Conventionally pulmonary embolism is classified as massive, sub massive based on
- Severity of obstruction
- Level of obstruction in pulmonary anatomy (MPA,Branch PA, Segmental etc )
- Thrombus burden
- Quantum of pulmonary vascular bed compromised
But it is always intriguing , the clinical outcome was not linearly correlating with the above parameters.
Instead the outcome seemed more dependent on the following .
- Degree of RV dilatation
- Systemic hypo-tension
- RV shock
So , whatever be the quantum of pulmonary embolism , it is the behavior of RV that is going to determine the outcome. The current wisdom demands , all hemo-dyanmically unstable pulmonary embolsim may be considered as massive or high risk pulmonary embolism and aggressive treatment is to be undertaken.
There is one major diagnostic issue if we depend more on hemo-dynamic instability . What is that ?
There is no valid method to identify Acuteness / chronicity of RA, RV dilatation . Consider this example , a patient with chronic thrombo -embolic PAH presents with acute deterioration due to a transient arrhythmia or non cardiac cause of hypotension . He is at risk of being labeled as acute pulmonary embolism since he may show some thrombus in his pulmonary circulation in CT scan . However , no great harm is done as long as he receives only heparin.