Cardiovascular Journal of Africa: Vol 28 No 6 (November/December 2017)

CARDIOVASCULAR JOURNAL OF AFRICA • Volume 29, No 1, January/February 2018

AFRICA

The centre line was determined for eachmajor coronary artery,

and cross-sectional images perpendicular to the vessel centre line

were subsequently reconstructed. The region of interest (ROI)

contour (size

1 mm

) was positioned in the centre of each cross-

sectional image. The mean luminal radiological attenuation (in

Hounsfield units, HU) was measured at 5-mm intervals from the

ostium to a distal level where the vessel cross-sectional area fell

below 2.0 mm

TAG was determined from the change in HU per 10-mm

length of the coronary artery and defined as the linear regression

coefficient between intraluminal radiological attenuation (HU)

and distance from the ostium (mm).

7,8

A TAG cut-off value

of –15.1 HU/10 mm was defined as significant, as previously

described.

The TAGs of all coronary arteries and of coronary

arteries with moderate stenosis were calculated on stress and rest

CCTA scans, and the TAG results were compared with perfusion

defects detected on CMR images.

Radiation dose estimation of coronary CTA

The effective radiation dose of CCTA was calculated by

multiplying the dose–length product (DLP) by the conservative

constant

(

0.014 mSv/mGy/cm), according to standard

methodology outlined in the European guidelines on quality

criteria for computed tomography.

Statistical analysis

All continuous variables are expressed as means

standard

deviations, whereas categorical data are expressed as percentages.

The diagnostic accuracy of CT-TAG for the detection of

perfusion defects was assessed using CMR as the reference

standard.

The sensitivity, specificity, positive predictive value (PPV)

and negative predictive value (NPV) were calculated and 95%

confidence intervals (CI) were reported for each parameter, which

were bias-adjusted by bootstrap resampling with replacement

200 times from the sample. Calculations were performed on

both an individual coronary vessel and individual patient basis.

All reported diagnostic values were based on consensus between

the two observers. A

value

0.05 was considered to indicate

statistical significance. Statistical analysis was performed using

MedCalc software (Mariakerke, Bergium).

Results

A total of 21 patients were included in this study. Of these, two

declined to undergo stress perfusion CMR after stress CCTA

because of chest discomfort during the CCTA scan, and another

two patients were excluded because of poor CT image quality

that was unsuitable for analysis. Three major coronary arteries

per patient were evaluated; therefore, a total of 17 patients

(mean age: 60.2

9.5 years; 52.9% men) and 51 coronary arteries

successfully underwent the evaluation, with good diagnostic

image quality. Patient characteristics are summarised in Table 1.

The mean estimated radiation effective doses for stress and

rest CCTA were 10.6

2.6 and 2.3

1.3 mSv, respectively. The

mean HR values were 85.5

25.4 bpm during stress and 64.6

10.5 bpm at rest (

0.018). The CT scan parameters are

summarised in Table 2.

Accuracy of TAG compared with stress perfusion

CMR

On ICA, all patients had at least one segment containing

≥

50%

stenosis. Six patients (6/17; 35.3%) had single-vessel disease, seven

(7/17; 41.2%) had two-vessel disease, and four (4/17; 23.5%) had

three-vessel disease. Overall, five vessels (5/51; 9.8%) in three

patients (3/17; 17.6%) were found to have at least one segment

with

≥

70% stenosis; these patients had three-vessel disease.

Of the 51 vessels, 19 (19/51; 37.3%) were classified as having

mild stenosis [three left anterior descending arteries (LAD),

seven left circumflex arteries (LCX) and nine right coronary

arteries (RCA)], 27 (27/51; 52.9%) were classified as having

moderate stenosis (13 LAD, eight LCX and six RCA), and five

vessels (5/51; 9.8%) were classified as having severe stenosis (one

LAD, two LCX and two RCA). The mean degree of coronary

stenosis in all coronary arteries was 55.1

17.3%.

Regarding TAG of stress CCTA, 22 vessels (22/51; 43.1%)

were classified as functionally significant stenosis with a TAG

less than –15.1 HU/10 mm, whereas 29 vessels (29/51; 56.9%) had

a TAG greater than –15.1 HU/10 mm, indicating functionally

non-significant stenosis.

In a patient-based analysis, the sensitivity, specificity, PPV

and NPV for TAG of stress CCTA in all patients were 90.0%

(9/10; 95% CI, 55.5–98.3%), 71.4% (5/7; 95% CI, 29.3–95.5%),

81.8% (9/11; 95% CI, 48.2–97.2%) and 83.3% (5/6; 95% CI,

36.1–97.2%), respectively. The corresponding values for TAG of

rest CCTA in all patients were 66.7% (6/9; 95% CI, 30.1–92.1%),

57.1% (4/7; 95% CI, 18.8–89.6%), 66.7% (6/9; 95% CI, 30.1–

92.1%) and 57.1% (4/7; 95% CI, 18.8–89.6%), respectively. The

diagnostic accuracy of the per-vessel analysis was slightly higher

than that of the per-patient analysis (Table 3).

In a vessel-based analysis, the sensitivity, specificity, PPV

and NPV for TAG of stress CCTA in all coronary arteries were

90.5% (19/21; 95% CI, 69.6–98.5%), 90.0% (27/30; 95% CI,

73.4–97.8%), 86.4% (19/22; 95% CI, 65.1–96.9%) and 93.1%

(27/29; 95% CI, 77.2–99.0%), respectively. The corresponding

Table 1. Baseline characteristics in 17 patients

Age (years)

60.2

9.5

Men/women

9/8

BMI (kg/m

)

25.0

4.9

Family history of CAD,

(%)

3 (17.6)

Diabetes,

(%)

5 (29.4)

Hypertension,

(%)

8 (47.1)

Hypercholesterolaemia,

(%)

6 (35.3)

Current smoker,

(%)

4 (23.5)

Data are presented as the mean

standard deviation or frequency (%).

BMI

body mass index; CAD

coronary artery disease.

Table 2. Stress and rest CCTA imaging parameters