7.5
Coronary CT Angiography in Patients with Chest Pain
A. Küttner, S. Schröder
CT are currently under clinical investigation. Ini- tial promising results with regard to the detection of coronary atherosclerosis have been reported for EBCT in that a large number of experimental and clinical studies demonstrated that this technique is useful to detect the presence of CAD by determining coronary calcifications (Erbel 2000, Rich 2002). In addition, EBCT was used to visualize the coronary arteries non-invasively. The results were encourag- ing, despite 25% non-assessable coronary segments (Achenbach 1998). Also, MRI coronary angiogra- phy was evaluated in a multi-center trial consist- ing of 109 patients. However, it is still in a state of clinical research, since analysis was restricted to proximal vessel segments only (84% with diag- nostic image quality), and specificity in excluding coronary lesions was low (42%) (Kim 2001). Due to improvements in temporal and spatial resolution, multi-slice CT scanners can be used for the non- invasive visualization of human coronary arteries (Ohnesorge 2000, Kopp 2000). Promising results were reported for the first-generation with 4 detec- tor slices (Nieman 2001, Achenbach 2001, Gerber 2002, Kopp 2002), and even better results for the second scanner generation with 16 detector slices.
The non-assessability of a significant portion of cor- onary segments has been reported as the main limi- tation of 4-slice CT, whereas no coronary segments, not even distal segments or side branches, had to be excluded in a study comparing the results in 58 patients with conventional ICA (Nieman 2002b). In that study, a 95% sensitivity and an 86% specificity in the detection of coronary stenoses >50% were reported (Nieman 2002b). The very recent introduc- tion of 64-slice CT has provided further enhance- ment of temporal and spatial resolution compared to 16-slice CT (Flohr 2004). This newest CT genera- tion holds promise that very high accuracy in the detection of hemodynamically significant coronary lesions can be achieved also in patients with higher heart rates (Leschka 2005).
In the following, we present our experience with regard to the usefulness of multi-slice coronary CTA as a first- line imaging technique for further clini- cal decision-making in patients with known or sus- pected CAD and low to intermediate probability of a severe coronary lesion. The data are discussed with respect to a cohort of consecutive patients that were
C o n t e n t s
7.5.1 Clinical Background 224 7.5.2 Methods and Protocols 225 7.5.3 Results in a Representative Patient Population
2267.5.4 Discussion 228
7.5.4.1 Current Indications and Limitations of Multi-slice CT Coronary Angiography 228 7.5.4.2 Image Quality of Non-invasive Multi-slice CT Coronary Angiography
2297.5.4.3 Usefulness of Multi-slice CT as an Imaging Technique in Patients with Unclear Chest
Pain
2297.5.4.4 Study Limitations 230 7.5.5 Conclusions 230 References
2307.5.1
Clinical Background
Coronary artery disease is the leading cause of morbidity and mortality in the Western world.
While conventional invasive coronary angiography
(ICA) is still the gold standard in the diagnosis of
CAD, it is limited by its invasiveness and related
possible complications. Mortality is quoted with
0.1% and the total risk of major complications with
1.7% (Scanlon 1999). The majority of all diag-
nostic ICAs are not followed by therapeutic inter-
ventions. For example, in 2001, 611,882 diagnostic
ICAs were performed in Germany alone, but coro-
nary interventions took place only in 195,280 cases
(Mannebach 2002). Thus, there is growing interest
in non-invasive technologies to diagnose and visual-
ize CAD (Achenbach 2001). Different non-invasive
imaging techniques have been evaluated in the past
few years, and EBCT, MRI, and multi-slice spiral
examined with 4-slice and 16-slice CT technology between the years 2001 and 2003. Although newer CT technology has become available in the mean- time, the conclusions that can be derived from these findings are still up to date and valid also for newer scanner generations. Remarks on potential improve- ments of clinical outcomes with the enhanced tem- poral and spatial resolution of newer 16- and 64-slice CT scanners are included in the respective sections.
7.5.2
Methods and Protocols
This section describes the results obtained for 136/142 (96%) consecutive patients who had been referred to the interdisciplinary Cardiac Imaging Outpatient Clinic of our institution to undergo non- invasive coronary angiography using multi-slice CT.
Based on encouraging results of comparative studies with ICA (Kopp 2002), multi-slice CT examinations of the heart were already being performed at our institution in selected patients on a routine clinical basis, e.g., for the exclusion of CAD.
The initial contact with potential candidates was by telephone to evaluate the indication for coro- nary imaging. All patients were advised to consult an established cardiologist to perform further non- invasive examinations (e.g. exercise ECG, echocar-
diography, blood tests) and to evaluate the necessity of further diagnostics. All patients had to be referred by a cardiology and/or internal medicine specialist to get an appointment in our Cardiac Imaging Out- patient Clinic.
Multi-slice CT examinations were indicated in the presented study group of patients based on clinical suspicion of CAD or progression of CAD after PTCA or CABG-surgery because of chest pain and/or posi- tive stress tests.
Cardiovascular risk factors had been evaluated by the referring doctors and were defined as follows:
smoking, hyperlipidemia, hypertension, or diabetes mellitus. Positive stress tests were defined as exami- nations (exercise ECG, myocardial perfusion imag- ing) with pathological results as judged by the refer- ring doctors.
7.5.2.1
Multi-slice CT Examination
Of the 136 multi-slice CT scans, 114 (84%) were per- formed using 4-slice CT and 22 (16%) with a 16- slice CT scanner. Routine protocols were used as mentioned elsewhere in this book. A native scan was performed to quantify coronary calcifications;
a contrast-enhanced scan was done to assess the vessel wall and the coronary lumen (Fig. 7.32).
Fig. 7.32a,b. 16-slice CT examination of a patient with chest pain. a A non-contrast scan is performed prior to the contrast-
enhanced study to evaluate the amount of calcifi cation. b The contrast-enhanced study demonstrates no hemodynamically relevant stenosis, and no coronary catheterization was recommended
a b
7.5.2.2
Interpretation of the Multi-slice CT Scans
Image quality was determined on contrast-media- enhanced axial slices for each coronary vessel seg- ment. For segmentation of the coronary arterial tree, a modified AHA classification was used. A coronary segment was considered to have diagnostic image quality if it was visualized in its entire length, and if the vessel lumen was accurately distinguishable from the adjacent tissue.
Image quality of the multi-slice CT scans was graded as: 1, excellent; 2, good; 3, sufficient; 4, not diagnostic according to the number of assessable segments with diagnostic image quality (10–11 seg- ments, excellent; 8–9 segments, good; 7–8 segments, diagnostic; <7 segments, not diagnostic).
7.5.2.3
Clinical Recommendations
Based on the clinical data and the multi-slice CT examination, the following recommendations were made:
Group I:
No coronary angiography recommended.
• Ia: No severe stenosis was detected on multi-slice CT scans, but the initiation of medical therapy (aspirin, lipid-lowering, β-blockade, ACE inhibi- tor, statin) was recommended.
• Ib: CAD was excluded by multi-slice CT (no calci- fi ed or non-calcifi ed plaques detectable, Agatston score: 0).
Group II:
Coronary angiography recommended. Additionally, the initiation of medical therapy (aspirin, lipid-low- ering, β-blockade, ACE inhibitor, statin) was recom- mended.
• IIa: Detection of a hemodynamically relevant lesion.
• IIb: Insuffi cient image quality or severe calcifi - cations prohibiting accurate determination of lesion severity.
7.5.2.4
Clinical Follow-Up
Patients were interviewed by telephone to inquire about their further clinical course. The following topics were evaluated: (a) whether the referring doc- tors complied with the recommendation based on the multi-slice CT examinations; (b) the results of coronary angiographies, if performed; (c) the cor- respondence between coronary angiography and multi-slice CT results; (d) the patient’s clinical symp- toms (graded as: 1, better; 2, equal; 3 worse), quality of life (graded as: 1, better; 2 equal; 3 worse), and with the Cardiac Imaging Outpatient Clinic (graded as: 1,very satisfied; 2, satisfied; 3, not satisfied). Also, the medication was evaluated at follow-up.
7.5.3
Results in a Representative Patient Population
In the study group of 136 patients, the following car- diovascular risk factors and clinical characteristics were reported (Table 7.10).
7.5.3.1
Indication for Performing a Multi-Slice CT Scan of the Heart
Of the 136 patients, 95 (69.8%) patients had the clini- cal suspicion of CAD: due to the finding of angina in 83 (87.4%), and/or pathological exercise ECG in 29 (30.5%), and/or pathological myocardial perfusion imaging in two (2.1%), and/or pathologic intimal media thickness in 14 (14.7%).
Known CAD with suspicion of progression of disease was found in 24 (17.6%) of the 136 patients:
due to the finding of angina in 16 (66.6%), and/or pathological exercise ECG in five (20.8%), and/or pathological myocardial perfusion imaging in one (4.2%).
Seventeen (12.5%) of the 136 patients had a CABG
in their medical history. Of these, cardiac-CT was
performed due to the finding of angina in 14 (82.4%),
and/or pathological exercise ECG in four (23.5%),
and/or pathological myocardial perfusion imaging
in one (5.9%).
7.5.3.2
Image Quality of Cardiac CT
Within the presented cohort of 136 patients, 40 scans were of excellent image quality, 27 were good, 60 had a diagnostic image quality, and nine were graded as not diagnostic. Of those nine scans, eight were 4-slice CT examinations but only one was a 16-slice CT examina- tion. The main reasons for non-assessable coronary segments in the not diagnostic exams were the pres- ence of severe calcification or motion artifacts.
7.5.3.3
Recommendations Based on Cardiac CT
Group I, for which ICA was not recommended, com- prised 77 (56.6%) of the 136 patients:
• Ia: In 51 (37.5%) patients because no severe ste- nosis was detected.
• Ib: In 26 (19.1%) patients because of exclusion of CAD.
Group II, for which ICA was recommended, com- prised 59 (43.4%) of the 136 patients:
• IIa: In 38 (27.9%) because of severe stenosis was detected.
• IIb: In 21 (15.4%) because of insuffi cient image quality (9/21) or severe calcifi cations prohibit- ing an accurate determination of lesion severity (12/21).
The severity of CAD in group I and group II was classified according to the multi-slice CT findings as follows:
• Ia: In 31 of the 51 patients, there were vessel wall alterations but no severe lesions: 1-vessel disease in seven patients, 2-vessel disease in two patients, and 3-vessel disease in 11 patients.
• Ib: CAD was excluded in all 26 patients.
• IIa: One-vessel disease was found in 18 of the 38 patients, fi ve had 2-vessel disease, and 15 had 3- vessel disease.
• IIb: Not applicable.
The Agatston-scores in group I and group II were as follows:
• Ia: 151 ± 251
• Ib: 0
• IIa: 395 ± 945
• IIb: 1111 ± 1957
7.5.3.4
Follow-Up Results
Clinical follow-up was through a telephone inter- view in 136 of the 142 (96%) patients who had been examined in the Cardiac Imaging Outpatient Clinic.
Of the remaining six (4%) patients who could not be contacted, two had died (1 patient because of esophageal carcinoma, 1 because of sudden death of unknown reason), one patient refused participation in the follow-up interview, and four patients could not be contacted because they had moved. Although ICA had been recommended based on the multi- slice CT results in 59 (43%) of the136 patients, it was actually performed in 27 (20%). The ICA findings corresponded to those obtained with multi-slice CT in 18 (67%) of these 27 patients. In two patients, false-negative multi-slice CT results became overt, and in seven patients false-positive results were revealed. The detailed follow-up results are sum- marized in Table 7.11.
7.5.3.5
Satisfaction, Symptoms, and Quality of Life at Follow-Up
Of the 136 patients, 58 (42%) reported improved clinical symptoms and 42 (31%) improved quality of life after multi-slice CT examination. Clinical
Table 7.10. Clinical characteristics in the study group. SD Stan-
dard deviation
N (± SD) %
Patient cohort 136 Patients (104 male, 32 female)
Age (years) 60 ± 10
Hypertension 103/136 75.6
Hyperlipidemia 98/136 72.1
Familiar predisposition 37/136 27.2
Smoking 24/136 17.6
Diabetes mellitus 19/136 13.9
β-blockade 47/136 34.6
Table 7.11. Clinical follow-up results according to telephone interviews focusing on the cor-
respondence between the results of invasive coronary angiography (ICA) and multi-slice CT (MSCT)
Patient group Group I (n = 77) Group II (n = 59)
Subgroup Ia (n = 51) Ib (n = 26) IIa (n = 38) IIb (n = 21)
ICA recommended 0 0 38 21
ICA performed 4 0 16 7
Corresponding results with MSCT 2 0 10 6
Non-corresponding results 2
a0 6
b1
ba
False-negative results.
b
False-positive results.
Table 7.12. Satisfaction, clinical symptoms and quality of life of the study group at follow-up
Group I (n = 77) Group II (n = 59) Level Ia (n = 51) Ib (n = 26) IIa (n = 38) IIb (n = 21)
Symptoms
a1 18 13 12 5
2 33 13 24 14
3 0 0 2 2
Quality of life
b1 16 10 12 4
2 35 16 25 15
3 0 0 1 2
Satisfaction
c1 18 11 7 6
2 32 14 28 14
3 1 1 3 1
a
Symptoms: 1 better, 2 equal, 3 worse.
b
Quality of life: 1 better, 2 equal, 3 worse.
c
Satisfaction: 1 very satisfied, 2 satisfied, 3 not satisfied.
symptoms were unchanged in 86 (61%) patients and quality of life was unchanged in 91 (67%). Four (3%) patients reported aggravated clinical symptoms, and three (2.2%) reduced quality of life. The results are summarized in Table 7.12.
7.5.4 Discussion
The presented study demonstrates that multi-slice coronary CTA can be useful in selected patients with unclear chest pain to close the gap between non-invasive modalities and ICA in the diagnosis of CAD. The false-negative examinations obtained with 4-slice CT, while rare, still occur and thus limit
wide clinical use of this technology. No false-nega- tive examinations were reported in our study in the sub-group of patients examined with 16-slice CT, which indicates a higher clinical reliability of this technique. Further increased robustness can be expected with the introduction 64-slice CT with even better temporal and spatial resolution (Fig. 7.33).
7.5.4.1
Current Indications and Limitations of Multi-slice CT Coronary Angiography
Since multi-slice coronary CTA is, by nature, a
purely diagnostic procedure, its application should
be restricted to patients who have a low or inter-
Fig. 7.33. 64-slice CT examination of a patient with chest pain.
