Pulmonary Embolism Treatment and the Use of Mechanical Thrombectomy

[Michael Barraza]
I'm curious to see what your personal indications are for treating these patients endovascularly.

[Thomas Tu]
I think most of the listeners are familiar with the standard risk stratification for pulmonary embolism, sorting out patients between massive, intermediate risk or sub-massive, and then low-risk patients. A lot of that has to do with presence or absence of RV strain as well as biomarker positivity and then presence or absence of cardiogenic shock. I think that that framework is commonly used and I think it's useful in identifying very grossly who's at short-term risk of mortality from PE. [The lines drawn by risk stratification are] based on systemic thrombolysis, which is, up until recently, the only approved therapy for pulmonary embolism. I think as we get safer and safer therapies, more effective therapies, we're going to see the risk stratification change according to a newer and safer way of doing things.

[Venkat Tummala]
The RV/LV ratio and the location of the clot [helps guide the clinical picture]. If massive, it's emergent, and we take the patient straightaway to the lab. If it's sub-massive, I'm with Tom. The literature is all over the place, but we do want to risk stratify it based on troponins and biomarkers, BNP. If they are positive and CT has a significant right heart strain, then we are more likely to intervene and whether it's going to be thrombolysis or thrombectomy, the more we are doing thrombectomy. We are seeing the results on the table with a significant drop in physiological pressures and clot reduction. The paradigm shift is happening, if it's not already, towards thrombectomy in this subset of patients.

[Thomas Tu]
Predominantly the goal for pulmonary embolism therapy has been a reduction in short-term mortality, so we've been trying to identify who's at high risk of dying and can we intervene in that subgroup? As we learn more about PE, we're having additional considerations that we have to account for. For instance, there is the acuity of PE. Someone who may not have a high chance of dying but may end up in the ICU for several days, may end up taking weeks to recover. If we can reduce that person's short-term acuity by allowing them to de-escalate, allow them to be discharged from the hospital faster, recover faster, that could also be a goal for therapy…And then there's also the long-term considerations of somebody who has a large clot burden. We know that all doesn't lyse completely either with endogenous fibrinolysis or exogenous therapies. What happens to that clot over time is that it becomes collagen laden. It transforms to elastin. It develops its own blood supply. It starts secreting hormones. And the way the body deals with chronic thrombus is to incorporate it into the wall of the pulmonary artery as opposed to this hope that it just lyses completely. And if that's a process that leads to CTEPH or some smaller form of that like CTED, I think hopefully we can reduce that incidence as well with more aggressive therapy.

[Venkat Tummala]
Right on, Tom. In my experience the majority of clots that are retrieved look like an organized thrombus. And it amazes me. We know that with clots that are predominantly organized, tPA may not work, but when a patient presents to the ER with an acute PE, the DVT that probably provoked the PE is probably an organized thrombus more often than not. And the more we are doing this and the more clot we retrieve and evaluate, it's shocking to see those long threads of organized thrombus. And I started believing in the efficacy of the treatment once direct feedback from the patients on the table sometimes. "I can breathe a whole lot better. I haven't breathed like this in 20 years." Those sort of things and supporting evidence with arterial pressures and subsequent follow-up echocardiogram to see resolution of right heart strain—this seems very promising.

[Thomas Tu]
If you look at the evolution of treatment for myocardial infarction and stroke where there was an initial interest in lytics and then that kind of faded once we had more effective non-lytic based catheter therapies, I think you'll see PE move in that same direction.