03. tbl. 94. árg. 2008

Fræðigrein

Diagnostic Accuracy of 64-Slice Computed Tomography Compared with Coronary Angiography

Greiningarhæfni 64 sneiða tölvusneiðmyndatækni til samanburðar við hefðbundna kransæðaþræðingu

Objective: The aim of this study was to evaluate the diagnostic accuracy (sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV)) of 64-slice multidetector computed tomography (MDCT) compared with quantitative coronary angiography (QCA) for detection of coronary artery disease (CAD).

Material and methods: Sixty-nine patients participating in a study of coronary in-stent restenosis were investigated. After a 64-slice MDCT scan patients were evaluated by QCA. The coronary arteries were divided into 15 segments and stenosis was graded for each segment by both methods. The diagnostic accuracy of 64-slice MDCT was evaluated using the QCA as the gold standard.

Results: Among the 69 patients included in the study 13 (19%) were female and 56 male. The mean age was 63 (SD 10) years. The following risk factors were present: high blood pressure 67%, elevated blood cholesterol 54%, diabetes 12% and family history of CAD 71%. Current smokers were 22% and previous smokers were 48%. Altogether 663 segments were examined. Of those 221 (33%) segments were excluded; 103 because of stents, 48 because of heavy calcification, 41 because of motion artifacts and 29 because the segments were less than 1.5 mm in diameter. The mean time between MDCT and QCA was 6.3 (SD 12.1) days. The sensitivity of 64-slice MDCT for diagnosing significant stenosis (>= 50% according to QCA) was 20%, the specificity was 94%, PPV was 16%, NPV was 95% and the accuracy was 89%.

Conclusion: High NPV and specificity indicates that MDCT is useful for accurately excluding significant CAD but the low sensitivity and low PPV indicate that the method is not accurate in diagnosing coronary artery stenosis of 50% or more according to QCA.

Correspondence: Karl Andersen, andersen@landspitali.is

Table I. The definition of terms used to assess the clinical accuracy of CT when diagnosing coronary artery disease.
Terms	Definition
Sensitivity	Incidence of positive results (critical stenosis) according to CT in segments that are known to have the condition (according to coronary angiogram).
Specificity	Incidence of negative results according to CT in segments that are healthy (according to coronary angiogram).
Positive predictive value	The odds that positive results according to CT is truly positive (according to coronary angiogram).
Negative predictive value	The odds that negative results according to CT is truly negative (according to coronary angiogram).
Accuracy	The ability of CT to classify each segment correctly considering critical stenosis.
CT = computed tomography

Figure 1. Coronary angiogram. Numbered segments that were examined.

Table II. Risk factors.
	Number / Total	Incidence (%)
Family history¹	47 / 66	71
High blood pressure²	46 / 69	67
High cholesterol³	37 /69	54
Previous smoker⁴	32 / 67	48
Current smoker	15 / 67	22
Diabetes mellitus⁵	8 / 69	12
¹Based on I° relatives (parents, children or siblings). ²Blood pressure ≥ 140/90 mmHg or receiving medication for high blood pressure. ³Total cholesterol ≥ 6,5 mmol/l or receiving medication for high blood cholesterol. ⁴Those who quit smoking more than 3 months ago. ⁵ Fasting serum glucose ≥ 7 mmol/l or if the diagnosis had already been made.

Table III. Calculation to assess the diagnostic accuracy of 64 slice CT for all segments.
		Coronary angiography (standard)
		Positive	Negative	Total
CT	Positive	5	27	32	PPV	16% (5/32)
CT	Negative	20	390	410	NPV	95% (390/410)
	Total	25	417	442
		Sensitivity	Specificity		Accuracy	89% (395/442)
		20% (5/25)	94% (390/417)
Positive ≥ 50% stenosis; Negative < 50% stenosis CT = computed tomography; PPV = positive predictive value; NPV = negative predictive value

Table IV. Diagnostic accuracy considering sex, age, coronary artery, location, heart rate.
	Sensitivity (%)	Specificity (%)	PPV (%)	NPV (%)	Accuracy (%)
Sex
- Male	22	93	14	96	89
- Female	14	96	25	93	90
Age
- Younger (< 70 years)	17	94	14	95	89
- Older (≥ 70 years)	29	93	29	96	90
Coronary artery
- Right (segments 1-4)	50	91	18	98	89
- Left (segments 5-16)	14	94	14	94	89
Location¹
- Distal	20	92	14	95	88
- Proximal	20	95	20	95	91
Heart rate
- Low (< 60 beat/min.)	27	93	15	96	90
- High (≥ 60 beat/min.)	11	95	20	91	87
¹The two first segments of the three larger arteries (right coronary artery, left circumflex artery and left anterior descending artery) were defined as the proximal segments as well as the left main artery, that is segments number 1,2,5,6,7,11 and 12. Other segments were defined as distal segments. PPV = positive predictive value; NPV = negative predictive value

Table V. Diagnostic accuracy in segments with and without coronary artery stents.
	Sensitivity (%)	Specificity (%)	PPV (%)	NPV (%)	Accuracy (%)
Segments without stents	20	94	16	95	89
Segments with stents (restenosis)¹	27	84	25	86	75
¹Haraldsdóttir S: Gagnsemi 64 sneiða tölvusneiðmyndatækis til greiningar á endurþrengslum í stoðnetum. Læknablaðið 2007;93:318 PPV = positive predictive value; NPV = negative predictive value

Table VI. Correlation of assessed stenosis (according to a six phase scale) between CT and coronary angiography in 442 segments.
		Coronary angiography
	Stenosis	1	2	3	4	5	6
CT	1	76	27	8	1	3	0
	2	77	102	18	6	4	1
	3	24	45	13	3	2	0
	4	1	19	5	2	2	0
	5	0	2	0	0	1	0
	6	0	0	0	0	0	0
(Total of 442 segments) Correlation coefficient r = 0,33 (Spearman’s rho), p < 0,01. Six category scale: 1 = normal; 2 < 30% stenosis; 3 = 30-49% stenosis; 4 = 50-69% stenosis; 5 ≥ 70% stenosis; 6 = total occlusion. CT = computed tomography.