Increased diagnosis of pulmonary embolism without a corresponding decline in mortality during the CT era
Introduction
The incidence of pulmonary embolism (PE) in the United States is approximately one per 1000 persons per year.1 Risk factors for PE include smoking, malignancy, obesity, age, hereditary thrombophilias, prolonged immobilization, and surgery.2 Clinical signs and symptoms are notoriously nonspecific, and diagnostic and therapeutic delays are commonly cited as a major source of morbidity and mortality.2, 3
Ventilation perfusion (VQ) scintigraphy had long been the primary diagnostic test for patients with suspected PE.4, 5, 6 Although normal and high-probability VQs are believed to be diagnostic in most cases, the prospective investigation of pulmonary embolism diagnosis (PIOPED) investigation revealed that the majority of VQs fall into the intermediate or low-probability categories, with a 33 and 12% risk of PE, respectively. Combining concordant clinical suspicion with scintigraphic findings improved the diagnostic accuracy of VQ, but still established the diagnosis or exclusion of PE in only a minority of patients.5
In 1978, Sinner7 introduced the concept of using computed tomography (CT) as a diagnostic technique for suspected PE. The development of helical CT enabled imaging of the relevant anatomy in a breath-hold, leading to an interest in CT as a primary imaging test for PE.8 In 1992, Remy-Jardin et al. published the first comparison of helical CT with pulmonary angiography for the diagnosis of central PE.9 Limited resolution at the subsegmental level was an early criticism of CT in the diagnosis PE.10, 11, 12 However, interobserver reliability for pulmonary angiography is only 40–60% at the subsegmental level, making angiography an imperfect reference standard.13 Later studies investigating the safety of using a CT-based algorithm to rule out PE revealed that a negative CT is equivalent to a negative pulmonary angiogram,14, 15 with a similar risk of subsequent venous thromboembolism during follow-up. The resultant change in practice patterns has been swift and dramatic. VQ, which had constituted over 80% of the imaging for patients with suspected PE in 1979, has steadily declined, while CT, constituting significantly less than 10% of studies in the mid 1990s, surpassed VQ in 2001 as the primary imaging method.16 The development of multidetector CT machines has increased the sensitivity of CT, enabling the detection of even subsegmental emboli with a high degree of accuracy.13, 17
The traditional mainstay of therapy for PE is anticoagulation with intravenous unfractionated heparin plus an oral vitamin K antagonist.18, 19 The efficacy of heparin therapy depends upon achieving a therapeutic level within the 24 h.20 However, some patients fail to reach therapeutic levels within 24 h and some remain persistently subtherapeutic.18, 19 Low molecular weight heparins, developed in the late 1990s, have similar safety and efficacy to intravenous unfractionated heparin, but are easier to use. A fixed dose is administered subcutaneously once or twice daily.18, 21, 22, 23
Thrombolytic therapy has been introduced to treat patients with massive PE. However, its value is unproven. In meta-analysis of 748 patients from 11 clinical trials, Wan et al.24, showed no significant advantage of thrombolytic therapy over heparin with regard to recurrent PE or death. An analysis of massive PE from the International Cooperative Pulmonary Embolism Registry also did not demonstrate a reduction in mortality or recurrent PE for those treated with thrombolysis.25
The aim of this study was to determine the association between the increasing use of helical CT for suspected PE on the annual rates of PE diagnosis and PE mortality, using time as a surrogate for CT use. It was hypothesized that CT use has lead to an increase in the diagnosis of PE without an accompanying decrease in mortality.
Section snippets
Design overview
We analysed summary data from New York State's (NYS) publicly available comprehensive patient discharge dataset, the Statewide Planning and Research Cooperative System (SPARCS).26 This database combines medical records and billing files into a single all-inclusive source. All Article 28 facilities in NYS defined as hospitals, emergency departments, and ambulatory surgery centres are required to submit data to SPARCS. In addition, we obtained NYS data regarding known risk factors for PE during
Results
The SPARCS data included 24,871,131 patients from 1 January 1994 through 21 December 2004, with 1996 excluded. Among these patients, there were 692,981 deaths. A total of 34,674 patients received a primary diagnosis of PE during the study period; of these, 1537 died. The number of admissions remained relatively stable over the study period (Table 1).
Discussion
The diagnosis of PE in NYS essentially doubled from 1994–2004, while deaths in patients with PE and hospital admissions remained relatively stable. Because databases tracking CT use for suspected PE were not, to the authors' knowledge, available, the data were analysed in the context of the literature. Overall, imaging for PE has increased with the advent of helical CT, despite reductions in VQ and pulmonary angiography. Prologo et al.27 described their experience in University Hospitals in
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