CT Findings and Long-Term Mortality After Pulmonary Embolism

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1 Cardiopulmonary Imaging Original Research Morris et al. CT and Long-Term Mortality After Pulmonary Embolism Cardiopulmonary Imaging Original Research Downloaded from by on 05/2/8 from IP address Copyright ARRS. For personal use only; all rights reserved Michael F. Morris Bruce A. Gardner 2 Michael B. Gotway 3 Kristine M. Thomsen 4 W. Scott Harmsen 4 Philip A. Araoz 2 Morris MF, Gardner BA, Gotway MB, Thomsen KM, Harmsen WS, Araoz PA Keywords: CT, outcome, pulmonary embolism, survival DOI:0.224/AJR..680 Received March 4, 20; accepted after revision May 27, 20. Department of Radiology, Mayo Clinic and Mayo Foundation, Scottsdale, AZ. 2 Department of Radiology, Mayo Clinic and Mayo Foundation, 200 First St SW, Rochester, MN Address correspondence to P. A. Araoz (araoz.philip@mayo.edu). 3 Scottsdale Medical Imaging, Scottsdale, AZ. 4 Department of Health Sciences Research, Division of Biostatistics, Mayo Clinic and Mayo Foundation, Rochester, MN. AJR 202; 98: X/2/ American Roentgen Ray Society CT Findings and Long-Term Mortality After Pulmonary Embolism OBJECTIVE. The utility of CT findings in predicting long-term mortality in patients with acute pulmonary embolism (PE) is unknown. The purpose of this study is to retrospectively determine whether three CT findings increased embolic burden, interventricular septal bowing toward the left ventricle, and right ventricle to left ventricle (RV/LV) diameter ratio greater than are independent predictors of long-term all-cause mortality after acute PE. MATERIALS AND METHODS. A total of 05 patients (47% female; mean age, 63 ± 6 years) with CT scans positive for PE from January, 997, to December 3, 2002, were included. Scans were independently interpreted by two observers, with a third independent observer reviewing discrepant cases. CT findings and clinical information were compared with all-cause mortality using univariate and multivariate logistic regression analyses. RESULTS. The median duration of survival was 6.2 years following acute PE, with estimated 0-year survival of 37.4%. CT-derived embolic burden was associated with a very small decrease in long-term all-cause mortality in both univariate (hazard ratio [HR], 0.97; p < 0.00) and multivariate (HR, 0.97; p < 0.00) analyses. Interventricular septal bowing and RV/LV diameter ratio were not significantly associated with long-term all-cause mortality. CONCLUSION. CT findings are not predictive of decreased long-term survival after acute PE. A cute pulmonary embolism (PE) is a common and potentially fatal disease [, 2]. Although the mortality risk from PE is greatest within the first 30 days, patients who survive beyond this period have an increased risk of death compared with the general population, which persists years beyond their initial diagnosis [3]. In patients with acute PE, CT imaging findings predictive of mortality have been sought to identify patients who might benefit from more aggressive intervention [4]. Many studies have found an association between 30-day mortality after an acute PE and CT findings of increased embolic burden, interventricular septal bowing toward the left ventricle, and right ventricle to left ventricle (RV/LV) diameter ratio greater than [5 9]. On the other hand, the association between these CT findings and long-term risk of death after acute PE has not been well studied. The few publications that assessed the impact of CT findings on long-term mortality have yielded conflicting results regarding the impact of CT-derived embolic burden scores and RV/LV diameter ratio, whereas interventricular septal bowing has not been found to be a significant risk factor for death [0 3]. In an effort to address these conflicting reports, we retrospectively examined a large cohort of patients with acute PE, with follow-up over a period of many years, to determine whether CT-derived embolic burden scores, interventricular septal bowing toward the left ventricle, and RV/LV diameter ratio are independent predictors of long-term all-cause mortality after acute PE. Materials and Methods Patient Selection Institutional review board approval was obtained, and patient information was reviewed in compliance with HIPAA regulations. The patient population for the current study was drawn from a database of patients with PE who were previously investigated for an association between 30-day mortality and pulmonary CT angiography findings [8]. Between January, 997, and December 3, 2002, radiologists dictating pulmonary CT angiograms assigned a code separate from the dictated report indicating whether PE was present or 346 AJR:98, June 202

2 CT and Long-Term Mortality After Pulmonary Embolism Downloaded from by on 05/2/8 from IP address Copyright ARRS. For personal use only; all rights reserved absent. During this period, 2249 patients had CT scans coded positive for PE. If the dictated CT report indicated no PE, even though the examination had been assigned a code positive for PE, the scan was considered to have been miscoded and the patient was excluded. The remaining CT scans were reviewed by two board-certified cardiothoracic radiologists to confirm the presence of PE and to assess for evidence of chronic PE. At the time of interpretation, the readers had 2 and 5 years of experience, respectively, as attending-level cardiothoracic radiologists. PE was defined as a discrete low-attenuation filling defect in the pulmonary arterial tree. In cases where observers and 2 disagreed on the presence of PE, a third board-certified radiologist blinded to the results of observers and 2 served as a tiebreaker. Patients were thus excluded if, by consensus, no PE was detected. Chronic PE was defined as laminated thrombus adherent to the pulmonary arterial wall, recanalized thrombus, webs within the lumen of pulmonary arteries, and small tapered pulmonary arteries. With observer 3 serving as a tiebreaker, patients were excluded if, by consensus, chronic PE was present. The complete exclusion criteria are detailed in Table, resulting in 05 patients included in the study. CT Angiography Acquisition All 05 CT scans were acquired without ECG gating, with a section thickness of 3 mm or less, depending on the type of scanner (Table 2). Contrast material injection rates were at least 4 ml/s, using at least 00 ml of iodinated contrast material. For optimal opacification of pulmonary arteries, either bolus timing or bolus tracking software was used, with a region of interest placed over the main pulmonary artery. CT Angiography Interpretation CT scans were electronically reviewed in the axial plane using commercially available software (efilm, version.5.3, efilm Medical) by two independent observers who were blinded to the clinical history. Each observer scored the embolic burden, evaluated for the presence or absence of interventricular septal bowing, and measured the RV/LV diameter ratio. Embolic burden The main, right and left, lobar, right interlobar, and segmental pulmonary arteries were scored for emboli, according to a Fig. Schematic of pulmonary arterial embolic burden scoring algorithm. Nonocclusive segmental pulmonary artery emboli are assigned score of. More proximal emboli are assigned score according to total number of segmental pulmonary arteries supplied by affected vessel. Reproduced with permission from [8]. TABLE : Exclusions Among 2249 Eligible Patients Reason for Exclusion No. of Patients CT prospectively read as negative 57 Embolic score = 0 (by consensus) 440 Chronic pulmonary embolism (by consensus) 05 CT not available 32 CT not of the chest 26 CT scan incomplete 9 Tumor thrombus 6 Incomplete clinical notes 5 No IV contrast 2 Refused research authorization 2 Total 44 TABLE 2: CT Scanner Type and Acquisition Parameters CT Scanner Type 2 5 No. (%) of Patients 3 Tube Current (ma) previously validated model [4]. Segmental pulmonary artery thrombus or isolated subsegmental embolus was assigned a score of, whereas thrombus in more proximal arteries was assigned a score equal to the number of segmental arteries supplied by the affected vessel [8] (Fig. ). If an occlusive thrombus was present, defined as an embolus filling the entire lumen of the artery, then the score was doubled. For example, the right middle pulmonary artery supplies two lung segments Tube Voltage (kvp) 2 4 Slice Thickness (mm) Electron beam 729 (66) Single detector 46 (4) MDCT 235 (2) MDCT 66 (6) MDCT 29 (3) AJR:98, June

3 Morris et al. Downloaded from by on 05/2/8 from IP address Copyright ARRS. For personal use only; all rights reserved Fig year-old woman with interventricular septal bowing. Axial contrast-enhanced chest CT scan shows bowing of interventricular septum (arrow) into left ventricular chamber. An isolated thrombus in the right middle lobe pulmonary artery was assigned a score of 2, whereas an occlusive thrombus received a score of 4. The maximal score was 36 for an occlusive thrombus in the main pulmonary artery. The mean score of observer and observer 2 was used for the embolic burden score in the statistical analysis. Interventricular septal bowing Interventricular septal bowing was visually assessed as being present if any images showed septal bowing toward the left ventricle [8] (Fig. 2). If this finding was not present, interventricular septal bowing was considered absent. In cases where observers and 2 disagreed on the presence of ventricular septal bowing, a third observer blinded to the results of observers and 2 served as a tiebreaker. RV/LV diameter ratio The RV diameter was obtained on the axial image where the tricuspid valve was widest, and the LV diameter was obtained on the axial image where the mitral valve was widest (Fig. 3), as described elsewhere [8]. Both ventricles were measured from subendocardial surface to subendocardial surface at the widest point in the chamber, and the RV/LV diameter ratio was then calculated. The mean value for observer and observer 2 was used for the RV/LV diameter ratio in the statistical analysis. Clinical Information Patient medical records were reviewed to determine the date of death or date of last documented correspondence through February 5, 200. For patients who were not listed as deceased by the medical record, a search of the Accurint database (LexisNexis Risk Solutions) was also performed to capture additional deaths during the study period not recorded in the patient medical record. The Accurint database includes public and nonpublic records, such as the Social Security Death Index. A Fig year old-man. Images show measurement of right ventricle to left ventricle (RV/LV) diameter ratio. A, Axial contrast-enhanced chest CT scan where tricuspid valve is widest. RV diameter (line) is measured from subendocardial surface to subendocardial surface. B, LV diameter (line) is measured from subendocardial surface to subendocardial surface at level where mitral valve is widest. Emboli are visible within both lower lobe pulmonary arteries, as is small pulmonary infarct (arrow) in right lower lobe. TABLE 3: Variables Associated With Clinical Presentation, Comorbid Conditions, and Treatment Variable Value Age at CT (y), mean ± SD 63 ± 6 Female sex 55 (47) Comorbid conditions Malignancy 456 (4) Ischemic heart disease 259 (23) Pulmonary disease or asthma 2 (9) History of thromboembolic disease 86 (7) Diabetes 65 (5) Immunocompromise 55 (4) Current thromboembolic disease 38 (3) Current anticoagulant use 30 (2) Congestive heart failure 93 (8) Pulmonary hypertension 66 (6) Prior inferior vena cava filter 36 (3) Organ transplant 3 () Clinical presentation Room air oxygen saturation < 90% 769 (70) Supplemental oxygen, no intubation 447 (4) Heart rate > 00 beats/min 250 (23) Systolic blood pressure < 00 mm Hg 62 (6) Intubation after clinical event but before CT 29 (3) Intubation before clinical event that prompted CT 22 (2) Treatment Anticoagulation 045 (95) Inferior vena cava filter 72 (6) No treatment 28 (3) Thrombolytics 5 () Thrombectomy 4 () B 348 AJR:98, June 202

4 CT and Long-Term Mortality After Pulmonary Embolism TABLE 4: Kaplan-Meier Survival Estimates Downloaded from by on 05/2/8 from IP address Copyright ARRS. For personal use only; all rights reserved Time to Death or Last Follow-Up (y) No. of Patients at Risk No. of Cumulative Deaths Charts were reviewed for age, sex, and 2 comorbid conditions at the time of CT: congestive heart failure, ischemic heart disease, pulmonary disease and asthma, pulmonary hypertension, malignancy, current anticoagulant use, organ transplantation, history of thromboembolic disease, current thromboembolic disease, diabetes, prior inferior vena cava filter, and immunocompromise. In risk factor assessment for association with survival, the presence of either pulmonary disease or asthma was considered as a single variable. Patient records were also reviewed for six clinical variables at the time the CT was ordered: room air oxygen saturation, heart rate, blood pressure, use of supplemental oxygen without intubation, intubation before the clinical presentation that prompted CT, and intubation after the clinical event but before CT. Age, heart rate, room air oxygen saturation, and blood pressure were converted into dichotomous variables (age > 65 years, heart rate > 00 beats/min, room air oxygen saturation < 90%, and systolic blood pressure < 00 mm Hg). Treatment during the initial presentation or hospitalization was recorded according to whether the patient received anticoagulation, thrombolysis, thrombectomy, inferior vena cava filter, or no treatment. Statistical Analysis The endpoint for the analysis was all-cause mortality. Univariate and multivariable Cox proportional hazards regression was used to assess the association of CT findings and clinical factors with patient survival. Embolic burden score was analyzed as both a continuous variable and as quartiles. The multivariable model used backward elimination, including as potential variables all 28 comorbid conditions, clinical presentations, treatments, and CT findings. Additional multivariate modeling with forward and stepwise selection procedures yielded similar results. The Kaplan-Meier method was used to estimate patient survival over time overall and by CT finding. The α-level was set at 0.05 for statistical significance. Cumulative No. of Patients Lost to Follow-Up Probability of Survival (95% CI) a 5.00 ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) a Same-day deaths. Fig. 4 Overall long-term survival after pulmonary embolism. Median survival is 6.2 years. Survival (%) Years of Follow-Up Results Forty-seven percent of patients were women. The mean age was 63 ± 6 years, and the most common comorbid condition was malignancy (Table 3). A total of 580 deaths were observed over the period of follow-up. Among the 525 patients who were known to be alive at last follow-up, a median of 7.4 years (interquartile range, years) elapsed between the date of CT and the last documented correspondence in the medical record. The median survival after CT was 6.2 years. Estimated survival at 5 and 0 years was 52.7% and 37.4%, respectively (Table 4 and Fig. 4). CT Findings A higher embolic burden score was associated with decreased all-cause mortality in both univariate (hazard ratio [HR], 0.97; p < 0.00) and multivariate (HR, 0.97; p < 0.00) analyses (Table 5). The univariate assessment of embolic burden score, categorized in quartiles (i.e., < 3.5, , , and > 4.0), was significantly associated with survival (p < 0.00), although significance was a score of greater than 4.0 relative to a patient with a score less than 3.5 (HR, 0.59; p < 0.00) (Fig. 5). A histogram of embolic burden score is provided in Figure 6. AJR:98, June

5 Morris et al. Downloaded from by on 05/2/8 from IP address Copyright ARRS. For personal use only; all rights reserved TABLE 5: Comorbid Conditions, Clinical Presentation, and Treatment Variables Associated With All-Cause Mortality by Univariate and Multivariate Cox Proportional Hazards Models Variable Univariate Model Multivariate Model HR (95% CI) p HR (95% CI) p Age > 65 y.79 (.5 2.3) < 0.00 a.48 (.22.78) < 0.00 a Female sex. ( ) Comorbid conditions Malignancy 3.2 ( ) < 0.00 a 3.8 ( ) < 0.00 a Congestive heart failure 2.32 ( ) < 0.00 a 2.02 ( ) < 0.00 a Pulmonary disease or asthma.88 ( ) < 0.00 a.69 ( ) < 0.00 a Immunocompromise.83 ( ) < 0.00 a.52 (.22.9) < 0.00 a Diabetes.48 (.2.83) < 0.00 a.33 (.06.64) 0.0a Ischemic heart disease.30 (.08.55) a Prior inferior vena cava filter.50 ( ) History of thromboembolic disease.22 (.00.50) Pulmonary hypertension.20 ( ) 0.27 Current anticoagulant use.09 ( ) 0.53 Organ transplant 0.99 ( ) Current thromboembolic disease 0.89 (0.69.5) Clinical presentation Intubation before clinical event that prompted CT 2.3 ( ) a Room air oxygen saturation < 90%.84 ( ) < 0.00 a.57 (.29.92) < 0.00 a Systolic blood pressure < 00 mm Hg.67 ( ) a.52 (.09 2.) 0.0 a Intubation after clinical event but before CT.65 ( ) a Supplemental oxygen, no intubation.39 (.8.63) < 0.00 a Heart rate > 00 beats/min.2 (.00.47) a.23 (.0.50) 0.04 a Treatment No treatment 2.55 ( ) < 0.00 a.86 ( ) 0.0 a Inferior vena cava filter.53 (.25.88) < 0.00 a Thrombectomy.47 ( ) Thrombolysis.2 ( ) Anticoagulation 0.48 ( ) < 0.00 a CT findings Embolic burden score, per point 0.97 ( ) < 0.00 a 0.97 ( ) < 0.00 a Embolic burden score in quartiles b Fourth quartile (> 4) 0.59 ( ) < 0.00 a Third quartile (7.5 4) 0.95 (0.76.8) 0.62 Second quartile (3.5 7).00 (0.8.25) First quartile (< 3.5) (Reference) Right ventricle to left ventricle diameter ratio 0.89 (0.67.5) Septal bowing 0.92 (0.7.9) Note Dashes indicate variable was included but not found to be statistically significant in the multivariate model. HR = hazard ratio. a Statistically significant, p < b Overall test of association, p < AJR:98, June 202

6 CT and Long-Term Mortality After Pulmonary Embolism Downloaded from by on 05/2/8 from IP address Copyright ARRS. For personal use only; all rights reserved Survival (%) Embolic Burden Quartile (Score) 20 4th Quartile (> 4)* 3rd Quartile (8 4) 2nd Quartile (4 7) st Quartile (< 4) Years of Follow-Up Fig. 5 Long-term survival after pulmonary embolism based on embolic burden score quartile. In univariate analysis, there was improved survival in patients with fourth quartile of embolic burden score compared with first quartile (hazard ratio, 0.970; 95% CI, ; p < 0.00). Asterisk indicates statistical significance (p < 0.05). In both univariate and multivariate analyses, there was no statistically significant association between all-cause mortality and interventricular septal bowing or RV/LV diameter ratio. Interobserver variability for embolic burden (intraclass correlation coefficient = 0.85), interventricular septal bowing (κ = 0.54), and RV/LV diameter ratio (intraclass correlation coefficient = 0.5) have been previously reported [8] and were not specifically reanalyzed. No. of Patients Comorbid Conditions, Clinical Presentation, and Treatment In the univariate analysis (Table 5), age and six of the 2 comorbid conditions were associated with increased risk of all-cause mortality. Of these, malignancy was associated with the highest risk (HR, 3.2; p < 0.00). All six clinical presentation variables were significantly associated with all-cause mortality; intubation before the clinical event was associated with the highest mortality risk (HR, 2.3; p = 0.002). The only significant treatment variable was for patients who received no treatment within 30 days of CT; these patients were more likely to die than were patients who received any treatment (HR, 2.55; p < 0.00). The patients who received no treatment either had contraindications to anticoagulation or were considered clinically too unstable for procedural intervention. In the multivariate analysis (Table 5), age and five comorbid conditions were associated with increased all-cause mortality, with malignancy associated with the highest mortality risk (HR, 3.8; p < 0.00). As opposed to the results of the univariate analysis, ischemic heart disease was no longer significantly associated with all-cause mortality. Three of the six clinical variables (i.e., room air oxygen saturation < 90%, heart rate > 00 beats/min, and systolic blood pressure < 00 mm Hg) remained significantly associated with all-cause mortality after multivariate analysis. Patients who received no treatment within 30 days of CT were again found to be more likely to die than were patients who received any treatment (HR, 2.30; p < 0.00) Embolic Burden Score Fig. 6 Histogram of embolic burden score in 05 patients (first quartile, < 4; second quartile, 4 7; third quartile, 8 4; fourth quartile, > 4). Discussion The results of the current study show that CT-derived embolic burden scores are associated with a very small decrease in long-term all-cause mortality in patients with PE, whereas interventricular septal bowing and RV/LV diameter ratio are not significantly associated with long-term all-cause mortality. The association between the highest quartile of embolic burden score and improved survival may seem paradoxical, but a similar trend, although not statistically significant, was recently reported in a retrospective analysis of CT risk factors associated with 90-day mortality []. Patients with massive PE who survive to undergo CT may represent a unique subset of patients who have an improved overall survival, as opposed to those with massive PE who die before imaging [5, 6]. Alternatively, the relationship between embolic burden and survival may be due to differences in treatment not accounted for in our study. Although our analysis controlled for multiple treatment variables, it is unknown whether patients with higher embolic burdens were treated in a fashion we did not take into consideration. It is possible, for example, that patients with the highest embolic burden may have been prescribed a longer duration of treatment or achieved a higher level of anticoagulation, even though there was no protocol in place at our institution that varied treatment according to embolic burden. Nevertheless, our data show that, using current treatment regimens, increased embolic burden is not associated with decreased long-term survival. This finding is in agreement with the few studies reporting the relationship between CT-derived embolic burden scores and survival after at least year [2, 7]. With regard to CT-derived interventricular septal bowing and RV/LV diameter ratio, our data show that these indexes are not independent risk factors for long-term death after PE. Prior studies investigating the association between CT findings and the risk of longterm mortality after PE have been limited by small numbers of patients, relatively limited follow-up (< year), and lack of accounting for type of treatment or other important prognostic factors. The current study, on the other hand, is based on a large number of patients, followed over many years, and accounts for multiple potential clinical and patient confounders. Our study has several limitations. This study examined all-cause mortality, which is more commonly reported in studies examining long-term mortality, rather than examining PE-specific mortality, which is commonly reported in studies examining short-term mortality. In this retrospective analysis, a substantial minority of patients had significant medical comorbidities, including malignancy, which AJR:98, June

7 Morris et al. Downloaded from by on 05/2/8 from IP address Copyright ARRS. For personal use only; all rights reserved would be expected to contribute long-term mortality. However, potential confounding was accounted for by including a large number of variables and performing multivariate logistic regression analysis. An additional limitation is that CT scans were acquired with either electron beam or older generation singledetector and multidetector scanners. Although older generation CT scanners have decreased sensitivity for the detection of subsegmental emboli compared with current generation CT scanners, they are accurate for the detection of emboli in the segmental pulmonary arteries [8, 9]. CT scans were also obtained without ECG gating, and right ventricular measurements were obtained in the axial plane rather than a four-chamber plane. Despite this, it has been suggested that nongated measurements of the right ventricle obtained in the axial plane are only minimally inferior to measurements obtained from ECG-gated images in the four-chamber plane [20]. In conclusion, CT-derived embolic burden scores, interventricular septal bowing, and RV/LV diameter ratio greater than are not predictive of decreased long-term survival. Because our study is based on the results from a single CT examination obtained at the time of diagnosis, future studies may be able to elucidate the significance of these findings at a time point more remote from the initial PE. References. Anderson FA Jr, Wheeler HB, Goldberg RJ, et al. A population-based perspective of the hospital incidence and case-fatality rates of deep vein thrombosis and pulmonary embolism: The Worcester DVT Study. Arch Intern Med 99; 5: Kurkciyan I, Meron G, Sterz F, et al. Pulmonary embolism as a cause of cardiac arrest: presentation and outcome. Arch Intern Med 2000; 60: Klok FA, Zondag W, van Kralingen KW, et al. Patient outcomes after acute pulmonary embolism: a pooled survival analysis of different adverse events. Am J Respir Crit Care Med 200; 8: Wu AS, Pezzullo JA, Cronan JJ, Hou DD, Mayo- Smith WW. CT pulmonary angiography: quantification of pulmonary embolus as a predictor of patient outcome initial experience. Radiology 2004; 230: Lu MT, Cai T, Ersoy H, et al. Interval increase in right-left ventricular diameter ratios at CT as a predictor of 30-day mortality after acute pulmonary embolism: initial experience. Radiology 2008; 246: Engelke C, Rummeny EJ, Marten K. Acute pulmonary embolism on MDCT of the chest: prediction of cor pulmonale and short-term patient survival from morphologic embolus burden. AJR 2006; 86: Ghaye B, Ghuysen A, Willems V, et al. Severe pulmonary embolism: pulmonary artery clot load scores and cardiovascular parameters as predictors of mortality. Radiology 2006; 239: Araoz PA, Gotway MB, Harrington JR, Harmsen WS, Mandrekar JN. Pulmonary embolism: prognostic CT findings. Radiology 2007; 242: Quiroz R, Kucher N, Schoepf UJ, et al. Right ventricular enlargement on chest computed tomography: prognostic role in acute pulmonary embolism. Circulation 2004; 09: van der Meer RW, Pattynama PM, van Strijen MJ, et al. Right ventricular dysfunction and pulmonary obstruction index at helical CT: prediction of clinical outcome during 3-month follow-up in patients with acute pulmonary embolism. Radiology 2005; 235: Moroni AL, Bosson JL, Hohn N, Carpentier F, Pernod G, Ferretti GR. Non-severe pulmonary embolism: prognostic CT findings. Eur J Radiol 200; 79: Subramaniam RM, Mandrekar J, Chang C, et al. Pulmonary embolism outcome: a prospective evaluation of CT pulmonary angiographic clot burden score and ECG score. AJR 2008; 90: Akram AR, Cowell GW, Logan LJ, et al. Clinically suspected acute pulmonary embolism: a comparison of presentation, radiological features and outcome in patients with and without PE. QJM 2009; 02: Qanadli SD, El Hajjam M, Vieillard-Baron A, et al. New CT index to quantify arterial obstruction in pulmonary embolism: comparison with angiographic index and echocardiography. AJR 200; 76: Turnier E, Hill JD, Kerth WJ, Gerbode F. Massive pulmonary embolism. Am J Surg 973; 25: Wood KE. Major pulmonary embolism: review of a pathophysiologic approach to the golden hour of hemodynamically significant pulmonary embolism. Chest 2002; 2: Miniati M, Monti S, Bottai M, et al. Survival and restoration of pulmonary perfusion in a long-term follow-up of patients after acute pulmonary embolism. Medicine (Baltimore) 2006; 85: Schoepf UJ, Costello P. CT angiography for diagnosis of pulmonary embolism: state of the art. Radiology 2004; 230: Schoepf UJ, Helmberger T, Holzknecht N, et al. Segmental and subsegmental pulmonary arteries: evaluation with electron-beam versus spiral CT. Radiology 2000; 24: Lu MT, Cai T, Ersoy H, et al. Comparison of ECGgated versus non-gated CT ventricular measurements in thirty patients with acute pulmonary embolism. Int J Cardiovasc Imaging 2009; 25: AJR:98, June 202