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MR angiography can guide ED management of suspected acute aortic dissection
YAJEM-56297; No of Pages 4 American Journal of Emergency Medicine xxx (2016) xxx–xxx
Contents lists available at ScienceDirect
American Journal of Emergency Medicine journal homepage: www.elsevier.com/locate/ajem
MR angiography can guide ED management of suspected acute aortic dissection☆ Gary X. Wang a, Sandeep S. Hedgire b, Thang Q. Le a, Jonathan D. Sonis c, Brian J. Yun c, Michael H. Lev d, Ali S. Raja c, Anand M. Prabhakar b,d,⁎ a
Department of Radiology, Harvard Medical School, Massachusetts General Hospital, Boston, MA, USA Division of Cardiovascular Imaging, Department of Radiology, Harvard Medical School, Massachusetts General Hospital, Boston, MA, USA Department of Emergency Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA d Division of Emergency Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA b c
a r t i c l e
i n f o
Article history: Received 17 September 2016 Received in revised form 15 November 2016 Accepted 15 November 2016 Available online xxxx Keywords: Aortic dissection Acute aortic syndrome Magnetic resonance angiography Emergency radiology ACR Appropriateness Criteria
a b s t r a c t Background: Aortic dissection is typically evaluated with computed tomography angiography (CTA). However, the feasibility of using magnetic resonance angiography (MRA) in the ED is unclear. This study examined the indications and outcomes of MRA in suspected aortic dissection evaluation in the ED. Methods: An IRB approved review identified patients who underwent MRA in the ED for acute thoracic aortic dissection from January 2010 to June 2016. Demographics, clinical assessment, CTA contraindications, outcomes, and ED disposition were analyzed. Results: 50 MRAs were ordered for suspected thoracic aortic dissection. 21 (42%) for iodinated contrast allergy, 21 (42%) for renal insufficiency, 2 (4%) due to both, 2 (4%) to spare ionizing radiation, 2 (4%) for further work-up after CTA, and 2 (4%) due to prior contrast enhanced CT within 24 h. Median ED arrival to MRA completion time was 311 min. 42 studies were fully diagnostic; 7 were limited. One patient could not tolerate the examination. 49 MRAs were completed: 2 (4%) patients had acute dissection on MRA and 47 (96%) had negative exams. 17 (35%) received gadolinium. 18 (37%) patients were discharged home from the ED with a median length of stay of 643 min. 2 (4%) were admitted for acute dissection seen on MRA and 29 (59%) for further evaluation. Conclusion: MRA has a clear role in the evaluation for acute thoracic aortic dissection in the ED in patients with contraindications to CTA, and can guide management and facilitate safe discharge to home. © 2016 Elsevier Inc. All rights reserved.
1. Introduction Chest pain accounted for 7 million emergency department (ED) visits in the United States in 2010, and was the leading principal cause for ED visits in patients over the age of 65 [1]. Acute thoracic aortic dissection is a potentially life threatening cause of chest pain. Hirst et al. reported a mortality rate of nearly 40% during the first 48 h, with a 1% rise in mortality per hour after onset of symptoms during the first day [2]. Early diagnosis is therefore critical for optimal outcome. A high index of clinical suspicion is required for diagnosis of this deadly-but-rare condition, which has an estimated prevalence of 5000 to 10 000 cases in the United States annually [3]. Although a lack of the classic clinical history of sudden-onset, severe, tearing pain; lack of a pulse differential or neurological deficits; or a normal chest radiograph all decrease the likelihood of acute aortic dissection, advanced imaging examination is
☆ Disclosures: None. ⁎ Corresponding author at: Division of Emergency Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, 55 Fruit St, Gray 2, Boston, MA 02114, USA. E-mail address: [email protected] (A.M. Prabhakar).
often necessary to rule out acute aortic dissection due to the deadly consequences of the missed diagnosis [4,5]. The most commonly used advanced imaging technique to evaluate for suspected acute dissection is computed tomography angiography (CTA) due to its high sensitivity and specificity, widespread aroundthe-clock availability, and fast scan time [6,7]. However, a subset of these patients cannot undergo CTA due to a known allergy to iodinated contrast material or history of renal insufficiency, and therefore require another exam for a definitive diagnosis. For these patients, the American College of Radiology (ACR) Appropriateness Criteria recommends magnetic resonance angiography (MRA) [8]. Compared to CTA, this technique has similarly high sensitivity and specificity and does not use iodinated contrast material. In patients with renal insufficiency, MRA can be performed without intravenous gadolinium-based contrast material [9]. Historically, MRA has not been commonly used in this setting due to limited scanner availability, relatively long scan times, and difficulties in monitoring and treating potentially unstable patients in the MRI suite [6]. The increased prevalence of MRI use in the ED over recent years, combined with continued technical advances in MRI techniques, point towards an increasing role for MRA in the ED [10]. Therefore, the
http://dx.doi.org/10.1016/j.ajem.2016.11.039 0735-6757/© 2016 Elsevier Inc. All rights reserved.
Please cite this article as: Wang GX, et al, MR angiography can guide ED management of suspected acute aortic dissection, American Journal of Emergency Medicine (2016), http://dx.doi.org/10.1016/j.ajem.2016.11.039
2
G.X. Wang et al. / American Journal of Emergency Medicine xxx (2016) xxx–xxx
purpose of this study was to characterize the indications and outcomes of MRA in the ED for evaluating suspected thoracic aortic dissection. 2. Methods 2.1. Human subject compliance This retrospective, HIPAA-compliant study was approved by the institutional review board, including waiver of patient consent. 2.2. Study site This study was completed in a 999-bed urban quaternary care academic center and Level 1 trauma center. Each year, there are approximately 104 000 ED visits, with approximately 105 000 ED diagnostic imaging studies performed and interpreted in the radiology department. 2.3. ED radiology staffing and equipment ED radiology department is staffed with a resident and/or ED Imaging fellow and ED Radiology attending physicians 24/7. A dedicated 1.5T Siemens MRI is available for ED patients. Approximately 8000 to 9000 MRI exams are performed in the ED annually.
Fig. 1. Types of iodinated contrast allergy or reaction in patients unable to undergo CTA.
2.4. Data collection and analysis Electronic medical record review identified patients who underwent MRA in the ED for suspected acute thoracic aortic dissection from January 2010 to June 2016. Age, gender, clinical assessment, CTA contraindications, MRA radiology report, clinical outcomes, and times of ED arrival and dismissal, and of MRA scan were collected. Primary outcomes determined from data analysis were MRA indications and results, and the length of time from ED arrival to MRA. Secondary outcomes included incidental findings from MRA radiology report, method of results communication, and ED length of stay and disposition.
completed due to inability of the patient to tolerate the sound of the MRI scanner. Of the total 49 completed exams, two (4%) showed acute dissection on MRA and 47 (96%) were negative. One patient had a true type A dissection (Fig. 2). For the one patient with a false-positive MRA, the exam report did note that the dissection could be artifact due to excess patient motion but could not be completely excluded. This patient could not undergo CTA due to anaphylaxis to iodinated contrast, and was determined to not have an aortic dissection based on further clinical evaluation. Gadolinium-based contrast material was used for 17 of 49 exams (35%), with 13/17 (76%) performed for patients with iodinated contrast
3. Results 3.1. Patient demographics There were 50 patient encounters in which MRA was ordered for evaluation of suspected acute thoracic aortic dissection during the study period. The mean age of patients in this cohort was 58 years old (range 14–89), with 58% women. 3.2. Indications for MRA For these 50 cases, MRA was requested instead of CTA for the following reasons: 21 (42%) due to iodinated contrast allergy, 21 (42%) due to severe renal insufficiency (eGFR b 30 ml/min/1.73 m2 or clinical concern for declining renal function), 2 (4%) due to both, 2 (4%) to spare ionizing radiation, 2 (4%) for further work-up after CTA, and 2 (4%) due to prior contrast-enhanced CT within 24 h. Among the patients with iodinated contrast allergies, the most common allergic reactions were hives (6/23, 26%), angioedema (4/23, 17%), and anaphylaxis (4/23, 17%) (Fig. 1). The average eGFR for patients who underwent MRA due to renal insufficiency was 21 ml/min/1.73 m2 (standard deviation 10.4, range 4–38). Though one of these patients was already on hemodialysis, the clinical record indicated that MRA was specifically requested by nephrology. 3.3. Imaging and clinical outcomes Forty-two studies were fully diagnostic and 7 were considered to be limited by the interpreting radiologist. One study could not be
Fig. 2. 85-year-old male with history of thoracic aortic aneurysm and chronic renal failure presented with acute onset chest tightness and dyspnea, and could not undergo CTA due to impaired renal function. Axial MRA image without contrast at the level of the left pulmonary artery demonstrates intimal flaps in the ascending (black arrow) and descending (white arrow) thoracic aorta, consistent with Type A aortic dissection. Patient was not a surgical candidate and died shortly after admission for medical management.
Please cite this article as: Wang GX, et al, MR angiography can guide ED management of suspected acute aortic dissection, American Journal of Emergency Medicine (2016), http://dx.doi.org/10.1016/j.ajem.2016.11.039
G.X. Wang et al. / American Journal of Emergency Medicine xxx (2016) xxx–xxx
allergy and none for those with renal insufficiency. In 12 cases, the contrast used was gadopentetate dimeglumine (or Magnevist); in 7 cases, gadofoveset (or Ablavar) was used. Thirty-two (65%) patients did not receive intravenous contrast: 24 (75%) had renal insufficiency and 2 (6%) were on hemodialysis. One patient refused contrast. It was unclear from the medical record why contrast was not used for the remaining five patients. For 39 exams (80%), the results were communicated by routine filing of the imaging report into the electronic medical record. In the other 10 cases (20%), exam results were conveyed by direct verbal communication by the radiologist to the clinical provider. 3.4. Incidental findings In 27 of 49 MRAs (55%), no findings were noted in the impression of the imaging report aside from either presence or absence of acute thoracic aortic dissection or acute aortic syndrome equivalent. Pleural effusion was noted in 6 (12%) exams, ascending thoracic aorta ectasia or aneurysm was noted in 6 (12%), and pericardial effusion was seen in 5 (10%) (Table 1). In one case, MRA demonstrated aortitis involving the aortic arch. This patient was subsequently evaluated by rheumatology and treated for suspected large vessel vasculitis with steroids, which led to resolution of patient's chest discomfort and aortic inflammation on follow-up MRA. 3.5. ED disposition Median time from ED arrival to obtaining an MRA was 311 min (interquartile range 203 to 503). Eighteen (37%) patients were discharged home from the ED; 2 (4%) were admitted for acute dissection seen on MRA and 29 (59%) for further evaluation after dissection was excluded or to manage an alternative diagnosis. Median length of stay in the ED for patients discharged directly to home was 643 min (interquartile range 431 to 858). 4. Discussion Timely, definitive diagnosis or exclusion of suspected acute thoracic aortic dissection in an ED patient is crucial due to its devastating mortality rate and is usually accomplished with CTA. Although MRA has been recommended for the subset of patients who cannot undergo CTA, its indications and outcomes for ED patients has not been demonstrated. Indeed, there are long-standing concerns regarding the usefulness of MRA in the ED for acute aortic dissection, in part due to prolonged scan time, lack of availability, and difficult in monitoring and resuscitating unstable patients. Our investigation into the use of MRA for evaluation of suspected thoracic aortic dissection produced several results that could impact the management of ED patients. First, nearly all of our patients who underwent MRA did so because iodinated contrast allergy and/or renal insufficiency precluded CTA, in Table 1 Incidental findings noted in the impression of MRA reports unrelated to aortic dissection. Number and percentage of exams with each finding is reported. More than one finding was reported for some exams. Incidental findings
Number (%)
None Pleural effusion Aortic aneurysm or ectasia Pericardial effusion Cholelithiasis Pneumonia Aortitis Left ventricular wall hypertrophy Syrinx Vertebral body compression fracture Vertebral marrow signal abnormality
27 (55%) 6 (12%) 6 (12%) 5 (10%) 2 (4%) 2 (4%) 1 (2%) 1 (2%) 1 (2%) 1 (2%) 1 (2%)
3
accordance with the ACR's Appropriateness Criteria for the evaluation of acute thoracic aortic dissection [8]. Acute dissection only affected one patient in our cohort. A negative MRA helped allow one-third of our patients to be discharged directly to home from the ED. Two-thirds of patients with negative MRAs were admitted to the hospital for further evaluation or management of an alternative diagnosis made in the ED. Thus, MRA aided emergency physicians in selecting the appropriate disposition for patients in whom acute dissection was initially suspected. In the vast majority of our cases, MRA allowed for confident exclusion of acute aortic dissection. These patients were spared the need to extend their stay either for clinical observation or for iodinated contrast-allergy premedication for CTA, the possible need to decide whether to risk further harm to renal function for a CTA, or to undergo an invasive transesophageal echocardiogram. Second, the median time from ED arrival to obtaining an MRA was 311 min, or 5.2 h. In comparison, analysis of the International Registry of Acute Aortic Dissection (IRAD), in which nearly all patients were evaluated using CTA, showed a mean time of 4.5 h from ED arrival to diagnosis of acute aortic dissection with an interquartile range of 1.5 to 24 h [7]. IRAD analysis also showed that mean time from diagnosis to surgery was 4.3 h [7]. Therefore, performing an MRA rather than CTA in an experienced institution would most likely result in, at most, a modest increase in time to diagnosis. Furthermore, since acute thoracic aortic dissection is a rare event that requires a high index of clinical suspicion and a low threshold for diagnostic imaging, CTA and MRA are likely to be requested most often to “rule out” this diagnosis rather than to urgently confirm it. The median time of 5.2 h from ED arrival to obtaining an MRA also suggests an MRA would not necessarily prolong length of ED stay since routine evaluation of chest pain commonly involves serial cycling of ECG and cardiac enzymes, and can take up to around 30 h [11,12]. Finally, for patients with mild to moderate iodinated contrast allergies, the 5.2 h to MRA completion is far shorter than the 13 h typically required for premedication for CTA. Third, our study demonstrated that an MRA for evaluation of thoracic aortic dissection is a high quality exam well-tolerated by ED patients. There are understandable concerns over the ability of ED patients in acute pain or distress to remain still and comply with breathing instructions over the length of an MRA scan. All except for one of the patients in our cohort were able to tolerate the exam sufficiently to allow for evaluation of acute thoracic aortic dissection. One advantage of MRA over CTA is that it can be performed without intravenous contrast material in patients with renal insufficiency. In our population, this accounted for almost half of all patients who underwent MRA. Non-contrast-enhanced MRA has continually evolved to improve imaging speed and diagnostic accuracy [13]. A recent study demonstrated 100% sensitivity and specificity of unenhanced balanced steady-state free precession (bSSFP) MRA for detection of thoracic aortic disease, with contrast enhanced MRA used as the reference standard [14]. Furthermore, noncontrast MRA is superior to contrast enhanced techniques for evaluation of the aortic wall and thus better demonstrates pathologies such as intramural hematoma and aortitis [15]. Our study has several limitations. First, we do not know how often an MRA is ordered but could not be performed, either due to patient factors or due to unavailability of the MRI scanner. These data would have allowed for more complete characterization of the usage pattern and feasibility of MRA in our ED. Nevertheless, our data clearly defines two types of ED patients for whom MRA is useful: those with iodinated contrast allergy or those with renal insufficiency. Our study is also likely limited in its generalizability, since our practice pattern and MRA results depend on around-the-clock availability of a dedicated ED MRI scanner, established MRA protocols, technologists familiar with the technique, and radiologists experienced in MRA interpretation. However, the usage of MRI in EDs has increased over recent years [10]. Furthermore, a 2008 study of EDs across the United States estimated that 66% had access to on-site MRI and that 39% had either an on-site or on-call technologist 24/7 [16]. Thus, it is likely that such capabilities will become more
Please cite this article as: Wang GX, et al, MR angiography can guide ED management of suspected acute aortic dissection, American Journal of Emergency Medicine (2016), http://dx.doi.org/10.1016/j.ajem.2016.11.039
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widespread and that MRA will become increasingly available as a diagnostic tool for the ED physician. 5. Conclusions This study demonstrates that MRA has a clear role in the evaluation for acute thoracic aortic dissection in the ED, where it can guide management and facilitate safe discharge to home directly from the ED with a median length of stay of just under 11 h. Nearly all MRA exams in this study cohort were performed when CTA was not possible, either due to severe renal insufficiency or iodinated contrast dye allergy. This supports the ACR Appropriateness Criteria recommendations for the imaging of patients suspected of acute thoracic aortic dissection and demonstrates the real-world indications and outcomes from the application of these recommendations in the ED. Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Acknowledgements None. References [1] National Center for Health Statistics. National Hospital Ambulatory Medical Care Survey: 2010 emergency department summary tables. https://www.cdc.gov/nchs/ data/ahcd/nhamcs_emergency/2010_ed_web_tables.pdf. [Accessed Sept 12, 2016]. [2] Hirst AE, Johns VJ, Kime SW. Dissecting aneurysm of the aorta: a review of 505 cases. Medicine (Baltimore) 1958;37:217–79. [3] Strayer RJ, Shearer PL, Hermann LK. Screening, evaluation, and early management of acute aortic dissection in the ED. Curr Cardiol Rev 2012;8:152–7.
[4] Baliga RR, Nienaber CA, Bossone E, Oh JK, Isselbacher EM, Sechtem U, et al. The role of imaging in aortic dissection and related syndromes. JACC Cardiovasc Imaging 2014;7:406–24. http://dx.doi.org/10.1016/j.jcmg.2013.10.015. [5] von Kodolitsch Y, Schwartz AG, Nienaber CA. Clinical prediction of acute aortic dissection. Arch Intern Med 2000;160:2977–82. [6] Evangelista A, Carro A, Moral S, Teixido-Tura G, Rodríguez-Palomares JF, Cuéllar H, et al. Imaging modalities for the early diagnosis of acute aortic syndrome. Nat Rev Cardiol 2013;10:477–86. http://dx.doi.org/10.1038/nrcardio.2013.92. [7] Hagan PG, Nienaber CA, Isselbacher EM, Bruckman D, Karavite DJ, Russman PL, et al. The international registry of acute aortic dissection (IRAD): new insights into an old disease. JAMA 2000;283:897–903. [8] Jill E. Jacobs, Larry A Latson, Suhny Abbara, Scott R Akers, Philip A Araoz, Kristopher W Cummings, et al. ACR appropriateness criteria acute chest pain: suspected aortic dissection. American College of Radiology; n.d. [9] Sommer T, Fehske W, Holzknecht N, Smekal AV, Keller E, Lutterbey G, et al. Aortic dissection: a comparative study of diagnosis with spiral CT, multiplanar transesophageal echocardiography, and MR imaging. Radiology 1996;199:347–52. http://dx. doi.org/10.1148/radiology.199.2.8668776. [10] Korley FK, Pham JC, Kirsch TD. Use of advanced radiology during visits to US emergency departments for injury-related conditions, 1998–2007. JAMA 2010;304: 1465–71. http://dx.doi.org/10.1001/jama.2010.1408. [11] Hoffmann U, Truong QA, Schoenfeld DA, Chou ET, Woodard PK, Nagurney JT, et al. Coronary CT angiography versus standard evaluation in acute chest pain. N Engl J Med 2012;367:299–308. http://dx.doi.org/10.1056/NEJMoa1201161. [12] May JM, Shuman WP, Strote JN, Branch KR, Mitsumori LM, Lockhart DW, et al. Lowrisk patients with chest pain in the emergency department: negative 64-MDCT coronary angiography may reduce length of stay and hospital charges. Am J Roentgenol 2009;193:150–4. http://dx.doi.org/10.2214/AJR.08.2021. [13] Morita S, Masukawa A, Suzuki K, Hirata M, Kojima S, Ueno E. Unenhanced MR angiography: techniques and clinical applications in patients with chronic kidney disease. Radiographics 2011;31:E13–33. http://dx.doi.org/10.1148/rg.312105075. [14] Krishnam MS, Tomasian A, Malik S, Desphande V, Laub G, Ruehm SG. Image quality and diagnostic accuracy of unenhanced SSFP MR angiography compared with conventional contrast-enhanced MR angiography for the assessment of thoracic aortic diseases. Eur Radiol 2010;20:1311–20. http://dx.doi.org/10.1007/s00330-0091672-3. [15] François CJ, Hartung MP, Reeder SB, Nagle SK, Schiebler ML. MRI for acute chest pain: current state of the art. J Magn Reson Imaging JMRI 2013;37:1290–300. http://dx.doi.org/10.1002/jmri.24173. [16] Ginde AA, Foianini A, Renner DM, Valley M, Camargo Jr CA. Availability and quality of computed tomography and magnetic resonance imaging equipment in U.S. emergency departments. Acad Emerg Med 2008;15:780–3. http://dx.doi.org/10.1111/j. 1553-2712.2008.00192.x.
Please cite this article as: Wang GX, et al, MR angiography can guide ED management of suspected acute aortic dissection, American Journal of Emergency Medicine (2016), http://dx.doi.org/10.1016/j.ajem.2016.11.039
Contents lists available at ScienceDirect
American Journal of Emergency Medicine journal homepage: www.elsevier.com/locate/ajem
MR angiography can guide ED management of suspected acute aortic dissection☆ Gary X. Wang a, Sandeep S. Hedgire b, Thang Q. Le a, Jonathan D. Sonis c, Brian J. Yun c, Michael H. Lev d, Ali S. Raja c, Anand M. Prabhakar b,d,⁎ a
Department of Radiology, Harvard Medical School, Massachusetts General Hospital, Boston, MA, USA Division of Cardiovascular Imaging, Department of Radiology, Harvard Medical School, Massachusetts General Hospital, Boston, MA, USA Department of Emergency Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA d Division of Emergency Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA b c
a r t i c l e
i n f o
Article history: Received 17 September 2016 Received in revised form 15 November 2016 Accepted 15 November 2016 Available online xxxx Keywords: Aortic dissection Acute aortic syndrome Magnetic resonance angiography Emergency radiology ACR Appropriateness Criteria
a b s t r a c t Background: Aortic dissection is typically evaluated with computed tomography angiography (CTA). However, the feasibility of using magnetic resonance angiography (MRA) in the ED is unclear. This study examined the indications and outcomes of MRA in suspected aortic dissection evaluation in the ED. Methods: An IRB approved review identified patients who underwent MRA in the ED for acute thoracic aortic dissection from January 2010 to June 2016. Demographics, clinical assessment, CTA contraindications, outcomes, and ED disposition were analyzed. Results: 50 MRAs were ordered for suspected thoracic aortic dissection. 21 (42%) for iodinated contrast allergy, 21 (42%) for renal insufficiency, 2 (4%) due to both, 2 (4%) to spare ionizing radiation, 2 (4%) for further work-up after CTA, and 2 (4%) due to prior contrast enhanced CT within 24 h. Median ED arrival to MRA completion time was 311 min. 42 studies were fully diagnostic; 7 were limited. One patient could not tolerate the examination. 49 MRAs were completed: 2 (4%) patients had acute dissection on MRA and 47 (96%) had negative exams. 17 (35%) received gadolinium. 18 (37%) patients were discharged home from the ED with a median length of stay of 643 min. 2 (4%) were admitted for acute dissection seen on MRA and 29 (59%) for further evaluation. Conclusion: MRA has a clear role in the evaluation for acute thoracic aortic dissection in the ED in patients with contraindications to CTA, and can guide management and facilitate safe discharge to home. © 2016 Elsevier Inc. All rights reserved.
1. Introduction Chest pain accounted for 7 million emergency department (ED) visits in the United States in 2010, and was the leading principal cause for ED visits in patients over the age of 65 [1]. Acute thoracic aortic dissection is a potentially life threatening cause of chest pain. Hirst et al. reported a mortality rate of nearly 40% during the first 48 h, with a 1% rise in mortality per hour after onset of symptoms during the first day [2]. Early diagnosis is therefore critical for optimal outcome. A high index of clinical suspicion is required for diagnosis of this deadly-but-rare condition, which has an estimated prevalence of 5000 to 10 000 cases in the United States annually [3]. Although a lack of the classic clinical history of sudden-onset, severe, tearing pain; lack of a pulse differential or neurological deficits; or a normal chest radiograph all decrease the likelihood of acute aortic dissection, advanced imaging examination is
☆ Disclosures: None. ⁎ Corresponding author at: Division of Emergency Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, 55 Fruit St, Gray 2, Boston, MA 02114, USA. E-mail address: [email protected] (A.M. Prabhakar).
often necessary to rule out acute aortic dissection due to the deadly consequences of the missed diagnosis [4,5]. The most commonly used advanced imaging technique to evaluate for suspected acute dissection is computed tomography angiography (CTA) due to its high sensitivity and specificity, widespread aroundthe-clock availability, and fast scan time [6,7]. However, a subset of these patients cannot undergo CTA due to a known allergy to iodinated contrast material or history of renal insufficiency, and therefore require another exam for a definitive diagnosis. For these patients, the American College of Radiology (ACR) Appropriateness Criteria recommends magnetic resonance angiography (MRA) [8]. Compared to CTA, this technique has similarly high sensitivity and specificity and does not use iodinated contrast material. In patients with renal insufficiency, MRA can be performed without intravenous gadolinium-based contrast material [9]. Historically, MRA has not been commonly used in this setting due to limited scanner availability, relatively long scan times, and difficulties in monitoring and treating potentially unstable patients in the MRI suite [6]. The increased prevalence of MRI use in the ED over recent years, combined with continued technical advances in MRI techniques, point towards an increasing role for MRA in the ED [10]. Therefore, the
http://dx.doi.org/10.1016/j.ajem.2016.11.039 0735-6757/© 2016 Elsevier Inc. All rights reserved.
Please cite this article as: Wang GX, et al, MR angiography can guide ED management of suspected acute aortic dissection, American Journal of Emergency Medicine (2016), http://dx.doi.org/10.1016/j.ajem.2016.11.039
2
G.X. Wang et al. / American Journal of Emergency Medicine xxx (2016) xxx–xxx
purpose of this study was to characterize the indications and outcomes of MRA in the ED for evaluating suspected thoracic aortic dissection. 2. Methods 2.1. Human subject compliance This retrospective, HIPAA-compliant study was approved by the institutional review board, including waiver of patient consent. 2.2. Study site This study was completed in a 999-bed urban quaternary care academic center and Level 1 trauma center. Each year, there are approximately 104 000 ED visits, with approximately 105 000 ED diagnostic imaging studies performed and interpreted in the radiology department. 2.3. ED radiology staffing and equipment ED radiology department is staffed with a resident and/or ED Imaging fellow and ED Radiology attending physicians 24/7. A dedicated 1.5T Siemens MRI is available for ED patients. Approximately 8000 to 9000 MRI exams are performed in the ED annually.
Fig. 1. Types of iodinated contrast allergy or reaction in patients unable to undergo CTA.
2.4. Data collection and analysis Electronic medical record review identified patients who underwent MRA in the ED for suspected acute thoracic aortic dissection from January 2010 to June 2016. Age, gender, clinical assessment, CTA contraindications, MRA radiology report, clinical outcomes, and times of ED arrival and dismissal, and of MRA scan were collected. Primary outcomes determined from data analysis were MRA indications and results, and the length of time from ED arrival to MRA. Secondary outcomes included incidental findings from MRA radiology report, method of results communication, and ED length of stay and disposition.
completed due to inability of the patient to tolerate the sound of the MRI scanner. Of the total 49 completed exams, two (4%) showed acute dissection on MRA and 47 (96%) were negative. One patient had a true type A dissection (Fig. 2). For the one patient with a false-positive MRA, the exam report did note that the dissection could be artifact due to excess patient motion but could not be completely excluded. This patient could not undergo CTA due to anaphylaxis to iodinated contrast, and was determined to not have an aortic dissection based on further clinical evaluation. Gadolinium-based contrast material was used for 17 of 49 exams (35%), with 13/17 (76%) performed for patients with iodinated contrast
3. Results 3.1. Patient demographics There were 50 patient encounters in which MRA was ordered for evaluation of suspected acute thoracic aortic dissection during the study period. The mean age of patients in this cohort was 58 years old (range 14–89), with 58% women. 3.2. Indications for MRA For these 50 cases, MRA was requested instead of CTA for the following reasons: 21 (42%) due to iodinated contrast allergy, 21 (42%) due to severe renal insufficiency (eGFR b 30 ml/min/1.73 m2 or clinical concern for declining renal function), 2 (4%) due to both, 2 (4%) to spare ionizing radiation, 2 (4%) for further work-up after CTA, and 2 (4%) due to prior contrast-enhanced CT within 24 h. Among the patients with iodinated contrast allergies, the most common allergic reactions were hives (6/23, 26%), angioedema (4/23, 17%), and anaphylaxis (4/23, 17%) (Fig. 1). The average eGFR for patients who underwent MRA due to renal insufficiency was 21 ml/min/1.73 m2 (standard deviation 10.4, range 4–38). Though one of these patients was already on hemodialysis, the clinical record indicated that MRA was specifically requested by nephrology. 3.3. Imaging and clinical outcomes Forty-two studies were fully diagnostic and 7 were considered to be limited by the interpreting radiologist. One study could not be
Fig. 2. 85-year-old male with history of thoracic aortic aneurysm and chronic renal failure presented with acute onset chest tightness and dyspnea, and could not undergo CTA due to impaired renal function. Axial MRA image without contrast at the level of the left pulmonary artery demonstrates intimal flaps in the ascending (black arrow) and descending (white arrow) thoracic aorta, consistent with Type A aortic dissection. Patient was not a surgical candidate and died shortly after admission for medical management.
Please cite this article as: Wang GX, et al, MR angiography can guide ED management of suspected acute aortic dissection, American Journal of Emergency Medicine (2016), http://dx.doi.org/10.1016/j.ajem.2016.11.039
G.X. Wang et al. / American Journal of Emergency Medicine xxx (2016) xxx–xxx
allergy and none for those with renal insufficiency. In 12 cases, the contrast used was gadopentetate dimeglumine (or Magnevist); in 7 cases, gadofoveset (or Ablavar) was used. Thirty-two (65%) patients did not receive intravenous contrast: 24 (75%) had renal insufficiency and 2 (6%) were on hemodialysis. One patient refused contrast. It was unclear from the medical record why contrast was not used for the remaining five patients. For 39 exams (80%), the results were communicated by routine filing of the imaging report into the electronic medical record. In the other 10 cases (20%), exam results were conveyed by direct verbal communication by the radiologist to the clinical provider. 3.4. Incidental findings In 27 of 49 MRAs (55%), no findings were noted in the impression of the imaging report aside from either presence or absence of acute thoracic aortic dissection or acute aortic syndrome equivalent. Pleural effusion was noted in 6 (12%) exams, ascending thoracic aorta ectasia or aneurysm was noted in 6 (12%), and pericardial effusion was seen in 5 (10%) (Table 1). In one case, MRA demonstrated aortitis involving the aortic arch. This patient was subsequently evaluated by rheumatology and treated for suspected large vessel vasculitis with steroids, which led to resolution of patient's chest discomfort and aortic inflammation on follow-up MRA. 3.5. ED disposition Median time from ED arrival to obtaining an MRA was 311 min (interquartile range 203 to 503). Eighteen (37%) patients were discharged home from the ED; 2 (4%) were admitted for acute dissection seen on MRA and 29 (59%) for further evaluation after dissection was excluded or to manage an alternative diagnosis. Median length of stay in the ED for patients discharged directly to home was 643 min (interquartile range 431 to 858). 4. Discussion Timely, definitive diagnosis or exclusion of suspected acute thoracic aortic dissection in an ED patient is crucial due to its devastating mortality rate and is usually accomplished with CTA. Although MRA has been recommended for the subset of patients who cannot undergo CTA, its indications and outcomes for ED patients has not been demonstrated. Indeed, there are long-standing concerns regarding the usefulness of MRA in the ED for acute aortic dissection, in part due to prolonged scan time, lack of availability, and difficult in monitoring and resuscitating unstable patients. Our investigation into the use of MRA for evaluation of suspected thoracic aortic dissection produced several results that could impact the management of ED patients. First, nearly all of our patients who underwent MRA did so because iodinated contrast allergy and/or renal insufficiency precluded CTA, in Table 1 Incidental findings noted in the impression of MRA reports unrelated to aortic dissection. Number and percentage of exams with each finding is reported. More than one finding was reported for some exams. Incidental findings
Number (%)
None Pleural effusion Aortic aneurysm or ectasia Pericardial effusion Cholelithiasis Pneumonia Aortitis Left ventricular wall hypertrophy Syrinx Vertebral body compression fracture Vertebral marrow signal abnormality
27 (55%) 6 (12%) 6 (12%) 5 (10%) 2 (4%) 2 (4%) 1 (2%) 1 (2%) 1 (2%) 1 (2%) 1 (2%)
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accordance with the ACR's Appropriateness Criteria for the evaluation of acute thoracic aortic dissection [8]. Acute dissection only affected one patient in our cohort. A negative MRA helped allow one-third of our patients to be discharged directly to home from the ED. Two-thirds of patients with negative MRAs were admitted to the hospital for further evaluation or management of an alternative diagnosis made in the ED. Thus, MRA aided emergency physicians in selecting the appropriate disposition for patients in whom acute dissection was initially suspected. In the vast majority of our cases, MRA allowed for confident exclusion of acute aortic dissection. These patients were spared the need to extend their stay either for clinical observation or for iodinated contrast-allergy premedication for CTA, the possible need to decide whether to risk further harm to renal function for a CTA, or to undergo an invasive transesophageal echocardiogram. Second, the median time from ED arrival to obtaining an MRA was 311 min, or 5.2 h. In comparison, analysis of the International Registry of Acute Aortic Dissection (IRAD), in which nearly all patients were evaluated using CTA, showed a mean time of 4.5 h from ED arrival to diagnosis of acute aortic dissection with an interquartile range of 1.5 to 24 h [7]. IRAD analysis also showed that mean time from diagnosis to surgery was 4.3 h [7]. Therefore, performing an MRA rather than CTA in an experienced institution would most likely result in, at most, a modest increase in time to diagnosis. Furthermore, since acute thoracic aortic dissection is a rare event that requires a high index of clinical suspicion and a low threshold for diagnostic imaging, CTA and MRA are likely to be requested most often to “rule out” this diagnosis rather than to urgently confirm it. The median time of 5.2 h from ED arrival to obtaining an MRA also suggests an MRA would not necessarily prolong length of ED stay since routine evaluation of chest pain commonly involves serial cycling of ECG and cardiac enzymes, and can take up to around 30 h [11,12]. Finally, for patients with mild to moderate iodinated contrast allergies, the 5.2 h to MRA completion is far shorter than the 13 h typically required for premedication for CTA. Third, our study demonstrated that an MRA for evaluation of thoracic aortic dissection is a high quality exam well-tolerated by ED patients. There are understandable concerns over the ability of ED patients in acute pain or distress to remain still and comply with breathing instructions over the length of an MRA scan. All except for one of the patients in our cohort were able to tolerate the exam sufficiently to allow for evaluation of acute thoracic aortic dissection. One advantage of MRA over CTA is that it can be performed without intravenous contrast material in patients with renal insufficiency. In our population, this accounted for almost half of all patients who underwent MRA. Non-contrast-enhanced MRA has continually evolved to improve imaging speed and diagnostic accuracy [13]. A recent study demonstrated 100% sensitivity and specificity of unenhanced balanced steady-state free precession (bSSFP) MRA for detection of thoracic aortic disease, with contrast enhanced MRA used as the reference standard [14]. Furthermore, noncontrast MRA is superior to contrast enhanced techniques for evaluation of the aortic wall and thus better demonstrates pathologies such as intramural hematoma and aortitis [15]. Our study has several limitations. First, we do not know how often an MRA is ordered but could not be performed, either due to patient factors or due to unavailability of the MRI scanner. These data would have allowed for more complete characterization of the usage pattern and feasibility of MRA in our ED. Nevertheless, our data clearly defines two types of ED patients for whom MRA is useful: those with iodinated contrast allergy or those with renal insufficiency. Our study is also likely limited in its generalizability, since our practice pattern and MRA results depend on around-the-clock availability of a dedicated ED MRI scanner, established MRA protocols, technologists familiar with the technique, and radiologists experienced in MRA interpretation. However, the usage of MRI in EDs has increased over recent years [10]. Furthermore, a 2008 study of EDs across the United States estimated that 66% had access to on-site MRI and that 39% had either an on-site or on-call technologist 24/7 [16]. Thus, it is likely that such capabilities will become more
Please cite this article as: Wang GX, et al, MR angiography can guide ED management of suspected acute aortic dissection, American Journal of Emergency Medicine (2016), http://dx.doi.org/10.1016/j.ajem.2016.11.039
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widespread and that MRA will become increasingly available as a diagnostic tool for the ED physician. 5. Conclusions This study demonstrates that MRA has a clear role in the evaluation for acute thoracic aortic dissection in the ED, where it can guide management and facilitate safe discharge to home directly from the ED with a median length of stay of just under 11 h. Nearly all MRA exams in this study cohort were performed when CTA was not possible, either due to severe renal insufficiency or iodinated contrast dye allergy. This supports the ACR Appropriateness Criteria recommendations for the imaging of patients suspected of acute thoracic aortic dissection and demonstrates the real-world indications and outcomes from the application of these recommendations in the ED. Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Acknowledgements None. References [1] National Center for Health Statistics. National Hospital Ambulatory Medical Care Survey: 2010 emergency department summary tables. https://www.cdc.gov/nchs/ data/ahcd/nhamcs_emergency/2010_ed_web_tables.pdf. [Accessed Sept 12, 2016]. [2] Hirst AE, Johns VJ, Kime SW. Dissecting aneurysm of the aorta: a review of 505 cases. Medicine (Baltimore) 1958;37:217–79. [3] Strayer RJ, Shearer PL, Hermann LK. Screening, evaluation, and early management of acute aortic dissection in the ED. Curr Cardiol Rev 2012;8:152–7.
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Please cite this article as: Wang GX, et al, MR angiography can guide ED management of suspected acute aortic dissection, American Journal of Emergency Medicine (2016), http://dx.doi.org/10.1016/j.ajem.2016.11.039