Computed Tomography Pulmonary Angiography Utilization in the Emergency Department During the COVID-19 Pandemic : Journal of Thoracic Imaging

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Computed Tomography Pulmonary Angiography Utilization in the Emergency Department During the COVID-19 Pandemic

Schulz, Kathryn DPhil*; Mao, Lu PhD; Kanne, Jeffrey MD, FACR, FCCP

Author Information
Journal of Thoracic Imaging: July 2022 - Volume 37 - Issue 4 - p 225-230
doi: 10.1097/RTI.0000000000000649
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Abstract

TAKE-HOME POINTS

  • There was a 61.8% increase in computed tomography pulmonary angiography (CTPA) ordering in the emergency department (ED) after the start of the COVID-19 pandemic.
  • COVID-positive patients do not appear to have a significantly higher incidence of pulmonary embolism (PE) than COVID-negative patients when initially presenting to the ED, and COVID-19 is not a significant predictive factor for acute PE at the time of presentation in the absence of other risk factors.
  • In COVID-positive patients, D-dimer is not a useful tool for determining the need for advanced imaging given the high likelihood of a positive result and low positive predictive value. If signs and symptoms are out of proportion with radiographic imaging, then CTPA may be a reasonable next step.
  • COVID-positive patients have significantly higher rates of nondiagnostic imaging, possibly due to disease-related symptoms which limit their ability to tolerate imaging studies. Clinicians should use clinical judgment to weigh the likelihood of PE against the risk of nondiagnostic results when determining whether to expose COVID-positive patients to high-dose radiation and contrast with CTPA.

INTRODUCTION

One of the earliest complications of COVID-19 to be recognized was an increased risk of thromboembolic events, particularly PE. Numerous studies emerged in 2020 demonstrating that hospitalized COVID-19 patients were experiencing a higher incidence of PE than COVID-negative patients with comparable disease acuity.1–5 COVID-associated PEs also appeared to be less closely associated with concurrent deep vein thrombosis (DVT) than those in other patients,2,6–8 raising the question of whether prepandemic risk factor assessments were sufficient to predict the likelihood of PE in COVID-positive patients.1,9

This early association between COVID-19 and coagulopathy has also impacted discussions about how best to image these patients. While noncontrast CT is used in some centers to characterize the severity of lung disease in COVID-19 infection, a few centers have considered universal screening with CTPA in order to assess simultaneously for PE.1 However, the benefit of universal screening with contrast-enhanced imaging remains controversial.10 It is also unclear to what extent knowledge of COVID-related coagulopathy has led to an increase in CTPA ordering even in the absence of universal screening.

Notably, many of the studies reporting this high incidence of PE focus primarily on patients who are in the intensive care unit or who have met certain thresholds of COVID-19 severity.5,11–15 These studies also report events that happen at any time during hospitalization. Fewer studies have focused on the ED setting, where the decision to order imaging is often made before a patient’s disease severity is fully known.9,10,16

In this study, we aimed to evaluate (1) the extent to which ordering of CTPA studies has increased in the emergent setting since the start of the COVID-19 pandemic; (2) whether there has been a corresponding increase in studies positive for PE; and (3) whether COVID-positive patients have a higher incidence of PE than COVID-negative patients when initially presenting to the ED. To address these questions, we conducted a retrospective review of CTPA utilization in an ED setting at a tertiary care center.

MATERIALS AND METHODS

This retrospective study was approved by the internal review board at our institution, which waived the need for patient consent.

Case Selection

We conducted a retrospective review of ED visits at a tertiary care academic medical center in an urban setting. Using the PerformanceBridge Productivity application (Philips Healthcare, Amsterdam, the Netherlands), we searched our electronic health record (Epic Systems, Verona, WI) for all CTPAs performed for adult (18 y and older) patients in 2019 and 2020. Because our health system saw a significant decrease in ED visits during the early months of the pandemic, we narrowed our search to studies performed between June 1 and December 31, 2019, and June 1 and December 31, 2020.

We included all cases that met the above criteria in which patients were evaluated for acute PE. We excluded cases in which patients were known to have existing or chronic PE. We also excluded cases for which no matching medical record number could be found in the electronic health record.

Data Extraction

Data categories were selected to reflect patient condition at presentation, risk factors for PE, and indications for CTPA. Data were extracted manually by chart review by K.S. Data points collected included demographic information such as patient age and sex; results of CTPA; chief complaint; signs and symptoms such as chest pain, tachycardia, hemoptysis, hypoxia, fever, dyspnea, or unilateral lower extremity pain/swelling; COVID-19 status; lab values including D-dimer and leukocyte count; recent surgery, hospitalization, or prolonged immobilization within 4 weeks before CTPA; and any known history of PE, DVT, malignancy, or other prothrombotic condition.

Results of CTPA were recorded as positive, negative, or nondiagnostic for PE based on the imaging report. All studies were interpreted by board-certified subspecialist thoracic radiologists. We did not review images directly. Studies were defined as nondiagnostic if either (1) the report explicitly stated that the study was inadequate to assess for PE, or (2) the radiologist indicated an inability to evaluate beyond the lobar level.

The chief complaint was obtained from the heading of the ED provider note, whenever one was recorded; otherwise, it was determined based on the opening line of the history of present illness. Hemoptysis was defined broadly and included cases that ranged from frankly bloody to blood-tinged sputum. Hypoxia was defined as any reading <95% on pulse oximetry recorded by emergency medical services or in the ED. Fever was defined as the presence of any single temperature reading above 100°F obtained in the ED, by emergency medical services, or as reported by the patient based on home measurement.

In addition to patients who tested positive for COVID-19 in the ED, any who reported testing positive within 14 days prior to presentation were considered COVID-positive for the purposes of this study. Patients who tested positive up to 30 days before presentation and did not subsequently receive a negative test were also included as COVID-positive. COVID-19 tests performed at our institution were sent to a state laboratory. There were no significant limitations in the availability of rapid, reliable testing.

We recorded any history of current or prior malignancy. Prothrombotic conditions noted included Factor V Leiden, atrial fibrillation, antiphospholipid syndrome, and first-degree relatives with a history of DVT/PE or clotting disorder.

Statistical Analysis

Statistical analysis was performed by L.M. Quantitative variables were analyzed using a Wilcoxon rank sum test. Categorical variables were evaluated using χ2 or Fisher exact test. Logistic regression analysis was performed to identify possible predictive features associated with PE.

RESULTS

Our initial search yielded 1090 cases (436 in 2019, 654 in 2020). Of these, 11 were excluded because no matching medical record number could be identified. Five cases were excluded because the patient was already known to have a PE before ordering CTPA, and 2 were excluded because CTPA was ordered outside the ED. Fifty-nine additional cases were identified on chart review as meeting our search criteria; these represented patients identified by our initial search who were found to have multiple separate encounters in the ED leading to CTPA evaluation during our periods of interest. This brought the total number of cases included for analysis to 1131 (432 in 2019, 699 in 2020) (Fig. 1). Patient characteristics are listed in Table 1. There were no significant differences between the 2019 and 2020 cohorts with respect to age, sex, prior history of blood clots, or recent immobilization.

F1
FIGURE 1:
Case selection and PE incidence. EHR indicates electronic health record; MRN, medical record number.
TABLE 1 - Patient Characteristics by Year
Variable 2019 (N=432) 2020 (N=699) P
Age (y) 60 (49-71) 61 (47-71) 0.874
Sex
 F 242 (56) 387 (55.4) 0.878
 M 190 (44) 312 (44.6)
PE
 − 374 (86.6) 608 (87) 0.61
 + 49 (11.3) 71 (10.2)
 ND 9 (2.1) 20 (2.9)
DVT
 − 417 (96.5) 690 (98.7) 0.024
 + 15 (3.5) 9 (1.3)
COVID-19
 − 0 (0) 479 (68.5) <0.0001
 + 0 (0) 91 (13)
 NT 432 (100) 129 (18.5)
D-dimer 1 (0.7-1.6) 1.1 (0.7-1.9) 0.084
WBC 8.3 (6.4-11.3) 8.2 (6.2-11.2) 0.54
Chest pain
 − 197 (45.6) 353 (50.5) 0.124
 + 235 (54.4) 346 (49.5)
Tachycardia
 − 260 (60.2) 449 (64.2) 0.192
 + 172 (39.8) 250 (35.8)
Hemoptysis
 − 411 (95.1) 664 (95) 1
 + 21 (4.9) 35 (5)
Hypoxia
 − 238 (55.1) 428 (61.2) 0.048
 + 194 (44.9) 271 (38.8)
Fever
 − 403 (93.3) 631 (90.3) 0.099
 + 29 (6.7) 68 (9.7)
Dyspnea
 − 152 (35.2) 235 (33.6) 0.635
 + 280 (64.8) 464 (66.4)
Leg swelling
 − 390 (90.3) 641 (91.7) 0.476
 + 42 (9.7) 58 (8.3)
Clotting history
 − 328 (75.9) 544 (77.8) 0.506
 + 104 (24.1) 155 (22.2)
Recent surgery/immobilization
 − 357 (82.6) 574 (82.1) 0.886
 + 75 (17.4) 125 (17.9)
Active malignancy
 − 329 (76.2) 573 (82) 0.022
 + 103 (23.8) 126 (18)
Quantitative variables are summarized by median (interquartile range).
Categorical variables are summarized by N (%).
F indicates female; M, male; ND, nondiagnostic; NT, not tested; PE, pulmonary embolism; WBC, white blood cell count.

There was a 61.8% increase in the number of CTPA studies ordered in the ED between our periods of interest in 2019 and 2020 (432 vs. 699, P<0.0001). COVID-positive patients accounted for 91 of the 699 studies analyzed from 2020, or 34% of the absolute increase compared with 2019. Patients in the 2020 cohort had a significantly lower incidence of DVT (3.5% vs. 1.3%, P=0.024), active malignancy (23.8% vs. 18%, P=0.022), or hypoxia (44.9% vs. 38.8%, P=0.048).

There was also an increase in D-dimer ordering between these 2 periods. In 2019, 224 of 432 (51.8%) patients undergoing CTPA had D-dimer values recorded. In 2020, 428 of 699 (61.2%) patients had D-dimer testing (P=0.0024). Even when excluding COVID-positive patients, in whom D-dimer testing was routinely indicated, the increase remained significant (224/432 or 51.8% vs. 357/608 or 58.7%, P=0.0312). There was no significant difference in the rate of positive D-dimer tests between 2019 and 2020 (98.2% vs. 98.1%, P=1).

In 2019, 49 of 432 (11.3%) CTPA studies were positive for PE. In 2020, 71 of 699 (10.2%) studies were positive. Although the rate of PE decreased slightly in 2020, this difference was not statistically significant (P=0.61). Nondiagnostic studies accounted for 2.1% of cases in 2019 (9/432) and 2.9% of cases in 2020 (20/699) (P=0.5619). The most commonly cited reason for a nondiagnostic study was poor imaging quality due to patient movement or respiratory artifact.

Within the 2020 cohort, there was a significant difference in overall CTPA findings by COVID-19 status (P=0.038). Of the 479 studies ordered for COVID-negative patients, 47 were positive for PE (9.8%); 10 of 91 (11%) studies in COVID-positive patients were positive for PE; and 14 of 129 (10.9%) studies were positive for PE in patients who were not tested for COVID-19. Nondiagnostic studies accounted for 2.5% of studies in COVID-negative patients, 7.7% in COVID-positive patients, and 0.8% in patients whose COVID-19 status was not assessed (P=0.007). Notably, when nondiagnostic studies were excluded, there was no significant difference in the rate of PE in COVID-positive versus other patients (11% vs. 10%, P=0.924).

Of the 9 COVID-positive patients whose imaging was nondiagnostic, 1 was subsequently found to have a PE. This patient developed acute chest pain 3 days after admission and had been refusing anticoagulation during hospitalization. One COVID-negative patient whose initial imaging was nondiagnostic subsequently developed bilateral PE after admission to the ICU with sepsis.

COVID-positive patients who underwent CTPA were less likely than COVID-negative patients to have concurrent DVT (0% vs. 0.8%), malignancy (5.5% vs. 21.1%), or prior history of clots (12.1% vs. 24.4%), but more likely to have hypoxia (51.6% vs. 40.5%) or fever (25.3% vs. 9.2%). They also had lower median D-dimer values (1 [IQ range 0.8 to 1.5] vs. 1.2 [0.7 to 2.2]) and leukocyte counts (6.1 [4.5 to 8.8] vs. 8.9 [6.8 to 12.3]) than COVID-negative patients undergoing imaging (Table 2, Fig. 2).

TABLE 2 - Patient Characteristics by COVID-19 Status in 2020
Variable Negative (N=479) Positive (N=91) NT (N=129) P
Age (y) 62 (50-72) 58 (43-68) 62 (44-69) 0.099
Sex
 F 251 (52.4) 53 (58.2) 83 (64.3) 0.045
 M 228 (47.6) 38 (41.8) 46 (35.7)
PE
 − 420 (87.7) 74 (81.3) 114 (88.4) 0.038
 + 47 (9.8) 10 (11) 14 (10.9)
 ND 12 (2.5) 7 (7.7) 1 (0.8)
DVT
 − 475 (99.2) 91 (100) 124 (96.1) 0.028
 + 4 (0.8) 0 (0) 5 (3.9)
D-dimer 1.2 (0.7-2.2) 1 (0.8-1.5) 0.9 (0.6-1.4) 0.002
WBC 8.9 (6.8-12.3) 6.1 (4.5-8.8) 7.7 (6-9.1) <0.0001
Chest pain
 − 264 (55.1) 51 (56) 38 (29.5) <0.0001
 + 215 (44.9) 40 (44) 91 (70.5)
Tachycardia
 − 287 (59.9) 62 (68.1) 100 (77.5) <0.0001
 + 192 (40.1) 29 (31.9) 29 (22.5)
Hemoptysis
 − 450 (93.9) 86 (94.5) 128 (99.2) 0.028
 + 29 (6.1) 5 (5.5) 1 (0.8)
Hypoxia
 − 285 (59.5) 44 (48.4) 99 (76.7) <0.0001
 + 194 (40.5) 47 (51.6) 30 (23.3)
Fever
 − 435 (90.8) 68 (74.7) 128 (99.2) <0.0001
 + 44 (9.2) 23 (25.3) 1 (0.8)
Dyspnea
 − 145 (30.3) 24 (26.4) 66 (51.2) <0.0001
 + 334 (69.7) 67 (73.6) 63 (48.8)
Leg swelling
 − 442 (92.3) 88 (96.7) 111 (86) 0.013
 + 37 (7.7) 3 (3.3) 18 (14)
Clotting history
 − 362 (75.6) 80 (87.9) 102 (79.1) 0.032
 + 117 (24.4) 11 (12.1) 27 (20.9)
Recent surgery/immobilization
 − 396 (82.7) 80 (87.9) 98 (76) 0.064
 + 83 (17.3) 11 (12.1) 31 (24)
Malignancy
 − 378 (78.9) 86 (94.5) 109 (84.5) 0.001
 + 101 (21.1) 5 (5.5) 20 (15.5)
Quantitative variables are summarized by median (interquartile range).
Categorical variables are summarized by N (%).
F indicates female; M, male; ND, nondiagnostic; NT, not tested; PE, pulmonary embolism; WBC, white blood cell count.

F2
FIGURE 2:
Patient characteristics by COVID-19 status in 2020. *Not statistically significant. †Excludes nondiagnostic studies.

On multivariate regression analysis (Table 3), DVT was associated with a 45.8% increased risk of PE (odds ratio [OR]: 1.458, 95% confidence interval [CI]: 1.314-1.685, P<0.0001). Patients with a prior history of clots or known clotting disorders had a 6.6% increased risk of PE (OR: 1.066, CI: 1.022-1.113, P=0.003). COVID-19 infection was associated with a nonsignificant 2.9% increased risk of PE (OR: 1.029, 95% CI: 0.959-1.103, P=0.426).

TABLE 3 - Logistic Regression of Positive PE for Patients in 2019-2020
Variable Odds Ratio 95% CI P
Age (y) 1 0.999-1.001 0.608
Sex
 M vs. F 1.022 0.986-1.06 0.228
COVID-19
 + vs. − 1.038 0.968-1.113 0.295
 NT vs. − 1.009 0.972-1.048 0.622
DVT
 + vs. − 1.458 1.287-1.652 <0.0001
WBC 1.003 0.999-1.006 0.095
Clotting history
 + vs. − 1.066 1.022-1.113 0.003
Recent surgery/immobilization
 + vs. − 1.026 0.979-1.074 0.288
Malignancy
 + vs. − 1.006 0.962-1.053 0.783
D-dimer was not included in regression analysis due to a large number of absent values.
F indicates female; M, male; NT, not tested; WBC, white blood cell count.

DISCUSSION

Our analysis found a significant increase (+61.8%, P<0.0001) in the ordering of CTPA studies in the emergent setting during the COVID-19 pandemic compared with the previous year. Despite this increase, the rate of positive findings did not change significantly from 2019 to 2020 (11.3% vs. 10.2%, P=0.61). While our rate of positive PE detection in 2019 was higher than has been reported in some other prepandemic ED settings,17,18 the stability of our detection rates from 2019 to 2020 suggests that the increase in study ordering was appropriate.

Despite similar positivity rates for PE, there was a statistically significant difference in the prevalence of key risk factors between our 2019 and 2020 cohorts. Patients with malignancy, DVT, and hypoxia accounted for a smaller proportion of patients undergoing CTPA in 2020 compared with the previous year, although the absolute number of the latter 2 conditions did increase. Malignancy, which is associated with multiple risk factors for PE, was present in 23.8% of patients undergoing CTPA in 2019 versus 18% in 2020 (P=0.022). Within the 2020 cohort, the COVID-negative group had a significantly higher number of patients with malignancy than the COVID-positive group (21.1% vs. 5.5%, P=0.001). The decrease in imaging for patients with malignancy is likely related to a combination of decreased detection of new malignancies through screening exams and increased reluctance among those with known malignancy to present to hospitals early in the pandemic.

The lower incidence of DVT in the 2020 cohort, and more specifically the absence of DVT among COVID-positive patients with PE (vs. 0.8% [COVID-negative] and 3.9% [not tested], P=0.028), is consistent with other studies which have shown a decreased link between PE and DVT in COVID-19 infection.1,2,6 While our overall incidence of concurrent DVT was relatively low in both years, the decrease in 2020 was statistically significant (1.3% vs. 3.5%, P=0.024). Within 2020, much of the difference appears to be driven by the relatively higher incidence of DVT among nontested patients, among whom clinically evident DVT may have led to CTPA ordering without first investigating further causative mechanisms, such as rule-out testing for COVID-19. This is supported by the relatively higher prevalence of unilateral leg swelling in the nontested group (14% vs. 7.7% [COVID-negative] and 3.3% [COVID-positive], P=0.013). Even despite low DVT prevalence among patients who were tested, though, DVT was 1 of only 2 significant predictors of PE detected on multivariate analysis, with patients with DVT being 45.8% more likely to have concurrent PE than those without DVT (P<0.0001).

The lower incidence of hypoxia in the 2020 cohort is surprising, given that COVID-positive patients were significantly more likely to present with hypoxia than COVID-negative patients. Along with lower median D-dimer and leukocyte counts in COVID-positive patients receiving imaging, this may reflect lower provider thresholds to obtain CTPA even in patients lacking classic risk factors during the pandemic.

Although there was an absolute increase of 267 studies in 2020 compared with 2019, COVID-positive patients accounted for only 91 (34%) of these additional cases. Again, this may point to an overall lower provider threshold to obtain imaging, given the knowledge of increased PE rates as a result of the pandemic. However, 2020 also saw a dramatic increase in the use of D-dimer testing in our ED. With multiple studies showing the prognostic value of this marker in COVID-19 infection,4,19–22 our ED physicians obtained D-dimer values before CTPA in 90% more patients in 2020 than in 2019. While negative D-dimer results are useful to exclude PE, though, this test has a low positive predictive value. When D-dimer is tested in a patient with COVID-19, a positive result is very likely to be related to their underlying infection, further lowering the test’s predictive value for determining the need for contrast-enhanced imaging. Increased testing in otherwise low-risk patients without COVID-19 is also likely to have revealed more incidentally elevated D-dimers, and a sense of obligation to follow up on these results likely contributed to further lower provider thresholds for imaging even among COVID-negative patients. This raises the question of whether the stable PE positivity rate observed in 2020 reflects clinically significant PEs in both groups, or whether some of these findings would have gone unnoticed by patients under prepandemic imaging practices.

Notably, our analysis revealed no significant difference in the incidence of PE among COVID-positive versus other patients (11% vs. 10%, P=0.9239). On multivariate analysis, COVID-19 infection was associated with only a 2.9% increased risk of PE, which was not statistically significant (P=0.426). These findings are consistent with those of other studies which have found little or no significant difference in PE rates between COVID-positive and COVID-negative patients in ED settings.9,10 It is likely that the high incidence of PE reported in COVID-19 infection is related, at least in part, to a pro-inflammatory stage of the disease which develops later in its course, after a patient’s other symptoms have warranted admission,10,23,24 as well as to the immobilization which comes with prolonged hospitalization.9

Although COVID-positive patients who underwent CTPA in the ED did not have a higher risk of PE than COVID-negative patients in that setting, they were significantly more likely to have nondiagnostic imaging (P=0.007). In most cases, poor imaging quality was attributed to the patient’s inability to remain still or hold their breath. This may be related to the severity of their COVID-19 symptoms, or it may reflect other comorbidities. The fact that the majority of these patients were not subsequently found to have thromboembolic events suggests that nondiagnostic imaging was not masking a high number of PEs. Therefore, the stable positivity rate between COVID-positive and COVID-negative patients in 2020 does seem to reflect a lack of significant difference in PE incidence at the time of presentation to the ED.

Given the risks associated with contrast administration in patients with acute illness or major comorbidities, it is important to consider the relatively high risk of nondiagnostic results when deciding whether to obtain CTPA in these patients. Although clinicians should remain aware of potential overlap between symptoms of COVID-19 infection and acute PE, COVID-19 alone may not be a sufficient predictive factor at the time of presentation to warrant ordering CTPA in the absence of other risk factors.

Our study has some limitations. First, the study is retrospective and limited to a single academic health system, which may not be reflective of ED and patient conditions in other centers. While our findings are strengthened by comparison to prepandemic conditions, we only used 1 year for comparison. We also only considered decision-making regarding CTPA at the time of presentation and in an ED setting. Thus, our analysis does not account for patients who may have received workup for acute PE after admission to an inpatient service.

While all studies were read by dedicated thoracic radiologists, these providers were not blinded to patients’ clinical data, which may have introduced an element of bias in their readings. In addition, a high number of patients in 2020 (129/699 or 18.5%) did not receive a COVID-19 test, which may have influenced our final results.

Finally, we relied on ED physicians to identify candidates for imaging based on clinical suspicion. Although clinicians may have had a lower threshold to obtain imaging in 2020 due to reports of increased coagulopathy in COVID-19 patients, our institution did not perform universal screening for PE in this group. Thus, we cannot comment on the overall incidence of PE in the COVID-positive population at the time of ED presentation. The possibility of variable provider thresholds for different patient groups also makes it difficult to interpret our stable CTPA positivity rate with certainty. However, our institution’s ED did have a relatively stable provider team across the study interval, as well as an institutional tendency to order imaging when D-dimer is positive. This stable provider group and imaging practice eliminates some of the risks of inter-provider variability and supports our discussion on the challenges of increased use of D-dimer testing in low-risk patients.

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Keywords:

COVID-19; pulmonary embolism; pulmonary angiography; emergency department

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