The decision to perform medical imaging is based on clinical reasoning, that is, the medical history, symptoms, and findings on physical examination, followed by an assessment of clinical probability. Probability testing
The most commonly used method to predict clinical probability, the Wells score, is a clinical prediction rule, whose use is complicated by multiple versions being available. In 1995, Philip Steven Wells, initially developed a prediction rule (based on a literature search) to predict the likelihood of PE, based on clinical criteria. The prediction rule was revised in 1998 This prediction rule was further revised when simplified during a validation by Wells et al. in 2000. In the 2000 publication, Wells proposed two different scoring systems using cutoffs of 2 or 4 with the same prediction rule. In 2001, Wells published results using the more conservative cutoff of 2 to create three categories. An additional version, the "modified extended version", using the more recent cutoff of 2 but including findings from Wellss initial studies were proposed. Most recently, a further study reverted to Wellss earlier use of a cutoff of 4 points to create only two categories.There are additional prediction rules for PE, such as the Geneva rule.
A Cochrane review found that there is no evidence of a difference between oral DTIs (dabigatran, rivaroxaban, edoxaban, apixaban) and standard anticoagulation in the prevention of recurrent pulmonary embolism.In people with cancer who develop pulmonary embolism, therapy with a course of LMWH is favored over warfarin or other oral anticoagulants. Similarly, pregnant women are treated with low molecular weight heparin until after delivery to avoid the known teratogenic effects of warfarin, especially in the early stages of pregnancy, but it can be used while breastfeeding.Anticoagulation therapy is usually continued for 3–6 months, or "lifelong" if there have been previous DVTs or PEs, or none of the usual transient risk factors is present. In those without a known cause that can be reversed 2 years of treatment may be better than 6 months. For those with small PEs (known as subsegmental PEs) the effects of anticoagulation is unknown as it has not been properly studied as of 2020. Thrombolysis
Massive PE causing hemodynamic instability (shock and/or low blood pressure, defined as a systolic blood pressure <90 mmHg or a pressure drop of 40 mmHg for >15 min if not caused by new-onset arrhythmia, hypovolemia or sepsis) is an indication for thrombolysis, the enzymatic destruction of the clot with medication. In this situation, it is the best available treatment in those without contraindications and is supported by clinical guidelines. It is also recommended in those in cardiac arrest with a known PE. Catheter-directed thrombolysis (CDT) is a new technique found to be relatively safe and effective for massive PEs.