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

Prospectively Gated Axial CT Coronary Angiography: Comparison of Image Quality and Effective Radiation Dose Between 64-and 256-Slice CT

OBJECTIVES: To compare image quality and effective radiation dose for prospectively gated axial CT coronary angiography on 64- and 256-slice CT.

METHODS: The patient cohort consisted of 80 consecutive patients undergoing imaging with 256-slice CT and 80 patients with 64-slice CT. The two patient groups were demographically matched according to age, gender, body mass index and heart rate. For both groups, two observers independently assessed image quality for all coronary segments on a five-point ordinal scale. The two groups were compared with regard to image quality and effective radiation dose. Image quality scores less than 3 were considered non-diagnostic.

RESULTS: Mean effective radiation dose did not significantly differ between the two groups (3.4 +/- 0.8 mSv in both groups; p > 0.1). Vessel-based image quality was significantly better in patients undergoing 256-slice CT compared with those undergoing 64-slice CT (p < 0.001). The proportion of assessable coronary segments significantly increased from 95.6% in the 64-slice group to 98.9% in the 256-slice group (p < 0.05).

CONCLUSION: Prospectively gated axial CT coronary angiography performed on 256-slice CT provides significantly improved and more stable image quality at an equivalent effective radiation dose compared with 64-slice CT.

PMID: 19915848

Validation of Magnetic Resonance Myocardial Perfusion Imaging with Fractional Flow Reserve for the Detection of Significant Coronary Heart Disease

OBJECTIVES: Magnetic resonance myocardial perfusion imaging (MRMPI) has a number of advantages over the other noninvasive tests used to detect reversible myocardial ischemia. The majority of previous studies have generally used quantitative coronary angiography as the gold standard to assess the accuracy of MRMPI; however, only an approximate relationship exists between stenosis severity and functional significance. Pressure wire-derived fractional flow reserve (FFR) values <0.75 correlate closely with objective evidence of reversible ischemia. Accordingly, we have compared MRMPI with FFR.

METHODS: One hundred three patients referred for investigation of suspected angina underwent MRMPI with a 1.5-T scanner. The stress agent was intravenous adenosine (140 microg . kg(-1) . min(-1)), and the first-pass bolus contained 0.1 mmol/kg gadolinium. In the following week, coronary angiography with pressure wire studies was performed. FFR was recorded in all patent major epicardial coronary arteries, with a value <0.75 denoting significant stenosis.

RESULTS: MRMPI scans, analyzed by 2 blinded observers, identified perfusion defects in 121 of 300 coronary artery segments (40%), of which 110 had an FFR <0.75. We also found that 168 of 179 normally perfused segments had an FFR > 0.75. The sensitivity and specificity of MRMPI for the detection of functionally significant coronary heart disease were 91% and 94%, respectively, with positive and negative predictive values of 91% and 94%.

CONCLUSIONS: MRMPI can detect functionally significant coronary heart disease with excellent sensitivity, specificity, and positive and negative predictive values compared with FFR.

PMID: 19917885

Recent Advances in Cardiac PET and PET/CT Myocardial Perfusion Imaging

OBJECTIVES: In 2005, 80% of cardiovascular disease (CVD) deaths occurred in low- to middle-income countries (i.e., developing nations). Cardiovascular imaging, such as myocardial perfusion SPECT, is one method that may be applied to detect and foster improved detection of at-risk patients. This document will review the availability and utilization for nuclear cardiology procedures worldwide and propose strategies to devise regional centers of excellence to achieve quality imaging around the world.

METHODS: As a means to establish the current state of nuclear cardiology, International Atomic Energy Agency member and non-member states were queried as to annual utilization of nuclear cardiology procedures. Other sources for imaging statistics included data from medical societies (American Society of Nuclear Cardiology, European Society of Cardiology, and the European Association of Nuclear Medicine) and nuclear cardiology working groups within several nations. Utilization was calculated by dividing annual procedural volume by 2007 population statistics (/100,000) and categorized as high (>1,000/100,000), moderate-high (250-999/100,000), moderate (100-249/100,000), low-moderate (50-9/100,000) and low (<50/100,000).

RESULTS: High nuclear cardiology utilization was reported in the United States, Canada, and Israel. Most Western European countries, Australia, and Japan reported moderate-high utilization. With the exception of Argentina, Brazil, Colombia and Uruguay, South America had low usage. This was also noted across Eastern Europe, Russia, and Asia.

CONCLUSIONS: Utilization patterns generally mirrored each country’s gross domestic product. However, nuclear cardiology utilization was higher for developing countries neighboring moderate-high “user” countries (e.g., Algeria and Egypt); perhaps the result of accessible high-quality training programs.

PMID: 19756909

Magnetic Resonance Imaging Versus Computed Tomography for Characterization of Pulmonary Vein Morphology Before Radiofrequency Catheter Ablation of Atrial Fibrillation

OBJECTIVES: The accurate assessment of pulmonary vein (PV) anatomy is important in planning radiofrequency catheter ablation (RFCA) of atrial fibrillation (AF). The aim of the present study was to perform a head-to-head comparison of magnetic resonance imaging (MRI) and multislice computed tomography (CT) for the evaluation of PV morphology before RFCA of AF.

METHODS: Contrast-enhanced MRI (on a 1.5-T system) and multislice CT (on a dual-source system) were performed for the evaluation of the PVs in 44 consecutive patients (31 men, mean age 56 +/- 10 years) admitted for RFCA of drug-refractory AF. Data on PV anatomy, ostial branching pattern, and ostial dimensions were compared between MRI and multislice CT.

RESULTS: Variant PV anatomy was observed in 21 patients (48%) with the 2 imaging approaches. The incidence of PV ostial branching, as assessed with MRI and multislice CT, was higher on the right and more common in the inferior than superior vein. Agreement between the 2 imaging modalities for the evaluation of variant PV anatomy (kappa = 0.87, 95% confidence interval 0.77 to 0.97) and ostial branching pattern (kappa = 0.84, 95% confidence interval 0.75 to 0.93) was nearly perfect. Assessment of PV ostial cross-sectional area as well as maximal and minimal ostial diameters resulted in strong agreement and correlation (r(2) = 0.75 to 0.99, p <0.001 for all) between the 2 imaging approaches.

CONCLUSIONS: In conclusion, MRI and multislice CT of the PVs appear to provide similar and detailed anatomic and quantitative information before RFCA of AF.

PMID: 19932789

Coronary Artery Aneurysms and Ectasia: Role of Coronary CT Angiography

OBJECTIVES: Coronary artery dilatations-aneurysms and ectasia-are an uncommon and frequently unrecognized incidental finding in patients with coronary artery disease.

METHODS: Aneurysms and ectasia are associated with a vast group of disorders, and the evaluation and characterization of coronary aneurysms and ectasia represent a great diagnostic task with clinical and therapeutic implications. The underlying etiology is variable and includes degenerative, congenital, inflammatory, infectious, toxic, and traumatic causes.

RESULTS: Unlike aneurysms, ectasia is more frequently seen in association with atherosclerosis or as a compensatory mechanism in those cases in which a proximal stenosis is noted in the opposite coronary artery; ectasia is also seen in some coronary artery anomalies, such as anomalous origin from the pulmonary artery, or as a result of a high-flow state, as seen in coronary artery fistulas. The diagnostic approach depends on the clinical scenario, and nowadays, noninvasive evaluation with multidetector computed tomography is possible. Imaging assessment should include evaluation of (a) the distribution, (b) maximal diameter, (c) presence or absence of intraluminal thrombi, (d) number, (e) extension, and (f) associated complications such as myocardial infarction.

CONCLUSIONS: This article presents an overview of the definition, classification, etiology, clinical manifestations, and potential complications of coronary artery aneurysms and ectasia.

PMID: 19926755

Nephrogenic Systemic Fibrosis: Change in Incidence Following a Switch in Gadolinium Agents and Adoption of a Gadolinium Policy- Report from Two U.S. Universities

OBJECTIVES: To determine the incidence of nephrogenic systemic fibrosis (NSF) in tertiary care centers of two U.S. universities following the switch from the use of gadodiamide to gadobenate dimeglumine and gadopentetate dimeglumine, and the adoption of restrictive gadolinium-based contrast agent (GBCA) policies.

METHODS: Institutional review board approval with waiver of informed consent was obtained for this Health Insurance Portability and Accountability Act-compliant retrospective study. NSF patients were identified between January 2000 and December 2006 at center A and between October 2003 and February 2007 at center B (preadoption periods); and from June 2007 to June 2008 at both centers (postadoption period). The numbers of patients who underwent gadolinium-enhanced magnetic resonance at each center, patients at risk for NSF at center A, and dialysis patients at center B were identified in the pre- and postadoption periods. Gadodiamide was the only agent used in the preadoption period. Gadobenate dimeglumine and gadopentetate dimeglumine were the agents used in the postadoption period. A restrictive GBCA policy that limits the use and dose of GBCAs in patients with risk factors was adopted in the postadoption period. Follow-up lasted 9 months from July 2008 to March 2009. Corresponding incidences were determined and compared with the Fisher exact test.

RESULTS: Respective total benchmark incidence of NSF at both centers, at-risk incidence of NSF at center A, and dialysis incidence of NSF at center B were 37 of 65 240, 28 of 925, and nine of 312 in the preadoption period and zero of 25 167, zero of 147, and zero of 402 in the postadoption period. All three incidences demonstrated significant differences (P < .0001, .024, and .001, respectively) between the pre- and postadoption periods.

CONCLUSIONS: Following the switch from gadodiamide to gadobenate dimeglumine and gadopentetate dimeglumine, and the adoption of restrictive GBCA policies, no NSF cases were observed at either center.

PMID: 19789233

CT Coronary Angiography in Patients Suspected of Having Coronary Artery Disease: Decision Making from Various Perspectives in the Face of Uncertainty

OBJECTIVES: To determine the cost-effectiveness of computed tomographic (CT) coronary angiography as a triage test, performed prior to conventional coronary angiography, by using a Markov model.

METHODS: A Markov model was used to analyze the cost-effectiveness of CT coronary angiography performed as a triage test prior to conventional coronary angiography from the perspective of the patient, physician, hospital, health care system, and society by using recommendations from the United Kingdom, the United States, and the Netherlands for cost-effectiveness analyses. For CT coronary angiography, a range of sensitivities (79%-100%) and specificities (63%-94%) were used to help diagnose significant coronary artery disease (CAD). Optimization criteria (ie, outcomes considered) were: revised posttest probability of CAD, life-years, quality-adjusted life-years (QALYs), costs, and incremental cost-effectiveness ratios (ICERs). Extensive sensitivity analysis was performed.

RESULTS: For a prior probability of CAD of less than 40%, the probability of CAD after CT coronary angiography with negative results was less than 1%. The Markov model calculations from the patient/physician perspective suggest that CT coronary angiography maximizes life-years respectively in 60-year-old men and women at a prior probability of less than 38% and 24% and maximizes QALYs at a prior probability of less than 17% and 11%. From the hospital/health care perspective, CT coronary angiography helps reduce health care and direct nonhealth care-related costs (according to UK/U.S. recommendations), regardless of prior probability, and lowers all costs, including production losses (Netherlands recommendations) at a prior probability of less than 87%-92%. Analysis performed from a societal perspective by using a willingness-to-pay threshold level of euro80 000/QALY suggests that CT coronary angiography is cost-effective when the prior probability is lower than 44% and 37% in men and women, respectively. Sensitivity analyses showed that results changed across the reported range of sensitivity of CT coronary angiography.

CONCLUSIONS: The optimal diagnostic work-up depends on the optimization criterion, prior probability of CAD, and the diagnostic performance of CT coronary angiography.

PMID: 19864509

Plaque Type and Composition as Evaluated Non-Invasively by MSCT Angiography and Invasively by VH IVUS in Relation to the Degree of Stenosis

OBJECTIVES: : Imaging of coronary plaques has traditionally focused on evaluating degree of stenosis, as the risk for adverse cardiac events increases with stenosis severity. However, the relation between plaque composition and severity of stenosis remains largely unknown.  To assess plaque composition (non-invasively by multislice computed tomography (MSCT) angiography and invasively by virtual histology intravascular ultrasound (VH IVUS)) in relation to degree of stenosis.

METHODS: 78 patients underwent MSCT (identifying three plaque types; non-calcified, calcified, mixed) followed by invasive coronary angiography and VH IVUS. VH IVUS evaluated plaque burden, minimal lumen area and plaque composition (fibrotic, fibro-fatty, necrotic core, dense calcium) and plaques were classified as fibrocalcific, fibroatheroma, thin-capped fibroatheroma (TCFA), pathological intimal thickening. For each plaque, percentage stenosis was evaluated by quantitative coronary angiography. Significant stenosis was defined >50% stenosis.

RESULTS: Overall, 43 plaques (19%) corresponded to significant stenosis. Of the 227 plaques analysed, 70 were non-calcified plaques (31%), 96 mixed (42%) and 61 calcified (27%) on MSCT. Plaque types on MSCT were equally distributed among significant and non-significant stenoses. VH IVUS identified that plaques with significant stenosis had higher plaque burden (67% (11%) vs 53% (12%), p<0.05) and smaller minimal lumen area (4.6 (3.8-6.8) mm(2) vs 7.3 (5.4-10.5) mm(2), p<0.05). Interestingly, no differences were observed in percentage fibrotic, fibro-fatty, necrotic core and dense calcium. Non-significant stenoses were more frequently classified as pathological intimal thickening (46 (25%) vs 3 (7%), p<0.05), although TCFA (more vulnerable plaque) was distributed equally (p = 0.18).

CONCLUSIONS: No evident association exists between the degree of stenosis and plaque composition or vulnerability, as evaluated non-invasively by MSCT and invasively by VH IVUS.

PMID: 19846418

In Vivo Myocardial Distribution of Multipotent Progenitor Cells Following Intracoronary Delivery in a Swine Model of Myocardial Infarction

OBJECTIVES: There are few data comparing the fate of multipotent progenitor cells (MPCs) used in cardiac cell therapy after myocardial infarction (MI). To document in vivo distribution of MPCs delivered by intracoronary (IC) injection.

METHODS: Using an anterior MI swine model, near-infrared (NIR) fluorescence was used for in vivo tracking of labelled MPCs [mesenchymal stromal (MSCs), bone marrow mononuclear (BMMNCs), and peripheral blood mononuclear (PBMNCs)] cells early after IC injection. Signal intensity ratios (SIRs) of injected over non-injected (reference) zones were used to report NIR fluorescence emission.

RESULTS: Following IC injection, significant differences in mean SIR were documented when MSCs were compared with BMMNCs [1.28 +/- 0.10 vs. 0.77 +/- 0.11, P < 0.001; 95% CI (0.219, 0.805), respectively] or PBMNCs [1.28 +/- 0.10 vs. 0.80 +/- 0.14, P = 0.005; 95% CI (0.148, 0.813), respectively]. Differences were maintained during the 60 min tracking period, with only the MSC-injected groups continuously emitting NIR fluorescence (SIR>1). This is correlated with greater cell retention for MSCs relative to mononuclear cells. However, there was evidence of MSC-related vessel plugging in some swine.

CONCLUSIONS: Our in vivo NIR fluorescence findings suggest that MPC distribution and retention immediately after intracoronary delivery vary depending on cell population and could potentially impact the clinical efficacy of cardiac cell therapy.

PMID: 19687154

Interventional Cardiovascular Magnetic Resonance Imaging: A New Opportunity for Image-Guided Interventions

Cardiovascular magnetic resonance (CMR) combines excellent soft-tissue contrast, multiplanar views, and dynamic imaging of cardiac function without ionizing radiation exposure.

Interventional cardiovascular magnetic resonance (iCMR) leverages these features to enhance conventional interventional procedures or to enable novel ones. Although still awaiting clinical deployment, this young field has tremendous potential.

We survey promising clinical applications for iCMR. Next, we discuss the technologies that allow CMR-guided interventions and, finally, what still needs to be done to bring them to the clinic.

PMID: 19909937

A Randomized Comparison of Transradial Versus Transfemoral Approach for Coronary Angiography and Angioplasty

OBJECTIVES: The aim of the study was to evaluate the safety, feasibility, and procedural variables by the transradial approach compared with the transfemoral access in a standard population of patients undergoing coronary catheterization. Coronary catheterization is usually performed via the transfemoral approach. Transradial access may offer some advantages in comparison with transfemoral access especially under conditions of aggressive anticoagulation and antiplatelet treatment.

METHODS: Between July 2006 and January 2008, a total of 1,024 patients undergoing coronary catheterization were randomly assigned to the transradial or transfemoral approach. Patients with an abnormal Allen’s test, history of coronary artery bypass surgery, simultaneous right heart catheterization, chronic renal insufficiency, or known difficulties with the radial or femoral access were excluded.

RESULTS: Successful catheterization was achieved in 494 of 512 patients (96.5%) in the transradial and in 511 of 512 patients (99.8%) in the transfemoral group (p < 0.0001). Median procedural duration (37.0 min, interquartile range [IQR] 19.6 to 49.1 min vs. 40.2 min, IQR 24.3 to 50.8 min; p = 0.046) and median dose area product (38.2 Gycm(2), IQR 20.4 to 48.5 Gycm(2) vs. 41.9 Gycm(2), IQR 22.6 to 52.2 Gycm(2); p = 0.034) were significantly lower in the transfemoral group compared with the transradial access group. A median amount of contrast agent was similar among both groups. Vascular access site complications were higher in the transfemoral group (3.71%) than in the transradial group (0.58%; p = 0.0008)

CONCLUSIONS: The findings of the present study show that transradial coronary angiography and angioplasty are safe, feasible, and effective with similar results to those of the transfemoral approach. However, procedural duration and radiation exposure are higher using the transradial access. In contrast to the transfemoral route, the rate of major vascular complications was negligible using the transradial approach.

PMID: 19926042

Image Quality of Coronary 320-MDCT in Patients with Atrial Fibrillation: Initial Experience

OBJECTIVE: Noninvasive coronary angiography has generally been contraindicated in patients with atrial fibrillation because of the difficulty in synchronizing an irregular heartbeat with table gantry movement. The objective of this study was to evaluate and compare the quality of 320-MDCT images obtained in patients with atrial fibrillation and in a control group of patients in sinus rhythm.

METHODS: Two reviewers were blinded to the patient groups and evaluated images of 15 coronary artery segments for each patient using 320-MDCT. The images were printed on glossy paper and scored subjectively as 1 or 2, meaning of diagnostic quality, or 3, meaning poor quality.

RESULTS: No statistical difference between the groups was noted in patient age: The mean age of the patients with atrial fibrillation was 67 years (age range, 52–82 years) and that of the patients in sinus rhythm was 59 years (36–86 years) (p = 0.3). Scores of 1 and 2 (diagnostic quality) were assigned to 100% in sinus rhythm and 96% in atrial fibrillation (p < 0.05). Scores of 3 were seen only in the atrial fibrillation group (7/175, 4%). Segment 15, the distal circumflex artery, was the segment that was most frequently assigned a score of 3 (2/7, 28.6%). A discrepancy in the two reviewers’ scores was seen in 25 segments (7%), requiring joint consensus. The segments that most frequently required consensus reading were segments 12 and 15. The overall mean image quality score for all three coronary arteries in atrial fibrillation was 1.25 ± 0.47 (SD) and 1.08 ± 0.26 in sinus rhythm (p < 0.001). The median effective dose was 19.28 and 13.55 mSv in the atrial fibrillation and sinus rhythm groups, respectively.

CONCLUSION: The analysis of our initial experience shows that imaging in patients with atrial fibrillation is possible using 320-MDCT, with images of most segments obtained being of diagnostic quality. Segment 15 was the most difficult to see on 320-MDCT because of the small caliber of the vessel; poor visualization of that segment mostly occurred in the setting of a dominant right coronary arterial system.

PMID: Pending

A Half Century of Selective Coronary Arteriography

The first “selective” coronary arteriogram was made 50 years ago by Dr. F. Mason Sones at the Cleveland Clinic. Soon afterward coronary arteriography was developed as a diagnostic method suitable for widespread clinical application. This method has revolutionized our understanding of coronary artery disease and has become the basis for selecting and evaluating therapeutic interventions. This viewpoint commemorates the achievements of the pioneers of coronary arteriography, the difficultiesthey encountered, and their impact on the development of  modern  cardiology. Developments during the last half century and prospects for the future are discussed in historical perspective

PMID:

Coronary Artery Calcification Screening: Estimated Radiation Dose and Cancer Risk

OBJECTIVES: Multidetector computed tomography has been proposed as a tool for routine screening for coronary artery calcification in asymptomatic individuals. As proposed, such screening could involve tens of millions of individuals, but detailed estimates of radiation doses and potential risk of radiation-induced cancer are not currently available. We estimated organ-specific radiation doses and associated cancer risks from coronary artery calcification screening with multidetector computed tomography according to patient age, frequency of screening, and scan protocol.

METHODS: Radiation doses delivered to adult patients were calculated from a range of available protocols using Monte Carlo radiation transport. Radiation risk models, derived using data from Japanese atomic bomb survivors and medically exposed cohorts, were used to estimate the excess lifetime risk of radiation-induced cancer.

RESULTS: The radiation dose from a single coronary artery calcification computed tomographic scan varied more than 10-fold (effective dose range, 0.8-10.5 mSv) depending on the protocol. In general, higher radiation doses were associated with higher x-ray tube current, higher tube potential, spiral scanning with low pitch, and retrospective gating. The wide dose variation also resulted in wide variation in estimated radiation-induced cancer risk. Assuming screening every 5 years from the age of 45 to 75 years for men and 55 to 75 years for women, the estimated excess lifetime cancer risk using the median dose of 2.3 mSv was 42 cases per 100 000 men (range, 14-200 cases) and 62 cases per 100 000 women (range, 21-300 cases).

CONCLUSIONS: These radiation risk estimates can be compared with potential benefits from screening, when such estimates are available. Doses and therefore risks can be minimized by the use of optimized protocols.

PMID: 19597067