Article, Cardiology

Limiting scan range of cardiac CT and the chance of missed acute aortic syndrome

a b s t r a c t

Purpose: Recently, dedicated cardiac computed tomography (CT) has been performed to rule out acute coronary syndrome in patients with chest pain equivalents. However, acute aortic syndrome (AAS) could mimic acute coronary syndrome. We investigated the reliability of CT with a limited scan range for the detection of AAS. Methods: Patients older than 18 years with a diagnosis of AAS were included for a 10-year period. We reviewed all patients’ electronic medical record and cardiac CT scan images. The AAS lesions outside of the upper or lower margin of the cardiac CT scan range were measured. Other abnormalities defined as indirect evidence of AAS such as pericardial effusion were also collected.

Results: Of a total of 309 cases, 6 (1.9%; 95% confidence interval, 0.71-4.17) patients had aortic lesions outside of the cardiac CT scan range. One patient had an aortic lesion above the cardiac CT scan range, and 5 patients had aortic lesions below the cardiac CT scan range.

Conclusions: Aortic lesions outside of the cardiac CT scan range were not rare. Therefore, using a cardiac CT might not guarantee ruling out AAS completely.

(C) 2016

Introduction

Acute chest pain is one of the most common complaints of patients who visit the emergency department (ED) and accounts for approxi- mately 20% of visits [1]. Clinicians in EDs focus on the early diagnosis of life-threatening diseases such as pulmonary embolism (PE), acute coronary syndrome (ACS), and Acute aortic syndrome , which includes aortic dissection (AD), aortic intramural hematoma (IMH), and penetrating atherosclerotic ulcer (PAU). Approximately 15 years ago, chest computed tomography was the best choice to detect AD and PE but not ACS [2]. However, with recent advances in radiology, cardiac CT has emerged as a new tool in the diagnosis of ACS in low- to intermediate-risk patients [3-6]. This development has led to the coining of a new term “triple rule-out”, which includes PE, AAS, and ACS; this term is gaining popularity, especially in EDs [7].

It has been questioned whether significant radiation exposure from the test can be justifiable in low-to intermediate-risk patients [8]. The radiation exposure of triple rule-out CT reaches approximately 14 to 22 mSv, whereas the radiation exposure of cardiac CT is approximately 8 to 12 mSv [9,10]. Although a single exposure would not cause acute

? Prior presentations: none.

?? Funding sources: none.

* Corresponding author at: Department of Emergency Medicine, Seoul National University Bundang Hospital, 82, Gumi-ro 173beon-gil, Bundang-gu, Seongnam-si, Gyeonggi-do 463- 707, Republic of Korea. Tel.: +82 31 787 7579; fax: +82 31 787 4055.

E-mail address: [email protected] (K. Kim).

1 The first 2 authors contributed equally to this study.

problems, there is always the possibility of long-term harmful effects. For this reason, most physicians should make an effort to minimize the individual radiation dose according to the principle of using the lowest dose that is reasonably achievable [10,11]. One very simple approach to this problem is limiting the scan range [12]. However, there is a theoretical chance of missed AAS and PE, which might lead to catastrophic results and significant lawsuits. For PE, we have a reliable clinical scoring system that might be useful when a physician needs to decide whether to limit the scan range [13]. However, there has been no reliable clinical scoring system for AAS, and some physi- cians might be concerned when they are considering the dose reduction technique. The purpose of this study was to estimate the risk of missed AAS and to determine whether cardiac CT with a limited scan range could be a reliable tool in ruling out AAS.

Materials and methods

Design

This study is a retrospective analysis of patients diagnosed as having AAS from July 2003 to September 2013.

Participants

We included patients older than 18 years who had been newly diagnosed as having AAS by the diagnostic code of the electronic medical record during the study period. Patients with the following

http://dx.doi.org/10.1016/j.ajem.2016.08.005

0735-6757/(C) 2016

2008 J. Park et al. / American Journal of Emergency Medicine 34 (2016) 20072010

Table 1

Demographics, past medical history, and imaging findings (N = 309)

Men

176 (57.0%)

Age

60.7 (+-15.2)

Chief complaint

Chest pain

144 (46.6%)

Back pain

60 (19.4%)

Abdominal pain

28 (9.1%)

Others

77 (24.9%)

Marfan syndrome

16 (5.2%)

Svensson

AD

235 (76.1%)

IMH

66 (21.4%)

PAU

6 (1.9%)

Pericardial effusion

51 (16.5%)

Pleural effusion

50 (16.2%)

Fig. 1. Inclusion and exclusion flow chart.

conditions were excluded from the study: patients whose initial diag- nostic CT image was unavailable and patients with known acute and chronic aortic syndrome and a traumatic aortic lesion (Fig. 1).

Data collection and analysis

We reviewed all patients’ electronic medical record and their initial diagnostic contrast CT scan images that included the whole thorax, such as routine chest CT, total aorta CT, chest aorta CT and pulmonary artery CT, and so on. Direct evidence of AAS was defined as the entry and exit sites of dissection, hematoma, and ulcerative lesions [14]. The proximal and distal ends of the distribution were marked.

We defined the scan range of the cardiac CT from the heart base to the subcarinal level according to a previous study [15]. Direct evidence outside of the scan range was collected. Other abnormalities suggestive of AAS, such as pericardial effusion, mediastinal fluid collection, and pleural effusion, which were defined as indirect evidence of AAS, were also gathered. Other demographics, such as past medical history, sex, age, chief complaint, and other imaging findings, were also collected (Fig. 2A and B).

Results

A total of 309 patients were included in the analysis. Male patients (57.0%) predominated. The average age of the patients was 60.7 years, and the most common chief complaint was chest pain (46.6%). Approxi- mately 5.2% of patients had underlying Marfan syndrome. We diagnosed AD in 235 (76.1%) patients, IMH in 66 (21.4%) patients, and PAU in 6 (1.92%) patients (Table 1).

Lesions involving the aortic valve (AV) were detected in 43% (133/309) of patients, and 84% (260/309) of patients had descending aortic lesions crossing the AV lesion. Six patients (1.9%; 95% confidence interval [CI],

0.71-4.17) had aortic lesions outside of the cardiac CT scan range (Table 2). Table 3 includes detailed descriptions of the lesions. There were 5 patients with chest pain (1.6%; 95% CI, 0.52-3.73), and 1 other

patient had back pain (0.3%; 95% CI, 0.008-1.78). Table 4 shows the chief complaints of the patients with AAS. One patient with an AD on the aortic arch had pleural effusion as indirect evidence of AAS. The other patients who had aortic lesions below the heart base had no indirect evidence, such as pleural effusion or pericardial effusion, because of the site of the lesions. Generally, physicians suggest that patients with a chief complaint of chest pain, neck pain, shoulder pain, back pain, dyspnea, syncope, or cardiac arrest might have PE, AAS, or ACS. If the other chief complaints are excluded, cardiac CT could miss 6 (1.9%; 95% CI, 0.71-4.17) AAS cases.

Discussion

In this study, we found that AAS lesions localized outside of the cardiac CT scan range are not very rare. This finding suggests that cardiac CT might not be a reasonable tool to rule out ACS and AAS perfectly in patients presenting with chest pain equivalents at the ED. Among the 309 patients analyzed, more than 30% of patients complained of symp- toms other than chest pain and back pain. Clinicians should consider the diagnosis of AD, despite the fact that the patients do not have chest pain. We identified 4 studies regarding the AAS rate among patients who had chest pain, and the number of their pooled population was 2220 [9,16-18]. The AAS was observed in 6 patients (0.27%; 95% CI,

0.09-0.58). These studies focused on the diagnostic efficiency of cardiac CT and chest CT in patients with a low to intermediate risk of ACS. Based on these results, we suggest that patients with chest pain have a very low possibility of AAS. However, AAS is a critical disease, and physicians should not miss a single case of this condition. The difference in the AAS incidence rate between our study and others is explained by the different research subject.

Fig. 2. (A and B) Vertical distance from the center of the AV opening to the proximal or distal end of the aortic lesion.

J. Park et al. / American Journal of Emergency Medicine 34 (2016) 20072010 2009

Table 2

Patterns of the AAS lesion distribution

Patterns of lesion distribution N

Lesions involving AV 133/309 (43.0%)

Descending aorta lesion crossing (or located below) AV level 260/309 (84.1%) Lesions outside of cardiac CT scan range 6/309 (1.9%)

Patients with chest pain 5/309 (1.6%)

Patients with other chief complaint 1/309 (0.3%)

Some researchers have investigated the effective predictable factors of AD. Those researchers suggested that to detect AD early, a physician should assess 3 clinical variables, ie, aortic pain with immediate onset, characteristic tearing or ripping, or both; mediastinal widening, aortic widening, or both on chest radiography; and pulse differentials, blood pressure differentials, or both. The probability of dissection is low in the absence of all 3 variables (7%). The assessment of these 3 clinical variables helped identify 96% of the acute ADs and stratify the patients into high-, intermediate-, and low-probability groupings of disease [19]. In addition to predictable factors based on clinical findings, some researchers claimed that the D-dimer test might be a valuable factor. Those researchers revealed that the presence of a tissue factor in the smooth muscle layer of the aorta causes sclerosis of the artery. In AAS, this tissue factor flows into the bloodstream and triggers the coagula- tion cascade [20,21]. Ultimately, fibrinolytic activity commences, and the formation of D-dimer is increased. In patients with a thrombosed false lumen, raw thrombi in the lumen could lead to an elevation of the D-dimer concentration via activation of the fibrinolytic system. However, another researcher did not agree with these results; that individual insisted that the diagnostic value of the D-dimer was not sufficient to rule out AAS [22]. The arguments of the usefulness of the D-dimer test to rule out AAS have continued for several years.

Recently, a scoring system in AAS with D-dimer has been developed for risk stratification and showed that a low probability score combined with a negative D-dimer could rule out AAS safely and efficiently [23]. If this scoring system is adapted, physicians could select dedicated cardiac CT by risk stratification.

radiation hazards in the medical area have been determined to be associated with cancer risk, and efforts to reduce radiation doses have been made. We believe that a scoring system could allow dedicated cardiac CT to be performed more safely in patients with chest pain equivalents, and this system could mitigate unnecessary radiation.

This study has several limitations. First, this was a retrospective observational study; therefore, there are biases intrinsic to the study design. Second, as commented on in the discussion, a scoring system or D-dimer was not available in this study. A prospective observational study is needed to determine whether a scoring system can reduce the missed rate of AAS with dedicated cardiac CT. Third, because this study was limited to adult patients, we did not consider the applicability to young patients with unusual conditions such as Marfan syndrome.

Aortic lesions outside of the cardiac CT scan range were not rare. Phy- sicians should not miss a single AAS case because of the critical fatality of the condition. Using a cardiac CT might not guarantee ruling out AAS

Table 4

Number of patients according to their chief complaint

Chief complaint Number

Chest pain

144

Neck pain

1

Shoulder pain

2

Back pain

60

Flank pain

4

Abdominal pain

28

Headache

5

Dyspnea

14

Hemoptysis

0

Neurologic motor change

7

Neurologic sensory change

1

Neurologic altered mentality

12

Neurologic dysarthria

1

Neurologic others

3

Syncope

3

Cardiac arrest

2

Incidental finding

17

Others

5

309

completely in patients with chest pain equivalents at the ED. If patients have a probability of AAS, physicians should be careful to use cardiac CT and to consider other CT scans with a wider scan range than cardiac CT.

Conflicts of interest

This study was supported in part by Seoul National University Invita- tion Program for Distinguished Scholar. All authors do not have any con- flicts of interest.

References

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    Table 3

    Demographics and clinical findings of patients with lesions outside of the scan range

    Sex

    Age

    Chief complaint

    Svensson

    Pericardial effusion

    Pleural effusion

    D-dimer level (ug/mL)

    Length from scan range margin to lesion (mm)

    Male

    60

    Chest pain

    AD

    Not significant

    Left

    14.10

    13

    Male

    51

    Chest pain

    AD

    Not significant

    Not significant

    n/a

    36

    Male

    74

    Chest pain

    AD

    Not significant

    Not significant

    n/a

    0

    Male

    78

    Chest pain

    IMH

    Not significant

    Not significant

    n/a

    50

    Male

    58

    Chest pain

    AD

    Not significant

    Not significant

    n/a

    50

    Female

    72

    Backpain

    PAU

    Not significant

    Not significant

    n/a

    10

    2010 J. Park et al. / American Journal of Emergency Medicine 34 (2016) 20072010

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