The characteristics of the thrombi of the lower limbs, as detected by ultrasonic scanning, do not predict pulmonary embolism

Pulmonary embolism

Pulmonary embolism (PE) remains one of the most challenging medical diseases in the emergency department. PE is a potentially life threatening diagnosis that is seen in patients with chest pain and/or dyspnea but can span the clinical spectrum of medical presentations. In addition, it does not have any particular clinical feature, laboratory test, or diagnostic modality that can independently and confidently exclude its possibility. This article offers a review of PE in the emergency department. It emphasizes the appropriate determination of pretest probability, the approach to diagnosis and management, and special considerations related to pregnancy and radiation exposure.

Silent pulmonary embolism in patients with deep venous thrombosis: a systematic review

PURPOSE

To determine, by systematic review of the literature, the prevalence of silent pulmonary embolism in patients with deep venous thrombosis.

METHODS

Twenty-eight included published investigations were identified through PubMed. Studies were selected if methods of diagnosis of pulmonary embolism were described; if pulmonary embolism was stated to be asymptomatic; and if raw data were presented. Studies were stratified according to whether silent pulmonary embolism was diagnosed by a high-probability ventilation-perfusion lung scan using criteria from the Prospective Investigation of Pulmonary Embolism Diagnosis, computed tomography pulmonary angiography, or conventional pulmonary angiography (Tier 1), or by lung scans based on non-Prospective Investigation of Pulmonary Embolism Diagnosis criteria (Tier 2).

RESULTS

Silent pulmonary embolism was diagnosed in 1665 of 5233 patients (32%) with deep venous thrombosis. This is a conservative estimate because many of the investigations used stringent criteria for the diagnosis of pulmonary embolism. The incidence of silent pulmonary embolism was higher with proximal deep venous thrombosis than with distal deep venous thrombosis. Silent pulmonary embolism seemed to increase the risk of recurrent pulmonary embolism: 25 of 488 (5.1%) with silent pulmonary embolism versus 7 of 1093 (0.6%) without silent pulmonary embolism.

CONCLUSION

Silent pulmonary embolism sometimes involved central pulmonary arteries. Because approximately one third of patients with deep venous thrombosis have silent pulmonary embolism, routine screening for pulmonary embolism may be advantageous.

Relationship between the extent of deep venous thrombosis and the extent of acute pulmonary embolism as assessed by CT angiography

The aim of our study is to investigate prospectively the quantitative relationship between deep venous thrombosis (DVT) and acute pulmonary embolism (PE). 110 patients clinically suspected of having venous thromboembolic disease underwent combined CT pulmonary angiography (CTPA) and venography of lower limb veins. 44 patients presented with clinical signs of DVT and positive ultrasonography or ascending venography, but no clinical sign of PE (Group 1). 66 patients presented with clinical signs of PE and positive CTPA (Group 2). Clot load in lower limb veins and pulmonary arteries were scored by two independent readers, each using two separate systems for DVT and two for PE. 27 (61%) patients in Group 1 also had PE, and 55 (83%) patients in Group 2 also had DVT. Correlations between PE and DVT scores were weak but statistically significant in Group 2 (r(s) ranging from 0.470-0.520; p< or =0.001), but only some were significant in Group 1 (r(s) ranging from 0.253-0.318; p-values ranging from 0.035-0.097). In conclusion, although PE occurs in a majority of patients with DVT, and vice versa, the amount/burden of clot load in one condition does not necessarily indicate - or indicates only weakly - the degree of burden in the other condition.

Pulmonary embolism: an unsuspected killer

The presentation of PE is often subtle and may mimic other diseases. Many pulmonary emboli invariably preclude diagnosis by their occult nature or by leading to rapid death from cardiopulmonary arrest. In patients who do manifest symptoms from PE, accurate diagnosis is essential. Often it is difficult to distinguish the vague symptoms of PE from other diagnoses, such as acute coronary syndrome, pneumonia, COPD, CHF,aortic dissection, myocarditis or pericarditis, pneumothorax, and musculo-skeletal or gastrointestinal causes. Regardless of the presentation, the most fundamental step in making the diagnosis of PE is first to consider it. Historical clues and risk factors should raise the clinician's suspicion.PE is an unsuspected killer with a nebulous presentation and high mortality. In all likelihood, PE will remain an elusive diagnosis despite advances in technology and a wealth of research. A high index of suspicion is required, but no amount of suspicion would eliminate all missed cases. Patients with significant underlying cardiopulmonary disease seem to be the most challenging. Patients with significant comorbidity have poor reserve and are likely to have poor outcomes, especially if the diagnosis is not made and anticoagulation is not initiated early. Controversy exists over the best diagnostic approach to PE. A battery of diagnostic studies is available, with few providing definitive answers. Studies such as CT may be helpful at some institutions but offer poor predictive value at others. Other diagnostic tests are not universally available. It is hoped that further research and improvements in current diagnostic modalities will clear some of the current confusion and controversy of this ubiquitous and deadly disease.

Proximal extent of pelvic vein thrombosis and its association with pulmonary embolism

OBJECTIVE

Conventional methods such as duplex ultrasound scanning do not provide accurate information about proximal extension of pelvic vein thrombosis. We evaluated proximal extent of thrombus toward pelvic veins with magnetic resonance imaging in patients with suspected deep vein thrombosis (DVT) proximal to the inguinal ligament on the basis of duplex ultrasound scans. In addition, frequency of pulmonary embolism (PE) and early (4 weeks) clinical outcome were evaluated.

METHODS

Two hundred twelve patients with acute symptomatic DVT proximal to the inguinal ligament, diagnosed at duplex ultrasound scanning, were enrolled in this prospective study. All patients underwent magnetic resonance imaging of the abdominal and pelvic veins, as well as lung scintigraphy to detect the presence of pulmonary embolism.

RESULTS

In 24 of 212 patients (11%), thrombus was restricted to the femoral vein. The thrombus extended into iliac veins in 142 patients (67%) and into the inferior vena cava in 46 patients (22%). The frequency of PE was not associated with the most proximal extension of thrombus (P =.61). No patients died as a consequence of thromboembolic events.

CONCLUSIONS

Extension of DVT into the inferior vena cava occurs relatively frequently. In our patients this finding was not associated with higher risk for PE compared with DVT of the femoral or iliac veins.

Nonspecific tests for pulmonary embolism

Many tests have been proposed as useful in the diagnostic evaluation of suspected PE, but nonspecific tests for PE can only add to the level of suspicion one has for the diagnosis. As Anderson indicates, "virtually all clinical and laboratory findings neither diagnose nor exclude the diagnosis of PE. They merely serve to heighten suspicion of the diagnosis and prompt the clinician to pursue additional diagnostic studies." D-dimer measurement is promising as a test to exclude PE in young healthy out-patients, and further study and improvements in technology, can clarify the usefulness of the different methods of performing this assay. For now, diagnostic algorithms for PE should continue to incorporate multiple tests and decision points, but the standard remains specialized imaging techniques.