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CT coronary angiogram.
Multislice computed tomography alternative to invasive coronary angiography.
CT angiography affords direct visualization of the coronary arteries with a negative predictive value approaching 100% for exclusion of obstructive coronary artery disease.
It is significantly more accurate diagnostically than myocardial perfusion imaging.
Coronary CT angiography (CCTA) provides electrocardiogram-gated acquisition with 100-120ms resolution, with submillimeter spatial resolution needed to adequately visualize coronary artery lumens.
CT coronary angiogram scan devices used today have a section thickness of 0.4mm allowing for imaging of small structures such as the coronary arteries.
CT coronary angiography anatomical information is different from functional information afforded by stress testing by electrocardiography, echocardiography, or myocardial perfusion scintigraphy assessing myocardial ischemia.
State of the art scans use a slip-ring rotating gantry that can revolve around the patient in 350 milliseconds or less, and with only a half rotation required to image the heart it can be imaged in 174 milliseconds or less.
Dual source CT scanners, using two radiation sources and radiation detectors at 90 degrees can reduce scanning time to 83 millisecond or less (Miller JC).
Present scanning techniques are of such short duration they can image the heart during diastole.
B-blockers are used to reduce heart rate to decrease motion artifacts in CTA.
Presently high temporal-resolution techniques allow imaging for patients with dysrhythmias such as atrial fibrillation (Oncel D).
Noninvasive CT scan are significantly more effective in identifying coronary artery disease in patients with chest pain than are commonly performed exercise stress test.
Diastolic imaging allows visualization of the coronary arteries the best, as the heart is nearly motionless at that time.
Information about left ventricular function requires imaging throughout the cardiac cycle.
Imaging of the heart requires synchronizing the imaging process with the cardiac cycle by prospective triggering and retrospective gating.
With prospective gating the scanner predicts when diastole will occur and the x-ray source is turned on after a preselected delay.
The Prospective Multicenter Imaging Study for Evluation of the Chest Pain (PROMISE) compared health outcomes in patients who present with new symptoms suggestive of CAD the required further evaluation then randomly assigned to anatomical testing with CTA or to functional testing: there was no improvement in outcomes will either plan over a median of two years follow up (Douglas PS et al).
With prospective gating the x-ray source is on briefly and turns off before the next QRS complex.
Prospective gating allows for imaging of the entire heart within a single heartbeat, such that the newer multidetector helical CT can reduce radiation exposure by 90% compared to retrospective gating techniques.
Retrospective gating techniques require that the x-ray source be on throughout the cardiac cycle and for how many beats required for the imaging.
Sensitivity and specificity for detecting 50% or greater diameter reduction in coronary artery segments ranges from 72-95% and 85-100%, respectively.
Per segment sensitivity 95% and specificity 98%.
A noninvasive test with a negative predictive value of nearly 100% for the detection of coronary artery disease.
Cardiac CT investigates the coronary arteries based on anatomical changes rather than on function, as with dobutamine stress tests, nuclear myocardial perfusion studies and PET.
CT angiogram cannot determine the hemodynamic significance of coronary artery disease, and even among CT identified obstructed stenoses confirmed by invasive coronary angiogram, fewer than half are ischemic causing.
There is an unreliable relationship between coronary artery stenosis and severity of ischemia and concerns exist that CT angiograms may precipitate unnecessary invasive coronary angiogram and coronary revascularization procedures for patients who do not had ischemia.
Overall CT angiography can diagnosis coronary artery disease as well as functional studies, such as dobutamine stress echocardiography, nuclear myocardial perfusion imaging, and invasive coronary angiography (Nixdorff U,Budoff MJ, Gaemperli O).
Coronary CT angiography has a very high negative predictive value for the detection of coronary disease.
In a randomized study of low-intermediate risk patients with possible ACS evaluated with CTTA vs standard care: no patient died or had a myocardial infarction within 30 days with a negative test (Litt HI).
In a study of 1370 subjects with low to intermediate risk patients presenting with possible acute coronary syndromes a coronary CT angiography strategy was a safe process for the expedited discharge from the emergency department of many patients who would otherwise be admitted (Litt HI et al).
In patients in the emergency department with symptoms suggestive of acute coronary syndromes incorporating coronary CT angiography into triage strategy improved efficiency of clinical decision-making but resulted in increased downstream testing and radiation exposure with no decrease in overall cost of care (Hoffmann U et al).
In the above study the triage was associated with the shorter length of stay in the hospital and more direct discharges from the emergency department.
Extensive coronary calcifications limit the interpretation of lumen stenosis often leading to an overestimation of the severity of the lesion.
90% positive and 95% negative predictive values for diagnosis of coronary artery disease.
Detection of greater than 50% stenosis in left main artery or greater than 70% stenosis in any other epicardial vessel makes these patients candidates for coronary artery surgery.
Prevalence and severity of calcifications increase with age and make it likely that study accuracy will decrease with age.
Average dose of radiation for a 75 kg patient is 8.1 mSv equivalent to 2-3 times the dose typically administered during a diagnostic angiogram and equivalent to radiation during a nuclear scintigraphic stress test.
On average one these studies, delivers the equivalent of 309 chest x-rays.
It is estimated that the cancer risk is 1 in every 270 forty year old women undergoing a CT coronary angiogram (Smith-Bindman).
It is estimated that 29,000 excess cancer cases will occur as a result of CT scan exposures done in 2007, and these neoplasms will appear over the next 20 to 30 years with a 50% mortality rate, causing approximately 15,000 deaths annually. (B2242ington de Gonzalez).
In the presence of coronary artery stents studies may not be accurate.
Should be avoided in patients with heart rate of 80 beats per minute or greater.
Reducing the heart rate is associated with decreased radiation dose exposure.
Images compromised by morbid obesity.
Among asymptomatic patients with diabetes, either type one or type two, use of coronary computed tomography angiography (CCTA) to screen for coronary artery disease did not reduce all cause mortality, nonfatal MI, or unstable angina requiring hospitalization at four years:i