Effectiveness of MR Angiography for the Primary Diagnosis of Acute Pulmonary Embolism: Clinical Outcomes at 3 Months and 1 Year

Pulmonary Embolism (PE) is an important cause of death in the industrialized world (1,2). Ionizing radiation administered for medical imaging is of increasing clinical concern, particularly for younger patients and female patients (3,4). In a recent epidemiological study, medical radiation at the 50 mSv level was shown to have increased incidence of brain malignancy and leukemia above what could be expected in an unexposed population (5). Chest radiation for younger women is potentially problematic due to its cumulative effects and the radiation sensitivity of breast tissue (3,6). In symptomatic patients with a clinical suspicion for pulmonary embolus, the currently accepted reference standard is computed tomographic angiography (CTA-PE) (7–12). An alternative test that requires no ionizing radiation for the detection of pulmonary embolism would be highly beneficial, so long as it has sufficient effectiveness (4–12). There is recent evidence showing that the number of pulmonary embolism (PE) diagnoses has significantly increased in the United States without a corresponding significant drop in death rate (13–15). CTA-PE is a frequently ordered test that maybe over-used (16). This high degree of usage by clinicians likely reflects the excellent performance (efficacy) of CTA-PE and its ability to diagnose even tiny, subsegmental pulmonary emboli. Recently, some authors have challenged the necessity to treat all sub-segmental PE with anti-coagulation (13,14,17), noting the 4–8% incidence of serious bleeding complications from treatment of PE (1,14,18,19). For this reason, alternative exams such as pulmonary MR angiography (MRA-PE), which have a lower accuracy (efficacy) than CTA-PE for diagnosis of subsegmental PE, may be more than adequate for detection of clinically significant emboli that require anticoagulation. (17,20–24). Use of patient outcomes for the determination of test effectiveness is often employed when there is no available reference standard to determine the efficacy of a test. Recently, Douglas and colleagues have suggested that the determination of test effectiveness, as established by patient outcomes, is actually much more important for the evaluation of clinical utility than test efficacy (29). Lack of a measurable adverse clinical event over the follow-up period is a useful surrogate for utility of a test in this situation. In the clinical evaluation of heart disease, the patient outcome surrogate is a Major Adverse Cardiac Event (MACE) during the chosen follow-up interval (29). In the nuclear medicine literature, outcomes analysis have be used for many years in the determination of test negativity in the workup of suspected PE (30). Use of 1-year outcomes for the determination of CTA-PE effectiveness has been reported by the highly respected cardio-pulmonary radiology group in Lille, France (31). They studied 185 patients and found that CTA-PE had a negative predictive value of 98%, with three episodes of fatal PE (31). Early work on the efficacy of MRA-PE was published in 1999 by Gupta and colleagues has now been shown to be on target with current results (25). They found that larger PEs (lobar and segmental) are well seen with contrast enhanced MRA-PE, but that the sub-segmental PEs were frequently missed (25). There are many studies showing that MRA-PE is a test of lower efficacy than CTA-PE for the diagnosis of subsegmental pulmonary embolism (20,21,28,32–34). However, a conclusion from the PIOPED III study was that if the MRA-PE could be performed in a technically adequate manner, that MRA-PE is highly diagnostic for this condition (20). The purpose of our retrospective study was to determine the effectiveness of MRA-PE in symptomatic patients, using the clinical outcome measure of Venous ThromboEmbolism (VTE, deep venous thrombosis and/or PE) or death from PE as determined by review of the electronic medical record (EMR) for 3 months following the MRA-PE and a second review at 1 year.