Volume 194 - Issue 12
A new algorithm for the management of stable coronary artery disease incorporating CT coronary angiography and fractional flow reserve: how we can improve outcomes and reduce costs
Authors: William J van Gaal and Kevin Allman
Med J Aust 2011; 194 (12): 666-669. || doi: 10.5694/j.1326-5377.2011.tb03165.x
Published online: 20 June 2011
Published online: 20 June 2011
To the Editor: Harper and Ko have ignored significant facts regarding myocardial perfusion scintigraphy and made unsubstantiated conclusions regarding computed tomography coronary angiography (CTCA) and fractional flow reserve (FFR).1
Their investigation algorithm for suspected and known stable coronary artery disease (CAD) is flawed. By definition, stable CAD patients cannot be categorised into a “suspected CAD” subgroup. CTCA is not an appropriate first-line investigation for patients presenting with atypical chest pain or equivalent syndromes. Being purely anatomical, CTCA cannot determine the functional significance of CAD, rendering it ineffective in intermediate disease. Furthermore, CTCA often overestimates stenoses due to partial voluming and blooming. Guidelines from the United Kingdom National Institute for Health and Clinical Excellence (NICE) state that “questions remain about the ability of multislice CT coronary angiography to accurately identify stenoses of functional significance ... in people with stable chest pain”.2 Harper and Ko’s algorithm will lead to more investigation, provide no differentiation over and above Step 2 (functional imaging), and increase radiation dose, contrast burden and delays between presentation and definitive treatment.
The real potential of CTCA lies in its ability to non-invasively assess plaque burden and therefore help rationalise long-term pharmacotherapy in high-risk, asymptomatic patients. However, because there is a lack of evidence for this approach, it has been largely ignored and instead the CTCA community has been “sidetracked” into comparing CTCA with functional imaging.
Harper and Ko claim that additional costs from the inevitable increase in CTCA scans would be “minor in comparison to the savings”. This is unproven, and not supported by NICE.2 For atypical symptoms, Harper and Ko recommend “the less expensive ECG [electrocardiogram] exercise test” to risk-stratify patients; however, stress ECG testing is poor at predicting the degree of myocardium at risk, a key factor in risk-stratifying patients. The exercise ECG lacks specificity, leading to unnecessary invasive testing, and many patients are unable to comply. NICE has abandoned exercise ECG testing completely.2
The authors state that a “wealth of data has validated the accuracy of FFR”. The original papers demonstrating a significant FFR of 0.75 were based on perfusion imaging.3,4 The review cited quotes a lower sensitivity and specificity of FFR compared with perfusion scintigraphy, and lists scintigraphy as the “clinical gold standard of ischemia”.5 This is because scintigraphy is the most sensitive technique for identifying functionally significant CAD, as it detects the first abnormality in the ischaemic cascade (reduced myocardial perfusion). Furthermore, the exact level of FFR significance (0.75 v 0.80) is debated. In practice, there is a large degree of operator “discretion” in deciding to revascularise, irrespective of the FFR value, which is often “intermediate” in itself. Harper and Ko question the cost of scintigraphy; however, it is more than $300 cheaper than FFR measurement. They overstate the cost of a standard guidewire by threefold.1
In just one study of over 5000 patients (three times the population of a recent FFR meta-analysis6), increasingly abnormal perfusion scans predicted death and myocardial infarction. There was a reduction in death following revascularisation according to defect severity.7 The nuclear substudy of the COURAGE trial confirmed this.8 No study of CTCA or FFR has been able to predict survival with revascularisation, as the technology is unable to define area at risk. Despite this, Harper and Ko conclude that the Medicare rebate for nuclear testing should be abolished. The authors state that “instituting these changes would undoubtedly result in improved outcomes and substantial savings”. This comment is opinionated, inflammatory and not based on current evidence. The only reasonable conclusion is that before a rebate for CTCA is even proposed, it should be proven diagnostically and prognostically equivalent to myocardial perfusion scintigraphy in predicting ischaemia.
References
- Harper RW, Ko BS. A new algorithm for the management of stable coronary artery disease incorporating CT coronary angiography and fractional flow reserve: how we can improve outcomes and reduce costs. Med J Aust 2011; 194: 186-189. 0_CBBFGDHH
- Cooper A, Calvert N, Skinner J, et al. Chest pain of recent onset: assessment and diagnosis of recent onset chest pain or discomfort of suspected cardiac origin. London: National Clinical Guideline Centre for Acute and Chronic Conditions, 2010. 0_CBBCCDBC
- Miller DD, Donohue TJ, Younis LT, et al. Correlation of pharmacological 99mTc-sestamibi myocardial perfusion imaging with poststenotic coronary flow reserve in patients with angiographically intermediate coronary artery stenoses. Circulation 1994; 89: 2150-2160. 0_CBBBGJIF
- Heller LI, Cates C, Popma J, et al. Intracoronary Doppler assessment of moderate coronary artery disease: comparison with 201Tl imaging and coronary angiography. FACTS Study Group. Circulation 1997; 96: 484-490. 0_CBBHHEIG
- Kern MJ, Samady H. Current concepts of integrated coronary physiology in the catheterization laboratory. J Am Coll Cardiol 2010; 55: 173-185. 0_i1095871
- Christou MA, Siontis GC, Katritsis DG, Ioannidis JP. Meta-analysis of fractional flow reserve versus quantitative coronary angiography and noninvasive imaging for evaluation of myocardial ischemia. Am J Cardiol 2007; 99: 450-456. 0_i1095873
- Hachamovitch R, Berman DS, Shaw LJ, et al. Incremental prognostic value of myocardial perfusion single photon emission computed tomography for the prediction of cardiac death: differential stratification for risk of cardiac death and myocardial infarction. Circulation 1998; 97: 535-543. 0_i1095875
- Shaw LJ, Berman DS, Maron DJ, et al. Optimal medical therapy with or without percutaneous coronary intervention to reduce ischemic burden: results from the Clinical Outcomes Utilizing Revascularization and Aggressive Drug Evaluation (COURAGE) trial nuclear substudy. Circulation 2008; 117: 1283-1291. 0_i1095879