ULTRAsound-assisted Catheter vs. STAndaRd Catheter Thrombolysis for Submassive Pulmonary Embolism

Acute pulmonary embolism (PE) carries a high morbidity and is the third-leading cause of cardiovascular mortality in the western world. It accounts for 5-10% of in-hospital deaths that for the United States translates to 200,000 deaths per year. Recent registries and cohort studies suggest that approximately 10% of all patients with acute PE die during the first 1 to 3 months after diagnosis. Studies that have observed survivors for >3 months have reported an incidence of chronic thromboembolic pulmonary hypertension (CTEPH) 1-5% within 2-3 years after PE. CTEPH is an incapacitating long-term complication of thromboembolic disease with a negative impact on the patient's quality of life and prognosis.

The management acute PE is mainly guided by the acuity and severity of clinical presentation. Initial systemic anticoagulation (AC) is the standard of care and treatment is escalated based on the clinical presentation and patient characteristics that may stratify them at a higher mortality risk. The goals of therapy are to primarily prevent mortality, and secondarily potentially prevent late onset chronic thromboembolic pulmonary hypertension (CTEPH) and improve quality of life.

Massive PE is defined as PE associated with sustained hemodynamic instability, whereas submassive PE (sPE) is defined as PE without hemodynamic instability but with abnormal right ventricular (RV) function and/or evidence of myocardial necrosis. It is notable that there is ongoing interest to accurately risk stratify sPE to identify the patients who are at increased risk of decompensating and/or dying. Clinical scores, imaging tests and biomarkers are under investigation, yet an ideal prognostic tool is still pending. A novel cardiac biomarker, heart-type fatty acid-binding protein (h-FABP), is emerging as a significant predictor of mortality in patients with submassive PE.

Systemic intravenous thrombolysis is universally recommended by all guideline bodies for massive pulmonary embolism, but remains controversial for submassive PE. In the most recent metaanalysis, the subgroup analysis of 8 submassive PE trials (1993-2014, n=1775) showed that thrombolytic therapy was associated with a mortality reduction (1.39% vs 2.92%) but with an increase in major bleeding (7.74% vs 2.25%).11 These results were mainly driven by the largest randomized trial (PEITHO, 1006 patients) which compared a single, weight-adapted i.v. bolus of tenecteplase with standard anticoagulation.

The recent development of catheter-directed therapies such as catheter-directed thrombolysis (CDT), ultrasound-accelerated thrombolysis (USAT), and pharmacomechanical or aspiration thrombectomy has introduced more tools for the treatment of acute PE. Proponents of these techniques suggest that they may provide a similar therapeutic benefit as systemic thrombolysis, while decreasing the dose of thrombolytic required and potentially decreasing the risk of adverse bleeding events. Both the American Heart Association and more recently European Society of Cardiology have acknowledged CDT as a viable treatment alternative for high risk acute sPE (echocardiographic RV dysfunction and elevated cardiac biomarkers), if appropriate expertise is available and particularly when the bleeding risk is high.