This was a randomised placebo controlled trial of alteplase (100 mg over 2 hours) with heparin v placebo with heparin in 256 patients with submassive pulmonary embolism (PE) defined as echocardiographically detected PE; pulmonary artery hypertension with confirmation of PE by spiral computed tomography (CT); precapillary pulmonary hypertension with confirmation by CT; or new electrocardiographic signs of right ventricular strain followed by CT. Exclusion criteria included age >80 years, haemodynamic instability, and presentation more than 96 hours after onset of symptoms. In the alteplase group there was less escalation of treatment (p=0.004) and a greater chance of 30 day event free survival (p=0.005). There was no difference in mortality or adverse events between the two groups.

This is the largest trial of thrombolysis in PE ever conducted, and it looks at the controversial group of patients with submassive PE showing significant benefit of alteplase. The absence of haemorrhagic complications was surprising.