heart failure (HF) who are at increased risk of cardiac events. The relationship of these biomarkers to the extent of hibernating myocardium and scar has not been previously characterized in patients with ischemic left ventricular dysfunction and HF.

METHODS

Patients with ischemic HF meeting recruitment criteria and undergoing perfusion and fluorodeoxyglucose-positron emission tomography to define myocardial hibernation and scar were included in the study. A total of 39 patients (mean age 67 ± 8 years) with New York Heart Association class II-IV HF and ischemic cardiomyopathy (ejection fraction [EF], 27.9% ± 8.5%) were enrolled in the study.

RESULTS

Serum NT-proBNP and hs-cTnT levels were elevated in patients with ≥ 10% hibernating myocardium compared with those with < 10% (NT-pro-BNP, 7419.10 ± 7169.5 pg/mL vs 2894.6 ± 2967.4 pg/mL; hs-cTnT, 789.3 ± 1835.3 pg/mL vs 44.8 ± 78.9 pg/mL; P < 0.05). The overall receiver operating characteristic under the curve value for NT-proBNP and hs-cTnT to predict hibernating myocardium was 0.76 and 0.78, respectively (P < 0.05). The NT-proBNP (P = 0.02) and hs-cTnT (P < 0.0001) levels also correlated with hibernation, particularly in patients with ≥ 10% scar, independent of EF, age, and estimated glomerular filtration rate. No differences were noted in biomarker levels for patients with vs those without ≥ 10% scar.

CONCLUSIONS

NT-proBNP and hs-cTnT levels are elevated in patients with ischemic HF hibernation and are correlated with the degree of hibernation but not with the presence or extent of scar. Taken together, these data support the novel concept that NT-proBNP and hs-cTnT release in patients with ischemic HF reflects the presence and extent of hibernating myocardium.

The role of nuclear cardiac imaging in risk stratification of sudden cardiac death

Sudden cardiac death (SCD) represents a significant portion of all cardiac deaths. Current guidelines focus mainly on left ventricular ejection fraction (LVEF) as the main criterion for SCD risk stratification and management. However, LVEF alone lacks both sensitivity and specificity in stratifying patients. Recent research has provided interesting data which supports a greater role for advanced cardiac imaging in risk stratification and patient management. In this article, we will focus on nuclear cardiac imaging, including left ventricular function assessment, myocardial perfusion imaging, myocardial blood flow quantification, metabolic imaging, and neurohormonal imaging. We will discuss how these can be used to better understand SCD and better stratify patient with both ischemic and non-ischemic cardiomyopathy.

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.

Long-Term Follow-Up of Outcomes With F-18-Fluorodeoxyglucose Positron Emission Tomography Imaging–Assisted Management of Patients With Severe Left Ventricular Dysfunction Secondary to Coronary Disease

Background—

Whether viability imaging can impact long-term patient outcomes is uncertain. The PARR-2 study (Positron Emission Tomography and Recovery Following Revascularization) showed a nonsignificant trend toward improved outcomes at 1 year using an F-18-fluorodeoxyglucose positron emission tomography (PET)–assisted strategy in patients with suspected ischemic cardiomyopathy. When patients adhered to F-18-fluorodeoxyglucose PET recommendations, outcome benefit was observed. Long-term outcomes of viability imaging–assisted management have not previously been evaluated in a randomized controlled trial.

Methods and Results—

PARR-2 randomized patients with severe left ventricular dysfunction and suspected CAD being considered for revascularization or transplantation to standard care (n= 195) versus PET-assisted management (n=197) at sites participating in long-term follow-up. The predefined primary outcome was time to composite event (cardiac death, myocardial infarction, or cardiac hospitalization). After 5 years, 105 (53%) patients in the PET arm and 111 (57%) in the standard care arm experienced the composite event (hazard ratio for time to composite event =0.82 [95% confidence interval 0.62–1.07]; P =0.15). When only patients who adhered to PET recommendations were included, the hazard ratio for the time to primary outcome was 0.73 (95% confidence interval 0.54–0.99; P =0.042).

Conclusions—

After a 5-year follow-up in patients with left ventricular dysfunction and suspected CAD, overall, PET-assisted management did not significantly reduce cardiac events compared with standard care. However, significant benefits were observed when there was adherence to PET recommendations. PET viability imaging may be best applied when there is likely to be adherence to imaging-based recommendations.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT00385242.

PET/MR Imaging in Heart Disease

Hybrid PET/MR imaging is a complex imaging modality that has raised high expectations not only for oncological and neurologic imaging applications, but also for cardiac imaging applications. Initially, physicians and physicists had to become accustomed to technical challenges including attenuation correction, gating, and more complex workflow and more elaborate image analysis as compared with PET/CT or standalone MR imaging. PET/MR imaging seems to be particularly valuable to assess inflammatory myocardial diseases (such as sarcoidosis), to cross-validate PET versus MR imaging data (eg, myocardial perfusion imaging), and to help validate novel biomarkers of various disease states (eg, postinfarction inflammation).

Cardiac Strain in a Swine Model of Regional Hibernating Myocardium: Effects of CoQ10 on Contractile Reserve Following Bypass Surgery

There is conflicting clinical evidence whether administration of coenzyme Q10 (CoQ10) improves function following coronary artery bypass graft surgery (CABG). Using a swine model of hibernating myocardium, we tested whether daily CoQ10 would improve contractile function by MRI at 4-week post-CABG. Twelve pigs underwent a thoracotomy and had a constrictor placed on the left anterior descending (LAD). At 12 weeks, they underwent off-pump bypass and received daily dietary supplements of either CoQ10 (10 mg/kg/day) or placebo. At 4-week post-CABG, circumferential strain measurements in the hibernating LAD region from placebo and CoQ10 groups were not different and increased to a similar extent with dobutamine (-14.7 ± 0.6 versus -14.8 ± 0.1, respectively (NS)). Post-sacrifice, oxidant stress markers were obtained in the mitochondrial isolates and protein carbonyl in the placebo, and CoQ10 groups were 6.14 ± 0.36 and 5.05 ± 0.32 nmol/mg, respectively (NS). In summary, CoQ10 did not improve contractile reserve or reduce oxidant stress at 4-week post-CABG.

Cardiovascular PET-CT imaging: a new frontier?

Cardiovascular positron-emission tomography combined with computed tomography (PET-CT) has recently emerged as an imaging technology with the potential to simultaneously describe both anatomical structures and physiological processes in vivo. The scope for clinical application of this technique is vast, but to date this promise has not been realised. Nonetheless, significant research activity is underway to explore these possibilities and it is likely that the knowledge gained will have important diagnostic and therapeutic implications in due course. This review provides a brief overview of the current state of cardiovascular PET-CT and the likely direction of future developments.

PET/MRI early after myocardial infarction: evaluation of viability with late gadolinium enhancement transmurality vs. 18F-FDG uptake

AIMS

F-18 fluorodeoxyglucose (FDG) myocardial PET imaging is since more than two decades considered to delineate glucose utilization in dysfunctional but viable cardiomyocytes. Late gadolinium enhancement (LGE) MRI was introduced more than a decade ago and identifies increased extravascular space in areas of infarction and scar. Although the physiological foundation differs, both approaches are valuable in the prediction of functional outcome of the left ventricle, but synergistic effects are yet unknown. We aimed to compare the improvement of LV function after 6 months based on the regional FDG uptake and the transmurality of scar by LGE in patients early after acute myocardial infarction (AMI).

METHODS AND RESULTS

Twenty-eight patients with primary AMI underwent simultaneous PET/MRI for assessment of regional FDG uptake and degree of LGE transmurality 5-7 days after PCI. Follow-up by MRI was performed in 20 patients 6 months later. Myocardium was defined 'PET viable' based on the established threshold of ≥ 50% FDG uptake compared with remote myocardium or as 'MRI viable' when LGE transmurality of ≤ 50% was present. Regional wall motion was measured by MRI. Ninety-five dysfunctional segments were further analysed regarding regional wall motion recovery. There was a substantial intermethod agreement for segmental LGE transmurality and reduction of FDG uptake (κ = 0.65). 'PET viable' and 'MRI viable' segments showed a lower wall motion abnormality score (PET: initial: 1.4 ± 0.6 vs. 1.9 ± 0.8, P < 0.008; follow-up: 0.5 ± 0.7 vs. 1.5 ± 1.0, P < 0.0001; MRI: initial: 1.5 ± 0.6 vs. 2.0 ± 0.8, P < 0.002; follow-up: 0.7 ± 0.8 vs. 1.6 ± 1.0, P < 0.0001) and a better regional wall motion improvement (PET: -0.9 ± 0.7 vs. -0.4 ± 0.7, P < 0.0007; MRI: -0.8 ± 0.7 vs. -0.4 ± 0.7, P < 0.009) compared with 'PET non-viable' or 'MRI non-viable' segments, respectively. Eighteen per cent of the dysfunctional segments showed discrepant findings ('PET non-viable' but 'MRI viable'). At follow-up, the regional wall motion of these segments was inferior compared with 'PET viable/MRI viable' segments (1.1 ± 0.8 vs. 0.5 ± 0.7, P < 0.01), had an inferior functional recovery (-0.5 ± 0.6 vs. -0.9 ± 0.7, P < 0.03), but showed no difference compared with concordant 'PET non-viable/MRI non-viable' segments.

CONCLUSION

The simultaneous assessment of LGE and FDG uptake using a hybrid PET/MRI system is feasible. The established PET and MRI 'viability' parameter prior to revascularization therapy also predicts accurately the regional outcome of wall motion after AMI. In a small proportion of segments with discrepant FDG PET and LGE MRI findings, FDG uptake was a better predictor for functional recovery.

Analysis of Myocardial (18)F-FDG Uptake by PET/CT in the Patients with Different Dialectically Classified Coronary Heart Diseases (CHD)

To quantify myocardial glucose metabolism by (18)F-FDG PET/CT in patients that have coronary heart disease (CHD) according to traditional Chinese medicine classification. Ninety patients with CHD were enrolled and were categorized into three groups. All patients underwent PET-CT examination for (18)F-FDG uptake quantification. In group A, the radioactive signals were weak in multiple segments in 27 cases (90 %). One case had no visualization and two had normal visualization (mean SUV = 4 ± 0.6). In group B, the radioactive signals were in some local areas in eight cases (26.7 %). Twenty cases had an overall increase in signal density (SUV ≥ 8) (66.7 %). One case had no visualization, and one case had normal visualization (mean SUV 4 ± 0.6). In group C, 23 cases had no visual or a weak visual (SUV ≤ 2 ± 0.3) (76.7 %). Seven cases had segmental weak signals or signal defects. Different types of CHD demonstrate different metabolisms of myocardium glucose. It is necessary to dialectically classify CHD and apply differential treatment.

Effect of time-of-flight and point spread function modeling on detectability of myocardial defects in PET

PURPOSE

A study was designed to investigate the impact of time-of-flight (TOF) and point spread function (PSF) modeling on the detectability of myocardial defects.

METHODS

Clinical FDG-PET data were used to generate populations of defect-present and defect-absent images. Defects were incorporated at three contrast levels, and images were reconstructed by ordered subset expectation maximization (OSEM) iterative methods including ordinary Poisson, alone and with PSF, TOF, and PSF+TOF. Channelized Hotelling observer signal-to-noise ratio (SNR) was the surrogate for human observer performance.

RESULTS

For three iterations, 12 subsets, and no postreconstruction smoothing, TOF improved overall defect detection SNR by 8.6% as compared to its non-TOF counterpart for all the defect contrasts. Due to the slow convergence of PSF reconstruction, PSF yielded 4.4% less SNR than non-PSF. For reconstruction parameters (iteration number and postreconstruction smoothing kernel size) optimizing observer SNR, PSF showed larger improvement for faint defects. The combination of TOF and PSF improved mean detection SNR as compared to non-TOF and non-PSF counterparts by 3.0% and 3.2%, respectively.

CONCLUSIONS

For typical reconstruction protocol used in clinical practice, i.e., less than five iterations, TOF improved defect detectability. In contrast, PSF generally yielded less detectability. For large number of iterations, TOF+PSF yields the best observer performance.

Recovery of hibernating myocardium: what is the role of surgical revascularization?

Myocardial responses to chronic ischemia represent a continuum of adaptations resulting, over time, in a stress-resistant phenotype. One such adaptation, hibernating myocardium (HM), has increased antioxidant capacity that protects against ischemia-induced oxidative stress. Studies have suggested that revascularization alone may not fully restore cardiac function, highlighting the need for targeted therapies to serve as adjuncts to the innate healing process following revascularization. In our review, we discuss current understanding of HM and the recovery process following surgical revascularization, focusing on animal models of HM to understand implications for human patients.

Cardiac PET: metabolic and functional imaging of the myocardium

Cardiac PET has evolved over the past 30 years to gain wider acceptance as a valuable modality for a variety of cardiac conditions. Wider availability of scanners as well as changes in reimbursement policies in more recent years has further increased its use. Moreover, with the emergence of novel radionuclides as well as further advances in scanner technology, the use of cardiac PET can be expected to increase further in both clinical practice and the research arena. PET has demonstrated superior diagnostic accuracy for the diagnosis of coronary artery disease in comparison with single-photon emission tomography while it provides robust prognostic value. The addition of absolute flow quantification increases sensitivity for 3-vessel disease as well as providing incremental functional and prognostic information. Metabolic imaging using (18)F-fluorodeoxyglucose can be used to guide revascularization in the setting of heart failure and also to detect active inflammation in conditions such as cardiac sarcoidosis and within atherosclerotic plaque, improving our understanding of the processes that underlie these conditions. However, although the pace of new developments is rapid, there remains a gap in evidence for many of these advances and further studies are required.

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.

Alternative Imaging Modalities in Ischemic Heart Failure (AIMI-HF) IMAGE HF Project I-A: study protocol for a randomized controlled trial

BACKGROUND

Ischemic heart disease (IHD) is the most common cause of heart failure (HF); however, the role of revascularization in these patients is still unclear. Consensus on proper use of cardiac imaging to help determine which candidates should be considered for revascularization has been hindered by the absence of clinical studies that objectively and prospectively compare the prognostic information of each test obtained using both standard and advanced imaging.

METHODS/DESIGN

This paper describes the design and methods to be used in the Alternative Imaging Modalities in Ischemic Heart Failure (AIMI-HF) multi-center trial. The primary objective is to compare the effect of HF imaging strategies on the composite clinical endpoint of cardiac death, myocardial infarction (MI), cardiac arrest and re-hospitalization for cardiac causes.In AIMI-HF, patients with HF of ischemic etiology (n = 1,261) will follow HF imaging strategy algorithms according to the question(s) asked by the physicians (for example, Is there ischemia and/or viability?), in agreement with local practices. Patients will be randomized to either standard (SPECT, Single photon emission computed tomography) imaging modalities for ischemia and/or viability or advanced imaging modalities: cardiac magnetic resonance imaging (CMR) or positron emission tomography (PET). In addition, eligible and consenting patients who could not be randomized, but were allocated to standard or advanced imaging based on clinical decisions, will be included in a registry.

DISCUSSION

AIMI-HF will be the largest randomized trial evaluating the role of standard and advanced imaging modalities in the management of ischemic cardiomyopathy and heart failure. This trial will complement the results of the Surgical Treatment for Ischemic Heart Failure (STICH) viability substudy and the PET and Recovery Following Revascularization (PARR-2) trial. The results will provide policy makers with data to support (or not) further investment in and wider dissemination of alternative 'advanced' imaging technologies.

TRIAL REGISTRATION

NCT01288560.

The amount of dysfunctional but viable myocardium predicts long-term survival in patients with ischemic cardiomyopathy and left ventricular dysfunction. Int J Cardiovasc Imaging. 2013;29:1645-1653. [PMID: 23744128 DOI: 10.1007/s10554-013-0254-2]

To evaluate the prognostic significance of combined myocardial perfusion SPECT and [18F]FDG PET viability scanning for the prediction of survival in patients with ischemic cardiomyopathy (iCMP) and left ventricular dysfunction. 244 patients (64.0 ± 10.6 years, 86 % men) with iCMP and LVEF ≤ 45 % underwent SPECT/PET. Percent scar tissue and SPECT/PET-mismatch (%-mismatch) were calculated and correlated with event-free survival according to the type of therapy (medical therapy with/out revascularization) provided after imaging. Death from any cause was defined as the primary endpoint. Early revascularization (ER) was performed in 113/244 (46 %) patients within 32 ± 52 days (26 bypass surgeries and 87 percutaneous coronary interventions). 65 patients died during follow-up for a median of 33 months. Kaplan-Meier analysis showed that those patients with ≥ 5 % mismatch not undergoing ER had significantly higher mortality than did the group with similar mismatch who did receive ER. Cox analysis identified both SPECT/PET-mismatch and the interaction of SPECT/PET-mismatch with ER as independent predictors for death due to all causes. A threshold of ≥ 5 % SPECT/PET-mismatch predicted best which patients with iCMP and LV dysfunction would benefit from ER in terms of long-term survival.

Incidental focal FDG uptake in heart is a lighthouse for considering cardiac screening

OBJECTIVES

Cardiac FDG uptake is known to show a variety of patterns under clinical fasting conditions. We hypothesized that focal FDG uptake in the heart (FUH) represents a sign of cardiac disease risk, especially in coronary artery disease (CAD).The aim of this study was to clarify the relationship between FUH and cardiac disease.

METHODS

Cases showing FUH were selected based on comments in diagnostic reports or identification on retrospective review. Quantitative analysis was performed using maximum standardized uptake value (SUVmax), with regions of interest drawn over focal uptake areas in the heart as confirmed by PET/CT and in lateral side of the same slice showing focal FDG uptake.

RESULTS

For the 20 patients (11 men, 9 women) with confirmed FUH, coronary artery stenosis or history of treatment for coronary disease was present in 11 patients (55.0 %), and 2 patients showed apical hypertrophy. Mean SUVmax of FUH did not differ significantly between patients with confirmed cardiac disease and those with no evidence of cardiac disease (P = 0.78).

CONCLUSIONS

FUH suggests a high likelihood of CAD in patients without myocardial symptoms. Cardiac screening or a check of the history of cardiac disease is thus worth considering when FUH is seen incidentally on FDG-PET/CT.

Hybrid PET/MR imaging of the heart: potential, initial experiences, and future prospects

PET/CT and other combined scanners have in the past decade rapidly emerged as important research tools and are proving to be invaluable for improved diagnostics in routine nuclear medicine. The design of hybrid PET/MR scanners presented a formidable technical challenge, and only recently were these instruments introduced to the market. Initial expectations of the performance of these scanners have been high, notably because of the potential for superior tissue contrast inherent in the MR modality, as well as the potential for multiparametric functional imaging in conjunction with PET. However, the additional value and potential clinical role that these new systems might bring to the cardiac field have yet to be documented. This review presents a comparative summary of the existing applications for PET and MR in the field of cardiology and suggests potential cardiac applications exploiting unique properties of the newly introduced combined instrumentation.