Acute pulmonary embolism: diagnostic value of digital subtraction angiography

Detection of simulated pulmonary embolism in a porcine model using hyperpolarized 3He MRI

Several radiological imaging modalities are available to assist with the clinical diagnosis of pulmonary embolism (PE). The most frequently used techniques-nuclear medicine ventilation-perfusion (VP) scan, computed tomography (CT), magnetic resonance angiography (MRA), and pulmonary angiography (PA)-all have literature-supported, substantial limitations with respect to timeliness and patient safety. Hyperpolarized 3He magnetic resonance gas distribution imaging (HP 3He MRI) recently has shown potential as a safer and faster alternative. In this study, we performed HP 3He MRI on a porcine model (N = 6) of simulated PE using selective occlusion balloon catheterization (N = 4) and nonselective aged autologous clot injection (N = 1). The technique was also performed on a normal pig and again after the animal was killed. Temporal depletion of regional HP 3He MRI signal intensity provided for a qualitative assessment of simulated PE (N = 4), and regional PAO2 (alveolar partial pressure of oxygen) was calculated in affected airspaces for a quantitative assessment of simulated PE (N = 1). The preliminary results suggest that HP (3)He MRI shows promise as a means of assessing regional pulmonary perfusion abnormalities in the porcine models of simulated PE that were used in this study.

Pulmonary embolism: comparison of angiography with spiral computed tomography, magnetic resonance angiography, and real-time magnetic resonance imaging

In the last decade, spiral computed tomography (CT) and magnetic resonance (MR) angiography (MRA) have become a viable alternative to conventional angiography in the diagnosis of acute pulmonary embolism. However, patients with dyspnea are often unable to hold their breath for a longer time and thus image degradation is frequently observed. Consequently, an imaging sequence that allows free breathing is desirable. The aim of this animal study was to compare contrast-enhanced spiral CT, MRA and a real-time MR sequence, the latter without breath-hold, with pulmonary angiography as reference gold standard. Nine pigs with artificially induced pulmonary embolism underwent this multimodality comparison. All images were independently evaluated for the presence of pulmonary emboli by two reviewers. Forty-three filling defects were detected by conventional angiography on lobar and segmental levels. Sensitivity of CT images was 72.1 and 69.8% for Readers 1 and 2, respectively, and sensitivity of MRA images was 79.1 and 81.4%. With real-time MR imaging, however, the detection rate was 97.7% for both readers. We conclude that, under experimental conditions, real-time MR imaging without the use of radiation or iodinated contrast material is comparable with angiography in the detection of pulmonary emboli.

High prevalence of detectable deep venous thrombosis in patients with acute pulmonary embolism

STUDY OBJECTIVES

Because specific studies are unavailable, the exact prevalence of detectable "residual" deep venous thrombosis (DVT) in patients with acute pulmonary embolism (PE) is unknown.

DESIGN

Review of clinical records and radiologic documents of consecutive patients.

SETTING

Pulmonary diseases and radiology departments at a university hospital.

PATIENTS

All patients hospitalized in the Department of Pulmonary Diseases with a diagnosis of acute PE during a 5-year period (1984 to 1988). During this period, the diagnosis of PE was based exclusively on pulmonary angiography, and bilateral lower limb venography was routine in patients with proven acute PE.

MEASUREMENTS AND RESULTS

Among 228 consecutive patients with angiography-proven PE, 213 underwent bilateral lower limb venography within 48 h of the diagnosis. Venography demonstrated DVT in 174 patients (81.7%; 95% confidence interval, 76.5 to 86.9%), including 128 patients (60%) with proximal DVT. Signs or symptoms of DVT were present in only 72 patients (42%) with DVT. The prevalence of detectable DVT was significantly lower in patients with recent pelvic surgery or delivery (6 of 12, 50%) than in the other patients, whatever their individual risk factors (p < 0.05). The mean pulmonary vascular obstruction was significantly lower in patients with normal venography than in patients with detectable DVT (37.6 +/- 20.9% vs 48.4 +/- 21.7%; p = 0.007).

CONCLUSIONS

Lower limb venography demonstrates a high prevalence (82%) of residual DVT in patients with angiography-proven PE. These data should be taken into account in the diagnostic and therapeutic management of patients with suspected or proven PE.

Modern management of pulmonary embolism

BACKGROUND

Pulmonary embolism is a significant cause of morbidity and death after operation. The introduction of new technologies in the diagnosis, and thrombolysis in the treatment, of pulmonary embolism has led to a need to reappraise the management of this condition.

METHODS

This review encompasses a comprehensive discussion of diagnostic modalities and therapeutic strategies used in the current management of pulmonary embolism. Relevant papers on the diagnosis and treatment of pulmonary embolism were identified from a Medline search for the period 1967-1998. Additional papers were derived from the reference lists of retrieved articles. Articles presenting prospectively gathered data have been referenced preferentially.

RESULTS AND CONCLUSION

Algorithms for the diagnosis and treatment of pulmonary embolism are presented.

Clinical follow-up of patients after a negative digital subtraction pulmonary arteriogram in the evaluation of pulmonary embolism

PURPOSE

This study was designed to examine the clinical course of patients following digital subtraction pulmonary arteriography (DSPA) interpreted as negative for pulmonary emboli (PE).

MATERIALS AND METHODS

Sixty-three patients underwent DSPA interpreted as negative for PE over a 27-month period. Follow-up data were collected by means of medical and diagnostic radiology record review, interviews of referring physicians, and patient telephone interviews.

RESULTS

Of 63 patients, two were excluded and seven were lost to follow-up, leaving a study population of 54 patients. Mean follow-up was 12.1 months (range, 0-28.5 months). Thirty-one reported no symptoms of PE. Of 13 patients reporting intermittent chest pain and/or dyspnea during their mean follow-up of 13.6 months, 10 had a history of cardiac, nonthrombotic pulmonary, or gastroesophageal reflux disease. There were no subsequent positive angiograms or ventilation/perfusion scans. Comorbid conditions in the 10 patients who died included cardiac events (n = 4), advanced cancer (n = 2), sepsis/pneumonia (n = 2), sarcoidosis (n = 1), and cerebrovascular accident (n = 1). No documented PE was identified.

CONCLUSION

The technique of DSPA is sufficiently sensitive to exclude clinically significant PE. The advantages of image post-processing, in addition to the savings in cost, time, and contrast media, support its use in the angiographic diagnosis of PE.

Digital subtraction versus film-screen angiography for detecting acute pulmonary emboli: evaluation in a porcine model

PURPOSE

To compare the diagnostic performance of digital subtraction angiography (DSA) to that of film-screen angiography (FSA) for detecting acute pulmonary embolism (PE) in a porcine model.

MATERIALS AND METHODS

DSA and FSA were performed in 13 pigs before and after central venous administration of autologous emboli. Results were compared to findings at necropsy with use of ex vivo pulmonary angiography to guide pathologic sectioning. The sensitivity and predictive value of a positive case for detecting each embolus were computed for each pulmonary artery branch order and compared with use of 95% confidence intervals. Interobserver variability among three readers for individual PE detection was calculated.

RESULTS

Pathologic examination of the lungs revealed 100 total PEs (location by vessel order: 1st = 1, 2nd = 0, 3rd = 15, 4th = 32, > 5th = 52). On average, FSA review identified 72 (72%) emboli and DSA review, 65 (65%). There was no significant difference in sensitivity or predictive value of a positive case between DSA and FSA for detecting emboli (P > .05). There was similar agreement among readers for individual PE detection with DSA (mean, 84%) and FSA (mean, 80%).

CONCLUSION

The diagnostic performance of DSA is equivalent to that of FSA for detecting emboli in porcine PA branches. Interobserver agreement for individual PE detection is similar for both imaging techniques.

Pulmonary angiography and the diagnosis of pulmonary embolism

Pulmonary angiography is the definitive study for the identification of embolism. The development of accurate noninvasive methods for the detection of deep venous thrombosis has altered the indications for angiography. Many angiographic techniques have been developed, providing the opportunity to tailor the angiogram to the clinical situation of individual patients. Strict criteria must be used for interpretation of angiographic studies, and using state of the art equipment will diminish technically unsatisfactory examinations. CT and MR angiography will assume a significantly larger role in the identification of PE in the very near future. MR may become the method of choice, because it is the one noninvasive technique that shows promise for the study of both the deep venous system of the legs and pelvis and the pulmonary circulation.