Brief Report

What proportion of patients with chest pain are potentially suitable for Computed tomography coronary angiography?

Sulieman Hamid MBBS ^a, Fiona Bainbridge MBBS ^a,

Anne-Maree Kelly MD FACEM ^b,c,?, Debra Kerr BN MBL ^b,c,d

^aDepartment of Emergency Medicine, Western Health, Footscray, Australia

^bJoseph Epstein Centre for Emergency Medicine Research @ Western Health, Sunshine Hospital, St Albans 3021, Australia

^cThe University of Melbourne, Victoria, Australia

^dVictoria University, Victoria, Australia

Received 19 February 2009; revised 4 March 2009; accepted 5 March 2009

Abstract

Objectives: Serial electrocardiographic and biomarker data are used to rule out acute coronary syndrome (ACS) in emergency department (ED) patients with chest pain. These do not identify coronary artery disease (CAD). functional tests are often used but have limitations. Multislice computed tomography coronary angiography (MSCT-CA) is evolving rapidly, raising the possibility of fast, accurate, and relatively noninvasive anatomical testing for CAD. We aimed to quantify the proportion of ED rule-out ACS patients suitable for MSCT-CA.

Methods: This retrospective cohort study (by explicit record review) included adult patients who underwent a rule-out ACS process in ED-associated short-stay units. Data collected included demographics, electrocardiographic and biomarker data, contraindications/factors likely to make MSCT- CA unsuccessful or difficult to interpret including irregular heart rhythm, high pulse rate (with Rate control contraindicated), renal or thyroid disease, contrast allergy, metformin use, pregnancy, and already confirmed CAD. Outcome of interest was the proportion of patients suitable for MSCT-CA. Data analysis is by descriptive statistics.

Results: Four hundred sixty patients were studied (63% male; median age, 63 years). Forty-nine percent (224/460; 95% confidence interval, 44%-53%) were suitable for MSCT-CA. One hundred eighty-one (39%) already had known CAD. Reasons for unsuitability of the remainder were metformin use 18 (6%), irregular heart rhythm 15 (5%), renal dysfunction 12 (4%), high pulse rate with contraindications

to rate control 8 (3%), thyroid disease 7 (3%), and contrast allergy 2 (0.7%).

Conclusion: Approximately half of ED patients with chest pain who have underwent ACS rule-out were potentially suitable for MSCT-CA to identify CAD. The best use of MSCT-CA in the investigation of patients with chest pain requires further clarification.

Crown Copyright (C) 2010 Published by

* Corresponding author. Joseph Epstein Centre for Emergency Medicine Research @ Western Health, Sunshine Hospital, St Albans 3021, Australia.

E-mail address: [email protected] (A.-M. Kelly).

Introduction

Assessment and investigation of patients presenting to emergency departments (EDs) with chest pain is an increasing challenge worldwide. In the United States,

0735-6757/$ - see front matter. Crown Copyright (C) 2010 Published by doi:10.1016/j.ajem.2009.03.005

nontraumatic chest pain contributes to approximately 4.6 million ED visits, an average of 22.7 visits per 1000 people [1]. In Australia, in excess of 100 000 ED visits are for the assessment of chest pain [2]. The dual challenges in the ED are to identify patients with an acute coronary syndrome (ACS) so that appropriate treatment can be given and the group who have significant coronary artery disease (CAD) without infarction so that interventions to minimize morbid- ity and mortality can be undertaken. The former group relies on biomarker and electrocardiographic analysis while the latter has, until recently, relied on functional tests and selective coronary angiography (SCA). Multislice computed tomography coronary angiography (MSCT-CA) is an emer- ging technology for the assessment of coronary arteries. Preliminary data suggest that it is feasible, practical, and accurate in the ED rule-out ACS population [3-6]. Multislice computed tomography coronary angiography has been shown to have good negative predictive value (NPV) for CAD (95%-100%) [6-9].

The place of MSCT-CA is still being elucidated [10]. In particular, not all patients undergoing ED evaluation are suitable for MSCT-CA. Those considered unsuitable include patients with irregular or fast heart rhythms, established CAD (because the presence of CAD has been established and functional testing is probably more usefully in assessing clinical impact), Renal impairment, contraindications to rate- reducing drugs, or hypersensitivity to intravenous contrast. The aim of this study was to quantify the proportion of ED rule-out ACS patients who might be suitable for MSCT-CA.

Methods

This study was conducted using retrospective medical record review methodology. It included all adult patients presenting to the ED of a community teaching hospital in Melbourne, Australia (ED census, 32 000), between January 1, 2006, and October 30, 2006, with nontraumatic chest pain and who underwent a rule-out ACS process in the ED or ED- associated ED short-stay units of 2 community teaching hospital (annual census, 32 000 and 70 000). Patients were identified from an ED management database. Patients were excluded from the study if they did not undergo serial 12-lead ECG/biomarker evaluation, there was a history of trauma, ACS was clearly not considered as a potential diagnosis, initial ECG showed ST-elevation myocardial infarction , or initial biomarker levels were elevated. Typical workup for rule-out ACS in the study institutions is serial ECG and biomarkers. This workup can occur within the confines of the ED or in an ED-associated short stay unit, the location being mainly based on available beds in these areas. Functional or other testing at the same presentation is not our normal practice for logistic reasons. The process of evalua- tion is the same irrespective of location.

Data were collected onto an explicit data collection form designed and trialed specifically for this study. Data collected

Table 1 Characteristics of the study sample Variable

Age (y)

Risk factor (may have

n = 460 %

Median 63

IQE 51-75

Known hypertension

more than 1; therefore, Known

250

195

54

42

% total is N100) hypercholesterolemia

Diabetes 110 24

Smoker 165 36

Family history 46 10

Sex Male 286 62

Female 173 38

National Heart High 101 22

Foundation risk, Intermediate 186 41

n (%); 7 missing data Low 166 37

TIMI risk scores, n (%); 6 2 0.4

4 missing data 5 13 3

4 50 11

3 86 19

2 135 30

1 129 28

0 41 9

included patient demographics, Cardiovascular risk factors, ECG and biomarker data, TIMI risk score [11], National Heart Foundation (Australia) risk stratification [12], contraindica- tions to MSCT-CA, discharge diagnosis, and ED disposition. Contraindications to MSCT-CA were defined as irregular heart rhythm, high pulse rate (N60 beats per minute) with contra- indications to rate control, significant renal (creatinine N130 umol/L) or thyroid disease, contrast allergy, taking metformin, pregnancy, and already known CAD. Already known CAD was defined as previous myocardial infarction, previous coronary artery stent or bypass grafts, stenosis of 50% or greater on coronary angiography, or positive exercise stress test. Although inclusion of CAD as a contraindication might be open to some debate, we decided to treat it as such because the primary goal of MSCT-CA in this setting is the identification of CAD and because the test would be an unlikely to provide additional information to assist clinical decision-making. Data collectors were not blinded to the study hypothesis. Data accuracy was assessed by interrater reliability testing.

Outcome of interest was the proportion of rule-out ACS patients without defined contraindications to MSCT-CA. Data analysis is descriptive and by ? analysis for agreement. All patients were included in analysis. Where data for a particular variable/item was missing, analysis was performed for those with available data. The study was approved under the National Health and Medical Research Council quality assurance guidelines.

Results

Five hundred thirty-nine cases were identified, of which 460 patients met the study criteria. Twenty-five patients had

renal dysfunction, 12 (4%); high pulse rate with contra- indications to rate control, 8 (3%); thyroid disease, 7 (3%); and contrast allergy, 2 (0.7%). Of note, 22% of the sample (63 patients) has TIMI score of 0 (41, or 15%) or a score of 1 due to age (14, or 5%) or aspirin use (7, or 2%) alone.

Table 2 Characteristics of the patients without known CAD Variable n = 279 %

Age (y)

Risk factor (may have

Median 58

IQR 48-70

Known hypertension 116 42

Foundation risk, Intermediate n (%); 6 missing data Low

TIMI risk scores, n (%); 4

115

97

7

42

36

3

Final diagnosis and disposition of the sample overall and the subgroup without known CAD are shown in Table 3.

more than 1; therefore, % total is N100)	Known hypercholesterolemia	78	30
	Diabetes	47	17
	Smoker	91	33
	Family history	34	12
Sex	Male	162	58
	Female	117	42
National Heart	High	61	22

Regarding interrater reliability, 7 data items were tested for 44 records (7.5% of sample). Agreement was 100% for sex (? = 1.00), 93% for history of diabetes (? = 0.87), 93% for history of hypertension (? = 0.86), 93% for presence of atrial fibrillation (? = 0.69), 91% for interpretation of presentation ECG (? = 0.66), 96% for study exclusions (? = 0.64), and 90% of presence of contraindications to MSCT- CA (? = 0.79).

3 missing data	3	32	11
	2	78	28
	1	118	43
	0	41	15

Discussion

elevated biomarkers at presentation, 19 had no biomarker measurements, 19 had a clear alternative diagnosis, 12 had no ECG performed, 3 had STEMI at presentation, and 1 had chest pain as the result of trauma. Sixty-three percent of patients were male, and median age was 63 years (range, 25- 98 years). Risk factor, TIMI score, and NHF risk group stratification distribution are shown in Table 1.

One hundred eighty-one patients had already known CAD (39%). One hundred forty-one (31%) had a myocardial infarction (85 STEMI), 82 (18%) had had coronary stents, 44 (10%) had had coronary artery bypass grafts, 5 (1%) had known >=50% stenosis without intervention, and 4 (1%) had positive exercise stress test without intervention.

Characteristics of the remaining 279 patients are shown in Table 2. Forty-nine percent of the total sample (224/460; 95% confidence interval, 44%-53%) were suitable for MSCT-CA. This represents 80% (95% confidence interval, 75%-85%) of the subgroup without known CAD. Reasons for unsuitability of patients without known CAD were metformin use, 18 (6%); irregular heart rhythm, 15 (5%);

We found that approximately half of patients undergoing a rule-out ACS process were potentially suitable for MSCT- CA, with the major reason for unsuitability being presence of known CAD. Available evidence shows MSCT-CA to have strong NPV for CAD (95%-100%) [6-9] and good prognostic value in the ED chest pain group (adverse cardiovascular event rate 0% at 30 days [5]; 2.8% at 15 months [6]). Eighty percent of those without known CAD were potentially suitable for MSCT-CA, although almost a quarter of these were from very low-risk groups. It could be argued in the patients at Very low risk, the risk-cost-benefit of further testing is dubious.

Overall, 33% of studied patients were admitted to hospital, 24% to the coronary care unit (CCU). Of the group without known CAD, 26% were admitted, 17% to the CCU. Non-STEMI was diagnosed in 5% of the total group and 4% of the group without known CAD, with angina diagnosed in 20% and 10% of the groups, respectively. Of the group overall, 65% of patients were discharged after completing the rule-out ACS process, 73% in the group without known ACS. Non-STEMI and discharge proportions are similar to those reported in studies of chest pain units

Table 3 Discharge diagnosis and disposition of the sample overall and the group without known CAD
Variable	Outcome	Sample overall	Subgroup without known
		(n = 460), n (%)	CAD (n = 279), n (%)
Disposition	Discharged home	173 (38)	119 (43)
	CCU	113 (24)	48 (17)
	Ward	41 (9)	25 (9)
	Transfer	9 (2)	4 (1.4)
	Short-stay unit	124 (27)	83 (30)
Final discharge diagnosis	Chest pain for investigation	329 (72)	229 (82)
	Non-STEMI	23 (5)	10 (4)
	Angina	93 (20)	29 (10)
	Other	15 (3)	11 (4)

[13]. Although reasons for admission were not specifically studied, they may include recurrence of symptoms, other comorbidities, and treating cardiologist preference.

The main alternative to MSCT-CA is functional testing, usually with physiological stress applied. Functional stress tests include exercise ECG testing, nuclear myocardial perfusion imaging (MPI), or stress echocardiography. Func- tional testing has moderate to good sensitivity (68%-77% for treadmill ECG testing [14], 81% for stress MPI [15], 85% for stress echocardiography [16]) and very good prognostic value (treadmill ECG testing NPVof 99%-100% [17], NPVof stress MPI at 36 months of 98.8% [18], and NPV at 33 months of 98.4% [19]). Preliminary data from the United States suggests that functional tests and MSCT-CA are comparable in terms of cost in that health system [19,20]. Functional testing may be the preferred further testing for those with known CAD to assess the pathophysiologic impact of any progression of disease rather than simply anatomical progression which MSCT-CA might identify.

A significant issue with MSCT-CA is radiation exposure

-about 15 mS for men and 23 mS for women. Other issues include timely access (including reporting), as ED chest pain assessment is a round-the-clock function. In addition, findings of minor levels of CAD that are not functionally significant may have negative impacts on patients in terms of insurance and employment.

The role of MSCT-CA in the ED evaluation of chest pain is in evolution. Given its high NPV, an argument could be made for use as a first-line investigation in suitable patients without known CAD. This would require extended avail- ability of scanning and timely expert interpretation but could see patients having CAD ruled out with confidence before leaving the ED. An alternative approach would be to reserve it for low- to intermediate-risk patients with equivocal functional tests, to determine the need for fluoroscopic SCA, with high-risk patients, and those with positive functional tests triaged direct to SCA. Both these approaches have strengths and weakness and will be, in part, governed by local expertise and test availability. Both seem reasonable, if tailored to individual patients. Multislice computed tomo- graphy coronary angiography may have a role in those who are unsuitable for Stress testing. It may also provide additional information in patients where alternative diag- noses (eg, pulmonary embolism, myocarditis, dissection) are under consideration; however, at this stage, dedicated MSCT-CA coronary protocols are not sensitive enough to be used for “triple rule-out” [21]. The small but appreciable risks of MSCT-CA (radiation, contrast reaction) are probably too high for patients at very low risk of CAD, for example, TIMI 0 or age or aspirin use as the only risk features (22% of our non-CAD subgroup). Further research is needed to better define the groups that benefit from this testing modality.

This study has some limitations that should be considered when interpreting the results. Data were collected retro- spectively, with the well-known limitations of that metho- dology, particularly missing data. We combated this by using

explicit data collection and testing interrater reliability. Our definitions of contraindications could be open to challenge. They include both absolute and more relative conditions. For example, metformin use itself may not be considered an absolute contraindication in an acute situation; however, many clinicians might choose an alternative pathway of investigation in patients taking it. Similarly, the pulse rate cutoff used (60 beats per minute) could be regarded as too low. Newer dual-source scanners can assess patients with higher heart rates successfully. This is a single-site study, so results are not necessarily generalizable to other settings. Our study did not explore access to MSCT-CA or compare it with alternative investigation strategies.

Conclusion

Approximately half of patients with chest pain who underwent ED ACS rule-out processes were suitable for MSCT-CA to identify CAD. The best use of MSCT-CA in the investigation of patients with chest pain requires further clarification.

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