Diagnostic Imaging Pathways - Coronary Syndrome (Acute)
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This pathway provides guidance on the imaging investigation of adult patients with suspected acute coronary syndrome.
Date reviewed: January 2012
Date of next review: 2017/2018
Published: January 2012
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SYMBOL | RRL | EFFECTIVE DOSE RANGE |
![]() | None | 0 |
![]() | Minimal | < 1 millisieverts |
![]() | Low | 1-5 mSv |
![]() | Medium | 5-10 mSv |
![]() | High | >10 mSv |
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Teaching Points
Teaching Points
- Noninvasive imaging is increasingly being used in the acute assessment of suspected acute coronary syndrome
- CTCA & TRO can help rule out important causes of chest pain & have been shown to reduce hospital admissions & lengths of stay. CT techniques can be done quickly & relatively cheaply
- MPS & stress testing (ECG and echo) remain important imaging techniques in the assessment of acute coronary syndrome
- The overall choice of non-invasive imaging technique depends on various factors, particularly local expertise & availability of services
acs
Acute Coronary Syndrome (ACS)
- Ischaemic heart disease and acute coronary syndrome (ACS) are major causes of morbidity and mortality throughout the western world. In Australia, they account for over 22000 deaths and 162000 hospitalisations per year 1
- In the emergency setting, acute chest pain represents around 5-10% of all presentations to Australian Emergency Departments, yet only 15-25% of patients have a final diagnosis of ACS. Only a small proportion are serious and require urgent re-perfusion therapy 2
- Despite better diagnostic tests and improved ACS detection rates, 2% of patients with acute myocardial infarction (AMI) are still missed and discharged inappropriately 3,4
- The current gold standard of excluding AMI is serial ECGs and repeat troponin. However, this requires the patient to wait in ED, adding time and cost to the health system
- Modern CT imaging may be useful as an early negative predictor as ACS, as well as providing diagnostic information regarding other life-threatening causes of acute chest pain
ct
Computed Tomopgraphy Coronary Angiogram (CTCA) / Triple Rule Out (TRO)
- Traditionally, computed tomography's main role in the ACS pathway was for diagnosis or exclusion of important differential diagnoses such as pulmonary embolism or aortic dissection 10
- Newer CT technologies (such as 64 slice multidetector CT (MDCT), dual source CT (DSCT) and ECG gating) have allowed CT to have the spatial and temporal resolution to image a heart within a single breath hold. This means that CT can now be used to diagnose or exclude ACS
- In the ED setting, two CT protocols have been evaluated for their utility in the exclusion of ACS
Computed Tomopgraphy Coronary Angiogram (CTCA)
- CTCA is an established technique that uses contrast to enhance the coronary arteries. Even with modern 64-slice MDCT, most protocols require the patient to have an optimal target heart rate around 65bpm, and IV beta-blockers may be administered to achieve this. The patient also needs to be able to take an adequate breath hold for around 10 seconds. The contraindications for CTCA are renal failure, contrast allergy, severe arrhythmia and haemodynamic insufficiency. With modern techniques and scanners, the radiation dose of a CTCA is around 3-6mSv
- The efficacy of CTCA has been validated in many single-centre trials examining its use in the ED setting for exclusion of ACS in low & intermediate risk patients. 11-18 The combined data from these trials show that CTCA has a very high sensitivity (77-100%, avg 92%), high specificity (74-96%, avg 89%), moderate PPV (25-95%, avg 41%), and very high NPV (89-100%, avg 99%). 19 CTCA has sufficient NPV to further exclude ACS in the low & intermediate risk groups. Follow up in these groups varied between 30d, 6m and 1yr, but in general, the number of major adverse cardiac events was nil or very low in the patients discharged with normal CTCA
Triple Rule Out (TRO)
- TRO is a recently introduced extended CTCA protocol aimed at ruling out the major life-threatening causes of acute chest pain (ie. ACS, PE & acute aortic syndrome) in a single scan. 20 TRO has a larger field of view (includes the entire chest) and scanning range (from aortic arch to adrenal glands) compared to CTCA. The acquisition time is slightly longer, requiring patients to breath hold for up to 15 seconds. It has the same contraindications as for CTCA. TRO is ideally suited for investigating patients with acute chest pain that is likely of non-cardiac origin. This is an emerging technique, and so far there is no standardised protocol, particularly with regard to contrast injection
- There have only been a handful of studies examining its utility. 21,22,23,24 They generally demonstrate that TRO has a very high NPV of 99-100%. In one trial of 201 patients, TRO provided a non-coronary diagnosis in 11% of patients and provided a clinically important non-coronary diagnosis that did not explain the patient's symptoms in 14% of patients. Follow up after 30 days showed that in patients with no or mild disease, there were no adverse outcomes. 76% of patients did not require further testing. 22 Another trial examined the use of TRO for imaging patients suspected of PE. 23 Of 125 patients, PE was confirmed in 21%, cardiovascular diagnosis in 7%, noncoronary diagnosis in 27%. Several studies have found that TRO could reduce time to diagnosis and total length of hospital stay 21,24
- The radiation exposure for TRO was previously around 18mSv (generally about 50% higher than CTCA) for 64 slice MDCT. 20 Various techniques such as tube current modulation, z-axis reduction and use of iterative reconstruction software have been demonstrated to reduce radiation exposure without reducing image quality. The radiation dose for TRO is now around 6mSv
- Larger multicenter trials are required to determine an appropriate protocol and further elucidate the role of TRO in the investigation of acute chest pain. TRO may be used in low risk patients, where there is clinical suspicion of PE or aortic syndrome
cxr
Chest Radiography
- Plain chest films are a useful routine initial investigation for patients with suspected ACS
- They can rule out conditions that masquerade as acute MI (such as pneumothorax, rib fractures and malignancies) or provide secondary indications of an MI (such as acute pulmonary oedema without cardiac enlargement)
- Other life-threatening conditions such as pulmonary embolism and aortic aneurysm may be diagnosed from a chest radiograph, though with a much lower sensitivity than CT 9
- A chest radiograph should not delay reperfusion therapy where indicated
mps
Myocardial Perfusion Scintigraphy (MPS)
- MPS using single photon emission computed tomography (SPECT) are a common and well validated method of functional cardiac imaging. 25 A radioactive tracer (such as technetium-99m or thallium-201) is injected, followed by imaging of the myocardial uptake via SPECT. This is usually done twice; once with the patient at rest and later with the patient under stress, either during exercise or after administration of a vasodilator (such as dipyridamole or adenosine). The images at rest and under stress are assessed together. Areas of myocardium that show reversible defects (i.e. tracer uptake at rest, but not under stress) represent myocardial ischaemia. Areas that show irreversible defects (no tracer uptake at rest or under stress) represent infarcted myocardium
- A large metaanalysis found that nuclear stress imaging using adenosine provided the best sensitivity and specificity (90%, 81% respectively) compared to exercise stress imaging and the use of other vasodilators 26
- In patients with suspected ACS who are at intermediate risk, MPS is indicated in early follow-up testing. In various trials, patients who have normal MPS, have very good outcomes with annual mortality rates <1%. 27,28 In patients with ischaemia on MPS, the extent of inducible ischaemia is strongly correlated to overall prognosis and can guide further therapy (i.e. medical management or revascularisation)
- The radiation dose from MPS varies depending on the isotope and protocols used. Generally, the radiation dose from MPS using technetium-99 is around 10mSv but can be >20mSv with thallium-201 29
risk
TIMI Risk Criteria
- The TIMI (Thromboylysis in Myocardial Infarction) score was derived from a large international, randomised, doube-blind trial (TIMI trial) 5
- This trial was initially designed to investigate the safety and efficacy of enoxaparin vs unfractionated heparin in the setting of acute myocardial infarction. Using baseline characteristics from one arm of the study, the investigators performed univariate and multivariate analyses to assess the statistical significance of each characteristic. Once these were elucidated, the risk score was developed. They then validated this score on the other arm of the trial, as well as on the both arms of another similar large trial (ESSENCE trial)
- It has since been validated among many other patient cohorts around the world, although no Australian validation studies exist yet 6,7,8
- TIMI scores are useful for prognostication, and also for separating patients in to risk categories. However, it is important to remember that they are an adjunct to and not a replacement for good clinical judgement
The TIMI Risk Score
Criteria | Score |
---|---|
Age ≥ 65yo | Y=1 |
≥ 3 risk factors for CAD Risk factors being: Diabetes Smoking Htn (BP >140/90, or on antihypertensives) Low HDL <40mg/dL Family history of premature CAD | Y=1 |
Known CAD (stenosis ≥ 50%) | Y=1 |
ASA (aspirin) use in past 7d | Y=1 |
Severe angina (≥ 2 episodes w/in 24 hrs) | Y=1 |
ST changes ≥ 0.5mm | Y=1 |
Positive cardiac markers (e.g. troponin rise) | Y=1 |
Risk | Score | Prognosis (% risk at 14d of all-cause mortality or significant cardiac event) |
---|---|---|
Low | 0-1 | 4.7% |
2 | 8.3% | |
Intermediate | 3 | 13.2% |
4 | 19.9% | |
High | 5 | 26.2% |
6-7 | 40.9% |
stress
Stress Echocardiogram & Stress Echocardiography
- These are both commonly used screening tests for CAD
- The testing method normally occurs as follows. A baseline resting reading is taken. The patient's heart is stressed through exercise (e.g. treadmill, supine bike) or pharmacologically (e.g. dipyridamole, adenosine). A second reading is taken while the patient is at peak stress. The two readings are then interpreted together
- A stress ECG test is considered positive if the stress elicits ST segment elevation or depression of ≥0.10 mV. The sensitivity of exercise treadmill testing to detect CAD is 70% and specificity 75%. The NPV is generally very high (89-100%) 30
- The main limitation with stress ECG is patients with pre-existing ECG changes. These changes (such as left bundle branch block, baseline ST depression, digoxin therapy or pacemakers) make interpretation difficult
- Stress echocardiography (stress echo) is considered positive if there is abnormal ventricular wall motion or thickness in response to stress. In a large metaanalysis, stress echo was shown to be slightly less sensitive (80% vs 90%) but more specific (87% vs 81%) than MPS. 26 In one head to head trial comparing all three modalities in patients without known CAD, pharmacological stress echo had similar sensitivity (~60%) when compared to exercise stress ECG, but was much more specific (96%) and had better overall diagnostic accuracy. However, overall, MPS was still the most sensitive and accurate 31
- As with other forms of ultrasound imaging, the quality and hence overall diagnostic accuracy of echocardiography is limited by the experience of the ultrasonographer and the interpreting physician
- In terms of overall accuracy, MPS > stress echo > stress ECG, and generally pharmacologic stress > exercise stress
References
References
References are graded from Level I to V according to the Oxford Centre for Evidence-Based Medicine, Levels of Evidence. Download the document
- Coronary heart disease. [Internet] AIHW; c2011 [cited 2015 Jan 12]. View the reference
- Cullen L, Than M, Brown AF et al. Comprehensive standardized data definitions for acute coronary syndrome research in emergency departments in Australasia. Emerg Med Australas. 2010;22:34-40. (Review article)
- Pope JH, Aufderheide TP, Ruthazer R, Woolard RH, Feldman JA, Beshansky JR, Griffith JL, Selker HP. Missed diagnoses of acute cardiac ischemia in the emergency department. N Engl J Med. 2000;342(16):1163-70. (Level II evidence)
- Schull MJ, Vermeulen MJ, Stukel TA. The risk of missed diagnosis of acute myocardial infarction associated with emergency department volume. Ann Emerg Med. 2006;48(6):647-55. (Level II evidence)
- Antman EM, Cohen M, Bernink PJ, McCabe CH, Horacek T, Papuchis G, Mautner B, Corbalan R, Radley D, Braunwald E. The TIMI risk score for unstable angina/non-ST elevation MI: a method for prognostication and therapeutic decision making. JAMA. 2000;284(7):835-42. (Level II evidence)
- Filipiak KJ, Koltowski L, Grabowski M, Karpinski G, Glowczynska R, Huczek Z, Kochman J, Majstrak F, Opolski G. Prospective comparison of the 5 most popular risk scores in clinical use for unselected patients with acute coronary syndrome. Circ J. 2010;75(1):167-73. (Level II evidence)
- Bradshaw PJ, Ko DT, Newman AM, Donovan LR, Tu JV. Validation of the Thrombolysis In Myocardial Infarction (TIMI) risk index for predicting early mortality in a population-based cohort of STEMI and non-STEMI patients. Can J Cardiol. 2007;23(1):51-6. (Level II evidence)
- Mahmoud WE, Hassanein MM, Nour El-Din MM, Elbeltagy SM, Sadaka MA. Validation of TIMI and GRACE acute coronary risk scores in Alexandria Governorate and their role in the comparison of quality of care between hospitals. J Egypt Public Health Assoc. 2010;85(1-2):1-28. (Level II evidence)
- American College of Radiology. ACR appropriateness ariteria: chest pain suggestive of acute coronary syndrome (revised). Accessed Sep 17, 2014. (Guideline). View the reference
- Gruettner J, Henzler T, Sueselbeck T, Fink C, Borggrefe M, Walter T. Clinical assessment of chest pain and guidelines for imaging. Eur J Radiol. 2012;81(12):3663-8. (Review article)
- Sato Y, Matsumoto N, Ichikawa M, et al. Efficacy of Multislice computed tomography for the detection of acute coronary syndrome in the emergency department. Circ J. 2005;69:1047-51. (Level III evidence)
- White CS, Kuo D, Kelemen M, et al. Chest pain evaluation in the emergency department: Can MDCT provide a comprehensive evaluation? AJR Am J Roentgenol. 2005;185:533-40. (Level III evidence)
- Hoffmann U, Nagurney JT, Moselewski F, Pena A, Ferencik M, Chae CU, et al. Coronary multidetector computed tomography in the assessment of patients with acute chest pain. Circulation. 2006;114:2251-60. (Level II evidence)
- Gallagher MJ, Ross MA, Raff GL, et al. The diagnostic accuracy of 64-slice computed tomography coronary angiography compared with stress nuclear imaging in emergency department low-risk chest pain patients. Ann Emerg Med. 2007;49:125-36. (Level II evidence)
- Rubinshtein R, Halon DA, Gaspar T, Jaffe R, Karkabi B, Flugelman MY, et al. Usefulness of 64-slice cardiac computed tomographic angiography for diagnosing acute coronary syndromes and predicting clinical outcome in emergency department patients with chest pain of uncertain origin. Circulation. 2007;115:1762-8. (Level III evidence)
- Goldstein JA, Gallagher MJ, O'Neill WW, Ross MA, O'Neil BJ, Raff GL. A randomized controlled trial of multi-slice coronary computed tomography for evaluation of acute chest pain. J Am Coll Cardiol. 2007;49:863-71. (Level II evidence)
- Hoffmann U, Bamberg F, Chae CU, Nichols JH, Rogers IS, Seneviratne SK, et al. Coronary computed tomography angiography for early triage of patients with acute chest pain: The ROMICAT (Rule Out Myocardial Infarction using Computer Assisted Tomography) trial. J Am Coll Cardiol. 2009;53:1642-50. (Level II evidence)
- Hollander JE, Chang AM, Shofer FS, McCusker CM, Baxt WG, Litt HI. Coronary computed tomographic angiography for rapid discharge of low-risk patients with potential acute coronary syndromes. Ann Emerg Med. 2009;53:295-304. (Level II evidence)
- Cury RC, Feuchtner G, Mascioli C, Fialkow J, Andrulonis P, Villanueva T, Pena CS, Janowitz WR, Katzen BT, Ziffer JA. Cardiac CT in the emergency department: Convincing evidence, but cautious implementation. J Nucl Cardiol. 2011;18(2):331-41. (Level I evidence)
- Lee HY, Yoo SM, White CS. Coronary CT angiography in emergency department patients with acute chest pain: triple rule-out protocol versus dedicated coronary CT angiography. Int J Cardiovasc Imaging. 2009;25(3):319-26. (Review article)
- Savino G, Herzog C, Costello P, Schoepf UJ. 64 slice cardiovascular CT in the emergency department: concepts and first experiences. Radiol Med. 2006;111(4):481-96. (Level III evidence)
- Takakuwa KM, Halpern EJ. Evaluation of a "triple rule-out" coronary CT angiography protocol: use of 64-Section CT in low-to-moderate risk emergency department patients suspected of having acute coronary syndrome. Radiology. 2008;248(2):438-46. (Level III evidence)
- Schertler T, Frauenfelder T, Stolzmann P, Scheffel H, Desbiolles L, Marincek B, et al. Triple rule-out CT in patients with suspicion of acute pulmonary embolism: findings and accuracy. Acad Radiol. 2009;16(6):708-17. (Level II evidence)
- Takakuwa KM, Halpern EJ, Shofer FS. A time and imaging cost analysis of low-risk ED observation patients: a conservative 64-section computed tomography coronary angiography "triple rule-out" compared to nuclear stress test strategy. Am J Emerg Med. 2011;29(2):187-95. (Level III evidence)
- Mastouri R, Sawada SG, Mahenthiran J. Current noninvasive imaging techniques for detection of coronary artery disease. Expert Rev Cardiovasc Ther. 2010;8(1):77-91. (Review article)
- Heijenbrok-Kal MH, Fleischmann KE, Hunink MG. Stress echocardiography, stress single-photon-emission computed tomography and electron beam computed tomography for the assessment of coronary artery disease: a meta-analysis of diagnostic performance. Am Heart J. 2007;154(3):415-23. (Level I evidence)
- Soman P, Parsons A, Lahiri N, Lahiri A. The prognostic value of a normal Tc-99m sestamibi SPECT study in suspected coronary artery disease. J Nucl Cardiol. 1999;6(3):252-6. (Level III evidence)
- Elhendy A, Schinkel A, Bax JJ, van Domburg RT, Poldermans D. Long-term prognosis after a normal exercise stress Tc-99m sestamibi SPECT study. J Nucl Cardiol. 2003;10(3):261-6. (Level III evidence)
- Einstein AJ, Moser KW, Thompson RC, Cerqueira MD, Henzlova MJ. Radiation dose to patients from cardiac diagnostic imaging. Circulation. 2007;116(11):1290-305. (Review article)
- Amsterdam EA, Kirk JD, Bluemke DA, Diercks D, Farkouh ME, Garvey JL, et al. Testing of low-risk patients presenting to the emergency department with chest pain: a scientific statement from the American Heart Association. Circulation. 2010;122(17):1756-76. (Guideline)
- Santoro GM, Sciagrà R, Buonamici P, Consoli N, Mazzoni V, Zerauschek F, et al. Head-to-head comparison of exercise stress testing, pharmacologic stress echocardiography, and perfusion tomography as first-line examination for chest pain in patients without history of coronary artery disease. J Nucl Cardiol. 1998;5(1):19-27. (Level II evidence)
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