Cardiac Computed Tomography and Myocardial Perfusion Scintigraphy for Risk Stratification in Asymptomatic Individuals Without Known Cardiovascular Disease: A Position Statement of The Working Group on Nuclear Cardiology and Cardiac CT of the European Society of Cardiology

OBJECTIVES: Cardiovascular events remain one of the most frequent causes of mortality and morbidity worldwide. The majority of cardiac events occur in individuals without known coronary artery disease (CAD) and in low- to intermediate-risk subjects. Thus, the development of improved preventive strategies may substantially benefit from the identification, among apparently intermediate-risk subjects, of those who have a high probability for developing future cardiac events. Cardiac computed tomography and myocardial perfusion scintigraphy (MPS) by single photon emission computed tomography may play a role in this setting. In fact, absence of coronary calcium in cardiac computed tomography and inducible ischaemia in MPS are associated with a very low rate of major cardiac events in the next 3–5 years.

METHODS: Based on current evidence, the evaluation of coronary calcium in primary prevention subjects should be considered in patients classified as intermediate-risk based on traditional risk factors, since high calcium scores identify subjects at high-risk who may benefit from aggressive secondary prevention strategies. In addition, calcium scoring should be considered for asymptomatic type 2 diabetic patients without known CAD to select those in whom further functional testing by MPS or other stress imaging techniques may be considered to identify patients with significant inducible ischaemia.

RESULTS: From available data, the use of MPS as first line testing modality for risk stratification is not recommended in any category of primary prevention subjects with the possible exception of first-degree relatives of patients with premature CAD in whom MPS may be considered.

CONCLUCIONS: However, the Working Group recognizes that neither the use of computed tomography for calcium imaging nor of MPS have been proven to significantly improve clinical outcomes of primary prevention subjects in prospective controlled studies. This information would be crucial to adequately define the role of imaging approaches in cardiovascular preventive strategies.

PMID: 20630895

Cumulative Exposure to Ionizing Radiation from Diagnostic and Therapeutic Cardiac Imaging Procedures: A Population-Based Analysis

OBJECTIVES: The purpose of this study was to describe radiation exposure from cardiac imaging procedures over time in a general population. Cardiac imaging procedures frequently expose patients to ionizing radiation, but their contribution to effective doses of radiation in the general population is unknown.

METHODS: We used administrative claims to identify cardiac imaging procedures performed from 2005 to 2007 in 952,420 nonelderly insured adults in 5 U.S. health care markets. We estimated 3-year cumulative effective doses of radiation in millisieverts from these procedures We then calculated population-based annual rates of radiation exposure to effective doses 3 mSv/year (background level ofradiation from natural sources), >3 to 20 mSv/year, or >20 mSv/year (upper annual limit for occupational exposure averaged over 5 years).

RESULTS: A total of 90,121 (9.5%) individuals underwent at least 1 cardiac imaging procedure using radiation. Among patients who underwent 1 cardiac imaging procedures, the mean cumulative effective dose over 3 years was 16.4 mSv (range 1.5 to 189.5 mSv). Myocardial perfusion imaging accounted for 74% of the cumulative effective dose. Overall, 47.8% of cardiac imaging procedures were performed in physician offices; this proportion was higher for myocardial perfusion imaging (74.8%) and cardiac computed tomography studies (76.5%). The annual population-based rate of receiving an effective dose of >3 to 20 mSv/year was 89.0 per 1,000; and 3.3 per 1,000 for cumulative doses >20 mSv/year. Annual effective doses increased with age and were generally higher among men.

CONCLUSIONS: Cardiac imaging procedures lead to substantial radiation exposure and effective doses for many patients in the U.S.

PMID:

Single-Photon Emission Computed Tomography Myocardial Perfusion Imaging and the Risk of Sudden Cardiac Death in Patients With Coronary Disease and Left Ventricular Ejection Fraction >35%

OBJECTIVES: The aim of this study was to determine whether single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) is an effective method of risk stratification for sudden cardiac death (SCD) in patients with coronary artery disease (CAD) and left ventricular ejection fraction (LVEF) >35%. Most victims of SCD have an LVEF >35%.

METHODS: The study population included 4,865 patients with CAD and LVEF >35% who underwent gated SPECT MPI. We used Cox proportional hazard modeling to examine the relationship between patient characteristics and SCD.

RESULTS: The median age of the population was 63 years (25th, 75th percentile: 54, 71 years), and the median LVEF was 56% (25th, 75th percentile: 50%, 64%). The median follow-up for all patients was 6.5 years (25th, 75th percentile: 3.6, 9.3 years). During follow-up, there were 161 SCDs (3.3%). After multivariable adjustment, LVEF, the Charlson index, hypertension, smoking, antiarrhythmic drug therapy, and the summed stress score (SSS) were associated with SCD (all p < 0.05). For each 3-U increase in the SSS, the hazard ratio for SCD was 1.13 (95% confidence interval: 1.04 to 1.23). The addition of perfusion data to the clinical history and LVEF was associated with increased discrimination for SCD events (c-index 0.728). Risk stratification with a derived SPECT nomogram did not result in statistically significant net reclassification improvement (p = 0.26) or integrated discrimination improvement (p = 0.38).

CONCLUSIONS: Among patients with CAD and LVEF >35%, the extent of stress MPI perfusion defects is associated with an increased risk of SCD. Future large prospective studies should address the role of perfusion imaging in the identification of high-risk patients with LVEF >35% who might benefit from ICD implantation.

PMID: 19808541

The Vascular Biology of Atherosclerosis and Imaging Targets

The growing worldwide health challenge of atherosclerosis, together with advances in imaging technologies, have stimulated considerable interest in novel approaches to gauging this disease. The last several decades have witnessed a burgeoning in understanding of the molecular pathways involved in atherogenesis, lesion progression, and the mechanisms underlying the complications of human atherosclerotic plaques. The imaging of atherosclerosis is reaching beyond anatomy to encompass assessment of aspects of plaque biology related to the pathogenesis and complication of the disease. The harnessing of these biologic insights promises to provide a plethora of new targets for molecular imaging of atherosclerosis. The goals for the years to come must include translation of the experimental work to visualization of these appealing biologic targets in humans.

PMID: 20395349

Cost-Effective Diagnostic Cardiovascular Imaging: When Does it Provide Good Value for the Money?

OBJECTIVES: To summarize the results of all original cost-utility analyses (CUAs) in diagnostic cardiovascular imaging (CVI) and characterize those technologies by estimates of their cost-effectiveness.

METHODS: We systematically searched the literature for original CVI CUAs published between 2000 and 2008. Studies were classified according to several variables including anatomy of interest (e.g. cerebrovascular, aorta, peripheral) and imaging modality under study (e.g. angiography, ultrasound). The results of each study, expressed as cost of the intervention to number of quality-adjusted life years saved ratio (cost/QALY) were additionally classified as favorable or not using $20,000, $50,000, and $100,000 per QALY thresholds. The distribution of results was assessed with Chi Square or Fisher exact test, as indicated.

RESULTS: Sixty-nine percent of all cardiovascular imaging CUAs were published between 2000 and 2008. Thirty-two studies reporting 82 cost/QALY ratios were included in the final sample. The most common vascular areas studied were cerebrovascular (n = 9) and cardiac (n = 8). Sixty-six percent (21/32) of studies focused on sonography, followed by conventional angiography and CT (25%, n = 8, each). Twenty-nine (35.4%), 42 (51.2%), and 53 (64.6%) ratios were favorable at WTP $20,000/QALY, $50,000/QALY, and $100,000/QALY, respectively. Thirty (36.6%) ratios compared one imaging test versus medical or surgical interventions; 26 (31.7%) ratios compared imaging to a different imaging test and another 26 (31.7%) to no intervention. Imaging interventions were more likely (P < 0.01) to be favorable when compared to observation, medical treatment or non-intervention than when compared to a different imaging test at WTP $100,000/QALY.

CONCLUSIONS: The diagnostic cardiovascular imaging literature has growth substantially. The studies available have, in general, favorable cost-effectiveness profiles with major determinants relating to being compared against observation, medical or no intervention instead of other imaging tests.

PMID: 20446040

Feasibility of FDG Imaging of the Coronary Arteries: Comparison Between Acute Coronary Syndrome and Stable Angina

OBJECTIVES: This study tested the hypothesis that fluorodeoxyglucose (FDG) uptake within the ascending aorta and left main coronary artery (LM), measured using positron emission tomography (PET), is greater in patients with recent acute coronary syndrome (ACS) than in patients with stable angina. Inflammation is known to play an important role in atherosclerosis. Positron emission tomography imaging with ¹⁸F-FDG provides a measure of plaque inflammation.

METHODS: Twenty-five patients (mean age 57.9 ± 9.8 years, 72% male, 10 ACS, and 15 stable angina) underwent cardiac computed tomographic angiography and PET imaging with ¹⁸F-FDG after invasive angiography. Images were coregistered, and FDG uptake was measured at locations of interest for calculation of target-to-background ratios (TBR). Additionally, FDG uptake was measured at the site of the lesion deemed clinically responsible for the presenting syndrome (culprit) by virtue of locating the stent deployed to treat the syndrome.

RESULTS: The FDG uptake was higher in the ACS versus the stable angina groups in the ascending aorta (median [interquartile ranges] TBR 3.30 [2.69 to 4.12] vs. 2.43 [2.00 to 2.86], p = 0.02), as well as the LM (2.48 [2.30 to 2.93] vs. 2.00 [1.71 to 2.44], p = 0.03, respectively). The TBR was greater for culprit lesions associated with ACS than for lesions stented for stable coronary syndromes (2.61 vs. 1.74, p = 0.02). Furthermore, the TBR in the stented lesions (in ACS and stable angina groups) correlated with C-reactive protein (r = 0.58, p = 0.04).

CONCLUSIONS: This study shows that in patients with recent ACS, FDG accumulation is increased both within the culprit lesion as well as in the ascending aorta and LM. This observation suggests inflammatory activity within atherosclerotic plaques in acute coronary syndromes and supports intensification of efforts to refine PET methods for molecular imaging of coronary plaques.

PMID: http://imaging.onlinejacc.org/cgi/content/abstract/3/4/388

18F-FDG PET Imaging of Myocardial Viability in an Experienced Center With Access to 18F-FDG and Integration With Clinical Management teams: The Ottawa-FIVE Substudy of the PARR 2 Trial

OBJECTIVES: (18)F-FDG PET may assist decision making in ischemic cardiomyopathy. The PET and Recovery Following Revascularization (PARR 2) trial demonstrated a trend toward beneficial outcomes with PET-assisted management. The substudy of PARR 2 that we call Ottawa-FIVE, described here, was a post hoc analysis to determine the benefit of PET in a center with experience, ready access to (18)F-FDG, and integration with clinical teams.

METHODS: Included were patients with left ventricular dysfunction and suspected coronary artery disease being considered for revascularization. The patients had been randomized in PARR 2 to PET-assisted management (group 1) or standard care (group 2) and had been enrolled in Ottawa after August 1, 2002 (the date that on-site (18)F-FDG was initiated) (n = 111). The primary outcome was the composite endpoint of cardiac death, myocardial infarction, or cardiac rehospitalization within 1 y. Data were compared with the rest of PARR 2 (PET-assisted management [group 3] or standard care [group 4]).

RESULTS: In the Ottawa-FIVE subgroup of PARR 2, the cumulative proportion of patients experiencing the composite event was 19% (group 1), versus 41% (group 2). Multivariable Cox proportional hazards regression showed a benefit for the PET-assisted strategy (hazard ratio, 0.34; 95% confidence interval, 0.16-0.72; P = 0.005). Compared with other patients in PARR 2, Ottawa-FIVE patients had a lower ejection fraction (25% +/- 7% vs. 27% +/- 8%, P = 0.04), were more often female (24% vs. 13%, P = 0.006), tended to be older (64 +/- 10 y vs. 62 +/- 10 y, P = 0.07), and had less previous coronary artery bypass grafting (13% vs. 21%, P = 0.07). For patients in the rest of PARR 2, there was no significant difference in events between groups 3 and 4. The observed effect of (18)F-FDG PET-assisted management in the 4 groups in the context of adjusted survival curves demonstrated a significant interaction (P = 0.016). Comparisons of the 2 arms in Ottawa-FIVE to the 2 arms in the rest of PARR 2 demonstrated a trend toward significance (standard care, P = 0.145; PET-assisted management, P = 0.057).

CONCLUSIONS: In this post hoc group analysis, a significant reduction in cardiac events was observed in patients with (18)F-FDG PET-assisted management, compared with patients who received standard care. The results suggest that outcome may be benefited using (18)F-FDG PET in an experienced center with ready access to (18)F-FDG and integration with imaging, heart failure, and revascularization teams.

PMID: 20237039

The Year in Cardiac Imaging

No Abstract Available. See Link Below.

The Year in Cardiac Imaging 2009

PMID:

Viability Assessment With Global Left Ventricular Longitudinal Strain Predicts Recovery of Left Ventricular Function After Acute Myocardial Infarction

OBJECTIVES: The extent of viable myocardial tissue is recognized as a major determinant of recovery of left ventricular (LV) function after myocardial infarction. In the current study, the role of global LV strain assessed with novel automated function imaging (AFI) to predict functional recovery after acute infarction was evaluated.

METHODS: A total of 147 patients (mean age, 61±11 years) admitted for acute myocardial infarction were included. All patients underwent 2D echocardiography within 48 hours of admission.

RESULTS: Significant relations were observed between baseline AFI global LV strain and peak level of troponin T (r=0.64), peak level of creatine phosphokinase (r=0.62), wall motion score index (r=0.52), and viability index assessed with single-photon emission computed tomography (r=0.79). At 1-year follow-up, LV ejection fraction was reassessed. Patients with absolute improvement in LV ejection fraction >5% at 1-year follow-up (n=70; 48%) had a higher (more negative) baseline AFI global LV strain (P<0.0001). Baseline AFI global LV strain was a predictor for change in LV ejection fraction at 1-year follow-up. A cutoff value for baseline AFI global LV strain of –13.7% yielded a sensitivity of 86% and a specificity of 74% to predict LV functional recovery at 1-year follow-up.

CONCLUSIONS: AFI global LV strain early after acute myocardial infarction reflects myocardial viability and predicts recovery of LV function at 1-year follow-up.

PMID: 19820202

Normal Stress-Only Versus Standard Stress/Rest Myocardial Perfusion Imaging Similar Patient Mortality With Reduced Radiation Exposure

OBJECTIVES: The aim of this study was to determine whether a normal stress-only single-photon emission computed tomographic myocardial perfusion tomography (SPECT) study confers the same prognosis as a normal SPECT on the basis of evaluation of stress and rest images. Current guidelines recommend stress and rest imaging to confirm that a SPECT study is normal.

METHODS: We determined all-cause mortality in 16,854 consecutive patients who had a normal gated stress SPECT. Median follow-up was 4.5 years. A stress-only protocol was used in 8,034 patients (47.6%), whereas 8,820 (52.4%) had both stress and rest imaging.

RESULTS: The overall unadjusted annual mortality rate in patients who had a normal SPECT with a stress-only protocol was lower than in those who required additional rest imaging (2.57% vs. 2.92%, p = 0.02). After adjustment for baseline clinical characteristics no significant differences in patient mortality were seen between the 2 imaging protocols, but the stress-only group received a 61% lower radiopharmaceutical dosage. Independent predictors of worse survival included increasing age, male sex, diabetes, history of coronary artery disease, and inability to exercise (all p < 0.001) but not the type of SPECT protocol used to image patients.

CONCLUSIONS: Patients determined to have a normal SPECT on the basis of stress imaging alone have a similar mortality rate as those who have a normal SPECT on the basis of evaluation of both stress and rest images. Our results support that additional rest imaging is not required in patients who have a normally appearing initial stress study. A significant reduction in radiation exposure can be achieved with such an approach.

PMID: 19913381

Non-Invasive Assessment and Clinical Strategy of Stable Coronary Artery Disease by Magnetic Resonance Imaging, Multislice Computed Tomography and Myocardial Perfusion SPECT

Coronary multislice computed tomography (MSCT) angiography and magnetic resonance angiography (MRA) have emerged as new diagnostic techniques that allow direct visualization of the coronary artery. These new modalities have both advantages and disadvantages concerning radiation exposure, the use of contrast medium, ability of visualizing heavily calcified artery lumens, and spatial and temporal resolution. However, these modalities only provide anatomical information of the coronary artery. Functional assessment of the severity of coronary artery disease (CAD) is essential for the management of patients with known or suspected CAD in practical clinical settings. Myocardial perfusion single-photon emission computed tomography is thought to be the most suitable diagnostic procedure for the determination of therapeutic strategy when coronary MSCT and MRA show significant and also insignificant coronary artery lesions.

PMID: 19966503

Prediction of New-Onset Refractory Congestive Heart Failure Using Gated Myocardial Perfusion SPECT Imaging in Patients With Known or Suspected Coronary Artery Disease: Subanalysis of the J-ACCESS Database

OBJECTIVES: The purpose of this study was to evaluate the predictive value of perfusion/function parameters measured by gated myocardial perfusion single-photon emission computed tomography (SPECT) in combination with clinical variables in patients with known or suspected coronary artery disease to predict refractory heart failure (HF).  The increasing number of HF patients requires the establishment of a prophylactic strategy that can identify patients at high risk of HF due to coronary artery disease.

METHODS: We analyzed clinical and stress/rest-gated SPECT data from the multicenter, prospective, and observational J-ACCESS (Japanese Assessment of Cardiac Events and Survival Study by Quantitative Gated SPECT) database of 3,835 known or suspected coronary artery disease patients in which new-onset congestive HF symptoms requiring aggressive medical treatment were observed in 71 patients for 3 years.

RESULTS: The multivariable Cox hazard model revealed that chronic renal dysfunction (hazard ratio (HR): 6.227 [95% confidence interval (CI): 2.920 to 13.279]), the end-systolic volume index (ESVI) (HR: 1.019 [95% CI: 1.011 to 1.029]), and moderate to high stress summed score (SSS) (HR: 3.012 [95% CI: 1.757 to 5.181]) independently (p < 0.0001) predicted HF. In addition to the close (p < 0.0001) correlation of ESVI and SSS with HF incidence, the combined tertiles of SSS and ESVI revealed high-risk patients with a maximally 17.3 times greater risk (5.2%/3 years) compared with the minimal risk (0.3%/3 years) at a normal to low SSS and lower ESVI. Chronic renal dysfunction combined with ESVI and SSS categories had the greatest (p < 0.005 to 0.001) incremental prognostic value with a global chi-square value (125.0) over single or other combined risks.

CONCLUSIONS: Chronic renal dysfunction, greater stress-induced perfusion abnormality, and higher ESVI provide independent and additive information for predicting the risk of refractory HF in known or suspected coronary patients, indicating the efficacy of perfusion/function parameters measured by stress-gated perfusion SPECT for identifying patients at greater risk of future refractory HF.

PMID:

Acute Myocardial Infarction: Serial Cardiac MR Imaging Shows a Decrease in Delayed Enhancement of the Myocardium During the 1st Week After Reperfusion

OBJECTIVES: To evaluate the time course of delayed gadolinium enhancement of infarcted myocardium by using serial contrast agent–enhanced (CE) cardiac magnetic resonance (MR) images obtained during the acute, subacute, and chronic stages of infarction.

METHODS: The study protocol was reviewed and approved by the local ethics committee, and written informed consent was obtained. Seventeen patients with reperfused acute myocardial infarction (AMI) underwent cine and CE cardiac MR a median of 1, 7, 35, and 180 days after reperfusion. Infarct size determined on the basis of delayed enhancement MR imaging at different times was compared by using nonparametric tests and Bland-Altman analysis. Extent of myocardial enhancement was compared with single photon emission computed tomographic (SPECT) measures of infarct size with Spearman correlation. Regional myocardial enhancement extent and contractility were analyzed with nonparametric tests.

RESULT: Infarct size was 18.3% of total myocardial LV volume on day 1 after AMI and decreased to 12.9% on day 7, 11.3% on day 35, and 11.6% on day 180 (all P < .001). Estimated infarct size on day 7, as compared with day 1 enhancement size, declined by 57.1% within the epicardium and by 6.3% within the endocardium (both P < .001). Infarct size on day 7 showed only minor changes at subsequent imaging and yielded a high correlation with SPECT measurements of infarct size (r = 0.84). Infarct size on day 7 inversely correlated with long-term wall thickening (P < .0001) and allowed prediction of contractile function.

CONCLUSIONS: In patients with AMI and successful coronary reperfusion, the size of delayed gadolinium enhancement at CE cardiac MR imaging significantly diminished during the 1st week after infarction. Thus, timing of CE cardiac MR imaging is crucial for accurate measurement of myocardial infarct size early after AMI.

PMID:

FDG-PET Can Distinguish Inflamed From Non-Inflamed Plaque in an Animal Model of Atherosclerosis

OBJECTIVES: The presence of activated macrophages is an important predictor of atherosclerotic plaque rupture. In this study, our aim was to determine the accuracy of (18)F- fluorodeoxyglucose (FDG) microPET imaging for quantifying aortic wall macrophage content in a rabbit model of atherosclerosis.

METHODS: Rabbits were divided into a control group and two groups post aortic balloon injury: 6 months high-cholesterol diet (HC); and 3 months HC followed by 3 months low-cholesterol diet plus statin (LCS). In vivo and ex vivo microPET, ex vivo well counting and histological quantification of the atherosclerotic aortas were performed for all groups.

RESULTS: Macrophage density was greater in the HC group than the LCS group (5.1 +/- 1.4% vs. 0.6 +/- 0.7%, P = 0.001) with a trend towards greater macrophage density in LCS compared to controls (P = 0.08). There was a strong correlation across all groups between macrophage density and standardized uptake value (SUV) derived from ex vivo microPET (r = 0.95, P = 0.001) and well counting (r = 0.96, P = 0.001). Ex vivo FDG SUV was significantly different between the three groups (P = 0.001). However, the correlation between in vivo microPET FDG SUV and macrophage density was insignificant (r = 0.16, P = 0.57) with no statistical differences in FDG SUV seen between the three groups.

CONCLUSIONS: This study confirms that in an animal model of inflamed and non-inflamed atherosclerosis, significant differences in FDG SUV allow differentiation of highly inflamed atherosclerotic aortas from those stabilized by statin therapy and low cholesterol diet and controls.

PMID: 19784796

Quantification of Regional Myocardial Oxygenation by Magnetic Resonance Imaging: Validation with Positron Emission Tomography

OBJECTIVES: A comprehensive evaluation of myocardial ischemia requires measures of both oxygen supply and demand. Positron-emission tomography (PET) is currently the gold standard for such evaluations, but its use is limited due to its ionizing radiation, limited availability, and high cost. A cardiac magnetic resonance imaging (MRI) method was developed for assessing myocardial oxygenation. The purpose of this study was to evaluate and validate this technique compared to PET during pharmacologic stress in a canine model of coronary artery stenosis.

METHODS: Twenty-one beagles and small mongrel dogs without coronary stenosis (controls), or with moderate to severe acute coronary artery stenosis underwent MRI and PET imaging at rest and during dipyridamole vasodilation or dobutamine stress to induce a wide range of changes in cardiac perfusion and oxygenation. MRI first-pass perfusion imaging was performed to quantify myocardial blood flow (MBF) and volume (MBV). The MRI blood-oxygen-level-dependent (BOLD) technique was used to determine the myocardial oxygen extraction fraction (OEF) during pharmacologic hyperemia. Myocardial oxygen consumption (MVO2) was determined by Fick’s law.

RESULTS: In the same dogs, (15)O-water and (11)C-acetate were used to measure MBF and MVO(2), respectively by PET. Regional assessments were performed for both MR and PET. MRI data correlated nicely with PET values for MBF (R(2) = 0.79, P < 0.001), MVO(2) (R(2) = 0.74, P < 0.001), and OEF (R(2) = 0.66, P < 0.01).

CONCLUSIONS: Cardiac MRI methods may provide an alternative to radionuclide imaging in settings of myocardial ischemia. Our newly developed quantitative MRI oxygenation imaging technique may be a valuable non-invasive tool to directly evaluate myocardial energetics and efficiency.

PMID: 19933371