A 58-year-old male with a past medical history significant for hypertension and hypercholesterolemia presents four hours after acute onset of substernal chest pain that rates eight on a scale of 10. There is no radiation of the pain or associated dyspnea. He describes diaphoresis and nausea. Cardiac enzymes are negative on admission, and the electrocardiogram (ECG) is unchanged. Can computed tomography (CT) coronary angiography effectively rule out coronary disease in this patient admitted with chest pain?
Approximately 5 million patients presented to U.S. hospitals in 2002 for evaluation of chest pain.1 Less than a third of these patients were ultimately diagnosed with acute coronary syndrome.2 Current strategies to differentiate acute coronary syndrome from non-cardiac causes of chest pain have included electrocardiography, cardiac enzymes, exercise treadmill, echocardiography, and nuclear perfusion.
Unfortunately, each of these modalities has false positive and negative rates that result in a significant number of patients undergoing further evaluation for coronary artery stenosis. Although coronary angiography is the current gold standard to evaluate coronary luminal obstruction, it has many drawbacks. It is costly and inconvenient for patients, invasive, and demonstrates only the later stages of atherosclerosis—not which plaques are prone to rupture. All these limitations necessitate a search for a non-invasive evaluation of the coronary vasculature.
Because 64-slice CT scanners allow for visualization of the cardiac anatomy and coronary vasculature without catheters, there has been increasing interest in this modality to evaluate for coronary artery stenosis in low- to intermediate-risk patients presenting with chest pain. Comparative studies have found it allows for faster, safer evaluation of chest pain with sensitivity and specificity comparable to traditional angiography and a negative predictive value superior to nuclear imaging.3,4
Additional advantages include easy access to CT scanners over cardiac catheterization facilities; 88% of community hospitals with six or more beds had CT scanners in 2004. Further, turnaround is faster (15 to 20 minutes for the CT angiography versus six to eight hours of observation after cardiac catheterization). Also, physicians can simultaneously exclude other life-threatening causes of chest pain including aortic dissection and pulmonary embolus.5 Finally, CT angiography is less expensive (about $800 to $1,000) than invasive coronary angiography (approximately $3,000 to $4,000).6
Review of the Data
Patients undergoing CT angiography require a target heart rate of less than 70 beats per minute. Oral or intravenous beta-blockers are typically given prior to the procedure.
Nitroglycerin 0.4-0.8 mg is also administered sublingually to enhance visualization of the coronary vasculature.