Myocardial 18F-FDG uptake after exercise-induced myocardial ischemia in patients with coronary artery disease

A novel method in myocardial injury risk stratification using intravenous fat emulsion as sole rapid preparation for unfasted patients to suppress myocardial 18F-fluorodeoxyglucose uptake for optimal cardiac PET imaging: a proof-of-concept randomized-crossover trial

Objectives

Optimal imaging of ischemic or inflammed myocardium via 18F-FDG PET imaging requires suppression of background carbohydrate metabolism in normal myocardium. Sole administration of intravenous lipid emulsion has not previously been used to rapidly prepare unfasted patients, such as in emergent clinical situations. In this proof-of-concept pilot, we posited that intravenous fat emulsion suppresses physiological metabolic uptake of in non-ischemic, non-inflammatory myocardium in unprepared and unfasted setting for enhanced cardiac positron emission tomography (PET) imaging.

Methods

We conducted an ethics-approved, single-blind, prospective randomized crossover trial of 10 healthy volunteers from January 2020 to June 2021. Participants were unfasted and rendered hyperglycemic before being administered either high dose intravenous lipid emulsion-1.5 ml kg of 20% lipid emulsion, followed by 15 ml/kg/hr for 30mins-or saline prior to 18F-FDG injection and subsequent cardiac PET imaging. Assessors undertook image analysis for maximum standard uptake value (SUVmax), minimum standard uptake value (SUVmin) and qualitative assessment, and groups were compared using univariate analysis.

Results

The study population age was 44.5 years [IQR 32.5-56.5], with 50% male and a median BMI of 22.75 [IQR 25.0-28.5] kg/m2. The study was feasible and there were no adverse side effects from the interventions. In these participants with normal myocardium, 18F-FDG uptake was reduced by intravenous lipid emulsion as assessed by SUVmax and qualitative assessment (p = 0.042, r = 0.454 and p = 0.009, r = -0.581, respectively).

Conclusions

Intravenous lipid emulsion suppresses background metabolic uptake of 18F-FDG even in unprepared and unfasted patients. Our findings prove and expand the possible applications for cardiac 18F-FDG PET in various settings, including in emergent settings as a means of rapid preparation in place of current more time-consuming standard protocols, allowing time-critical management to be effected.

Incremental prognostic value of 18F-fluorodeoxyglucose myocardial ischemic memory imaging for major adverse cardiovascular events in patients with suspected unstable angina

BACKGROUND

The additional prognostic value of 18F-flurodeoxyglucose positron emission tomography (18F-FDG PET) myocardial ischemic memory imaging for patients with suspected unstable angina (UA) is not well established. This study aimed to determine whether 18F-FDG PET imaging provides incremental prognostic information for predicting major adverse cardiac events (MACEs) compared to clinical risk factors, Global Registry of Acute Coronary Events (GRACE) score, and coronary artery calcium score (CACS) in patients with suspected UA.

METHODS

In this post hoc analysis of a prospective study, 265 patients suspected with UA (62.3% male, mean age: 65.0±9.4 years) were enrolled. 18F-FDG positivity was defined as focal or focal on diffuse uptake patterns. MACEs included cardiovascular death, acute myocardial infarction, heart failure, rehospitalization for UA, and stroke. Multivariable Cox regression was used to identify predictors of MACEs, and the incremental prognostic value of 18F-FDG PET imaging was assessed using the Concordance Index (C-index), net reclassification improvement (NRI), and integrated discrimination improvement (IDI).

RESULTS

Over a median follow-up of 25 months, 51 patients (19.2%) experienced MACEs. 18F-FDG positivity (hazard ratio [HR]=3.220, 95% confidence interval [CI]: 1.630-6.360, P<.001), as well as 18F-FDG standardized uptake ratio (HR=1.330, 95% CI: 1.131-1.564, P=.0006) and Extent (HR=1.045, 95% CI: 1.028-1.062, P<.0001), were independent predictors of MACE. The addition of 18F-FDG PET imaging significantly improved risk stratification beyond clinical factors, the GRACE score, and CACS, with improved C-index (.769 vs .688, P=.045), NRI (.324, P=.020), and IDI (.055, P=.027).

CONCLUSION

18F-FDG PET myocardial ischemic memory imaging significantly improves prognostic assessment for patients with suspected UA, providing valuable additional risk stratification beyond clinical risk factors, GRACE score, and CACS.

Incremental value of 18F-FDG cardiac PET imaging over dobutamine stress echocardiography in predicting myocardial ischemia in patients with suspected coronary artery disease

BACKGROUND

To assess the incremental value of 18F-fluorodeoxyglucose (FDG) cardiac positron emission tomography (PET) over dobutamine stress echocardiography (DSE) in predicting myocardial ischemia in patients with suspected coronary artery disease (CAD).

METHODS

Forty-one patients with suspected CAD underwent within 7 days apart rest-stress cardiac PET with 82Rb and DSE followed by cardiac 18F-FDG PET imaging. 18F-FDG images were scored on a 0 (no discernible uptake) to 2 (intense uptake) scale. Logistic regression analysis was performed to identify predictors of stress-induced ischemia. The incremental value of 18F-FDG PET over DSE in detecting ischemia at 82Rb PET cardiac imaging was assessed by the likelihood ratio chi-square and net reclassification index.

RESULTS

On 82Rb-PET imaging, myocardial ischemia (ischemic total perfusion defect ≥ 5%) was detected in 20 (49%) patients. Inducible ischemia was found in 22 (54%) patients on DSE (biphasic or worsening response pattern in ≥ 1 segment) and in 21 (51%) patients on 18F-FDG PET (uptake score of 2 in ≥ 1 segment). 18F-FDG PET resulted as statistically significant predictor of ischemia on 82Rb-PET. The addition of 18F-FDG PET to DSE increased the likelihood of ischemia on 82Rb-PET (P < .05). 18F-FDG PET was able to reclassify the probability of stress-induced myocardial ischemia on both patient and vessel analyses.

CONCLUSION

18F-FDG PET performed after dobutamine stress test may provide incremental value to DSE in the evaluation of myocardial ischemia. These results suggest that stress-induced myocardial ischemia can be imaged directly using 18F-FDG PET after dobutamine stress test.

Shining Damaged Hearts: Immunotherapy-Related Cardiotoxicity in the Spotlight of Nuclear Cardiology

The emerging use of immunotherapies in cancer treatment increases the risk of immunotherapy-related cardiotoxicity. In contrast to conventional chemotherapy, these novel therapies have expanded the forms and presentations of cardiovascular damage to a broad spectrum from asymptomatic changes to fulminant short- and long-term complications in terms of cardiomyopathy, arrythmia, and vascular disease. In cancer patients and, particularly, cancer patients undergoing (immune-)therapy, cardio-oncological monitoring is a complex interplay between pretherapeutic risk assessment, identification of impending cardiotoxicity, and post-therapeutic surveillance. For these purposes, the cardio-oncologist can revert to a broad spectrum of nuclear cardiological diagnostic workup. The most promising commonly used nuclear medicine imaging techniques in relation to immunotherapy will be discussed in this review article with a special focus on the continuous development of highly specific molecular markers and steadily improving methods of image generation. The review closes with an outlook on possible new developments of molecular imaging and advanced image evaluation techniques in this exciting and increasingly growing field of immunotherapy-related cardiotoxicity.

Myocardial 18F-FDG Uptake Pattern for Cardiovascular Risk Stratification in Patients Undergoing Oncologic PET/CT

Objective: Positron emission tomography/computed tomography with ¹⁸F-fluorodeoxy-glucose (¹⁸F-FDG-PET/CT) has become the standard staging modality in various tumor entities. Cancer patients frequently receive cardio-toxic therapies. However, routine cardiovascular assessment in oncologic patients is not performed in current clinical practice. Accordingly, this study sought to assess whether myocardial ¹⁸F-FDG uptake patterns of patients undergoing oncologic PET/CT can be used for cardiovascular risk stratification. Methods: Myocardial ¹⁸F-FDG uptake pattern was assessed in 302 patients undergoing both oncologic whole-body ¹⁸F-FDG-PET/CT and myocardial perfusion imaging by single-photon emission computed tomography (SPECT-MPI) within a six-month period. Primary outcomes were myocardial ¹⁸F-FDG uptake pattern, impaired myocardial perfusion, ongoing ischemia, myocardial scar, and left ventricular ejection fraction. Results: Among all patients, 109 (36.1%) displayed no myocardial ¹⁸F-FDG uptake, 77 (25.5%) showed diffuse myocardial ¹⁸F-FDG uptake, 24 (7.9%) showed focal ¹⁸F-FDG uptake, and 92 (30.5%) had a focal on diffuse myocardial ¹⁸F-FDG uptake pattern. In contrast to the other uptake patterns, focal myocardial ¹⁸F-FDG uptake was predominantly observed in patients with myocardial abnormalities (i.e., abnormal perfusion, impaired LVEF, myocardial ischemia, or scar). Accordingly, a multivariate logistic regression identified focal myocardial ¹⁸F-FDG uptake as a strong predictor of abnormal myocardial function/perfusion (odds ratio (OR) 5.32, 95% confidence interval (CI) 1.73–16.34, p = 0.003). Similarly, focal myocardial ¹⁸F-FDG uptake was an independent predictor of ongoing ischemia and myocardial scar (OR 4.17, 95% CI 1.53–11.4, p = 0.005 and OR 3.78, 95% CI 1.47–9.69, p = 0.006, respectively). Conclusions: Focal myocardial ¹⁸F-FDG uptake seen on oncologic PET/CT indicates a significantly increased risk for multiple myocardial abnormalities. Obtaining and taking this information into account will help to stratify patients according to risk and will reduce unnecessary cardiovascular complications in cancer patients.

A pilot study of cardiopulmonary exercise testing and cardiac stress positron emission tomography before major non-cardiac surgery

Cardiac events are a common cause of peri-operative morbidity. Cardiopulmonary exercise testing can objectively assess risk, but it does not quantify myocardial ischaemia. With appropriate dietary preparation to suppress basal myocardial glucose uptake, positron emission tomography with ¹⁸ F-fluorodeoxyglucose can identify post-ischaemic myocardium, providing an attractive complement to exercise testing. We aimed to investigate the feasibility of this diagnostic algorithm. Patients referred for cardiopulmonary exercise testing before major cancer surgery were prospectively recruited. Exercise testing and positron emission tomography imaging were performed after a high fat-low carbohydrate meal. Protocol feasibility (primary end-point) included compliance with pre-test diet instructions and the completion of tests. Stress myocardial perfusion imaging was performed if either exercise testing or positron emission tomography was equivocal or positive for ischaemia. We recorded cardiac complications for 30 postoperative days. We enrolled 26 participants, 20 of whom completed protocol. Twenty-one participants proceeded to surgery: myocardial injury or infarction was diagnosed in three participants, two of whom had positive or equivocal positron emission tomography but negative myocardial perfusion imaging. We have shown that pre-operative cardiac positron emission tomography after cardiopulmonary exercise testing is feasible; protocol deviations were minor and did not affect image quality. Our findings warrant further investigation to compare the diagnostic utility of cardiac positron emission tomography imaging with standard pre-operative stress tests.

Feasibility of myocardial PET imaging using a benzylguanidine analog: meta-(3-[18F]fluoropropyl)benzylguanidine ([18F]mFPBG)

INTRODUCTION

Global and regional sympathetic activity in the heart can be evaluated using [¹²³I]meta-iodobenzylguanidine ([¹²³I]mIBG) imaging. However, [¹²³I]mIBG is associated with low image spatial resolution and sensitivity in cardiac imaging. We investigated the capability of an F-18-labeled mIBG derivative, meta-(3-[¹⁸F]fluoropropyl)benzylguanidine ([¹⁸F]mFPBG), for identifying ischemic and viable myocardium in a rat model of myocardial infarction.

MATERIALS AND METHODS

The ex vivo biodistribution and in vivo metabolic stability of [¹⁸F]mFPBG were investigated in Sprague-Dawley rats. Selective cardiac adrenergic activation was confirmed via a blocking experiment involving pretreatment with desipramine (2 mg kg^-1), followed by the administration of [¹⁸F]mFPBG. Imaging properties of [¹⁸F]mFPBG were compared with those of traditional cardiac imaging radiotracers ([¹²³I]mIBG and [^99mTc]MIBI) in a rat model of myocardial infarction. Non-invasive image-based measurements of infarct sizes were then compared with histological findings by using Bland-Altman analysis.

RESULTS

The differences in infarct sizes determined using histological analysis and [¹⁸F]mFPBG PET were -2.55 ± 4.99% (range: -12.33 to 7.22), -2.35 ± 3.32% (range: -8.87 to 4.16), and -3.15 ± 6.16% (range: -15.24 to 8.93) at 5, 20, and 40 min, respectively. Furthermore, [¹⁸F]mFPBG PET was superior to traditional imaging methods in assessing the degree of ischemia in areas of myocardial infarction, as well as the actual infarct size.

CONCLUSION

Compared to [¹²³I]mIBG, [¹⁸F]mFPBG showed improved spatial resolution and sensitivity in a rat model of myocardial infarction. This result suggested that [¹⁸F]mFPBG is a promising cardiac PET imaging agent for potential diagnostic application in PET cardiology.

Dual-time-point myocardial 18F-FDG imaging in the detection of coronary artery disease

Background

Myocardial ¹⁸F-deoxyglucose (¹⁸F-FDG) uptake has been observed to be enhanced in patients with coronary artery disease (CAD) under fasting conditions. However, whether the increased ¹⁸F-FDG is induced by myocardial ischemia and how to discriminate ischemic from physiological ¹⁸F-FDG uptake have rarely been investigated.

Methods

Under fasting conditions, ¹⁸F-FDG PET imaging was performed in 52 patients with suspected CAD. Two ¹⁸F-FDG imaging sessions were conducted within two hours after a single administration of ¹⁸F-FDG (dual-time-point imaging), and with an intervention of an exercise test after the first imaging. Abnormal ¹⁸F-FDG uptake was determined by the classification of the ¹⁸F-FDG distribution pattern, and the changes of the ¹⁸F-FDG distribution between the two PET imaging sessions were analyzed. ^99mTc-sestamibi was injected at peak exercise and myocardial perfusion imaging (MPI) was conducted after ¹⁸F-FDG imaging. Coronary angiography was considered the reference for diagnosing CAD.

Results

Overall, 54.8% (17/31) of CAD patients and 36.2% (21/58) of stenotic coronaries showed exercise-induced abnormal uptake of ¹⁸F-FDG. Based on the classification of the ¹⁸F-FDG distribution pattern, the sensitivity and specificity of exercise ¹⁸F-FDG imaging to diagnose CAD was 80.6% and 95.2% by patient analysis, 56.9% and 98.0% by vascular analysis, respectively. Compared with MPI, ¹⁸F-FDG imaging had a tendency to have higher sensitivity (80.6% vs 64.5%, P = 0.06) on the patient level.

Conclusion

Myocardial ischemia can induce ¹⁸F-FDG uptake. With the classification of the ¹⁸F-FDG distribution pattern, dual-time-point ¹⁸F-FDG imaging under fasting conditions is efficient in diagnosing CAD.

Use of resting myocardial 18F-FDG imaging in the detection of unstable angina

OBJECTIVE

Increased myocardial glucose metabolism occurs with the onset of myocardial ischemia and may persist even after the restoration of blood flow, termed as 'ischemic memory'. Previous studies have demonstrated that 18F-fluorodeoxyglucose (18F-FDG) is a sensitive marker of myocardial ischemia and may have potential utility in diagnosing unstable angina (UA). This study aimed to explore the value of F-FDG PET/CT in diagnosing UA.

PATIENTS AND METHODS

Thirty-four patients (17 male patients; mean age, 59 ± 6 years) with suspected UA were prospectively recruited. Resting myocardial F-FDG PET/CT imaging was performed 21 ± 9 h (2-46 h) after the latest onset of angina pectoris. Resting or exercise myocardial perfusion imaging (MPI) and coronary angiography were performed. 'Focal' or 'focal on diffuse' myocardial F-FDG uptake was defined as abnormal, whereas other patterns of myocardial uptake, including 'focal' uptake on the basal segments, were considered as normal. The final diagnosis of UA was based on a comprehensive analysis of ECG, MPI, and coronary angiography.

RESULTS

Of the 21 patients with a final diagnosis of UA, 18 had increased 18F-FDG uptake (sensitivity 85.7%), whereas, of the 13 patients without UA, only one had abnormal 18F-FDG uptake (specificity 92.3%). The sensitivity of resting 18F-FDG imaging was higher than that of resting MPI (85.7 vs. 52.4%, P=0.016). Moreover, six UA patients with only exercise-induced ischemia showed abnormal F-FDG uptake at rest.

CONCLUSION

This pilot study demonstrated that resting 18F-FDG PET/CT imaging is an accurate and sensitive technique for the identification of UA.

Direct myocardial ischemia imaging: a new cardiovascular nuclear imaging paradigm

Myocardial perfusion imaging (MPI), using radiotracers, has been in routine clinical use for over 40 years. This modality is used for the detection of coronary artery disease (CAD), risk stratification, optimizing therapy, and follow-up of patients with CAD. Molecular cardiovascular imaging using targeted radiotracers provides a unique opportunity for imaging biochemical and metabolic processes, and cell membrane transporter and receptor functions at a cellular and molecular level in experimental animal models as well as in humans. Cardiac imaging using radiolabeled free fatty acid analogues and glucose analogues enable us to image myocardial ischemia directly as an alternative to stress-rest MPI. Direct ischemia imaging techniques can avoid and overcome some of the limitations of standard stress-rest MPI. This article describes recent studies using (18) F-fluorodeoxyglucose ((18) FDG) for myocardial ischemia imaging.

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.

Recent advances in metabolic imaging

Abnormalities in myocardial substrate metabolism play a central role in the manifestations of most forms of cardiac disease such as ischemic heart disease, heart failure, hypertensive heart disease, and the cardiomyopathy due to either obesity or diabetes mellitus. Their importance is exemplified by both the development of numerous imaging tools designed to detect the specific metabolic perturbations or signatures related to these different diseases, and the vigorous efforts in drug discovery/development targeting various aspects of myocardial metabolism. Since the prior review in 2005, we have gained new insights into how perturbations in myocardial metabolism contribute to various forms of cardiac disease. For example, the application of advanced molecular biologic techniques and the development of elegant genetic models have highlighted the pleiotropic actions of cellular metabolism on energy transfer, signal transduction, cardiac growth, gene expression, and viability. In parallel, there have been significant advances in instrumentation, radiopharmaceutical design, and small animal imaging, which now permit a near completion of the translational pathway linking in-vitro measurements of metabolism with the human condition. In this review, most of the key advances in metabolic imaging will be described, their contribution to cardiovascular research highlighted, and potential new clinical applications proposed.

Ischaemic memory imaging using metabolic radiopharmaceuticals: overview of clinical settings and ongoing investigations

"Ischaemic memory" is defined as a prolonged functional and/or biochemical alteration remaining after a particular episode of severe myocardial ischaemia. The biochemical alteration has been reported as metabolic stunning. Metabolic imaging has been used to detect the footprint left by previous ischaemic episodes evident due to delayed recovery of myocardial metabolism (persistent dominant glucose utilization with suppression of fatty acid oxidation). β-Methyl-p-[(123)I]iodophenylpentadecanoic acid (BMIPP) is a single-photon emission computed tomography (SPECT) radiotracer widely used for metabolic imaging in clinical settings in Japan. In patients with suspected coronary artery disease but no previous myocardial infarction, BMIPP has shown acceptable diagnostic accuracy. In particular, BMIPP plays an important role in the identification of prior ischaemic insult in patients arriving at emergency departments with acute chest pain syndrome. Recent data also show the usefulness of (123)I-BMIPP SPECT for predicting cardiovascular events in patients undergoing haemodialysis. Similarly, SPECT or PET imaging with (18)F-FDG injected during peak exercise or after exercise under fasting conditions shows an increase in FDG uptake in postischaemic areas. This article will overview the roles of ischaemic memory imaging both under established indications and in ongoing investigations.

Targeted metabolic imaging to improve the management of heart disease

Tracer techniques are powerful methods for assessing rates of biological processes in vivo. A case in point is intermediary metabolism of energy providing substrates, a central feature of every living cell. In the heart, the tight coupling between metabolism and contractile function offers an opportunity for the simultaneous assessment of cardiac performance at different levels in vivo: coronary flow, myocardial perfusion, oxygen delivery, metabolism, and contraction. Noninvasive imaging techniques used to identify the metabolic footprints of either normal or perturbed cardiac function are discussed.

Treadmill exercise inducing mild to moderate ischemia has no significant effect on skeletal muscle or cardiac 18F-FDG uptake and image quality on subsequent whole-body PET scan

We report the effects of treadmill exercise on (18)F-FDG uptake in skeletal muscles and image quality of torso PET and compare stress myocardial perfusion imaging patterns with myocardial (18)F-FDG uptake. There were 3 groups of patients: 48 patients underwent PET within 8 h after a treadmill test (Ex 8), 45 patients within 48 h after a treadmill test (Ex 48), and 34 patients without prior exercise. Mean workload (8.4 ± 2.3 [Ex 8] vs. 8.9 ± 2.6 metabolic equivalents [Ex 48]) was similar in both exercise groups. Muscle uptake was assessed by standardized uptake value. Myocardial uptake patterns were compared visually. Minor differences between patient groups were noted only for maximum standardized uptake value in quadriceps muscles. There was no correlation between perfusion defects and myocardial (18)F-FDG uptake patterns. Thus, treadmill exercise does not affect muscle (18)F-FDG uptake or image quality on subsequent PET. Cardiac (18)F-FDG uptake on torso PET scans is unrelated to myocardial perfusion status.

Utility of high fat and low carbohydrate diet in suppressing myocardial FDG uptake

INTRODUCTION

Fluoro-deoxy-glucose (FDG) can be used to visualize inflammation in atherosclerotic plaques in coronary arteries, if myocardial FDG uptake is adequately suppressed. Prolonged fasting for suppressing myocardial FDG uptake is inconsistent. We evaluated the feasibility to consistently suppress myocardial FDG uptake with a low carbohydrate high fat protein permitted (LCHFPP) diet.

MATERIALS AND METHODS

This was a prospective study. 50 patients were included in fasting group (>12 hours fasting) and 60 patients were included into LCHFPP diet. Fasting group had no special dietary preparation. Patients in LCHFPP diet group were asked to consume LCHFPP diet the night before and 4 hours prior to the study. Visual analysis of myocardial FDG uptake was done on maximum intensity projection image. Using CT images for localization, the ability to delineate possible FDG uptake in the left coronary artery was assessed in the corresponding PET image and the studies were classified as "interpretable" or "Not interpretable".

RESULTS

60 patients (mean age 47 years) from LCHFPP diet group and 50 patients (mean age 49.9 years) from fasting group were included. None of the patients were known diabetics. The mean blood glucose level was 96 mg/dL. Forty-eight patients had consumed LCHFPP diet as per protocol. Twelve had consumed LCHFPP diet only on the night before the study (non-compliant). The average duration of fasting in compliant patients was 5.9 ± 0.9 hours in the diet group and 14.6 hours in fasting group. In LCHFPP diet group, the myocardial FDG uptake was classified as complete suppression in 31; minimal uptake in 15; moderate inhomogenous uptake in 8 and homogenous intense uptake in 6 patients. Fifty-four of the 60 patients had interpretable study. When non-compliant patients were excluded, 84% of the patients had significant FDG uptake suppression and 94% of the studies were classified as interpretable. In the fasting group, complete myocardial suppression of FDG uptake was noticed in 16; minimal in 8; moderate inhomogenous in 15; and homogenous intense in 11 patients. 27 patients (54%) had interpretable study.

CONCLUSION

Consistent and significant myocardial FDG uptake suppression is possible in most patients using LCHFPP diet. The LCHFPP diet, if taken as per protocol, leads to consistent myocardial FDG uptake suppression to allow for adequate evaluation of the left coronary artery inflammation in nearly all the patients. LCHFPP diet is also significantly more efficacious than prolonged (>12 hours) fasting protocol in suppressing myocardial FDG uptake.

Imaging myocardial metabolic remodeling

Myocardial metabolic remodeling is the process in which the heart loses its ability to utilize different substrates, becoming dependent primarily on the metabolism of a single substrate such as glucose or fatty acids for energy production. Myocardial metabolic remodeling is central to the pathogenesis of a variety of cardiac disease processes such as left ventricular hypertrophy, myocardial ischemia, and diabetic cardiomyopathy. As a consequence, there is a growing demand for accurate noninvasive imaging approaches of various aspects of myocardial substrate metabolism that can be performed in both humans and small-animal models of disease, facilitating the crosstalk between the bedside and the bench and leading to improved patient management paradigms. SPECT, PET, and MR spectroscopy are the most commonly used imaging techniques. Discussed in this review are the strengths and weaknesses of these various imaging methods and how they are furthering our understanding of the role of myocardial remodeling in cardiovascular disease. In addition, the role of ultrasound to detect the inflammatory response to myocardial ischemia will be discussed.

Recent advances and future trends in multimodality cardiac imaging

The cardiovascular imaging field has experienced marked growth and technical advancement in the past several decades. In the future, multimodality imaging will provide enhanced characterisation of disease states. Myocardial perfusion imaging will become more quantitative, permitting measurement of absolute blood flow and coronary flow reserves during stress states. A greater use of positron emission tomography (PET) can be expected for both assessing blood flow quantitatively and molecular imaging of atherosclerotic plaques and myocardial disease states. SPECT and PET imaging of myocardial metabolism and cardiac neuronal imaging have already shown great promise for identifying high-risk patients with coronary heart disease and nonischaemic cardiomyopathy. Further progress will occur in computed tomography imaging of the heart and coronary arteries and cardiac magnetic resonance imaging including quantitative estimates of coronary blood flow, coronary and peripheral vessel plaque characterisation, and detection of myocardial cellular dysfunction. Fusion imaging, in which two disparate image data sets are merged into one functional image, will become commonplace. Major breakthroughs in CV imaging will depend on discoveries in basic research, further refinement of instrumentation and software for image processing and analysis, and outcomes research demonstrating the worth of imaging technologies in reducing cardiovascular death and morbidity.

Microvascular dysfunction, myocardial ischemia, and progression to heart failure in patients with hypertrophic cardiomyopathy

Microvascular dysfunction can be demonstrated in most patients with hypertrophic cardiomyopathy (HCM), both in the hypertrophied and nonhypertrophied myocardial walls, mostly due to intimal and medial hyperplasia of the intramural coronary arteries and subsequent lumen reduction. As a consequence, regional myocardial ischemia may be triggered by exercise, increased heart rate, or arrhythmias, in areas which are unable to increase myocardial blood flow. In patients with HCM, microvascular dysfunction leading to severe myocardial hypoperfusion during maximal hyperemia represents a strong predictor of unfavorable outcome, left ventricular remodeling with progressive wall thinning, left ventricular dysfunction, and heart failure. Accurate quantitative assessment of microvascular dysfunction and myocardial ischemia is not easily feasible in clinical practice. Although signs of inducible myocardial ischemia may be detected by electrocardiogram, echocardiography, or myocardial scintigraphy, the vasodilator response to dipyridamole by positron emission tomography is considered the method of choice for the assessment of maximal regional and global flow. Cardiac magnetic resonance provides further information, by late gadolinium enhancement (LGE), which may show areas where replacement fibrosis has occurred following microvascular ischemia and focal necrosis. LGE areas colocalize with severe regional microvascular dysfunction, are associated with increased prevalence of ventricular arrhythmias, and show more extensive distribution in the late stages of the disease, when heart failure is the dominant feature. The present review aims to provide a concise overview of the available evidence of microvascular dysfunction and ischemia eventually leading to disease progression and heart failure in HCM patients.

Ischemic patterns assessed by positron emission tomography predict adverse outcome in patients with idiopathic dilated cardiomyopathy

BACKGROUND

Although patients with idiopathic dilated cardiomyopathy (DCM) have no coronary artery disease, regional impairment of myocardial perfusion combined with preserved metabolism has been found using positron emission tomography (PET). Our aim was to assess the prognostic relevance of PET-mismatch between stress myocardial perfusion and glucose uptake on clinical outcome in DCM.

METHODS

In 24 patients with DCM who underwent both myocardial perfusion and metabolism PET scanning, "mismatch" was assessed and the association with clinical outcome (hospitalization, mortality, and heart transplantation) was investigated.

RESULTS

Mismatch was found in 16 patients (66.7%). Univariate analysis showed that the presence of mismatch was associated with adverse outcome (P = 0.03). After adjustment for sex and age, the association remained significant with an adjusted relative risk of 10.4 (95% CI 1.1-103; P = 0.04) for death, heart transplant, or hospitalization. Univariate analysis also showed that a higher extent of mismatch was significantly associated with adverse outcome (P = 0.02). After adjusting for sex and age, the association remained significant with an adjusted relative risk of 6.5 [95% CI 1.2-36; P = 0.03] for death, heart transplantation, or hospitalization.

CONCLUSION

PET stress perfusion-metabolism mismatch, indicative for ischemia, is frequently found in DCM patients and related to a poorer outcome.