The goal of this study was to assess the percentage of CT-PA that could have been avoided by use of validated algorithms for the evaluation of patients presenting to the ED with suspected PE. We found that use of PERC or Wells/D-dimer would have safely reduced the number of CT-PA performed by 9.2% and 13.8%, respectively.
Fourteen (9.2%) of the subjects in our study population met PERC and all were PE-negative. These findings are similar to those of prior prospective evaluations of PERC demonstrating high sensitivities. A multicenter study of over 8,000 patients with a 6.9% prevalence of VTE demonstrated PERC to have a sensitivity of 94.7% in low-risk patients.1
A smaller study of 120 ED patients with suspected PE and a 12% prevalence of PE demonstrated a sensitivity of 100%.5
Use of the PERC is recommended in patients with a low pretest probability for suspected PE by clinical gestalt. Not all patients who meet PERC are considered low-risk by clinical gestalt, and the rule’s applicability to this patient group is unknown. As all patients underwent imaging in our study, it may be that gestalt assessment was not considered to be low-risk by the treating physician.
When applying the Wells score to our study population, 72% of patients were classified as “PE Unlikely/Low Risk” based on scores ≤ 4. Per the Wells score algorithm, these patients should have undergone D-dimer testing before receiving CT-PA. Of the 110 low-risk patients by Wells score, only 35% underwent D-dimer testing in the ED. A possible explanation for clinicians’ reluctance to order a D-dimer may be the high frequency of false-positive results. Of the 110 low-risk patients in our study, 81% had elevated D-dimer results, of whom only eight of 89 (9.0%) met the primary outcome of PE. Nevertheless, 21 of the 110 low-risk patients had normal D-dimers, and could have avoided imaging; none of these patients met the primary outcome of PE. Our results are similar to those of previous prospective studies evaluating the dichotomized Wells score. In a multicenter study of 3,306 patients, 1,057 were classified as “PE unlikely” and had negative D-dimer results, with five patients (0.5%) receiving diagnoses of VTE on three-month follow-up, with no deaths.6
A criticism of the Wells score is that it is not entirely objective, as the algorithm contains the subjective variable “an alternative diagnosis is less likely than PE.” This may allow for clinician judgment to enter into the decision rule, placing the patient into a higher or lower risk category given the three-point value to this variable. In addition, other variables may be more predictive for PE than those that are currently included in validated algorithms. A recent multi-center study of almost 8,000 patients showed that in symptomatic patients being considered for possible PE, non-cancer-related thrombophilia, pleuritic chest pain, and family history of VTE increased the probability of PE or deep vein thrombosis.7
None of these variables are part of the Wells score or PERC.
Overuse of CT-PA is likely to have important economic and medical consequences. As a secondary outcome, we evaluated ED LOS and CT-PA time. We found that the median CT-PA time (160 minutes) comprised a substantial fraction of overall median ED LOS (295 minutes). However, whether avoidance of CT-PA in low-risk patients reduces LOS cannot be determined from our study, due to the absence of an appropriate comparison group. Time waiting for potentially unnecessary imaging may contribute to crowding, which has been associated with poor care in the ED, including delays in medications and increased mortality rates.8–11
CT-PA also contributes to increased health care expenditures.12
The use of CT has increased dramatically in the United States over the past two decades, and approximately 14% of all emergency patients now undergo CT scans during their ED visits.13
This not only increases resource use, financial costs, and LOS, but also increases patient exposure to contrast media and radiation exposure risks. The median effective dose for chest CT for suspected pulmonary embolism is 10 mSv.14
An increased risk of cancer has been demonstrated among long-term survivors of the Hiroshima and Nagasaki atomic bombs, who received exposures of 10 to 100 mSv.15–17
Contrast-induced nephropathy is another recognized adverse consequence from contrast-enhanced imaging, and leads to increased morbidity and mortality. A recent study of ED patients receiving intravenous contrast for CT demonstrated an 11% rate of contrast-induced nephropathy.18
Other unintended consequences of contrast-enhanced imaging, such as significant allergic reactions and extravasation of contrast, are rare but clinically important.
Validated clinical decision rules have the potential to reduce unnecessary CT-PA and its associated adverse consequences. However, such rules were underutilized in our study and in other settings.4
One potential barrier to use of these rules is that physicians may feel that clinical gestalt is similar or superior. Several studies have compared clinical gestalt assessment to the Wells score and have found comparable results in assessing pretest probability.19–21
Moreover, some clinicians may err on the side of ordering unnecessary CT-PA in low-risk patients for fear of litigation. Runyon et al. demonstrated that only half of physicians who are familiar with commonly used clinical decision rules use them in more than half of appropriate patients. In addition, the physicians’ spontaneous recall of the rules was low to moderate.4
More work is needed to understand the barriers to implementation of decision rules for PE in the ED and to formulate strategies for overcoming these barriers. Future investigations are needed to evaluate the ability of electronic clinical decision support to aid in the assessment of pretest probability. Larger studies showing a significant benefit of decision rules over gestalt for suspected PE are also likely needed, to persuade physicians of the worth of these diagnostic tools.