Pulmonary Embolism Support Group
By far the most common form of pulmonary embolism is a thromboembolism, which occurs when a blood clot, generally a venous thrombus, becomes dislodged from its site of formation and embolizes to the arterial blood supply of one of the lungs. Symptoms may include difficulty breathing, pain during breathing, and more rarely circulatory instability and death.
"Because tPA is such a strong treatment, it can only be used under certain circumstances. For example, a patient must not have any existing bleeding disorders since a side effect of tPA is a much greater risk of excessive bleeding than with either heparin or warfarin. In addition, a definite diagnosis of DVT must be made by a venography before tPA treatment will be considered, and the DVT must usually have been present for less than three days. The limitations of tPA treatment make thrombolytic medications less favorable than heparin or warfarin, so tPA is usually only used as a DVT treatment in specific circumstances"
It's main purpose is for those suffering a stroke or heart attack and must be administered within a few hours after symptoms begin (see - http://www.americanheart.org/presenter.jhtml?identifier=4751).
Hopes this sheds some light.
Regards,
Tom