Prelude to CHD: Role of cardiac CT angiography

Column-Dr Ramon Abarquez photoMedicine is Not an Exact Science

Ramon F. Abarquez, Jr., MD, EFACC, FAsCC, FPCP, FPCC, CSPSH

NON-INVASIVE cardiac imaging, in stable coronary artery disease (CAD) diagnosis and prognosis involves nuclear single photon emission computed tomography (SPECT), PET, stress echocardiography, and cardiac magnetic resonance imaging (CMRI). Most modalities detect ischemia, but lack the ability to define coronary anatomy or evaluate for subclinical atherosclerosis, or accurately diagnosing obstructive CAD. but also early identification of nonobstructive CAD lesions.

Cardiac computerized tomographic angiography (CCTA) has the potential to detect or exclude luminal stenosis, as well as identify and quantify subclinical atherosclerosis in the absence if luminal narrowing. Can CCTA be utilized as a first line test in establishing the diagnosis and prognosis of CAD, pior to or even in the absence of coronary angiogram? (Aljizeeri, J Nucl Cardiol. 2013 Jun;20(3):465-72) Caution, the dye used in CCTA can be a great risk in the presence of renal insufficiency.

CCTA in a previous article, is a noninvasivetest that approximates the invasive findings related to coronary angiography. In women with angina, estrogen use and gestational DM were independent occlusive CAD predictors during CCTA evaluation. How about among younger cases with angina?

DFM – DCS versus CCTA

The ability of the Diamond and Forrester method (DFM) (NEJM 1979;300:1350-58) and the Duke Clinical Score (DCS, Pryor, Am J Med, 1983;75:771-80) to predict obstructive coronary artery disease (CAD) based on CCTA was determined. Using the Appropriate Use Criteria, the indications for CCTA were classified according to the DFM and DCS pretest probability and previous testing. The CCTA results were classified as revealing obstructive (=70 percent stenosis), non-obstructive (<70 percent), or no CAD.

When the patients’ risks were classified using the DFM, 18 percent were low, 65 percent intermediate and 17 percent high risk compared to CCTA. When using the DCS, 53 percent of patients had a reclassification of their risk, (50 percent low, 19 percent intermediate, 35 percent high risk). The net reclassification improvement for the prediction of obstructive CAD was 51 percent (p = 0.01). Of the 37 patients who were reclassified as low risk, 36 (97 percent) lacked obstructive CAD. Appropriateness for CCTA was reclassified for 13 percent of patients when using the DCS instead of the DFM, and the number of appropriate examinations was significantly fewer (68 percent vs 55 percent, p <0.001).

Thus, using DCS instead of DFM resulted in improved prediction of obstructive CAD on CCTA, especially in low-risk patients. More patients were categorized as high pretest probability of CAD, hence the need for improved pretest risk scores for noninvasive tests such as CCTA. (Wassfy, Am J Cardiol. 2012 Apr 1;109(7):998-1004.)

CCTA in the young

The prevalence of CAD and major adverse cardiac events (MACE) in patients (< 45 years old) with intermediate pretest likelihood of CAD, has CCTA to determine pretest CAD likelihood based on Diamond and Forrester risk score. Follow-up was completed in 427 patients (94.5 percent) with a median follow-up period of 1081 days. No plaque was noted in 83.6 percent, non-significant CAD in 7.7 percent and significant CAD in 8.7 percent. At the end of the follow-up period, 2.8 percent experienced MACE. The annualized event rate was 0.2 percent in patients with no plaque, 2.0 percent in patients with non-significant CAD, and 7.3 percent in patients with significant CAD.

Hypertension, smoking, and significant CAD in CCTA were significant predictors of MACE based on univariate analysis. CCTA remained a predictor (P < .001) of events after multivariate correction (hazard ratio: 8.345, 95 percent CI: 3.438-17.823, P < .001). The prevalence of CAD and MACE in young adults with an intermediate pretest likelihood of CAD was considerable. (Hou, Acad Radiol. 2012 Nov;19(11):1309-15) What is the predictive score for CCTA?

Metaanalysis for CCTA

A total of 386 studies were identified on initial literature review with: (1) prospective study with =1 month follow-up, (2) CCTA in the emergency department (ED) setting, (3) ACC/AHA definitions for ACS and MACE assessment, (4) =30 patients, and (5) with initial non-diagnostic ECGs and negative biomarkers.

Nine studies (N = 1349), 52 ± 2 years of age, 51 percent male and with low to intermediate pretest probability for ACS. Risk factors included 12 percent diabetes, 42 percent hypertension, 35 percent smokers, 29 percent had hyperlipidemia, and 7 percent known CAD. ACS was subsequently diagnosed in 10 percent of patients.

The sensitivity of CCTA for ACS diagnosis was 95 percent (88-100) and specificity was 87 percent (83-92), with a negative likelihood ratio of 0.06 (0-0.14) and positive likelihood ratio of 7.4 (4.8-10). The 30-day event rate included no deaths and no additional MI. CCTA demonstrates a high sensitivity and a low negative likelihood ratio of 0.06, and is effective in ruling out the presence of ACS in low to intermediate risk patients with acute chest pain (Samad, J Nucl Cardiol. 2012 Apr;19(2):364-76) Among symptomatic patients with CAC zero, after 2 years, 1-2 percent potentially obstructive CAD occurs but without adverse prognosis. (Hulten, Atherosclerosis. 2014 Mar;233(1):190-5)

SPECT and CCTA

Hybrid myocardial perfusion imaging with SPECT and CCTA has the potential to play a major role in patients with non-conclusive SPECT or CCTA results. In total, 98 patients (mean age 62.5 ± 10.1 years, 68.4 percent male) with stable anginal complaints and a median pre-test likelihood of 87 percent (range 22-95 percent) prospectively had Hybrid SPECT/CCTA prior to conventional coronary angiography (CA) with fractional flow reserve (FFR) measurements.

Significant CAD (57.9 percent) had non-conclusive SPECT or CCTA in 32.7 percent. SPECT had a sensitivity of 93 percent, specificity 79 percent, PPV 85 percent, and NPV 89 percent. CCTA had a sensitivity of 98 percent, specificity 62 percent, PPV 77 percent, and NPV 96 percent. Hybrid analysis of SPECT and CCTA improved the overall performance: sensitivity, specificity, PPV, and NPV for the presence of significant CAD to 96, 95, 96, and 95 percent, respectively.

Thus, in > 40 percent of the patients with a high pre-test likelihood no significant CAD was demonstrated. “Hybrid SPECT/CCTA was able to accurately diagnose and exclude significant CAD surpassing stand alone myocardial SPECT and CCTA, vs. a reference standard of FFR measurements.” (Schaap, Eur Heart J Cardiovasc Imaging. 2013 Jul;14(7):642-9)

SPECT/CCTA was able to accurately diagnose and exclude significant CAD versus invasive FFR. In a metaanalysis, CCTA is effective in ruling out the presence of ACS in low to intermediate risk patients with acute chest pain even in the young (< 45 years) adults and among symptomatic cases with zero CAC.

VitalSigns Issue 68 Vol. 3, October 1-31, 2014

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