MEETING HIGHLIGHTS: VIEWPOINT
Highlights of the 2006 Scientific Sessions of the American Society of Nuclear Cardiology
Montreal, Canada, September 7 to 10, 2006
Jeroen J. Bax, MD, PhD*,*,
Brian G. Abbott, MD ,
Robert S. Beanlands, MD ,
Frank Bengel, MD ,
Daniel S. Berman, MD||,
Ernest V. Garcia, PhD¶,
Robert C. Hendel, MD#,
Jennifer H. Mieres, MD**,
Leslee J. Shaw, PhD¶ and
Frans J. Th. Wackers, MD, PhD
* Leiden University Medical Center, Leiden, the Netherlands
Brown Medical School, Providence, Rhode Island
University of Ottawa Heart Institute, Ottawa, Canada
Johns Hopkins University Medical Center, Baltimore, Maryland
|| Cedars-Sinai Medical Center, Los Angeles, California
¶ Emory University School of Medicine, Atlanta, Georgia
# Midwest Heart Specialists, Chicago, Illinois
** NYU Medical Center, New York, New York
Yale University Medical School, New Haven, Connecticut
Manuscript received November 3, 2006;
accepted November 7, 2006.
* Reprint requests and correspondence: Dr. Jeroen J. Bax, Leiden University Medical Center, Albinusdreef 2, 2333 ZA Leiden, the Netherlands. (Email: j.j.bax{at}lumc.nl).
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Abbreviations and Acronyms
| | CAC = coronary artery calcium | | CAD = coronary artery disease | | CT = computed tomography | | FDG = 18F-fluorodeoxyglucose | | LV = left ventricular | | MIBG = 123I-metaiodobenzylguanidine | | MMP = matrix metalloproteinase | | MRI = magnetic resonance imaging | | PET = positron emission tomography | | SPECT = single-photon emission computed tomography |
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The 11th Annual Scientific session of the American Society Nuclear Cardiology (ASNC, chaired by Dr. Daniel Berman) was held from September 7 through 10, 2006, in Montreal, Canada, with more than 1,100 registrants in attendance. This 4-day meeting was divided into 4 major tracks (plenary sessions, core curriculum, advanced track, and investigative track) as well as read-with-the-expert sessions and satellite symposia. In addition, original research was contributed in the form of abstract presentations and included a competition in the Young Investigator Award.
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Plenary Sessions
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The Mario Verani Memorial Lecture: evolving challenges and opportunities for nuclear cardiology (Dr. Ami Iskandrian).
The Mario Verani lecture is presented each year at the ASNC annual meeting by a prominent nuclear cardiologist in memory of Dr. Mario Verani (1943 to 2001), a pioneer in nuclear cardiology and founder and past-president of ASNC. In the fifth Mario Verani Lecture, Dr. Iskandrian addressed new challenges and opportunities for nuclear cardiology. He noted that although American Heart Association/American College of Cardiology guidelines recognize many class 1 indications for radionuclide imaging, there is a paucity of evidence-based (Level 1) data. Prospective multicenter trials, such as the INSPIRE (AdenosINe Sestamibi Post-InfaRction Evaluation) trial, that use radionuclide imaging end points are much needed.
Dr. Iskandrian also discussed the use of radionuclide imaging for defining end points of novel therapies, such as regenerative therapy with stem cells. He emphasized the importance of quantification of myocardial perfusion and/or function, especially in view of the substantial interobserver variability even among expert readers using visual analysis. Accordingly, the Food and Drug Administration has now accepted quantitative image analysis as an alternative for multiple readers' visual interpretation.
Another technique discussed by Dr. Iskandrian is neuronal imaging with 123I-metaiodobenzylguanidine (MIBG). Several multicenter studies are now underway using MIBG single-photon emission computed tomography (SPECT) to explore which patients are at risk for sudden cardiac death and which benefit from implantable cardioverter-defibrillator therapy. The role of imaging in special populations, including those with chronic kidney disease, also was highlighted. Forty-seven percent of these patients die from cardiovascular complications. However, even after coronary revascularization, survival remains poor. Moreover, many patients die with normal left ventricular (LV) ejection fraction, and patients with normal myocardial perfusion have worse outcome as compared with the normal population. Thus, unresolved issues remain in patient management, including the use of radionuclide imaging in renal dysfunction.
Detecting the high-risk patient.
Dr. William Wijns discussed the clinical value of radionuclide imaging and computed tomographic (CT) angiography in detection of the high-risk patient. In the past, visualization of the coronary arteries was the domain of invasive angiography and the threshold for angiography was relatively high. Myocardial perfusion imaging served efficiently as the gatekeeper to this invasive procedure. However, with the recent introduction of noninvasive CT angiography, the threshold has become considerably lower, and low-risk patients may have their coronary anatomy visualized. This development resulted in detection of coronary artery disease (CAD) at an earlier stage with more mild and nonobstructive CAD detected than before. To better understand the clinical significance of these findings and decide on appropriate clinical management, new demands and questions are put on myocardial perfusion imaging. For example, in a study of 140 patients with intermediate likelihood of CAD who all had multislice CT angiography, no CAD was found in approximately one-third of patients, nonobstructive CAD in another one-third, and obstructive CAD (>50% luminal narrowing) in another one-third of patients. However, 40% of patients with nonobstructive CAD had abnormal perfusion on stress SPECT, and 50% of patients with obstructive CAD had normal perfusion on stress SPECT.
Invasive tools used during cardiac catheterization to evaluate coronary flow reserve and, thus, the entire coronary arterial system, demonstrate a substantial spread and overlap of coronary flow reserve in patients with obstructive and nonobstructive CAD, suggesting that many of the apparently false-positive stress SPECT studies may be due to abnormal coronary flow reserve. Conversely, patients with false-negative stress SPECT studies may have adequate collateral circulation. Invasive interrogation of the coronary flow reserve clearly demonstrates the limitations of coronary anatomy as visualized by either invasive or noninvasive coronary angiography. The prior experience with invasive angiography now needs to be translated into noninvasive cardiac imaging techniques to aid physicians in making appropriate clinical decisions. Noninvasive imaging also may aid coronary angiography in patient populations that are at higher risk, but who are still underdiagnosed and undertreated, such as patients with diabetes, women, and the elderly. Dr. Wijns concluded that noninvasive cardiac imaging is well positioned to play an important role to guide therapy in the high-risk patient. More than ever, there is a need for accurate evaluation of the hemodynamic significance of individual coronary stenoses. The knowledge derived from invasive evaluation of vulnerable, non–flow-limiting plaques needs to be transferred to noninvasive imaging. This requires "crosstalk" between interventional cardiologists and noninvasive cardiac imagers. Ultimately, the incremental cost-effectiveness of diagnostic imaging procedures will have to be demonstrated.
Nuclear imaging in special populations.
Dr. Avjit Lahiri pointed out that, by the year 2030, the number of patients with type 2 diabetes mellitus worldwide will amount to 370 million. The risk for developing CAD is 2- to 4-fold higher in patients with diabetes than in nondiabetic patients, and in many patients with diabetes, CAD is asymptomatic. Stress myocardial perfusion imaging has been shown to be equally effective in detecting the presence of CAD and in estimating prognosis as in patients without diabetes. However, for any given size of myocardial perfusion abnormality, the mortality in patients with diabetes was 2-fold greater. In addition, the long-term outcome in patients with diabetes and normal SPECT images was 1.5- to 3-fold worse than patients without diabetes. Several studies assessed the prevalence of silent CAD in truly asymptomatic patients with diabetes. Dr. Lahiri proposed the use of CT coronary calcium scoring (CAC) as a prescreening tool to enrich the target population. If only diabetic patients with CAC  100 Agatston units would be screened with stress SPECT imaging, approximately 50% of patients can be anticipated to have abnormal SPECT images, with 20% being markedly abnormal, far greater than noted when examining all asymptomatic diabetics. The use of CAC scoring and stress myocardial SPECT are therefore synergistic in predicting cardiovascular mortality and morbidity and may prove to be a cost-effective approach in asymptomatic patients with diabetes.
Value of radionuclide imaging in patients with heart failure.
Dr. Prem Soman discussed the value of radionuclide imaging in patients with heart failure. Myocardial perfusion imaging has been used extensively in patients with heart failure for the detection of CAD (to differentiate between ischemic and nonischemic cardiomyopathy), in the assessment of myocardial viability, for risk stratification, and in the quantification of LV (dys)function. Radionuclide imaging has been useful in the identification of the 70% of patients with ischemic cardiomyopathy, ischemic, and/or dysfunctional but viable myocardium who can benefit from revascularization with improvement in symptoms, regional and global LV function, and survival.
The use of neurohumoral imaging with MIBG predicts outcome in both ischemic and nonischemic cardiomyopathy and may be used to monitor response to heart failure therapy. Dr. Leslee Shaw also addressed the role of nuclear imaging in women. Before the introduction of contemporary techniques, myocardial perfusion imaging was notable for a lower diagnostic accuracy in women than in men because of technical issues (e.g., breast attenuation) but also pathophysiological issues (e.g., women more often have small vessel disease and more nonobstructive CAD). Recent advances in SPECT imaging, including the use of attenuation correction and prone imaging, have significantly improved diagnostic accuracy in women.
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Core Curriculum: Advances in Nuclear Cardiology
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Quantitative analysis.
The visual assessment of scintigraphic images remains problematic because of attenuation artifacts, poor interobserver agreement, and lack of precise quantification of defect extent and severity. With the currently available software programs, accurate and reproducible quantitative analysis is possible, not only for assessment of myocardial perfusion and function but also for evaluation of tracer lung uptake, transient ischemic dilation, LV shape and eccentricity, and LV mass. Drs. Ernest Garcia and Guido Germano discussed recent advancements in the field of quantification, including phase analysis (evaluating LV systolic dyssynchrony) and the assessment of diastolic function (by defining the derivative of the time-volume curve to estimate peak filling rates).
Myocardial perfusion imaging with positron emission tomography (PET).
In clinical cardiology, PET has been used mainly for viability assessment with 18F-fluorodeoxyglucose (FDG) imaging, but recent studies have reported on the use of PET perfusion imaging to detect and evaluate CAD, noting the improved image quality with PET as compared with SPECT imaging. Dr. Timothy Bateman explained that the advantages of PET include improved spatial and contrast resolution, greater count density, improved scatter counts, and the automatic use of attenuation correction algorithms. Particularly in patients with a nondiagnostic SPECT study, these technical advantages of PET assist in disease evaluation and also offer the potential to provide absolute quantification of myocardial perfusion, which contributes to more accurate detection of CAD, particularly in patients with multivessel CAD. In these patients, a SPECT study may be normal because a balanced reduction in myocardial perfusion will be present; absolute quantification, however, will note the balanced reduction in the different coronary territories. Also, a PET perfusion study can be completed in <20 min, which may allow higher patient throughput. Finally, there is now growing evidence on the prognostic value of PET perfusion studies, showing similar abilities for risk stratification as with SPECT.
Dr. Marcelo Di Carli discussed the expanding role of hybrid PET-CT imaging. Anatomical information on coronary artery anatomy and extent of atherosclerosis, as well as functional information regarding ischemia and perfusion, can be obtained and combined together in a "fused" image. Various studies have shown that CT angiography has an extremely high negative predictive value, indicating that a normal CT angiogram virtually excludes CAD. Conversely, in the presence of atherosclerosis on CT angiography, the PET perfusion information may indicate the hemodynamic significance of the lesions. Whether this integrated information provides superior prognostic information remains to be shown, although clearly this technique has great promise.
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Advanced Clinical Track: Merits of Different Imaging Modalities
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Imaging to evaluate coronary plaques.
The detection of active plaques at risk of rupture would allow the identification of vulnerable patients. Dr. Mari Aparici highlighted the value of nuclear imaging to target specific molecular and cellular processes of the vulnerable plaque. Radiolabeled agents to detect a vulnerable plaque imaging target several aspects of the atherosclerotic process, include inflammation (using FDG uptake by macrophages and monocytes), apoptosis (using 99mTc-labeled annexin-V), matrix metalloproteinase activity (using labeled matrix metalloproteinases [MMPs]), proliferating vascular endothelial and smooth muscle cells (using 111In-Z2D3 and labeled  vß3 integrins). Preliminary data in carotid arteries suggest that the best results are currently obtained with annexin-V and FDG, which provide high contrast between lesions and normal vessels. Additionally, diffuse inflammation can be identified on FDG-PET. However, the process of vascular inflammation is not stable over time, and FDG uptake may vary. Calcification of lesions may be caused by apoptosis and, therefore, some researchers have suggested that annexin-V may become a better indicator. Dr. William Strauss pointed out that precise localization of the disease activity (as detected by nuclear imaging) may be difficult, but hybrid systems such as PET-CT and SPECT-CT may permit plaque imaging with accurate anatomical co-registration.
Dr. Zahi Fayad addressed the role of magnetic resonance imaging (MRI) for the evaluation of plaque composition. Recent studies using 3-T MRI have indeed shown superior evaluation of plaque composition and visualization of plaque hemorrhage. Another potential of MRI is the combination with intravascular probes for plaque evaluation and visualization.
Dr. William Wijns addressed the value of invasive imaging techniques. Recent developments include improved evaluation of plaque composition with intravascular ultrasound using virtual histology analysis. Very precise quantification of plaque volume and components is possible with optical coherence tomography. These newer invasive imaging techniques may have the potential to distinguish between stable and unstable atherosclerotic plaques.
Imaging to evaluate therapy.
During recent years, large databases examining risk stratification with (gated) SPECT perfusion imaging have been published, and perfusion imaging is now used frequently as an end point to evaluate and compare therapies, as discussed by Drs. Leslee Shaw and John Mahmarian. These trials range from small studies evaluating novel revascularization or regenerative therapies, to large randomized, controlled trials evaluating global management or comparisons between different testing strategies. Evaluations of novel therapies include laser revascularization, gene therapy, and stem cell therapy. Examples of large studies evaluating global management are the INSPIRE trial, the ACME (Angioplasty Compared to Medical Therapy) trial, and the COURAGE (Clinical Outcomes Using Revascularization and Aggressive Drug Evaluation) trial. In these trials, the relative effects of revascularization and drug therapy on ischemia were evaluated using myocardial perfusion imaging. The DIAD (Detection of Ischemia in Asymptomatic Diabetics) trial is an example of a comparison of different testing strategies: asymptomatic diabetic patients undergo risk stratification based on routine clinical work-up or with the inclusion of myocardial perfusion imaging (to assess ischemia). Finally, because the reproducibility of (gated) SPECT is high, perfusion imaging is ideal for serial monitoring of effect of different medical therapies, and improvement in perfusion has been demonstrated after beta-blockers, statins, and angiotensin-converting enzyme inhibitors.
Drs. Paolo Raggi and Zahi Fayad discussed the potential roles of electron beam CT and MRI to evaluate progression or regression of atherosclerosis. Both techniques appear promising for sequential imaging, whereas multislice CT (because of the high radiation dose) at present is not suited for sequential imaging.
Imaging in heart failure.
Different imaging modalities often provide complementary information in patients with heart failure. Radionuclide imaging continues to provide key clinical information on LV function, ischemia, and hibernation, which are important in therapeutic decision making for the patient with heart failure. More work is needed to understand the desired outcomes in patients with heart failure because it is clear that the improvement in LV function after revascularization does not always translate into better outcome. In addition, interest in autonomic nervous system imaging is increasing, and the role of MIBG imaging to predict outcome in patients with heart failure is being evaluated in a multicenter study. Dr. James Fallavolita noted that hibernating myocardium is associated with partial denervation, as evidenced by reduced 11C-hydroxyephrine uptake on PET, which may indicate high risk for sudden cardiac death.
New echo techniques also are important in evaluation of patients with heart failure; particularly, 3-dimensional echocardiography may provide optimal information on LV function and shape in addition to the presence/etiology of mitral regurgitation. A very important issue is selection for cardiac resynchronization therapy, which is mainly based on assessment of LV dyssynchrony. At present, echocardiography using tissue Doppler imaging and strain (rate) imaging appears well suited for assessment of LV dyssynchrony.
The role of MRI in patients with heart failure is mainly to assess LV function and, using contrast-enhanced imaging, to precisely delineate the presence and extent of scar tissue/presence of viable myocardium. Dr. Chris Kramer indicated that, for optimal prediction of functional recovery after revascularization, the assessment of scar tissue (with contrast-enhanced MRI) should be combined with the assessment of contractile reserve (with low-dose dobutamine MRI).
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Advanced Clinical Track: Update in Instrumentation
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The principal hurdle in cardiac PET-CT is artifact caused by transmission misalignment. This can be improved by gating both cardiac and respiratory motion and is the focus of current research. Technology improvements continue to search for new detector materials, improved design, and improved resolution. Lutetium oxyorthosilicate and Bismuth-Germanate currently have the highest density and highest effective Z coordinate, respectively, among the more widely available detectors; however lutetium-yttrium oxyorthosilicate and Lanthanum bromide may provide high light output and stopping power. Time of flight will lead to increased resolution that will improve lesion contrast. The true incremental value of this for cardiac imaging remains to be seen but could become particularly important if plaque imaging becomes a clinical reality. From the CT aspect, the potential advantages of 64-slice CT need to be considered: 64-slice cameras increase scan speed, which improves contrast resolution and permits a shortened breath hold, which means, for CT, a higher spatial resolution resulting in detailed vascular mapping, more accurate measurement of coronary artery stenosis, and optimal 3D visualization. In the future, dual-source CT (2 X-ray tubes rotating) may improve temporal resolution and permit tissue characterization, especially at higher heart rates and reduce patient radiation dose by imaging twice as fast.
With regard to SPECT imaging, attenuation correction has been and remains available. Although recommended by ASNC, only few centers are actually using attenuation correction in SPECT imaging. An exciting development is new devices that may enable dynamic SPECT imaging, permitting absolute quantification of perfusion. New methods, such as motion frozen perfusion or "thin plate spline warping," may improve image quality by bringing images to diastolic position.
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Investigative Track: Nuclear Imaging and Basic Science
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The investigative track comprised 3 sessions, which all were dedicated to advanced topics involving nuclear imaging primarily on a basic science level. The first session was dedicated to the role of genomics, proteomics, and imaging on the pathway toward personalized medicine. Dr. Joseph Wu summarized existing genomic techniques. Applications of such gene-targeted approaches seem to get closer to the clinics, but costs associated with gene chips and subsequent confirmatory analyses are not negligible. Although genomic analyses identify certain candidate genes associated with a disease, it needs to be emphasized that the pure presence of a gene does not reflect its level of transcription and translation into a protein as the true effector molecule. Proteomic analysis is thus considered an important aspect of molecular analysis of disease, and proteomic techniques were outlined by Dr. Anrzej Chruscinski. A variety of unbiased techniques to identify previously unknown proteins associated with disease conditions are available. The substantial challenge of integrating genomics, proteomics, and imaging to achieve the visionary goal of individualized health care was then outlined by Dr. Frank Bengel. It was proposed that results from gene expression profiles, proteomic profiles, clinical information, and imaging are being integrated into models to predict individual diagnosis, risk, and therapy response. Imaging can play a key role in this integrative process by allowing for a precise description of the individual phenotype. A consensus of the session was that despite the well-perceived complexity of the topic, the common visionary goal of personalized medicine should stimulate increasing interaction between imagers, clinicians and molecular scientists.
The second session was dedicated to novel molecular diagnostic approaches in heart failure and examined a variety of novel therapeutic approaches. Dr. Albert Sinusas explained the role of MMPs in the pathophysiology of LV remodeling as a key feature of heart failure development and progression. Novel MMP ligands for SPECT imaging have been introduced recently and provide robust signals from infarct and peri-infarct areas. Metabolic alterations as another critical component of LV dysfunction were reviewed by Dr. Pablo Soto. Nuclear imaging with SPECT and PET allows for identification of the relative utilization of glucose and fatty acids as substrates for energy consumption. As part of the early disease process, shifts in substrate use may occur within the cardiomyopathic heart, thereby contributing to disease progression and decrease of contractile performance. The role of receptor systems in heart failure is well known and has stimulated the development of several drugs used for treatment. Dr. Frank Bengel emphasized that imaging of postsynaptic receptors is a significant challenge for nuclear imaging. Imaging of presynaptic innervation itself may thus be a sufficiently accurate molecular approach to characterize involvement of the adrenergic nervous system in heart failure progression. The session successfully demonstrated that several very specific biologic imaging approaches are on the horizon that may allow for improved stratification of patients with heart failure in the future.
The third session was dedicated to imaging as a tool to provide insights into vascular biology and disease. Dr. Flordeliza Villanueva outlined the potential of ultrasound for targeted imaging of vascular structures. Microbubbles can be used as contrast agents, which can be specifically targeted toward intravascular molecules if the bubbles are coupled with molecular ligands. An innovative strategy for detection of the accumulation of small amounts of radionuclides within the vessel wall could be the use of intravascular probes. Dr. William Strauss outlined this novel strategy, which is based primarily on beta-particle sensitive scintillators incorporated in small intravascular catheters. These catheters can even be combined with other techniques such as intravascular thermography to measure inflammation. Finally, the role of targeted imaging of vß3 integrin, an adhesion molecule involved in angiogenesis, was highlighted. Dr. Albert Sinusas provided an overview of recently available integrin-targeted SPECT tracers and their accumulation in ischemically damaged tissue. Integrin expression occurs to some degree in atherosclerotic lesions but more so in graft arteriopathy, as outlined by Dr. Mehran Sadeghi in the final talk of the session. Such novel tracers and techniques are thus expected to significantly improve the understanding of vascular biology, and they may enter the clinical arena as markers of disease outcome or therapy response.
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Original Research: Abstract Contributions
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A total of 110 abstracts were selected from a group of competitive submissions after peer review. All selected abstracts were published in the July/August issue of the Journal of Nuclear Cardiology. A brief synopsis of these presentations is provided herein
Young investigator award.
This symposium comprised 6 oral presentations focusing mainly on clinical aspects of myocardial perfusion imaging. Somekh et al. (1) presented results of a comparative study of the performance of a dedicated chest pain unit, a hospitalist service, and a private attending service for handling patients with chest pain but without an acute coronary syndrome. Strategies included the usage of myocardial perfusion imaging, which was used most efficiently in the chest pain unit, where outcomes seemed to be best. Shah et al. (2) analyzed the independent predictors of outcome in elderly patients (age >75 years) undergoing myocardial perfusion-gated SPECT and observed that patients who were not able to exercise had higher event rates, whereas perfusion abnormalities and LV ejection fraction were also independent predictors of outcome. Mehta et al. (3) won the young investigator award, reporting on the clinical application of the American College of Cardiology Foundation (ACCF)/ASNC appropriateness criteria for perfusion SPECT. These authors observed that 82% of the appropriately indicated studies were associated with less normal results and more severe abnormalities on SPECT than in the inappropriate-indicated studies. Still, there were 31% abnormal studies in the inappropriately referred group, a finding that requires further investigation. Mohmed et al. (4) presented a novel 3-dimensional iterative algorithm for gated SPECT reconstruction and observed excellent correlation with standard filtered back-projection data. The setting was a high-count stress study, and it was concluded that further tests in low-count studies are warranted.
Druz et al. (5) observed that discharge of implantable cardioverter defibrillators was not associated with residual ischemia on gated SPECT but rather with ongoing LV remodeling, as indicated by lower LV ejection fraction and larger volumes. Finally, Moloo et al. (6) evaluated FDG uptake as a marker of plaque inflammation in carotid arteries of patients before endarterectomy. The authors concluded that significant FDG uptake occurred not only in the artery scheduled for surgery but also in the contra-lateral artery, suggesting diffuse inflammatory atherosclerotic disease.
Contemporary clinical contributions.
Various abstracts were related to the diagnosis of CAD using SPECT myocardial perfusion imaging. Both transient ischemic LV cavity dilation and tracer lung uptake after stress were related to severe CAD (7,8). Conversely, small poststress LV dimensions were related to less-extensive CAD (9). Inferior perfusion defects were considered to be related to less extensive ischemia (and generally invasive angiography is not performed in these patients), but Kardan et al. (10) demonstrated a high frequency (76%) of multivessel CAD on angiography in patients with ischemia in the inferior wall on SPECT.
Attenuation artifacts remain a problem with SPECT imaging, particularly with obese patients (11). Two studies indicated the superior diagnostic performance when X-ray attenuation correction was included (12,13). With the new SPECT-CT scanners, attenuation correction may become implemented in the daily routine (14), but Goetze et al. (15) pointed out that misregistration between the 2 techniques is not infrequent and that re-registration is often needed (16).
Several studies compared CT angiography with SPECT imaging for assessment of CAD (17,18). Schepsis et al. (18) demonstrated that the techniques provide complementary information and integration of the 2 techniques may optimize diagnosis of CAD. Fusion of the CT and SPECT images may be problematic, but algorithms to fuse these images are being developed (19).
Using gated SPECT, Oba et al. (20) compared regional wall motion abnormalities to those noted with MRI and demonstrated good agreement between the 2 techniques, even in the presence of perfusion defects. The prognostic use of SPECT imaging was confirmed in different subpopulations, including the elderly (21) and patients undergoing preoperative risk stratification before abdominal aortic aneurysm surgery (22).
A retrospective analysis of 374 patients with atrial fibrillation, compared with age- and gender-matched controls revealed a high incidence of perfusion abnormalities in both groups, but the prognostic yield was not greater in patients with atrial fibrillation, suggesting that routine screening with SPECT may not be justified (23).
Also, the prognostic value of different variables derived from gated SPECT imaging was addressed. One study demonstrated that patients with normal perfusion on stress SPECT study had an excellent prognosis, suggesting that in these patients a resting study may be omitted (24). Wexler et al. (25) demonstrated the incremental prognostic value of LV end-systolic volume over LV ejection fraction and perfusion variables, most outspoken in women. Another study reported on the prognostic value of reversible wall motion abnormalities on gated SPECT, which most likely represents postischemic stunning and was associated with poor outcome (26).
PET.
Folks et al. (27) reported on the development of normal limits for perfusion imaging with PET and 82rubidium, whereas Goeke et al. (28) provided normal limits for stress-induced changes in LV function and volumes using gated 82rubidium PET in women. Quantitative blood flow using 13N-ammonia and 15O-labeled water PET in an animal model of acute infarction revealed that both approaches compared closely with blood flow assessed using microspheres (29). Alexanderson et al. (30) used 13N-ammonia PET to demonstrate endothelial dysfunction in patients with primary hypercholesterolemia. Free fatty acid metabolism can be studied with using 11C-palmitate and PET, and Ukkonen et al. (31) showed that an acute reduction in availability of free fatty acids (used for aerobic metabolism) resulted in a decrease in LV systolic function and myocardial efficiency in heart failure patients. This was an unexpected finding, because it generally was believed that, in the failing heart, the absence of free fatty acids results in a switch to cardiac glucose metabolism, which is associated with superior cardiac efficiency.
In another PET study with FDG, it was demonstrated that hyperinsulinemic euglycemic clamping maximally stimulated regional glucose utilization, both in patients with and without diabetes and reduced LV function, although greater regional glucose utilization was noted in patients with normal LV function (32).
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Conclusions
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These Scientific Sessions demonstrated the continued important clinical role of nuclear cardiology, in the evaluation, management, and determination of treatment strategies for patients with cardiovascular disease. In addition, nuclear cardiology studies provide insight with regard to the evaluation of the pathophysiological processes of cardiovascular disease. Renewed emphasis was placed on the use of radionuclides to better understand molecular processes while also demonstrating the important clinical role that SPECT and PET imaging plays in routine clinical practice. With a continued attendance of more than 1,000 specialists in nuclear cardiology, these Annual Sessions continue to generate worldwide interest. Next year's meeting will be held in San Diego, California, from September 6 to 9, 2007.
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Acknowledgments
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The authors acknowledge Linda Garrard for her help in preparing the summary of the advanced track.
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Footnotes
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Dr. Bax has received research grants from Guidant, Medtronic, GE Healthcare, and BMS Medical Imaging; Dr. Beanlands has received research grants from GE Healthcare and MSD Nordion and is on the advisory board of BMS Medical Imaging; Dr. Berman has received research grants from BMS Medical Imaging and Astellas Pharma US, Inc., and is a consultant at Mallinckrodt; Dr. Garcia has received research grants from Bracco Diagnostics Inc., BMS Medical Imaging, and GE Healthcare and is on the speakers bureau for GE Healthcare; he also has received an honoraria from GE Healthcare; Dr. Hendel has received research grants from GE Healthcare and is on the advisory bureau of BMS Medical Imaging; Dr. Mieres has received research grants from GE Healthcare and is on the speakers bureau for Astellas Pharma US, Inc.; Dr. Shaw has received research grants from GE Healthcare and is on the speakers bureau at GE Healthcare; and Dr. Wackers has received research grants from BMS Medical Imaging, Astellas Pharma US, Inc., and GE Healthcare; royalties from MedX, WLCQ software; and is on the advisory board of King Pharmaceuticals.
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References
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