The American Journal of Medicine
Volume 121, Issue 5 , Pages 358-359, May 2008

Can Computed Tomography Coronary Angiography Replace Noninvasive Functional Stress Testing?

  • Pui-Wai Lee, MBChB
    • ,
  • Patricia A. Pellikka, MD

      Affiliations

    • Corresponding Author InformationRequests for reprints should be addressed to Patricia A. Pellikka, MD, Mayo Clinic, 200 First Street SW, Rochester, MN 55905.

Division of Cardiovascular Diseases, Department of Internal Medicine, Mayo Clinic College of Medicine, Rochester, Minn

Article Outline

 

Intuitively, the most accurate way to diagnose coronary artery disease is by direct visualization of coronary atherosclerosis; the gold standard to localize coronary lesions is invasive coronary angiography (ICA).1 However, in practice, ICA is not used routinely as the first-line investigation because it is invasive, costly, and risky and because anatomic measures of coronary atherosclerosis have limitations in delineating the physiologic implications of coronary diseases. Thus, diagnosis of coronary artery disease has focused on the detection of myocardial ischemia (ie, physiologic manifestations) instead of the coronary lesions per se (ie, anatomic evidence),1 and ICA has been reserved for confirmation of high-risk anatomy in patients who may benefit from revascularization. The recent introduction of multidetector computed tomographic angiography (CTA) has allowed noninvasive, high-resolution imaging of the coronary arteries, challenging the traditional function-based diagnostic approach to the detection of coronary artery disease.

An abundance of data have established the sensitivity and specificity of various modalities of functional stress testing for detection of angiographic coronary artery disease. A meta-analysis of 27 studies of functional testing using ICA as the gold standard indicated the following values for sensitivity and specificity: exercise electrocardiography 68% and 77%, myocardial perfusion imaging (MPI) 88% and 77%, stress echocardiography (SE) 76% and 88%, and positron emission tomography 91% and 82%, respectively2; the sensitivity was even higher (93%-98%) for 3-vessel or left main disease.3

It has been consistently reported that CTA has an excellent negative predictive power in excluding coronary artery disease using ICA as the reference standard. In a meta-analysis4 of 29 studies, including 9 using a 64-slice computed tomography (CT) scanner, the per-segment sensitivity, specificity, and negative predictive values of CTA were 81%, 93%, and 96.5%, respectively. In contrast, the per-segment positive predictive value was only 68%. The per-patient analysis showed a sensitivity of 96% but a specificity of 74%.

However, it must be appreciated that percentage of stenosis is only a modest surrogate of functional significance of a coronary lesion, which also depends on other lesion characteristics, such as its length, shape, and location.5 Moreover, myocardial perfusion is modified by physiologic factors such as vasomotor tone and microvascular resistance, which also would not be appreciated by CTA.6 In a study comparing CTA and MPI in patients with suspected coronary artery disease, despite an excellent agreement between CTA and ICA, only 45% with abnormal CTA findings had abnormal MPI findings. Even in patients with obstructive (>50% stenosis) lesions on CTA, 50% still had normal MPI findings.7 Physiologic approaches for risk stratification, whether noninvasive or invasive, have been shown to be superior to anatomic approaches in terms of clinical outcomes and cost-effectiveness.8

An abundance of prognostic information is available for functional imaging9, 10, 11; less prognostic data are available for CTA. The prognostic value of SE has been established in large numbers of patients in various clinical settings, including stable angina, dyspnea, post-myocardial infarction, in both genders, the elderly, diabetic persons, and post-coronary artery bypass surgery.11 Similar data exist for MPI. The likelihood of myocardial infarction and cardiac death occurring after normal MPI or SE findings is extremely low, with annualized event rates of 0.45% per year for MPI and 0.54% per year for SE.10 In a recent study of the prognostic value of CTA in 100 patients with coronary artery disease, a cardiac event rate of 63% in 16 months was observed in the presence of obstructive disease on CTA; however, the event rate of 8% observed in patients with nonobstructive coronary artery disease was not insignificant.12 A particular advantage of CTA is that it may allow detection of vulnerable plaques that are hemodynamically silent but prone to rupture, leading to acute coronary obstruction.13 The feasibility of noninvasive assessment of the characteristics of disrupted atherosclerotic plaques by CTA has been evaluated.14 These high-risk plaques may be the “blind spots” of functional imaging, and noninvasive identification of these lesions may be a future strategy for risk stratification.

If functional imaging and CTA provide independent but complementary diagnostic information, which imaging modality should be performed in the initial evaluation of a patient with chest pain? In a study randomizing low-risk patients who presented with acute chest pain, 25% of those undergoing CTA as the first-line investigation required further functional evaluation because of inadequate image quality or inability to determine the physiologic significance of intermediate severity coronary lesions.15 CTA is particularly helpful in low-risk patients with equivocal results on functional imaging because a normal CTA is reassuring and may avoid downstream unnecessary, invasive investigations in many patients. If CTA demonstrates coronary atherosclerosis, initiation of medical therapy should be strongly considered. Whether revascularization will confer benefit depends on the extent of ischemic and viable myocardium, the left ventricular function, and the severity of symptoms. Functional imaging provides prognostic information that will aid in deciding on the aggressiveness of treatment. Rapid advances in multidetector CT technology may allow simultaneous anatomic and functional assessment of coronary artery lesions in the future.16 The limitations of testing must be remembered. First, neither CTA nor functional imaging is indicated in the evaluation of an asymptomatic, low-risk patient. Next, although CTA is noninvasive, it is not without risk. Radiation doses are substantial, and contrast is nephrotoxic. Coronary imaging by CTA will frequently not replace ICA; if coronary revascularization is indicated, ICA is still required. Finally, we must establish that our implementation of new technology, however attractive, will translate into improvement in patient outcome.

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PII: S0002-9343(08)00076-4

doi:10.1016/j.amjmed.2007.10.041

The American Journal of Medicine
Volume 121, Issue 5 , Pages 358-359, May 2008

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