Multimodality Imaging of the Brain-Heart-Axis after Ischemic Stroke Reveals Acute and Chronic Cardiac Dysfunction after Cerebral Ischemia

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): DFG; Ev Studienwerk Villigst

Introduction

Cerebral ischemia remains a major contributor to global morbidity and mortality. Beyond neurological dysfunction, cerebral stroke also increases risk of subsequent cardiac events and development of chronic heart failure. The mechanisms underlying this brain-heart communication are poorly characterized, but systemic inflammation is thought to play a role.

Purpose

We hypothesized that cerebral ischemic stroke evokes systemic inflammation contributing to acute cardiac stress and persistent contractile dysfunction, which may be monitored by serial molecular imaging by positron emission tomography (PET).

Methods

C57Bl6 mice underwent transient (30min) intraluminal middle cerebral artery occlusion (MCAo, n = 88) to induce stroke or sham surgery (n = 18). Serial 18F-GE180 PET at 24h, 7d, and 21d after injury identified translocator protein (TSPO) in brain microglia and peripheral macrophages as a marker of inflammation. Magnetic resonance imaging (MRI) determined stroke size and characterized cardiac function at 1 and 3wk after MCAo. Imaging signals were confirmed by autoradiography, immunohistochemistry and fluorescence-activated cell sorting.

Results

  MCAo in mice induced cerebral stroke of variable size (median 44.68mm3, range:5.12-139.60mm3). Localized inflammation in the injured hemisphere was observed by TSPO PET covering territory consistent to the stroke location, with marked increase in the neuroinflammatory signal at 7d relative to the contralateral hemisphere (% injected dose (ID)/g max: 3.82 ± 0.84 vs 2.51 ± 0.32, p < 0.001). TSPO signal was similarly elevated in the stroke region compared to sham animals (%ID/g max: 3.82 ± 0.84 vs 2.59 ± 0.72, p < 0.001). Corresponding with neuroinflammation, a heightened global myocardial TSPO signal was observed 7d after MCAo compared to sham (%ID/g: 7.75 ± 2.79 vs 5.61 ± 1.98, p = 0.041). TSPO PET signal remained elevated 21d after stroke in brain (3.20 ± 1.15 vs 2.46 ± 0.37, p = 0.012) and heart (8.62 ± 2.43 vs 5.85 ± 0.66, p = 0.022). Cerebral stroke was associated with reduced contractile function compared to sham at 1wk (ejection fraction, EF: 49.58 ± 16.90 vs 62.17 ± 5.25%, p = 0.025) and 3wk (54.30 ± 5.70 vs 66.06 ± 3.48%, p = 0.009). Larger stroke size identified early after injury by T2 weighted MRI, reflecting the focal injury and penumbra edema, correlated with worse subsequent cardiac function at 21d (r = 0.745, p = 0.009). Despite increased TSPO signal, flow cytometry showed comparable CD45+ leukocyte content in the left ventricle after MCAo compared to sham at 7d (p = 0.749).

Conclusions

Ischemic stroke evoked parallel cerebral and cardiac TSPO upregulation and persistent contractile dysfunction, beginning early after injury. The extent and severity of brain injury predicts left ventricle dysfunction, but the role of inflammation requires further investigation. Molecular imaging may identify risk and guide novel therapies to improve cardiac outcome after stroke.

Diagnosis and treatment of cardiac amyloidosis: position statement of the German Cardiac Society (DGK)

Systemic forms of amyloidosis affecting the heart are mostly light-chain (AL) and transthyretin (ATTR) amyloidoses. The latter is caused by deposition of misfolded transthyretin, either in wild-type (ATTRwt) or mutant (ATTRv) conformation. For diagnostics, specific serum biomarkers and modern non-invasive imaging techniques, such as cardiovascular magnetic resonance imaging (CMR) and scintigraphic methods, are available today. These imaging techniques do not only complement conventional echocardiography, but also allow for accurate assessment of the extent of cardiac involvement, in addition to diagnosing cardiac amyloidosis. Endomyocardial biopsy still plays a major role in the histopathological diagnosis and subtyping of cardiac amyloidosis. The main objective of the diagnostic algorithm outlined in this position statement is to detect cardiac amyloidosis as reliably and early as possible, to accurately determine its extent, and to reliably identify the underlying subtype of amyloidosis, thereby enabling subsequent targeted treatment.

Position paper nuclear cardiology: Update 2008

Nuclear cardiology is well established in clinical diagnostic algorithms for many years. This is an update 2008 of the first common position paper of the German Association of Nuclear Medicine and the German Association of Cardiology, Heart and Circulation Research published in 2001 aiming at an overview of state-of-the-art scintigraphic methods.

Standardised uptake values from PET/CT images: comparison with conventional attenuation-corrected PET

PURPOSE

In PET/CT, CT-derived attenuation factors may influence standardised uptake values (SUVs) in tumour lesions and organs when compared with stand-alone PET. Therefore, we compared PET/CT-derived SUVs intra-individually in various organs and tumour lesions with stand-alone PET-derived SUVs.

METHODS

Thirty-five patients with known or suspected cancer were prospectively included. Sixteen patients underwent FDG PET using an ECAT HR+scanner, and subsequently a second scan using a Biograph Sensation 16PET/CT scanner. Nineteen patients were scanned in the reverse order. All images were reconstructed with an iterative algorithm (OSEM). Suspected lesions were grouped as paradiaphragmatic versus distant from the diaphragm. Mean and maximum SUVs were also calculated for brain, lung, liver, spleen and vertebral bone. The attenuation coefficients (mu values) used for correction of emission data (bone, soft tissue, lung) in the two data sets were determined. A body phantom containing six hot spheres and one cold cylinder was measured using the same protocol as in patients.

RESULTS

Forty-six lesions were identified. There was a significant correlation of maximum and mean SUVs derived from PET and PET/CT for 14 paradiaphragmatic lesions (r=0.97 respectively; p<0.001 respectively) and for 32 lesions located distant from the diaphragm (r=0.87 and r=0.89 respectively; p<0.001 respectively). No significant differences were observed in the SUVs calculated with PET and PET/CT in the lesions or in the organs. In the phantom, radioactivity concentration in spheres calculated from PET and from PET/CT correlated significantly (r=0.99; p<0.001).

CONCLUSION

SUVs of cancer lesions and normal organs were comparable between PET and PET/CT, supporting the usefulness of PET/CT-derived SUVs for quantification of tumour metabolism.

The regulatory background of nuclear cardiology in Europe: a survey by the European Council of Nuclear Cardiology

PURPOSE

Nuclear cardiology is a well-validated, non-invasive imaging modality that is highly cost-effective as a diagnostic and prognostic tool in the evaluation of patients with known or suspected coronary artery disease. However, the number of procedures in Europe is very far from that which would be expected on the basis of epidemiological data, particularly when comparison is made with the USA. As a preliminary step for future action aimed at improving and increasing nuclear cardiology practice in Europe, the European Council of Nuclear Cardiology performed a survey to identify the regulatory issues and the training components pertaining to the practice of nuclear cardiology.

METHODS

a questionnaire was sent to 31 national nuclear medicine societies and to 40 national cardiology societies. The main areas covered by the survey were: (1) the license requirements, (2) the theoretical and practical aspects of training and (3) supervision of the stress test during a nuclear cardiology study.

RESULTS

The results show that, in a setting of wide heterogeneity of national regulations, education and professional practice, nuclear medicine is a restricted and closely regulated specialty. This situation guarantees the quality and safe use of radionuclides; at the same time, however, it limits integration of nuclear medicine into the clinical arena.

CONCLUSION

Cardiologists should become more involved in nuclear cardiology, to further stimulate the use of this powerful diagnostic and prognostic imaging modality.

The future of cardiovascular imaging and non-invasive diagnosis☆A joint statement from the European Association of Echocardiography, the Working Groups on Cardiovascular Magnetic Resonance, Computers in Cardiology, and Nuclear Cardiology of the European Society of Cardiology, the European Association of Nuclear Medicine and the Association for European Paediatric Cardiology

Advances in medical imaging now make it possible to investigate any patient with cardiovascular disease using multiple methods which vary widely in their technical requirements, benefits, limitations, and costs. The appropriate use of alternative tests requires their integration into joint clinical diagnostic services where experts in all methods collaborate. This statement summarises the principles that should guide developments in cardiovascular diagnostic services.

EANM/ESC procedural guidelines for myocardial perfusion imaging in nuclear cardiology

The European procedural guidelines for radionuclide imaging of myocardial perfusion and viability are presented in 13 sections covering patient information, radiopharmaceuticals, injected activities and dosimetry, stress tests, imaging protocols and acquisition, quality control and reconstruction methods, gated studies and attenuation-scatter compensation, data analysis, reports and image display, and positron emission tomography. If the specific recommendations given could not be based on evidence from original, scientific studies, we tried to express this state-of-art. The guidelines are designed to assist in the practice of performing, interpreting and reporting myocardial perfusion SPET. The guidelines do not discuss clinical indications, benefits or drawbacks of radionuclide myocardial imaging compared to non-nuclear techniques, nor do they cover cost benefit or cost effectiveness.

Myocardial blood flow and coronary flow reserve in children with "normal" epicardial coronary arteries after the onset of Kawasaki disease assessed by positron emission tomography

Myocardial blood flow (MBF) was investigated in children (14.2 +/- 5.01 years) with "resolved" coronary involvement after the onset of Kawasaki disease and angiographically normal epicardial coronary arteries. Ten asymptomatic children with a history of Kawasaki disease had electrocardiography, echocardiography, and positron emission tomography (PET) 10.3 +/- 6.01 years after onset of the acute illness. Myocardial perfusion was assessed by NH(3)- PET at rest and after vasodilatation and compared with that of 10 healthy volunteers (26.1 +/- 6.3 years). No patient had signs of myocardial ischemia; on echocardiography ventricular function was normal without dyskinetic areas or signs of enlargement or stenosis of the proximal coronary arteries. There was no statistical significant difference between patients and volunteers in MBF at rest (0.86 +/- 0.27 vs 0.77 +/- 0.17 ml/g/min), whereas MBF after vasodilatation (2.42 +/- 0.81 vs 3.10 +/- 0.8 ml/g/min) and coronary flow reserve (CFR) (2.89 +/- 0.26 vs 4.09 +/- 1.01 mmHg/ml/g/min) were significantly attenuated in the Kawasaki group. No stress-induced perfusion defects could be detected. In children with a history of Kawasaki disease and angiographically normal epicardial coronary arteries, there is a significant attenuation of MBF after vasodilatation and a significant reduction of CFR. Impairment of vasoreactive ability may indicate residual damage of the coronary arteries and may be a risk factor for atherosclerosis in adulthood.

Myocardial blood flow and flow reserve in response to short-term cyclical hormone replacement therapy in postmenopausal women

OBJECTIVES

To measure the effects of combined cyclical hormone replacement therapy (HRT) on myocardial blood flow (MBF) in postmenopausal women at high risk for coronary heart disease (CHD) and in women with documented CHD.

BACKGROUND

Estrogen restores endothelium-dependent vasodilation in response to acetylcholine in postmenopausal women, and it has a direct, endothelium-independent vasodilatory effect on coronary arteries.

METHODS

To determine whether coronary microcirculation can be affected by short-term, combined HRT, we performed positron emission tomography (PET) in two groups of women without previous HRT. Group I (n = 10) had one or more risk factors for CHD; group II (n = 8) had documented CHD and previous myocardial infarction. Group II was older (54 +/- 4 vs 59 +/- 5 y, P = .03) and had lower total cholesterol levels at baseline because of lipid-lowering therapy (244 +/- 31 vs 203 +/- 40 mg/dL, P = .03). Patients underwent baseline dynamic PET with N-13 ammonia at rest and during maximal adenosine-induced hyperemia to assess MBF. Each then began taking HRT (conjugated equine estrogen alone or with medroxyprogesterone acetate (MPA), administered in cyclical fashion), and returned for follow-up PET 46 +/- 12 days later.

RESULTS

There was no difference in resting MBF between groups I and II prior to starting therapy or at follow-up. Stress MBF and flow reserve (FR) tended to be higher in group I patients at baseline. MBF values remained unchanged at follow-up and resulted in similar FR values at baseline and during HRT for both groups. Women using only estrogen (n = 6) tended to show higher FR values after estrogen therapy, however.

CONCLUSIONS

Short-term HRT in postmenopausal women did not lead to improvements in MBF or FR. Combined cyclical HRT may not exert measurable effects on coronary microcirculation. MPA may attenuate estrogen effects on the coronaries, which may be largely endothelium-dependent.

Preoperative evaluation of pancreatic masses with positron emission tomography using 18F-fluorodeoxyglucose: diagnostic limitations

Identification of pancreatic cancer in patients presenting with an enlarged pancreatic mass is a major diagnostic problem. Positron emission tomography (PET) using the radiolabeled glucose analogue 18F-fluorodeoxyglucose (FDG) has been suggested to provide excellent accuracy for noninvasive determination of suspicious pancreatic masses. We conducted a prospective study to verify these results. Forty-two patients admitted for pancreatic surgery underwent PET scanning. Image analysis was based on visual film evaluation and quantification of regional tracer uptake. PET imaging was visually analyzed by three observers blinded for the results of other diagnostic tests; they qualitatively graded the scans using a five-point scale (I = low to V = high) for the presence and intensity of focal FDG uptake. Diagnosis was proven by histology (n = 38) or follow-up (n = 4). Furthermore, the results of PET were compared with helical computed tomography (CT) and conventional ultrasonography (US), done during the routine diagnostic workup before pancreatic cancer surgery. Regarding only the results with scores of IV and V as positive for representing definite malignancy yielded a sensitivity of 71% and a specificity of 64% for film reading. Quantification of regional tracer uptake contributed no significant diagnostic advantage for differentiation between benign and malignant tumors. Helical CT revealed a sensitivity of 74% and a specificity of 45.5% and abdominal US 56% and 50%, respectively. We concluded that PET imaging provides only fair diagnostic accuracy (69%) for characterizing enlarged pancreatic masses. PET does not allow exclusion of malignant tumors. In doubtful cases, the method must be combined with other imaging modalities, such as helical CT. The results indicate that the number of invasive procedures is not significantly reduced by PET imaging.

Regional pre- and postsynaptic sympathetic system in the failing human heart--regulation of beta ARK-1

OBJECTIVES

Regional presynaptic sympathetic innervation varies considerably in the cardiomyopathic human heart, as shown in previous studies in vivo and in vitro. The goal of the present study was to correlate markers of presynaptic sympathetic innervation with local measurement of the postsynaptic beta-adrenergic system in failing human hearts.

METHODS AND RESULTS

In nine left ventricular regions of hearts explanted from patients suffering from dilated cardiomyopathy, we measured the density of uptake(1) carriers ([3H]mazindol binding) as a marker of presynaptic function as well as beta-receptor density ([3H]CGP 12177 binding) and beta ARK-1 levels as the pivotal compounds of postsynaptic adrenergic signal transduction. Additionally, a subgroup of the patients was examined in vivo by HED-PET prior to heart transplantation. The density of uptake(1) was related to local hydroxyephedrine (HED) retention (as determined by pre-operative PET, r=0.65), whereas it was inversely correlated to regional beta ARK-1 levels (r=-0.61, P=0.04). In contrast, beta-adrenergic receptor density was not significantly correlated either to uptake(1) density or to local HED retention (r=0.15 and r=0.21).

CONCLUSIONS

Regional beta ARK-1 levels rather than beta-adrenergic receptor density were correlated with presynaptic alterations in cardiomyopathic human left ventricles. It can be assumed that in the cardiomyopathic human heart, regional beta-adrenergic desensitization might be determined by differences in local beta ARK levels rather than by changes in beta-receptor density.