A Brief Discussion of Submassive Pulmonary Embolism
The best that can be said for the idea of treating submassive pulmonary embolism (PE) with thrombolytic therapy is that it is unsupported by the available literature, which is very limited.
A submassive PE is one which does not cause hypotension but produces changes on echocardiography, particularly on right heart strain. This is suggestive of increased pulmonary pressure. Massive PE is commonly defined as one that does cause hypotension. Note that these definitions do not necessarily relate to the actual size of a PE or total clot burden. It should also be noted that literature can be found using other definitions. These patients might be at increased risk for worse outcomes than those without such changes on echocardiography (Grifoni 2000).
Recent reviews of this topic (Worster 2007, Ramakrishnan 2008) have concluded that there is no scientific support for thrombolytic therapy in such cases. In fairness, however, it should be noted that there is limited primary research and existing randomized trials are small. While they do not demonstrate a benefit to thrombolytic therapy, neither do they exclude the possibility, as they are probably underpowered to do so.
The testimony under review was given in July of 2005. The witness seems to frequently reference Rosen’s Emergency Medicine: Concepts and Clinical Practice. The 5th edition was published in 2002 and seems highly likely to be the one referred by the witness (a 6th edition was published in 2006). The 5th edition states that patients with submassive PE should be treated with thrombolytic therapy. The reference cited for this statement (Jerjes-Sanchez 1995) does, indeed, seem to show a benefit to streptokinase in submassive PE (this paper defines “massive” PE according to the number of pulmonary segments occluded on V/Q scanning). However, the very small number of patients, (eight) and the clinical differences between the treatment and control groups would cause any critical reader to question the accuracy of the results.
Grifoni, S. et al., Short-term clinical outcome of patients with acute pulmonary embolism, normal blood pressure, and echocardiographic right ventricular dysfunction. Circulation. 2000. 101:2817.
Jerjes-Sanchez, C. et al., Streptokinase and Heparin versus Heparin Alone in Massive Pulmonary Embolism: A Randomized Controlled Trial. Journal of Thrombosis and Thrombolysis. 1995. 2:227.
Ramakrishnan, N., Thrombolysis is not warranted in submassive pulmonary embolism: a systematic review and meta-analysis. Critical Care and Resuscitation Journal. 2008. 9:357.
Worster, A. et al., Thrombolytic Therapy for Submassive Pulmondaye Embolism? Annals of Emergency Medicine. 2007. 50:78.