Saad Tarabichi, Eric Smith.

Response/Recommendation: Advances in imaging have resulted in an increased ability to visualize emboli in the lungs, some of which may be clinically non-significant and may even not be a true pulmonary embolism (PE). The “gold standard” for diagnosis of PE is still the computer tomography pulmonary angiography (CTPA).

Strength of Recommendation: Strong.

Rationale: The risk of deep venous thrombosis (DVT) and PE in patients undergoing surgery is well established. In the context of orthopaedic surgery, patients undergoing elective total hip/knee replacement are considered at highest risk for developing venous thromboembolism (VTE). Manifestation of VTE in these patients includes DVT and subsequent PE that can be fatal. Prior to rapid post-operative patient mobilization, some historical estimates have put the incidence of DVT without prophylaxis to be between 40% and 84% after total knee arthroplasty (TKA), and around 39% to 74% for patients undergoing total hip arthroplasty (THA)¹. Over the years, comprehensive guidelines on venous thromboembolism prevention have been established. These include measures such as prevention with effective preoperative and postoperative anticoagulation, to more conservative measures like early and aggressive postoperative mobilization, pneumatic compression stockings, and tools to identify high-risk patients². Despite this, the National Institute of Health (NIH) projects that the number of patients needing joint arthroplasty and consequently the number of thromboembolic complications is on the rise³.

In the past, the gold standard for the diagnosis of suspected PE was the two-dimensional ventilation-perfusion (V/Q) scan. Sostman et al.⁴, estimated the sensitivity and specificity of a V/Q scan, when used to diagnose PE, to be around 77.4% and 97.7%, respectively. However, the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) I clinical trials showed that V/Q imaging reported an uncertain likelihood for PE in 65% of confirmed PE cases, indicating that a V/Q scan could not make a reliable diagnosis⁵. Parvizi et al.⁶, showed that over their study period of five years, the incidence of PE rose from 0.21% when using V/Q scans to 0.98% with spiral CT and peaked at 1.72% with the introduction of multidetector CT. Newer techniques like the multidetector-row CTPA proved to be more sensitive for detecting PE. CTPA has also been shown to have exceptionally high specificity for diagnosing PE. The PIOPED II trial estimated that CTPA had a sensitivity of 83% and specificity of 96%, respectively⁷. Despite only being introduced in 1998, by 2006 several institutions documented a 7-to-13-fold increase in the utilization of CTPA^8–11. It is now considered the gold standard for the diagnosis of PE. Parvizi et al. ⁶, also suggested that more advanced imaging techniques, like CTPA, have led to an increase in incidence of non-clinically significant PE. In other words, they have caused a rise in detection of abnormalities that are not harmful and cause no increase in morbidity or mortality. Previous investigators have examined trends in incidence of PE before and after the introduction of CTPA. An 81% increase in incidence of PE was noted with no significant increase in mortality. Furthermore, there was a 71% increase in complications secondary to anticoagulation¹². Overdiagnosis of PE resulting in unnecessary harm to patients who are anticoagulated for non-clinically significant PE is an important clinical issue. Ranji et al., reported that 25.4% of their patients had false-positive CTPA findings and were subsequently treated with anticoagulants¹³. Another benefit is that CTPA can identify the location of the emboli within pulmonary arteries. Some studies have shown that the size and location (central versus segmental or subsegmental) of clots correlate with clinical severity. Auer et al.⁸, stated that patients with central PE were more likely to require intensive care unit (ICU) admission and had higher 30-day mortality rates. Additionally, the authors of a different study proposed that subsegmental emboli are non-clinically significant even when they are left untreated¹⁴. However, Valle et al., found that there is no association between PE location and clinical severity (calculated by employing the PE Severity Index)¹⁵.

Outcomes in patients with VTE have significantly improved over the last two decades. Despite a recent rise in incidence of DVT and PE following orthopaedic procedures, recent studies have shown that morbidity and mortality secondary to these disorders is at an all-time low⁶. This is due to the established international guidelines on preoperative optimization and risk stratification of patients undergoing surgery¹⁶. Additionally, our ability to effectively diagnose patients with PE has substantially increased since the worldwide incorporation of the CT scan. We now know that once commonly used imaging modalities, such as V/Q scans, are not as reliable as previously believed. With constant developments in medical imaging, we must ensure judicious use of advanced imaging. Currently, CTPA appears to be the most accurate and effective imaging modality for the diagnosis of suspected PE. Given the risks posed to patients receiving anticoagulation with clinically non-significant emboli, we recommend the prudent use of CTPA only in patients with high clinical suspicion or high pretest probability of pulmonary embolus.

References:

1.        Westrich GH, Haas SB, Mosca P, Peterson M. Meta-analysis of thromboembolic prophylaxis after total knee arthroplasty. The Journal of Bone and Joint Surgery. 2000;82(6):795-800. doi:10.1302/0301-620X.82B6.9869

2.        Flevas DA, Megaloikonomos PD, Dimopoulos L, Mitsiokapa E, Koulouvaris P, Mavrogenis AF. Thromboembolism prophylaxis in orthopaedics: an update. EFORT Open Reviews. 2018;3(4):136-148. doi:10.1302/2058-5241.3.170018

3.        Kurtz S. Prevalence of Primary and Revision Total Hip and Knee Arthroplasty in the United States From 1990 Through 2002. The Journal of Bone and Joint Surgery (American). 2005;87(7):1487. doi:10.2106/JBJS.D.02441

4.        Sostman HD, Stein PD, Gottschalk A, Matta F, Hull R, Goodman L. Acute Pulmonary Embolism: Sensitivity and Specificity of Ventilation-Perfusion Scintigraphy in PIOPED II Study. Radiology. 2008;246(3):941-946. doi:10.1148/radiol.2463070270

5.        The PIOPED Investigators. Value of the Ventilation/Perfusion Scan in Acute Pulmonary Embolism. JAMA. 1990;263(20):2753. doi:10.1001/jama.1990.03440200057023

6.        Parvizi J, Smith EB, Pulido L, et al. The rise in the incidence of pulmonary embolus after joint arthroplasty: is modern  imaging to blame? Clinical orthopaedics and related research. 2007;463:107-113. doi:10.1097/BLO.0b013e318145af41

7.        Moore AJE, Wachsmann J, Chamarthy MR, Panjikaran L, Tanabe Y, Rajiah P. Imaging of acute pulmonary embolism: an update. Cardiovascular Diagnosis and Therapy. 2018;8(3):225-243. doi:10.21037/cdt.2017.12.01

8.        Auer RC, Schulman AR, Tuorto S, et al. Use of Helical CT Is Associated with an Increased Incidence of Postoperative Pulmonary Emboli in Cancer Patients with No Change in the Number of Fatal Pulmonary Emboli. Journal of the American College of Surgeons. 2009;208(5):871-878. doi:10.1016/j.jamcollsurg.2008.12.030

9.        Donohoo JH, Mayo-Smith WW, Pezzullo JA, Egglin TK. Utilization Patterns and Diagnostic Yield of 3421 Consecutive Multidetector Row Computed Tomography Pulmonary Angiograms in a Busy Emergency Department. Journal of Computer Assisted Tomography. 2008;32(3):421-425. doi:10.1097/RCT.0b013e31812e6af3

10.      Weir ID, Drescher F, Cousin D, et al. Trends in use and yield of chest computed tomography with angiography for diagnosis of pulmonary embolism in a Connecticut hospital emergency department. Connecticut medicine. 2010;74(1):5-9. http://www.ncbi.nlm.nih.gov/pubmed/20175366

11.      Wittram C, Meehan MJ, Halpern EF, Shepard J-AO, McLoud TC, Thrall JH. Trends in Thoracic Radiology Over a Decade at a Large Academic Medical Center. Journal of Thoracic Imaging. 2004;19(3):164-170. doi:10.1097/01.rti.0000117623.02841.e6

12.      Wiener RS, Schwartz LM, Woloshin S. Time trends in pulmonary embolism in the United States: Evidence of overdiagnosis. Archives of Internal Medicine. 2011;171(9):831-836. doi:10.1001/archinternmed.2011.178

13.      Ranji SR, Shojania KG, Trowbridge RL, Auerbach AD. Impact of reliance on CT pulmonary angiography on diagnosis of pulmonary embolism: A Bayesian analysis. Journal of Hospital Medicine. 2006;1(2):81-87. doi:10.1002/jhm.71

14.      CARRIER M, RIGHINI M, WELLS PS, et al. Subsegmental pulmonary embolism diagnosed by computed tomography: incidence and clinical implications. A systematic review and meta-analysis of the management outcome studies. Journal of Thrombosis and Haemostasis. 2010;8(8):1716-1722. doi:10.1111/j.1538-7836.2010.03938.x

15.      Gonzalez Della Valle A, Blanes Perez A, Lee Y, et al. The Clinical Severity of Patients Diagnosed With an In-Hospital Pulmonary Embolism Following Modern, Elective Joint Arthroplasty Is Unrelated to the Location of Emboli in the Pulmonary Vasculature. The Journal of Arthroplasty. 2017;32(4):1304-1309. doi:10.1016/j.arth.2016.11.023

16.      Geerts WH, Pineo GF, Heit JA, et al. Prevention of Venous Thromboembolism. Chest. 2004;126(3):338S-400S. doi:10.1378/chest.126.3_suppl.338S