ACC/AHA 17-Segment Coronary Model

Comparative studies of coronary CT angiography (CTA) versus angiographic quantitative coronary analysis (QCA) assessment of coronary anatomy usually are performed comparing the presence or absence of angiographically significant stenosis (>50%) among the “17-segment model” of coronary anatomy.

Imaging Coronary Arteries: Luminal Assessment

Imaging of the coronary artery lumen is a particular challenge for CT scanning, given:

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  The small luminal size (especially when diseased)

  
  
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  The rapid motion (up to 150 mm/sec, particularly for the arteries in the atrioventricular grooves) through several phases of the cardiac cycle (early systole, early diastole and late diastole—if in sinus rhythm)

  
  
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  The potential of rhythm or rate irregularity during scanning/acquisition

  
  
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  The need for the patient to hold his or her breath during the procedure

  
  
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  The presence of stents and the tendency of diseased coronary arteries to attract calcification—both of which confer problematic signal “blooming” (partial volume averaging) artifacts.

  
  
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  The combination of motion, blooming artifact, and partial signal averaging effect that substantially reduces the depiction of the lumen within calcified and stented coronary arteries

Attaining equivalence in accuracy between CTA and catheter angiography is a challenge that has not been met as of 2014. Catheter angiography has substantially greater imaging resolution (spatial and especially temporal) and hugely greater versatility, yielding clinically adequate images despite calcification and stents, irregular cardiac rhythms, variable cardiac heart rates, and spontaneous or mechanical ventilation, on stable ambulatory patients and patients in cardiogenic shock ( Table 6-1 ).

Thus, catheter-based angiography has logarithmically greater temporal resolution and several-fold better spatial resolution than contemporary CTA. CTA technology is developing in terms of both spatial and, more importantly, temporal resolution, but the technology gap is notable, and the clinical performance gap is broad in real life. Patients undergoing catheter-based coronary angiography are extremely heterogeneous with respect to many parameters that are relevant to CTA imaging:

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  Variable heart rates:

  
  
  
  
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    Low (due to physiologic, pathologic or pharmacologic reasons) to tachycardic

    
    
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    β-blocker tolerant to β-blocker intolerant

    
    
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    Unstable heart rates

  
  
  
  
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  Heart rhythm: normal sinus rhythm to arrhythmia of all forms

  
  
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  Variable potential for artifact:

  
  
  
  
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    No calcification or minor calcification to heavy calcification

    
    
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    No stents

    
    
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    Multiple stents, including stenting within stenting

    
    
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    Stenting within calcified areas

  
  

Given the inherent lesser spatial resolution of CTA, its best coronary application, and probably its earliest, will be to establish that the lumens of large coronary vessels and bypass grafts are not stenotic.

Magnetic resonance angiography (MRA) is becoming increasingly capable and exhibits comparable sensitivity and specificity and accuracy to coronary CTA (at least the older 16-CT) when compared to QCA for vessels 1.5 mm or larger in very highly selected patients and select centers. Comparison of cardiac magnetic resonance (CMR) with current state-of-the-art equipment does not confirm contemporary equivalence of CMR and CTA. A 3-tesla system with increased signal-to-noise ratio (SNR) allows for increased spatial resolution in whole-heart MRA techniques.

Because the motion, size, and orientation of coronary arteries are different, the accuracy of 64-slice multislice CT (64-MSCT) for the detection of coronary stenoses depends on which vessel is being investigated, due to differences in vessel size and the amount of motion through diastole. The right coronary artery and the left circumflex artery are subject to more motion than the left anterior descending (LAD) artery due to the mechanical effect or motion imparted by atrial contraction ( Table 6-2 ).

In patients with normal heart rates, multisegment reconstruction algorithms tend to have superior diagnostic accuracy and image quality compared with half-scan reconstruction algorithms. Automatic selective phase acquisition software in large detector platforms (≥256 slice) and single cardiac cycle acquisition are expected to optimize acquisition with respect to avoidance of diastolic motion and image reconstruction artifacts resulting from multicycle reconstructions.

Calcium, Calcium Scoring, and Calcium Artifact

The presence of calcium, while useful for calcium scoring, is a problem for coronary CTA. The presence of calcium leads to false-positive determination of stenosis as well as overestimation of stenosis. It is more difficult to visualize the lumen in the presence of calcium, due to the “blooming artifact” (i.e., partial volume averaging) of calcium, which is responsible for overestimation of plaque size and stenosis severity. Any motion encountered during acquisition further compounds the blooming and increases the overestimation of stenosis and underestimation of lumen. Blooming artifact is seen less frequently with 64-CCT but remains a significant problem.

The addition of calcium scoring to coronary CTA does not add significantly to the determination of disease. A high calcium score should be seen as a reason not to proceed with CTA, however.

Evidence-Based Review of Coronary Cta

Since about 2005, an accelerating body of evidence has been developing that establishes that coronary CTA is feasible, but within limits that require careful patient selection and preparation. The many limits are represented by the numerous patient exclusions seen in published studies. As the technology has developed, the list of limitation, particularly in terms of patient selection and preparation, has diminished, but exclusions remain numerous and define the nature of use of CTA.

To date, CTA studies have been most useful in excluding disease or classifying disease, if it is present, rather than in performing the vital task of providing a roadmap to plan revascularization procedures in patients with significant disease.

The earliest series using 4-slice CCT equipment, entirely as expected, yielded results inferior to 16-CCT, which currently is considered the bare minimum technology to use for coronary CTA. Today the current standard is 64-CCT or >64-CCT, as presented in the tables in this chapter. Significantly, 64-CCT has not been proven equivalent to conventional angiography. The recent arrival of 256- and 320-CCT, which enable whole heart acquisition in a single cardiac cycle, is expected to provide further imaging benefits, and results of these techniques are eagerly anticipated. Whether they are not just improvements but improvements that render CCT comparable to conventional catheter angiography remains to be seen.

All studies published to date reflect a high degree of selection of patients, establishing that although CTA is feasible, it is not universally feasible, unlike catheter-based techniques. As the temporal resolution of coronary CTA improves, the possibility of including patients with heart rates greater than 75 bpm (who currently are excluded) is emerging, as is the possibility of including patients with irregular heart rhythms. As temporal resolution improves, false-negative CTA studies due to motion artifacts may become less common.

Most comparative studies performed before the introduction of 64-CCT in 2005 are notable for:

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  Use of a segment-by-segment comparison, which predictably increases the power of the study

  
  
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  Comparison of only vessels ≥1.5 (or ≥2.0) mm in luminal size versus all segments, which is not realistic in excluding CAD or in planning revascularization techniques

  
  
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  Comparison of assessable vessels

More recent studies have strived to include:

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  All segments, regardless of size

  
  
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  Vessel comparison (single-, double-, triple-vessel disease)

  
  
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  Patient comparison (disease vs. no disease)

To achieve the greatest plausibility and comparative power for conventional coronary angiography, the ideal and most credible studies of coronary CTA will entail no more exclusions than those of coronary angiography and will validate that the use of coronary CTA in the context of potential use of conventional angiography provides a significant outcome or cost benefit.

Summary of CTA for the Detection of CAD

The use of CTA for the detection of CAD is summarized in Figure 6-1 and Tables 6-3 through 6-10 .

A, Plot and table of per-segment sensitivity of multislice computed tomography–coronary angiography (MSCT-CA) compared with coronary angiography (CA). B, Plot and table of per-segment specificity of MSCT-CA compared with CA. CI, confidence interval; df, degrees of freedom.

(Reprinted with permission from Hamon M, Biondi-Zoccai GG, Malagutti P, et al. Diagnostic performance of multislice spiral computed tomography of coronary arteries as compared with conventional invasive coronary angiography: a meta-analysis. J Am Coll Cardiol. 2006;48(9):1896-1910.)

TABLE 6-3

4-CCT Assessment of Native Coronaries

AUTHOR	JOURNAL	YEAR	n	NONASSESS. (%)	SENSITIVITY (%)	SPECIFICITY (%)	PPV (%)	NPV (%)
Achenbach et al.	Circ	2001	64	32	85	76	59	98
Becker et al.	JCAT	2002	28	5	81	90	97	89
Knez et al.	Am J Card	2001	42	6	78	98	—	—
Kopp et al.	Eur Heart J	2002	102	16	86	96	—	—
Lau et al.	Radiology	2005	50	—	79	95	—	—
Nieman et al.	Lancet	2001	31	27	56	97	—	—
Nieman et al.	Lancet	2001	31	27	81	97	—	—
Nieman et al.	Circ	2002	59	7	95	86	—	—
Nieman et al.	Heart	2002	53	30	58	76	—	—
Nieman et al.	Radiology	2003	24	33	85	73	—	—
Vogl et al.	Radiology	2002	64	—	75	91	—	—
Kuettner et al.	JACC	2004	66	—	37	99	—	—

 

CCT, cardiac CT; nonassess., nonassessable; NPV, negative predictive value; PPV, positive predictive value.

TABLE 6-4

12-CCT Assessment of Native Coronaries

AUTHOR	JOURNAL	YEAR	n	NONASSESS. (%)	SENSITIVITY (%)	SPECIFICITY (%)	PPV (%)	NPV (%)
Ropers et al.	Circ	2003	77	12	93	92	79	97

 

CCT, cardiac CT; nonassess., nonassessable; NPV, negative predictive value; PPV, positive predictive value.

TABLE 6-5

16-CCT Assessment of Native Coronaries

AUTHOR	JOURNAL	YEAR	n	NONASSESS. (%)	SENSITIVITY (%)	SPECIFICITY (%)	PPV (%)	NPV (%)
Achenbach et al.	Eur Heart J	2005	57	5	94	97	—	99
Achenbach et al.	Circ	2004	22	—	82	88	—	—
Heuschmid et al.	Am J Roent	2005	37	0	59	87	—	—
				CAC < 1000	93	94	68	99
Hoffmann M et al.	JAMA	2005	103	6	95	98	—	99
Hoffmann U et al.	Circ	2004	33	—	63	96	64	96
				(good image quality)	82	93	—	—
Kefer et al.	JACC	2005	52	—	82	79	—	—
Kuettner et al.	JACC	2004	58	16	72	97	—	—
				(Agatston <1000)	98	98	—	—
Kuettner et al.	Heart	2005	72	7	85	98	—	96
Kuettner et al.	JACC	2005	72	0	82	98	87	97
Martuscelli et al.	Eur Heart J	2004	64	16	89	98	90	98
Mollet et al.	JACC	2004	128	7	92	95	79	98
Mollet et al.	JACC	2005	51	n/a	95	98	87	99
Morgan-Hughes et al.	Heart	2005	58	2	83	97	—	97
Romeo et al.	JACC	2005	53	12% transplant pt	83	95	71	95
Schuijf et al.	Am J Cardiol	2005	45	6	83	97	—	97
Cademartiri et al.	Radiol Med (Torino)	2005	60	2	93	97	99	86
Cademartiri et al.	Am J Roentgenol	2006	38	0	92	96	87	97
Cademartiri et al.	Radiol Med (Torino)	2005	40	0	96	96	86	99
Dewey et al.	Invest Radiol	2005	129	9	83	86	—	96
Fine et al.	Int J Cardiac Imaging	2004	50	2	87	97	—	98
Kaiser et al.	Eur Heart J	2005	149	23	30	91	—	83
Aviram et al.	Int J Cardiovasc Intervent	2005	22	—	86	98	—	98
Garcia et al.	JAMA	2006	187	29	85	91	—	99
Gulati et al.	Natl Med J India	2005	31	14	85	94	76	96

 

CCT, cardiac CT; nonassess., nonassessable; NPV, negative predictive value; PPV, positive predictive value.

TABLE 6-6

32-CCT

AUTHOR	JOURNAL	YEAR	n	NONASSESS. (%)	SENSITIVITY (%)	SPECIFICITY (%)	PPV (%)	NPV (%)
Cordeiro et al.	Heart	2005	30	20	76	94	—	96

 

CCT, cardiac CT; nonassess., nonassessable; NPV, negative predictive value; PPV, positive predictive value.

TABLE 6-7

40-CCT

AUTHOR	JOURNAL	YEAR	n	NONASSESS. (%)	SENSITIVITY (%)	SPECIFICITY (%)	PPV (%)	NPV (%)
Lim et al.	Clin Radiol	2005	30	0	99	98	94	99

 

CCT, cardiac CT; nonassess., nonassessable; NPV, negative predictive value; PPV, positive predictive value.

TABLE 6-8

64-CCT Assessment of Native Coronaries

AUTHOR	JOURNAL	YEAR	n	NONASSESS. (%)	SENSITIVITY (%)	SPECIFICITY (%)	PPV (%)	NPV (%)
Leber et al.	JACC	2005	59		64	97
				No severe calcium	87	98
Leschka et al.	Eur Heart J	2005	57	n/a	94	97		99
Mollet et al.	Circ	2005	52	2	99	95	76	99
Raff et al.	JACC	2005	70	12	86	95	66	98
Pugliese et al.	Eur Radiol	2005	35	6	99	96	78	99
Ropers et al.	Am J Cardiol	2006	84	4	93	97		100
Fine et al.	Am J Cardiol	2006	66	6	95	96	97	92
Nikolaou et al.	AJR	2006	72	6	97	79		96
Weustink et al.	JACC Per segment	2007	100 1489 100		95 [90–97]	95 [90–97]	95 [90–97]	95 [90–97]
	Per patient				95 [90–97]	95 [90–97]	95 [90–97]	95 [90–97]
Schuijf et al.	Am J Cardiol	2006	61	1	85	98
Ehara et al.	Circ	2006	99	8	90	94
					Pre-test probability	Post-test negative	Post-test positive
Meijboom et al.	JACC	2007	254
			105	High probability	87	17	96
			83	Intermediate probability	53	0	88
			66	Low probability	13	0	68
Shabestari et al.	Am J Cardiol	2007	35		92	97	77	99
				Agatston <100		83
				Agatston >400		60
Meijboom et al.	Heart	2007	104		92	91	60	99
Miller et al. 55	NEJM	2008	291	Agatston <600, >1.5 mm	85 [79–90]	90 [83–94]	91 [85–95]	83 [75–89]
Budoff et al.	JACC	2008	230	1%
		≥50% stenosis	55		95	83	64	99
		≥70% stenosis	31		94	83	48	99
Meijboom et al.	JACC	2008	360	Per patient	99 [98–100]	64 [55–73]	86 [82–90]	97 [94–100]
				Per segment	88 [85–91]	90 [89–92]	47 [44–51]	99 [98–99]

 

CCT, cardiac CT; nonassess., nonassessable; NPV, negative predictive value; PPV, positive predictive value.

TABLE 6-9

64-CCT Assessment of Native Coronaries

PATIENTS (NO.)	NOT EVALUABLE (%)	SENSITIVITY (%)	SPECIFICITY (%)	PPV (%)	NPV (%)
701	3.8 (27/701) (95% CI: 2.6–5.6)	98 (398/404) (95% CI: 95–99)	90 (263/293) (95% CI: 86–93)	93 (394/4240) (95% CI: 90–95)	95 (263/273) (95% CI: 93–98)

 

CCT, cardiac CT; NPV, negative predictive value; PPV, positive predictive value.

Data from Schroeder S, Achenbach S, Bengel F, et al. Cardiac computed tomography: indications, applications, limitations, and training requirements: report of a Writing Group deployed by the Working Group Nuclear Cardiology and Cardiac CT of the European Society of Cardiology and the European Council of Nuclear Cardiology. Eur Heart J . 2008;29(4):531-556.

TABLE 6-10

64-CCT Assessment of Native Coronaries

ANALYSIS	NO.	SENSITIVITY (95% CI)	SPECIFICITY (95% CI)
Per segment	22,798	0.81 (0.72-0.89)	0.93 (0.90-0.97)
Per vessel	2,726	0.82 (0.80-0.85)	0.91 (0.90-0.92)
Per patient	1,570	0.96 (0.94-0.98)	0.74 (0.65-0.84)

 

CCT, cardiac CT.

Data from Hamon M, Biondi-Zoccai GG, Malagutti P, et al. Diagnostic performance of multislice spiral computed tomography of coronary arteries as compared with conventional invasive coronary angiography: a meta-analysis. J Am Coll Cardiol . 2006;48(9):1896-1910.

Coronary CTA

Review of coronary CTA usually begins with a review of axial images and then moves on to maximum intensity projection (MIP) images and reformats (e.g., multiplanar reconstructions and cross-sectional multiplanar reconstructions) to follow the course of the coronary arteries. Workstation software has increasingly included features to assist with coronary (or other) vessel extraction and then depiction. “Seed” markers are placed by the origin of the vessel of interest and distally along its course. Using edge detection algorithms, the vessel is “extracted” and depicted. As the images of the extracted vessel become, to some extent, abstract (for example, a curved artery is depicted in a straightened fashion), reference MIP and 3D images often are displayed concurrently to depict the course of the vessel. These images are usually shown as curved reformations with a single-pixel-thick line coursing down the center of the vessel. Edge detection algorithms allow for maintenance of the center line positioning as the vessel curves. The curve can be represented in any degree of rotation around the center line, which can aid in visualizing eccentric lesions. In addition, cross-sectional “cuts” or planes perpendicular to the long axis of the curved reformations allow for circumferential evaluation of any segment of the analyzed coronary artery ( Figs. 6-2 through 6-23 ; ).

Multiple reconstructions from a cardiac CT study in a 58-year-old woman with a history of angina and an indeterminant myocardial perfusion imaging (MPI) study. The straight and curved reconstructions demonstrate two complex, severe lesions within the proximal right coronary artery (RCA). Cross-sectional evaluation across the more proximal lesion demonstrates mixed plaque, and near-total occlusion. The distal RCA has an approximately 50% soft plaque lesion proximal to the crux. A patent ductus arteriosus (PDA), however is free of disease and is a good-sized vessel. The patient went on to angiography, which demonstrated high-grade stenosis in the proximal RCA, and multiple proximal RCA collaterals. Faint contrast is seen coursing through the remainder of the RCA, but with poor visualization of the other lesions and the non-stenosed PDA. See

Same patient as Figure 6-2 . Multiple cardiac CT reconstructions through a large obtuse marginal branch in a 58-year-old woman with a history of angina and indeterminate myocardial perfusion imaging study. These images demonstrate mild proximal circumflex and obtuse marginal disease. The proximal portion of the large obtuse marginal branch has a severe 70% stenosis. Cross-sectional images demonstrate this to be a mixed plaque stenosis. Conventional coronary angiography (left anterior oblique projection) demonstrates a 70% proximal obtuse marginal branch stenosis. See Figures 6-1 and 6-2 and

A 57-year-old man with typical angina. The patient underwent a nuclear medicine stress perfusion study ( A and B ). Stress views are located superiorly, and the resting views are located inferiorly, with short-axis views on the left and long-axis views on the right. No evidence of a resting or stress perfusion defect is seen. The patient, however, subsequently was referred for a cardiac CT study. Images from that study follow ( C–E ), and corresponding conventional angiographic images are shown in parts F – H. C and F, There is a mixed 50% stenosis in the proximal left circumflex artery and a severe 70% stenosis in the mid-left circumflex artery, imaged on both the CCT and the coronary angiogram. D and G, A tight 80% to 90% mid-right coronary artery stenosis is present, imaged on both the CCT and the coronary angiogram. E and H, A complex 70% to 80% proximal-to-mid left anterior descending artery stenosis is present, imaged on both the CCT and the coronary angiogram. Severe triple-vessel disease was present. The lack of any corresponding regions of perfusion abnormality on the myocardial perfusion imaging study is plausibly due to the occurrence of balanced ischemia, a known challenge/pitfall of nuclear medicine imaging. See

A 57-year-old man with chest pain, and an equivocal myocardial perfusion imaging (MPI) study. A, A mild (<30%) stenosis within the mid-right coronary artery. B, MIP reconstruction of the left main coronary artery demonstrates a moderate amount of mixed plaque in the distal left main coronary artery causing a 50% to 60% left main stenosis. These findings were confirmed on the patient’s conventional angiogram to the right. The patient was referred for surgical consultation. See

A 74-year-old man presents with an acute coronary syndrome. A, Coronary CTA reveals a complete occlusion of the right coronary artery (RCA) due to mixed plaque that is mostly “soft.” B, Corresponding angiogram image corroborates the occlusion of the RCA. C, 3D volume-rendered image depicts the RCA occlusion and collaterals from the distal left anterior descending artery toward acute marginal territory. D, Maximum intensity projection image reveals the acute marginal branches by which (some of the) reconstitution of the ongoing RCA occurs. See Video 6-8.

Multiple images from a 47-year-old man with chest pain. A and B, Nuclear medicine myocardial perfusion imaging study demonstrated a moderate-sized, partially reversible inferior wall defect. Stress images are placed superiorly with rest images inferiorly. The patient went on to have coronary CT angiography ( C ). A second panel demonstrates a curved multiplanar reconstruction of the right coronary artery (RCA) ( D ). A severe soft plaque stenosis is seen in the mid-RCA. Stretched views of the RCA had been obtained with corresponding cross-sectional views in the proximal RCA, through the mid-RCA lesion, and just distal to the mid-RCA lesion. The cross-sectional views ( E and F ) confirm the severe stenosis and the soft plaque component to the stenosis. The bottom left images show a noncontrast calcium score study. The patient’s overall calcium score was zero. There is a moderate-sized area of low attenuation seen in the basal inferior wall. This is also identified on the axial source CTA image ( F ). This area of low attenuation represents fatty metaplasia, and a prior chronic infarct, corresponding with the nuclear medicine study. These CT images, however, are limited in their ability to determine how much residual viability is associated with the region of the prior infarct.

A 52-year-old man presented with typical angina and an indeterminant myocardial perfusion study. Curved reformatted images through the circumflex and obtuse marginal branch do not demonstrate any evidence of a circumflex system stenosis. The corresponding conventional angiogram confirms no obstructive circumflex lesion. See Figures 6-9 and 6-10 and

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