Saddle Pulmonary Embolism: Is It the Same as 'Massive' PE?

Abstract & Commentary

By David J. Pierson, MD Professor Emeritus, Pulmonary and Critical Care Medicine, University of Washington, Seattle.

This article originally appeared in the November 2011 issue of Critical Care Alert. It was peer reviewed by William Thompson, MD. Dr. Thompson is Associate Professor of Medicine, University of Washington, Seattle. Drs. Pierson and Thompson report no financial relationships relevant to this field of study.

Synopsis: Saddle pulmonary embolism was found in 37 of 680 patients with documented pulmonary embolism (PE) in this community hospital study. The great majority of these patients did well on standard therapy without thrombolytics, emphasizing that the radiographic finding of saddle PE should not by itself be equated with the much more serious clinical entity of massive PE.

Source: Sardi A, et al. Saddle pulmonary embolism: Is it as bad as it looks? A community hospital experience. Crit Care Med 2011;Jun 23. [Epub ahead of print]

Saddle pulmonary embolism (SPE) is defined as the presence of a thromboembolus located at the bifurcation of the main pulmonary artery. Once identified at post-mortem examination or by pulmonary arteriography, SPE is now most commonly encountered by clinicians as a radiographic finding on computed tomography angiography (CTA). The authors of this retrospective study of all CTAs that were read as positive for PE over a 4.75-year period at Albert Einstein Medical Center in Philadelphia sought to determine the clinical features, associated findings, management, and outcomes of all patients with SPE. Patients older than 18 years were identified by IDC-9 codes indicating a positive CTA for PE, and the images were then reviewed independently by two radiologists who were unaware of the patients' clinical status or other data. The findings on transthoracic echocardiography (TTE) on patients determined to have SPE by CTA were assessed by standardized criteria, and other clinical information was extracted from the patients' charts.

During the study period, which ended in early 2009, 680 patients had the diagnosis of PE established by CTA, and 37 (5.4%) of them met the authors' criteria for SPE. With a median age of 60 years, these patients were predominately women (60%) and African American (84%), and 81% of them were admitted through the emergency department. The most frequent comorbidities were history of stroke (24%), surgery within 3 months (24%), and malignancy (22%). Fifteen of the 37 patients (41%) were admitted to the ICU and one required mechanical ventilation.

The amount of thrombus present by CTA in the patients with SPE, estimated using a 40-point clot burden score, was a median of 31 points, believed to correspond to 79% occlusion. The median radiographic right-to-left ventricle diameter ratio was 1.39 (normal < 0.7), with a median pulmonary artery-to-aorta diameter ratio of 1.0 and a median superior vena cava diameter 23 mm. TTE was performed in 27 of the 37 patients with SPE (73%); 21 (78%) had right ventricular enlargement, which was severe in seven patients, moderate in eight, and mild in six. Right ventricular dysfunction by TTE was noted in 21 patients (78% — severe in five, moderate in eight, and mild in seven), and 18 (67%) had elevated pulmonary arterial systolic pressure (not defined). Interventricular septum flattening and/or leftward deviation was found in seven patients (26%).

Transient hypotension occurred in six patients (16%) and persistent shock (systolic blood pressure 90 mmHg or less after intravenous administration of at least 500 mL of crystalloid) was present in three (8%). Most of the patients (87%) were treated with unfractionated heparin, and only four (11%) received thrombolytics. One heparin-treated patient had a gastrointestinal bleed; two who were given thrombolytics had major and a third had a minor hemorrhagic complication. Seventeen patients (46%) received inferior vena cava filters. Two patients died, one in the emergency department, presumably of PE, and one 2 weeks after admission with multiple-organ failure.

Commentary

This study's authors asked the following research question: "What are the demographics, laboratory findings, TTE results, CTA findings, treatment, and outcomes of patients with SPE in our institution?" This is the type of question that can be addressed pretty well in a retrospective study, as long as relevant data are available on a high proportion of all patients with the variable of interest (SPE in this case). A more important (though unstated) research question would be, "What are the clinical implications of the radiographic finding of SPE among patients with CTA-confirmed PE?" Unfortunately, the present study cannot help us with this second question, which would require comparing the information in the paper with the same data from an appropriately-selected control group — in this instance, a sample of the 94.6% of all patients with PE who did not have SPE. As it is, while the description of this consecutive case series adds to the literature on SPE, the applicability of the findings beyond the authors' institution is uncertain, and the most important questions about what the clinician should do when the radiologist reports the finding of SPE remain unanswered.

One thing this study brings out, though, is the distinction between SPE and massive pulmonary embolism (MPE). MPE is a clinical syndrome with high mortality defined by the degree of hemodynamic compromise present in a patient with acute PE — essentially, cardiogenic shock or persistent hypotension, further specified as a systolic blood pressure persistently < 90 mmHg, or a drop in baseline blood pressure of at least 40 mmHg for > 15 minutes.1 SPE is very common among patients with MPE, but the reverse is not necessarily the case, as the data of Sardi et al illustrate. CTA has become the gold standard for diagnosing PE, and is performed far more often today than in past decades. Today, clinicians are increasingly likely to hear the words "massive pulmonary embolism" from a radiologist, meaning that the clot burden visualized on the exam is extensive, and it is important to realize that this term can be used in more than one way. Additional studies are needed to determine whether the finding of SPE by itself constitutes an important prognostic factor, or whether it should be taken into consideration separately from other clinical information in deciding how the patient with acute PE should be managed.

Reference

1. Kucher N, Goldhaber SZ. Management of massive pulmonary embolism. Circulation 2005;112:e28-32.