Noninvasive Coronary Angiography with MSCT
Noninvasive Coronary Angiography with MSCT
Special Report
By Harold L. Karpman, MD, Clinical Professor of Medicine, UCLA School of Medicine. Dr. Karpman reports no financial relationship to this field of study.
Invasive coronary angiography as of this time remains the gold standard of coronary arterial imaging and, even though the risks of this procedure are quite small (total complication rate of 1.8% and mortality rate of 0.1%), catheterization does expose patients to potential discomfort and, therefore, its use is usually restricted by relatively stringent clinical indications and guidelines.1,2 Multislice computed tomography (MSCT) is a relatively recently developed imaging technique which has demonstrated a high level of reliability and accuracy in the visualization of the coronary arterial tree.3-6 Patients require virtually no preparation and receive only a single intravenous iodinated contrast agent injection followed by a saline flush during the performance of the study. According to many enthusiastic investigators, continuing hardware and software development have evolved this technique to a level of accuracy which is equivalent to or in some ways even better then conventional diagnostic invasive coronary angiography.
Hoffman and his associates10 enrolled 103 patients in a study using a 16 detector row CT scanner in a single center and compared the results with invasive coronary angiography performed in the same patients. The ultrafast MSCT scanner permitted noninvasive coverage of the coronary tree within a single breath-hold of less than 25 seconds.7 Temporal resolution was enhanced by using electrocardiogramgated acquisition and combining the projection data from consecutive heart cycles in order to overcome the need to lower the heart rate to below 65 beats per minute.6,9 Of the 1384 coronary arterial segments identified on the invasive coronary angiograms, nondiagnostic image quality of MSCT acquired segments was identified in only 6.4% of these segments primarily due to faster heart rates (ie, greater than 80 BPM). Compared with invasive coronary angiography for detection of lesions greater than 50% stenosis, segment-based sensitivity, specificity, and positive and negative predictive values of MSCT were 95%, 98%, 87%, and 99% respectively. Results revealed that MSCT identified patients who might have been candidates for revascularization (ie, greater than 50% left main artery stenosis and/or greater than 70% stenosis in any other epicardial vessel) with a high degree of accuracy.
Commentary
Hoffman10 has clearly demonstrated that 16 slice MSCT studies when compared with invasive coronary angiography are able to detect hemodynamically significant obstructive coronary artery lesions with great accuracy. The newer 64 slice MSCT units which are now in operation in an increasing number of hospital and outpatient settings require shorter breath-holds (5-12 seconds), use less contrast (60-100 mL), and have increased spatial and temporal resolution. These units will almost certainly reduce the percentage of nondiagnostic image studies significantly from the 6.4% achieved by the 16 slice units to perhaps 2-3 percent and further enhance the sensitivity, specificity, and positive and negative predictive values beyond the superb results which already had been demonstrated with the 16 slice CT unit.10 Despite imaging artifacts which may be related to obesity, elevated heart rate or irregularity and/or coronary artery calcification, continuing improvements in technology and software programs will undoubtedly diminish or eliminate the importance of these confounding factors and lead progressively to even better image quality and resolution. In addition, 64 slice MSCT will almost certainly improve temporal resolution compared to the 16 slice scanner even at faster heart rates and should prove to be of great value in routinely identifying patients who, while clinically suspect, are unlikely to have clinically significant disease. MSCT has proven to be accurate in detecting graft patency (ie, virtually 100% sensitive and specific); stent visualization is somewhat less accurate (ie, 78% sensitivity and 100% specificity) but accuracy will almost certainly improve as scanners and stents continue to evolve. Finally, it should be clearly recognized that the average dose of ionizing radiation in the Hoffman study was 8.1 mSv for a 75 kg patient. This dose is equivalent to 2 to 3 times the dose typically administered during a diagnostic invasive angiogram11 but equivalent to the dose received during a nuclear scintigraphic stress test;12 however, although the long-term risks associated with this level of radiation exposure are relatively low it raises concern about repetitive examinations or its use in younger individuals or women of childbearing age.
Despite any negative features of this technology, I feel quite convinced that MSCT will be almost as significant an advance in cardiology as was echocardiography in the early 1970s. MSCT will not replace prognostic information derived from lipid analysis, electrocardiography, nuclear perfusion studies or stress echocardiography however, the promise of being able to assess atherosclerotic soft plaque by MSCT could prove to be of enormous value in guiding preventive and therapeutic strategies and, in fact, soft plaque evaluation (with MSCT) and/or therapy may to prove to be of greater overall value than simply determining the degree of coronary artery stenosis and/or obstruction. The best use of the catheterization laboratory in the future may be only for therapeutic percutaneous coronary intervention (or for triaging prior to cardiac surgery) in most clinical situation since diagnostic quality MSCT studies will already have been performed. In my opinion, MSCT is not only here to stay but almost certainly will revolutionize our approach to the diagnosis and treatment of both symptomatic and asymptomatic coronary artery disease.
References
1. Scanlon P, et al. ACC/AHA guidelines for coronary angiography. A report of the American College of Cardiology/American Heart Association Task Force on practice guidelines (Committee on Coronary Angiography). Developed in collaboration with the Society for Cardiac Angiography and Interventions. J Am Coll Cardiol. 1999;33:1756-1824.
2. Bashore TM, et al. American College of Cardiology/Society for Cardiac Angiography and Interventions Clinical Expert Consensus Document on cardiac catheterization laboratory standards. A report of the American College of Cardiology Task Force on Clinical Expert Consensus Documents. J Am Coll Cardiol. 2001; 37:2170-2214.
3. Mollet N, et al. Multislice spiral computed tomography coronary angiography in patients with stable angina pectoris. J Am Coll Cardiol. 2004;43:2265-2270.
4. Nieman K, et al. Reliable noninvasive coronary angiography with fast submillimeter multislice spiral computed tomography. Circulation. 2002;106:2051-2054.
5. Ropers D, et al. Detection of coronary artery stenoses with thin-slice multi-detector row spiral computed tomography and multiplanar reconstruction. Circulation. 2003;107:664-666.
6. Hoffman MH, et al. Noninvasive coronary angiography with 16-detector row CT: effect of heart rate. Radiology. 2005; 234:86-97.
7. Manzke R, et al. Automatic phase determination for retrospectively gated cardiac CT. Med Phys. 2004;31:3345-3362.
8. Schoenhagen P, et al. Noninvasive imaging of coronary arteries: current and future role of multi-detector row CT. Radiology. 2004;232:7-17.
9. Grass M, et al. Helical cardiac cone beam reconstruction using retrospective ECG gating. Phys Med Biol. 2003;48: 3069-3084.
10. Hoffman MH, et al. Noninvasive coronary angiography with multislice computed tomography. JAMA. 2005;293: 2471-2478; Erratum in: JAMA. 2005;294:1208.
11. Huda W, et al. Effective doses to patients undergoing thoracic computed tomography examinations. Med Phys. 2000;27: 838-844.
12. Crean A, et al. Cardiac imaging using nuclear medicine and positron emission tomography. Radiol Clin North Am. 2004;42:619-634.
Invasive coronary angiography as of this time remains the gold standard of coronary arterial imaging and, even though the risks of this procedure are quite small (total complication rate of 1.8% and mortality rate of 0.1%), catheterization does expose patients to potential discomfort and, therefore, its use is usually restricted by relatively stringent clinical indications and guidelines.Subscribe Now for Access
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