Clinical History A 46-year-old woman with a history of supraventricular tachycardia, benign positional vertigo, and a meningioma was admitted after being found unresponsive at the bottom of a stairway. During her index hospitalization, no arrhythmias were noted; and a technically difficult transthoracic cardiac ultrasound revealed mild to moderate mitral regurgitation, inferior hypokinesis, and an estimated left ventricular ejection fraction of 44%. The initial neurological workup was unremarkable, and the patient refused any further cardiovascular workup. Following discharge, she consented to a cardiac CTA evaluation, and was scanned at MGH with a latest generation high-pitch, dual source ("Flash") CT scanner.
(Click on images to enlarge)
Figure 1: Volume Rendered 3D views of high pitch dual source (“flash“) CTA show normal right and left coronary arterial systems.
Figure 2: Multiplanar reformation of flash coronary CTA shows normal right coronary artery.
Figure 3: Curved multiplanar reformations of flash coronary CTA shows normal left anterior descending (LAD) and circumflex (LCX) coronary arteries.
Findings Cardiac CTA revealed no evidence for anomalous coronary arteries. There was right coronary artery dominance, without evidence of any coronary artery disease. There was no evidence of aortic dissection or aneurysm, and her pulmonary vasculature was unremarkable. Discussion The evaluation of coronary arteries by cardiac CTA in patients with a cardiomyopathy of unclear etiology is an established indication1 and has a negative predictive value of 98% in excluding coronary artery disease as a potential etiology2. Our patient was scanned in the "Flash" mode using the new high-pitch CT scanner, which has a scanning speed of up to 43 cm/s and a temporal resolution of 75 ms. Therefore, an entire chest examination can be completed in just 0.6 seconds. The "Flash" mode can be used reliably in patients with a heart rate of less than 65 and regular rhythm3. Our patient's examination lasted 0.43 seconds, and her total radiation exposure was 1.07 millisieverts (mSv), compared to an average effective dose of 7 mSv for a diagnostic cardiac catheterization and an average effective dose of 15.6 mSv for a myocardial perfusion imaging study (SPECT)4.
Hendel RC et al. ACCF/ACR/SCCT/SCMR/ASNC/NASCI/SCAI/SIR 2006 Appropriateness Criteria for Cardiac Computed Tomography and Cardiac Magnetic Resonance Imaging. JACC 2006, 48:1474-1497
Ghostine S et al. Non-invasive diagnosis of ischaemic heart failure using 64-slice computed tomography. Eur. Heart J. 2008;29:2133-2140
Achenbach S et al. Coronary computed tomography angiography with a consistent dose below 1 mSV using prospective electrocardiogram-triggered high-pitch spiral acquisition. Eur Heart J. 2010;31:340-346
Fazel R et al. Exposure to low-dose ionizing radiation from medical imaging procedures. NEJM 2009;361:849-57
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