Detection and characterization of hibernating myocardium

Growing applications of FDG PET-CT imaging in non-oncologic conditions

As the number of clinical applications of 2-[fluorine 18]fluoro-2-deoxy-D-glucose (FDG) positron emission tomography/computed tomography (PET-CT) grows, familiarity with the conditions that can be diagnosed by this modality and when relevant pieces of additional information can be obtained becomes increasingly important for both requesting physicians and nuclear medicine physicians or radiologists who interpret the findings. Apart from its heavy use in clinical oncology, FDG PET-CT is widely used in a variety of non-oncologic conditions interconnecting to such disciplines as general internal medicine, infectious diseases, cardiology, neurology, surgery, traumatology, orthopedics, pediatrics, endocrinology, rheumatology, psychiatry, neuropsychology, and cognitive neuroscience. The aim of this review was to summarize the current evidence of FDG PET-CT applications in evaluating non-oncologic pathologies and the relevant information it can add to achieve a final diagnosis.

Preclinical evaluation of biopolymer-delivered circulating angiogenic cells in a swine model of hibernating myocardium

BACKGROUND

Vasculogenic cell-based therapy combined with tissue engineering is a promising revascularization approach targeted at patients with advanced coronary artery disease, many of whom exhibit myocardial hibernation. However, to date, no experimental data have been available in this context; we therefore examined the biopolymer-supported delivery of circulating angiogenic cells using a clinically relevant swine model of hibernating myocardium.

METHODS AND RESULTS

Twenty-five swine underwent placement of an ameroid constrictor on the left circumflex artery. After 2 weeks, animals underwent echocardiography, rest and stress ammonia-positron emission tomography perfusion, and fluorodeoxyglucose positron emission tomography viability scans. The following week, swine were randomized to receive intramyocardial injections of PBS control (n=10), circulating angiogenic cells (n=8), or circulating angiogenic cells+collagen-based matrix (n=7). The imaging protocol was repeated after 7 weeks. Baseline positron emission tomography myocardial blood flow and myocardial flow reserve were reduced in the left circumflex artery territory (both P<0.001), and hibernation (mismatch) was observed. At follow-up, stress myocardial blood flow had increased (P≤0.01) and hibernation decreased (P<0.01) in the cells+matrix group only. Microsphere-measured myocardial blood flow validated the perfusion results. Arteriole density and wall motion abnormalities improved in the cells+matrix group. There was also a strong trend toward an improvement in ejection fraction (P=0.07).

CONCLUSIONS

In this preclinical swine model of ischemic and hibernating myocardium, the combined delivery of circulating angiogenic cells and a collagen-based matrix restored perfusion, reduced hibernation, and improved myocardial wall motion.

Cell-based vasculogenic studies in preclinical models of chronic myocardial ischaemia and hibernation

INTRODUCTION

Coronary artery disease commonly leads to myocardial ischaemia and hibernation. Relevant preclinical models of these conditions are essential to evaluate new therapeutic options such as cell-based vasculogenic therapies.

AREAS COVERED

In this article, the authors first review basic concepts of myocardial ischaemia/hibernation and relevant techniques to assess myocardial viability. Then, preclinical models of chronic myocardial ischaemia and hibernation, induced by devices such as ameroid constrictors, Delrin stenosis, hydraulic occluders, and coils/stents are described. Lastly, the authors discuss cell-based vasculogenic therapy, and summarise studies conducted in large animal models of chronic myocardial ischaemia and hibernation.

EXPERT OPINION

Approximately one-third of patients with viable myocardium do not undergo revascularisation; however, this population is at high risk for cardiac events and would surely benefit from effective cell-based therapy. Because of the modest benefits in clinical studies, preclinical models accurately representing clinical myocardial ischemia/hibernation are necessary to better understand and appropriately direct regenerative therapy research.

Pain-related somatosensory evoked potentials and functional brain magnetic resonance in the evaluation of neurologic recovery after cardiac arrest: a case study of three patients

This case series investigates whether painful electrical stimulation increases the early prognostic value of both somatosensory-evoked potentials and functional magnetic resonance imaging in comatose patients after cardiac arrest. Three single cases with hypoxic-ischemic encephalopathy were considered. A neurophysiological evaluation with an electroencephalogram and somatosensory-evoked potentials during increased electrical stimulation in both median nerves was performed within five days of cardiac arrest. Each patient also underwent a functional magnetic resonance imaging evaluation with the same neurophysiological protocol one month after cardiac arrest. One patient, who completely recovered, showed a middle latency component at a high intensity of stimulation and the activation of all brain areas involved in cerebral pain processing. One patient in a minimally conscious state only showed the cortical somatosensory response and the activation of the primary somatosensory cortex. The last patient, who was in a vegetative state, did not show primary somatosensory evoked potentials; only the activation of subcortical brain areas occurred. These preliminary findings suggest that the pain-related somatosensory evoked potentials performed to increase the prognosis of comatose patients after cardiac arrest are associated with regional brain activity showed by functional magnetic resonance imaging during median nerves electrical stimulation. More importantly, this cases report also suggests that somatosensory evoked potentials and functional magnetic resonance imaging during painful electrical stimulation may be sensitive and complementary methods to predict the neurological outcome in the acute phase of coma. Thus, pain-related somatosensory-evoked potentials may be a reliable and a cost-effective tool for planning the early diagnostic evaluation of comatose patients.

Clinical molecular imaging with radiotracers: current status

Molecular imaging is defined as the visualization, characterization, and measurement of biological processes at the molecular and cellular levels in humans and other living systems. Most clinical molecular imaging is currently done using radioisotope-labeled agents to define the activity of various metabolic pathways in vivo or to determine the distribution and density of various receptors relevant to human disease. This paper briefly reviews most of the commonly used radiopharmaceuticals in nuclear medicine, as well as newer agents that are likely to become available in the near future. The metabolic pathways include those relevant to the thyroid, parathyroid, heart, brain, bones, kidneys, liver, pancreas, adrenals and tumor. The receptor systems include agents useful in evaluating movement disorders, dementia, cardiac sympathetic enervation and neoangiogenesis. Receptor systems relevant to tumors include somatostatin receptors (neuroendocrine tumors), prostate-specific membrane antigen, carbonic anhydrase IX (renal cancer), and CD-20 (lymphoma). These agents, and newer agents that are being developed, are likely to become critical in the development of personalized medicine, where it will become increasingly important to determine whether a treatment that is targeted to a specific metabolic pathway or receptor is likely to be successful.

Heart Failure Following Anterior Myocardial Infarction: An Indication for Ventricular Restoration, a Surgical Method to Reverse Post-Infarction Remodeling

Anterior myocardial infarction produces abrupt left ventricular (LV) dysynergy and global systolic dysfunction. Rapid intense neurohumoral activation, infarct expansion, and early ventricular chamber dilatation all contribute to restoring a normal stroke volume despite a persistently depressed ejection fraction. Continued neurohumoral activation provokes late remodeling of the remote non-infarcted myocardium, characterized by an abnormal progressively increasing LV volume/mass ratio that leads to further LV remodeling. Heart failure is a progressive disorder of LV remodeling. Heart failure from post-infarction remodeling is unique because of the persistent non-functioning scar that self- perpetuates abnormal loading conditions and neurohumoral activation. Medical therapy attenuates remodeling and improves survival but does not change the size of the scar. Surgical ventricular restoration to exclude the non-functioning infarct from the ventricular cavity decreases ventricular volumes, increases global ejection fraction, attenuates neurohumoral activation and yields an excellent 5-year survival. Combined medical and surgical therapy is recommended in this patient population.

Combined CT-PET criteria for myocardial viability and scar: a preliminary report

Identification of hibernating myocardium and its differentiation from scar tissue is an important clinical task for implementing different treatment options. The recognition of combined criteria in spiral-CT and PET for hibernating myocardium and scar will be important as hybrid CT-PET moves into the main stream of routine oncologic and cardiovascular imaging. A review of three cases, initially referred for CT evaluation of cardiac or pulmonary conditions with subsequent F-18 FDG body PET imaging, was presented for illustration as a combined CT-PET cardiac evaluation. The real value of this combined anatomical and functional evaluation will be with the upcoming concurrent CT and PET imaging using dedicated multi-slice CT-PET scanners.

Characterization of hibernating myocardium with NOGA electroanatomic endocardial mapping

Because the terms "hibernation" and "viability" are not interchangeable, the recognition of hibernating myocardium within viable segments remained elusive for NOGA electroanatomic endocardial mapping. The aim of the present study was to determine the characteristics of hibernating myocardium in NOGA mapping. Baseline and follow-up endocardial mapping, thallium-201 myocardial perfusion scintigraphy at rest, and contrast ventriculography were performed in 28 patients who had proved viable myocardium before and 7.3 +/- 2.5 months after percutaneous coronary intervention. Significantly improved regional wall motion in the revascularized territory (region of interest) was confirmed in 9 patients (group 1) at follow-up (from -2.11 +/- 0.87 to -1.48 +/- 0.43 SD/chord, p <0.05), whereas no change in regional wall motion was observed in 19 patients (group 2; from -2.56 +/- 0.88 to -2.79 +/- 0.91 SD/chord). Average normalized thallium uptake at rest increased significantly in groups 1 and 2 after revascularization. A trend toward increased unipolar voltages in the region of interest was observed in group 1 at follow-up (from 10.6 +/- 3.5 to 11.7 +/- 4.0 mV, p = 0.073), whereas no change was observed in group 2 (from 8.7 +/- 4.4 to 8.9 +/- 3.8 mV). A significant increase in local linear shortening was measured only in group 1 (from 7.5 +/- 5.2% to 10.3 +/- 3.9%, p <0.05). Hibernating myocardial segments exhibited significantly higher unipolar voltages and late thallium uptake at rest at baseline. Receiver-operator characteristic analysis showed a mean unipolar voltage of 9.0 mV (predictive accuracy 0.708, common sensitivity and specificity 72%) in the region of interest for prediction of functional recovery. In conclusion, for characterizing the hibernating myocardium within viable segments, NOGA endocardial mapping offers on-line guidance for percutaneous coronary and noncoronary myocardial revascularization.

Pathology in patients with ventricular assist devices

BACKGROUND

Ventricular assist devices (VADs) are used as a bridge to cardiac transplantation or as a permanent or sometimes temporary treatment for end stage heart failure.

METHODS

Our autopsy and surgical pathology experience with VADs prior to August 2002 was reviewed. Noted were patient's age, sex, underlying (UCOD) and proximate causes of death (PCOD), duration of VAD implantation, presence of native or prosthetic valvar disease and organ complications. Myocardium from biopsies and explanted hearts were blindly assessed for coagulative necrosis (CN), contraction bands (CB), myocytolysis (MC), increased eosinophilia (IE), myocyte waviness (MW) and fibrosis (F). Each was graded as either mild (score 1), moderate (score 2) or severe (score 3).

RESULTS

Autopsy patients: Twenty-one patients, with mean age 55 years (range 10-73), comprised 10 women and 11 men. UCOD was ischemic disease in 16 patients, dilated cardiomyopathy in 4 and aortic valve disease in 1. The mean duration of VAD implantation was 125.7 days (range 1-1095 days, S.D.=253.6). Five patients had biventricular VADs, and 16 had LVAD only. Acquired aortic valve fusion was noted in three patients. PCOD was VAD related in six, donor heart problem in four, cerebrovascular accident in four, miscellaneous in three, pulmonary hypertension in two and aortic disease in two patients. Morbidity: local liver necrosis in seven, acquired aortic valve disease in four, gut infarction in three, abdominal aortic aneurysm in two and host cell assault against VAD porcine aortic valves in one case. Biopsies and explanted hearts: Twenty-four patients had a mean age of 53 years (range 38-68, S.D.=8.6). VADs were implanted for 177.8 days (range 7-593 days, S.D.=151.1). Comparison of histologic scores of biopsies with explanted hearts showed the following: CN 1.33 (S.D.=1.4)/0.21 (S.D.=0.66; P<.001); CB: 2.1 (S.D.=0.93)/0.83 (S.D.=0.28; NS); MC: 0.88 (S.D.=1.19)/0.13 (S.D.=0.34; P<.01); IE: 1.71 (S.D.=1.27)/0.38 (S.D.=0.65; NS); fibrosis: 1.08 (S.D.=1.35)/1.75 (S.D.=1.26; NS); and MW: 1.50 (S.D.=1.22)/0.59 (S.D.=0.73; P<.01). Acquired aortic stenosis developed in six hearts, and one heart showed thrombotic occlusion of the left ventricular outflow tract below an aortic bioprosthesis.

CONCLUSIONS

VAD significantly reduced the amount of CN, MC and MW in the left ventricle but may lead to acquired aortic stenosis of native aortic valves or total occlusive thrombosis of aortic prosthetic valves. Proximate cause of death was, most often, VAD related.

An assessment of wall motion, perfusion and glucose metabolism in recent myocardial infarction: a comparison in patients with and without revascularization

The aim of this study was to compare the extent and severity of wall motion abnormalities, perfusion and glucose metabolism, in recent myocardial infarction in patients with and without revascularization. Forty-nine patients were studied (82% men; mean age 58 years) by using echocardiography, 201Tl single photon emission computed tomography (SPECT) rest and redistribution, and 2-[18F]fluoro-2-deoxy-D-glucose (18F-FDG) SPECT at a mean of 9.2 days (range, 1-24 days) after myocardial infarction. Twenty-seven of the 49 patients underwent revascularization while the other 22 received medical therapy before echocardiography and studies using radionuclides. A contrast angiogram was obtained for each patient. A follow-up echocardiogram at 3 months was obtained for 44 patients. Images were read blindly, using a 17 segment model, with semi-quantitative analysis. In the whole group, the extent of hypokinesia was 15%+/-14 (mean+/-SD); the extent of mild defects was determined as 5%+/-6 by using 201Tl at rest, 6%+/-9 by using 201Tl redistribution, and 4%+/-6 by using 18F-FDG (P<0.0005, echocardiogram/radionuclides). Echocardiography showed that the extent of akinesia-dyskinesia was 16%+/-18 in revascularized patients and 28%+/-18 in non-revascularized patients (P=0.017). With regard to moderate and severe defects, 201Tl rest showed 19%+/-16 and 28%+/-17, respectively (P=0.047); 201Tl redistribution 17%+/-15 and 26%+/-15, respectively (P=0.043); and 18F-FDG 17%+/-13 and 24%+/-15, respectively (NS). In echocardiography, the extent of hypokinetic segments decreased from 16%+/-15 at baseline to 10%+/-11 at 3 months (P=0.045), in revascularized patients. It is concluded that, in recent myocardial infarction, hypokinesia extent on echocardiogram is greater than mild perfusion or metabolic defect extent, reflecting stunning and so the use of radionuclide techniques appear more accurate for defining the extent of myocardial infarction. Non-revascularized patients showed a significantly greater extent of akinesia-dyskinesia and moderate-severe perfusion defects than did revascularized patients, which can be considered a result of therapy. It is suggested that 201Tl rest perfusion be used for the assessment of myocardial infarction soon after revascularization.

[Magnetic resonance imaging early after acute myocardial infarction. A visual analysis of myocardial perfusion based on a 17 segment model]

Magnetic resonance imaging allows an accurate calculation of the left ventricular ejection fraction and left ventricular volumes. Additionally, it makes possible to assess myocardial perfusion after gadolinium chelate injection. Late after the injection, the presence of a myocardial hyper-enhancement can be visualized. The present study has used the 17 segment standardized nomenclature for tomographic imaging of the heart as recommended for all cardiac imaging modalities. Sixty nine patients were studied after a revascularised myocardial infarction. All patients had Timi grade 3 flow in the infarct-related artery after therapy. Regional and global function was studied using cine MR short axis slices. The gadolinium chelate first pass was scored using a 5 level scale reflecting the transmural extent of the segmental myocardial enhancement. The delayed enhancement due to gadolinium accumulation in the myocardium 10 min post injection was scored in the same manner. Left ventricular ejection fraction was 51 +/- 13%. Segmental thickening parameters (systolic thickness, absolute thickening and relative thickening) appeared statistically related to the hypoperfusion and delayed enhancement scores. Absolute myocardial thickening varied from 4.8 +/- 2.7 mm in the myocardial segments free of any delayed enhancement to 2.4 +/- 2.1 mm in segments presenting with a transmural extent of the delayed hyper-enhancement. Scores obtained after gadolinium injection were also well correlated with the global left ventricular function (r = 0.65, p < 0.01 for late enhancement). Magnetic resonance imaging of the heart allows a precise characterisation of revascularised myocardium which makes this technique very attractive for evaluating the treatments designed to improve myocardial microperfusion.