64-slice CT for diagnosis of coronary artery disease: a systematic review

Contraindications and side effects of commonly used medications in coronary CT angiography

For certain clinical applications, coronary CT angiography (CCTA) has become a useful tool for the noninvasive evaluation of coronary artery atherosclerosis. To optimize image quality in CCTA, medications are often given prior to scanning to slow the heart rate or distend the arteries. These medications have side effects and are contraindicated in certain patient populations. Metoprolol is the ß-blocker of choice in CCTA, and it has been shown to be effective in achieving the goal heart rate of less than 65 beats per minute for CCTA and in minimizing variability of heart rate. It is contraindicated in patients with hypotension or high degree AV block, and it must be used with caution in patients with asthma or obstructive pulmonary disease, patients with decompensated heart failure, and those with vasospastic or vasoocclusive disease. Diltiazem, the calcium channel blocker of choice in CCTA, is a reasonable alternative for heart control, particularly in patients with asthma or bronchospastic disease, and patients with orthotopic heart transplants that have been sympathetically denervated. Sublingual nitroglycerin is especially useful in order to dilate distal arteries to improve stenosis visibility. However, it is contraindicated in patients on erectile dysfunction medications and those with severe anemia. It must be used cautiously in patients with aortic stenosis or other preload-dependant cardiac pathologies.

Imaging biomarkers of atherosclerosis

Atherosclerosis imaging plays a significant role in an understanding of the natural history of vascular disease and is increasingly used to assess the efficacy of novel therapeutics. Furthermore, the concepts of 'vulnerable plaque' and, more recently, of 'vulnerable patient' have driven cardiovascular imaging technologies to develop methods for expanded qualitative and quantitative analyses. Indeed, developmental efforts are underway to better demonstrate thin fibrous cap and large necrotic cores, and to determine the correlation between these findings and subsequent cardiovascular events. In this article, we consider a wide variety of cardiovascular imaging techniques that are used as biomarkers of atherosclerosis. These technologies include traditional imaging such as angiography, as well as advanced imaging techniques using both invasive and noninvasive approaches.

Radiation dose from single-heartbeat coronary CT angiography performed with a 320-detector row volume scanner

PURPOSE

To determine radiation doses from coronary computed tomographic (CT) angiography performed by using a 320-detector row volume scanner and evaluate how the effective dose depends on scan mode and the calculation method used.

MATERIALS AND METHODS

Radiation doses from coronary CT angiography performed by using a volume scanner were determined by using metal-oxide-semiconductor field-effect transistor detectors positioned in an anthropomorphic phantom physically and radiographically simulating a male or female human. Organ and effective doses were determined for six scan modes, including both 64-row helical and 280-row volume scans. Effective doses were compared with estimates based on the method most commonly used in clinical literature: multiplying dose-length product (DLP) by a general conversion coefficient (0.017 or 0.014 mSv.mGy(-1).cm(-1)), determined from Monte Carlo simulations of chest CT by using single-section scanners and previous tissue-weighting factors.

RESULTS

Effective dose was reduced by up to 91% with volume scanning relative to helical scanning, with similar image noise. Effective dose, determined by using International Commission on Radiological Protection publication 103 tissue-weighting factors, was 8.2 mSv, using volume scanning with exposure permitting a wide reconstruction window, 5.8 mSv with optimized exposure and 4.4 mSv for optimized 100-kVp scanning. Estimating effective dose with a chest conversion coefficient resulted in a dose as low as 1.8 mSv, substantially underestimating effective dose for both volume and helical coronary CT angiography.

CONCLUSION

Volume scanning markedly decreases coronary CT angiography radiation doses compared with those at helical scanning. When conversion coefficients are used to estimate effective dose from DLP, they should be appropriate for the scanner and scan mode used and reflect current tissue-weighting factors. (c) RSNA, 2010.

Current noninvasive imaging techniques for detection of coronary artery disease

The development and widespread use of noninvasive imaging techniques have contributed to the improvement in evaluation of patients with known or suspected coronary artery disease. Stress echocardiography and single-photon computed tomography are well-established noninvasive techniques with a proven track record for the diagnosis of coronary atherosclerosis. These modalities are generally widely available and provide a relatively high sensitivity and specificity along with an incremental value over clinical risk factors for detection of coronary artery disease. PET has a high diagnostic performance but continues to have limited clinical use because of the high expense of the dedicated equipment and difficulties in obtaining adequate radionuclides. Cardiac MRI and multislice computed tomography constitute the most recent addition to the cardiac imaging armamentarium. Cardiac MRI offers a comprehensive cardiac evaluation, which includes wall-motion analysis, myocardial tissue morphology, rest and stress first-pass myocardial perfusion, as well as ventricular systolic function. Cardiac computed tomography allows coronary calcium scanning along with noninvasive anatomic assessment of the coronary tree. It can be combined with functional imaging to provide a complete evaluation of the presence and physiological significance of the atherosclerotic coronary disease. No single imaging modality has been proven to be superior overall. Available tests all have advantages and drawbacks, and none can be considered suitable for all patients. The choice of the imaging method should be tailored to each person based on the clinical judgment of the a priori risk of cardiac event, clinical history and local expertise.

Usefulness of age and gender in the early triage of patients with acute chest pain having cardiac computed tomographic angiography

To identify the age- and gender-specific subpopulations of patients with acute chest pain in whom coronary computed tomographic angiography (CTA) will yield the greatest diagnostic benefit. Subjects with acute chest pain and an inconclusive initial evaluation (nondiagnostic electrocardiograhic findings, negative cardiac biomarkers) underwent contrast-enhanced 64-slice coronary CTA as a part of an observational cohort study. Independent investigators determined the presence of significant coronary stenosis (>50% luminal narrowing) and the occurrence of acute coronary syndrome (ACS) during the index hospitalization. We determined the diagnostic accuracy and effect on pretest probability of ACS using Bayes' theorem by age and gender. Of 368 patients (age 52.7 +/- 12 years, 61% men), 8% had ACS. The presence of significant coronary stenosis on CTA and the occurrence of ACS increased with age for both men and women (p <0.001). Cardiac CTA was highly sensitive and specific in women <65 years of age (sensitivity 100% and specificity >87%) and men <55 years of age (sensitivity 100% for men <45 years and 80% for men 45 to 54 years old; specificity >88.2%). Moreover, in these patients, coronary CTA led to restratification from low to high risk (for positive findings on CTA) or from low to very low risk (for negative findings on CTA). In contrast, a negative result on CTA did not result in restratification to a low-risk category in women >65 years and men >55 years old. In conclusion, the present analysis provides initial evidence that men <55 years and women <65 years might benefit more from cardiac CTA than older patients. Thus, age and gender might serve as simple criteria to appropriately select patients who would derive the greatest diagnostic benefit from coronary CTA in the setting of acute chest pain.

Coronary CTA: stenosis classification and quantification, including automated measures

The development of larger multidetector computed tomography (CT) systems has allowed increased accuracy in quantifying obstructive lesions involving the coronary arteries. This article reviews the accuracy of coronary CT angiography (CTA) in quantifying obstructive lesions, evaluating the extent of coronary artery disease, and classifying the composition of coronary plaques. In addition, several outcomes studies and some promising automated techniques for quantifying coronary CTA are reviewed.

Recent advances in the management of coronary artery disease: highlights from the literature

The recent advances in the multidisciplinary management of coronary artery disease (CAD) have been significant. The assessment of patients before percutaneous coronary intervention is likely to change significantly. National compliance with clinical guidelines in the preprocedural assessment of myocardial ischemia should be encouraged. Multislice computed tomographic coronary angiography continues to improve and is already an excellent screening test for CAD. Coronary stenting has an increasing role in multivessel and left main CAD, although further outcome trials are indicated, especially in the elderly. Although off-pump coronary artery bypass graft (CABG) surgery reduces postoperative atrial fibrillation, further major outcome advantages have not been shown in comprehensive meta-analyses when compared with on-pump CABG surgery. Although an intra-aortic balloon pump reduces mortality in high-risk CABG surgery, it may be replaced gradually by the percutaneous left ventricular-assist device, which has shown clinical benefit in this challenging setting. Statin therapy significantly improves clinical outcome after CABG surgery, even when begun postoperatively. There is strong evidence that, unless contraindicated, all CABG patients should receive statin therapy. Clopidogrel therapy just before CABG surgery is still associated with prolonged hospital stay because of significant bleeding complications. This risk will be exacerbated with the advent of the more potent platelet inhibitor, prasugrel. There is a clinical necessity for readily reversible platelet blockade to minimize the bleeding risks in CABG surgery.

Coronary computed tomography and magnetic resonance imaging

Cardiac computed tomography and magnetic resonance are relatively new imaging modalities that can exceed the ability of established imaging modalities to detect present pathology or predict patient outcomes. Coronary calcium scoring may be useful in asymptomatic patients at intermediate risk. Computed tomographic coronary angiography is a first-line indication to evaluate congenitally abnormal coronary arteries and, along with stress magnetic resonance myocardial perfusion imaging, is useful in symptomatic patients with nondiagnostic conventional stress tests. Cardiac magnetic resonance is indicated for visualizing cardiac structure and function, and delayed enhancement magnetic resonance is a first-line indication for assessing myocardial viability. Imaging plaque and molecular mechanisms related to plaque rupture holds great promise for the presymptomatic detection of patients at risk for coronary events but is not yet suitable for routine clinical use.

Coronary CT angiography (CCTA) and advances in CT plaque imaging

The goal of this review is to highlight current advances in the non-invasive detection of clinically significant atherosclerotic disease including the so-called vulnerable plaque with computed tomography. Atherosclerotic disease encompasses stages of plaque progression, stabilization, and even regression. Traditionally, the focus of diagnostic imaging has been the detection of lumen-occluding atheroma. However, advances in our understanding of the pathophysiology of atherosclerotic plaque have shown that, in certain stages of plaque progression, plaque is "vulnerable" and able to cause acute coronary syndromes despite "non-significant" vascular occlusion at baseline. This provides a rationale to improve our non-invasive imaging technology. Presented here are improvements in soft-tissue resolution with technical advancements as well as contrast-enhancement and lately even nanotechnology-based technology which are geared to detect the clinically elusive vulnerable plaque and provide an opportunity for preventative therapy.