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CT Pulmonary Angiography: A Comparative Analysis of the Utilization Patterns in Emergency Department and Hospitalized Patients Between 1998 and 2003

¹ Department of Radiology, University Hospitals of Cleveland, 11100 Euclid Ave., Cleveland, OH 44106.
² Department of Biostatistics, Case Western Reserve University College of Medicine, Cleveland, OH.
³ Case Western Reserve University College of Medicine, Cleveland, OH.

Received January 8, 2004; accepted after revision April 26, 2004.

 
Address correspondence to J. D. Prologo.

Abstract

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OBJECTIVE. The purpose of our study was to objectively examine the temporal utilization patterns of CT pulmonary angiography in emergency department and hospitalized patients in an academic tertiary care center.

SUBJECTS AND METHODS. Patients who underwent CT examination for suspected pulmonary embolism either through our emergency department or as inpatients during a recent 9-month interval were identified. The absolute number of studies and incidence of positive results and ancillary findings were compared with similar data published from our institution during the corresponding 9-month interval in 1997–1998.

RESULTS. The overall number of patients imaged for pulmonary embolism was significantly greater in the 2002–2003 period than in the 1997–1998 period (homogeneity of rates = 88.45, p < 0.0001). The absolute number of scans obtained was significantly greater in both the emergency department (² = 167.03, p < 0.0001) and inpatient (² = 210.62, p < 0.0001) groups in the more recent population. Significantly fewer ancillary findings were reported in both the emergency department (² = 5.93, p = 0.019) and inpatient (² = 6.03, p = 0.015) groups in the more recent population. The incidence of CT-detected pulmonary embolism was significantly less in both the emergency department (² = 34.26, p < 0.0001) and inpatient (² = 8.52, p < 0.01) groups in the more recent population. This decrease in the incidence of scans with positive findings for pulmonary embolism over time was significantly greater in the emergency department group than the inpatient group (homogeneity of odds = 0.003, p < 0.007).

CONCLUSION. The evolution of CT pulmonary angiography utilization has led to a significant increase in the number of patients being imaged for pulmonary embolism with a coincident significant decrease in the rates of CT-detected pulmonary embolism and ancillary findings both in emergency department and hospitalized patients.

Introduction

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Estimated annual incidences of pulmonary embolism have been reported as 500,000 in the United States, 100,000 in France, and at least 60,000 in Italy, with an overall 3-month mortality rate of 15–17.5% [1–4]. Numerous diagnostic imaging techniques exist to support the diagnosis of pulmonary embolism, including ventilation–perfusion scanning, interventional pulmonary angiography, venous sonography with or without venography, chest radiography, MRI, echocardiography, and CT pulmonary angiography. Available nonimaging tests include arterial blood gas analysis, ECG, and D-dimer and troponin assays. The optimal diagnostic approach to this complex diagnosis, however, has been difficult to determine [5–9].

With the advent of helical CT and its subsequent technologic improvements, clinicians acquired a powerful noninvasive tool for the evaluation of patients with suspected pulmonary embolism. The resulting CT angiograms reveal the presence of thromboembolism through detectable filling defects in the pulmonary vasculature within the time that most patients can hold their breath [10] (Fig. 1). Over recent years, studies have shown improvement in the ability of CT pulmonary angiography to detect pulmonary embolism, with some reports describing confident assessment of the subsegmental pulmonary arteries, acceptable clinical outcomes for patients after a negative finding on CT pulmonary angiography, and the ability of CT pulmonary angiography to detect concurrent or mimicking disease [11–19]

View larger version (75K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1. —Axial image from CT pulmonary angiography performed in 67-year-old woman who presented with hypoxia and chest pain shows filling defect in a segmental artery to right lower lobe, indicative of thromboembolism.

The purpose of this study was to objectively examine the temporal changes in the utilization of CT pulmonary angiography given the recent increased availability and acceptance of this technique for the evaluation of pulmonary embolism. The incidences of pulmonary embolism and ancillary findings in emergency department and hospitalized populations in an academic tertiary care center were compared during 9-month intervals in 1997–1998 and 2002–2003.

Subjects and Methods

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Patients who underwent CT pulmonary angiography for suspected pulmonary embolism either through our emergency department or as inpatients from December 2002 through August 2003 were identified. Appropriate institutional review board approval was obtained and guidelines followed regarding enrollment into and execution of this study. All patients were examined with either single-detector CT (n = 34) or MDCT (n = 816) in a cephalocaudal direction during a single breath-hold from the thoracic inlet through the domes of the diaphragms. Patients were given a bolus of 90–120 mL of IV contrast material. Automated bolus tracking was used in patients undergoing MDCT examinations. Single-detector CT (PQ5000, Philips Medical Systems) was performed with 3-mm collimation and pitch of 1.7 (120 kV, 250 mA). MDCT (MX8000 IDT, Philips Medical Systems) was performed with 2-mm collimation and pitch of 1 (120 kV, 250 mA).

Attending radiologists prospectively interpreted images at workstations with multiplanar reconstructions and lung and mediastinal window settings available. Images were assessed for pulmonary artery filling defects and the presence of ancillary findings.

CT pulmonary angiography examinations were tracked electronically through our hospital requisition database. After review of reports and charts, patient population demographics, absolute number of studies, incidences, gross distribution of detected pulmonary embolism, and presence of ancillary findings were compared with similar data published from our institution during the corresponding 9-month interval in 1997–1998. During the earlier period, all patients were examined on our single-detector scanner utilizing the parameters described above [17]. Tests for differences in means, counts, proportions, and homogeneity of odds ratio were used to assess the statistical significance of the results [20].

Results

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The 2002–2003 patient population included 349 patients (119 men, 230 women; age range, 18–91 years; mean age ± SD, 57.3 ± 21.6 years) who underwent CT pulmonary angiography through the emergency department and 501 (195 men, 306 women; age range, 18–95 years; mean, 59.4 ± 21.0 years) as inpatients. In 1997–1998, 25 men and 54 women (age range, 18–93 years; mean, 63.6 ± 17.9 years) were scanned as emergency department patients and 60 men and 75 women (age range, 22–96 years; mean, 64.1 ± 16.1 years) as inpatients. Patient demographics were similar between groups except that the group of 1997–1998 inpatients was somewhat older (Student's t test = 3.78, p < 0.001) and included a larger proportion of men (44.44% vs 34.00%, ² = 4.47, p < 0.036) than its 2002–2003 counterpart.

The overall number of patients imaged for pulmonary embolism with CT pulmonary angiography, ventilation–perfusion, or pulmonary angiography was significantly greater in 2002–2003 than 1997–1998 (homogeneity of rates = 88.45, p < 0.0001) (Table 1). The absolute number of CT scans obtained for pulmonary embolism was significantly greater in the more recent population in both the emergency department (² = 167.03, p < 0.0001) and inpatient (² = 210.62, p < 0.0001) groups. The incidence of pulmonary embolism detected on CT pulmonary angiography was significantly less in the 2002–2003 population in both the emergency department (² = 34.26, p < 0.0001) and inpatient (² = 8.52, p < 0.01) groups. The decrease in incidence of pulmonary embolism detected on CT pulmonary angiography was greater in the emergency department group than in the inpatient group between the two time periods (homogeneity of odds = 0.003, p < 0.007) (Table 2). With regard to distal clots, no isolated subsegmental emboli were reported in the 1997–1998 population. Thirteen of the scans with positive findings in the 2002–2003 population (12.7%) were interpreted as showing findings either suspicious for or definitely indicative of an isolated subsegmental embolism; this result is a significant increase when compared with 1997–1998 (Fisher's exact = 9.61, p = 0.0023). Two of these patients subsequently underwent pulmonary angiography, and both studies were positive for subsegmental embolism.

The overall number of scans interpreted as showing normal findings was significantly greater in the more recent population (Table 3). That is, the overall incidence of findings other than pulmonary embolism including pneumonia, pleural effusion, adenopathy, pulmonary fibrosis, tumor, edema, esophagitis, nodules, thyroid nodule or mass, hiatal hernia, chronic obstructive pulmonary disease, tracheobronchitis, pericardial effusion, vascular disease or malformation, mucus plug, abscess, or pleuritis was significantly less in both the emergency department (² = 12.67, p = 0.0004) and inpatient (² = 8.418, p = 0.0045) groups in the 2002–2003 population.

Discussion

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The radiologic evaluation of pulmonary embolism has undergone considerable recent change [11, 21–25]. Historically, ventilation–perfusion scanning has been the imaging method of choice in patients with suspected pulmonary embolism [26]. Although ventilation–perfusion scans showing normal and high-probability findings have significant predictive value, numerous studies at major academic centers have shown that most ventilation–perfusion scans are nondiagnostic [8, 27, 28]. Invasive pulmonary angiography, although historically considered the gold standard for pulmonary embolism diagnosis with sensitivity and specificity exceeding 95%, is rarely used, especially in community centers [29, 30]

The development of helical CT technology provided a noninvasive way to study the pulmonary vasculature and led to a widespread adjustment in the imaging approach to patients with suspected pulmonary embolism [25]. Early work indicates that the sensitivity and specificity of CT pulmonary angiography—with values approaching 100% for proximal clots and variable reported numbers (60–94%) in the distal vasculature—are comparable to the sensitivity and specificity of ventilation–perfusion scanning and pulmonary angiography [11–13, 31]. The subsequent development of MDCT scanners and optimization of scanning protocols via thinner collimation and faster scanning times have greatly improved the ability of the interpreter to examine the peripheral segmental and subsegmental pulmonary vasculature [14–16, 32, 33]. Withholding anticoagulation therapy from patients with a negative finding on CT pulmonary angiography has recently been shown to be safe in several series that included emergency department and hospitalized patient populations, thus increasing clinical confidence in the technique [34–37]. The ability of CT pulmonary angiography to detect ancillary findings or findings indicative of an alternative diagnosis expands its diagnostic usefulness, especially in the emergent outpatient setting where clinicians must care for a large number of patients with limited histories [18, 19, 38] (Fig. 2).

View larger version (72K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2. —Axial image from CT pulmonary angiography performed in 51-year-old man with new-onset chest pain shows unsuspected ascending aortic dissection. This case is an example of alternative diagnosis provided by CT pulmonary angiography.

This combination of technologic improvement, diagnostic accuracy, and excellent patient outcomes has resulted in a phenomenon well demonstrated in this study: a significant increase in the use of CT pulmonary angiography. Our results reveal a proportionally greater increase in the utilization of CT pulmonary angiography for the emergency department patients than for hospitalized patients. Our results also indicate significant coincident decreases, greater for emergency department patients than for hospitalized patients, in the incidence of pulmonary embolism detected on CT pulmonary angiography from 1997–1998 to 2002–2003 and a significant overall increase in the number of normal examinations in the recent population. Although additional research needs to be done, these findings suggest that clinicians, especially those in the emergency department, may be using CT pulmonary angiography as a screening test in patients with suspected cardiothoracic disease.

This trend raises new clinical questions. The Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) investigators reported a 33% prevalence of pulmonary embolism in patients selected for pulmonary angiography compared with an overall pulmonary embolism prevalence of 12% in patients selected for CT pulmonary angiography [9]. These data highlight the need for detailed analyses regarding the appropriate clinical setting for the use of CT pulmonary angiography. Similarly, as seen in our study, the large number of scans being obtained on newer MDCT scanners is likely to continue to result in an increased number of small subsegmental emboli being detected. Will the findings in each of these patients warrant the well-documented risk of anticoagulation treatment [39]? In the same way, will the effect on the overall population radiation dose by the increased utilization of CT for pulmonary embolism be justified [40]? In light of the increasing availability and acceptance of CT pulmonary angiography as a first-line imaging technique, these and other questions need to be addressed as investigators continue to define the precise role of CT in the workup of suspected acute pulmonary embolism.

References

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