Updated: Dec 23, 2020
The treatment of pulmonary embolism (PE) continues to evolve. There are a variety of emerging new endovascular therapies that can be employed for submassive or massive PE without the need for lysis with tPA. Interventional Cardiologist Dr. Thomas Tu and Interventional Radiologist Dr. Venkat Tummala discuss risk stratification and examine the role of mechanical thrombectomy in treating pulmonary embolism.
We’ve provided the highlight reel below, but you can listen to the full podcast on BackTable.com.
The BackTable Brief
Early risk stratification is critical in the treatment and management of pulmonary embolism; For patients with sub-massive, or intermediate risk pulmonary embolism, Dr. Tummala and Dr. Tu both agree that risk classification entails positive BNP, elevated troponin, and right ventricular strain without cardiogenic shock.
Most pulmonary embolisms, intermediate or high-risk, are treated with systemic anticoagulation. When there is contraindication to thrombolytic therapy or failure with initial treatment, other interventions include catheter directed therapy (CDT) and surgical embolectomy; Dr. Tummala states that clot location and burden helps him decide when to proceed with mechanical thrombectomy versus CDT.
Mechanical thrombectomy has emerged as a viable treatment option for pulmonary embolism in the paradigm shift toward non-lytic based therapies; Dr. Tu notes mechanical thrombectomy’s potential in decreasing short-term acuity and in managing chronic thromboembolic pulmonary hypertension (CTEPH). Dr. Tummala reports on the effectiveness of mechanical thrombectomy in targeting an organized thrombus.
Image courtesy of Brandon Awalt
Disclaimer: The opinions expressed by participants of the BackTable Podcast belong solely to the participants, and do not necessarily reflect the views of BackTable.
Risk Stratification for Pulmonary Embolism
Dr. Tu and Tummala discuss how they risk stratify patients with pulmonary embolism. Both agree that positive BNP and elevated troponin biomarkers in the setting of right ventricular dysfunction without hemodynamic instability is classified as intermediate-risk, submassive pulmonary embolism. Dr. Tu states that pulmonary embolism risk stratification guidelines are currently based on potential response to systemic thrombolysis, but Dr. Tummala sees a paradigm shift toward thrombectomy as the treatment of choice in intermediate-risk, submassive patients.
I'm curious to see what your personal indications are for treating these patients endovascularly.
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.
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.
Treatment of Pulmonary Embolism: Lytic and Non-Lytic Therapies
While systemic thrombolysis with tPA is the mainstay treatment for pulmonary embolism, it is not always successful. Repeat systemic thrombolysis, catheter-directed thrombolysis, mechanical thrombectomy, and surgical embolectomy are all possible treatment options when initial systemic thrombolysis fails. Although the optimal therapy for submassive, intermediate-risk pulmonary embolism is unknown, both Dr. Tu and Dr. Tummala advocate for mechanical thrombectomy. For Dr. Tu, factors such as how quickly the clot needs to be removed to restore RV function, the effectiveness of lytics, and risk exposure help determine if and when to proceed with non-lytic therapy. Dr. Tummala also adds that he considers clot location when deciding how aggressively to treat with catheter-based therapies.
Let's get into the endovascular treatment options for pulmonary embolism. What do you think is the role for tPA now, either systemically or with a catheter when you've got all of these options available?
I think it's important to take a step back and recognize that over 90% of significant pulmonary embolisms, intermediate or high-risk, are still treated just with anticoagulation and transition to oral therapies. So I think there's a long way to go just in offering advanced therapies to patients who are currently being treated just with anticoagulation. You have the lytic-based therapies, whether that's systemic or catheter-directed and then you have the non-lytic based therapies, which I would say mechanical thrombectomy with FlowTriever is a major component of that as well as surgery. And it really comes down to how quickly you need to remove the clot and restore RV function, how effectively you think lytics are going to work versus mechanical thrombectomy, and then what risk you want to expose the patient to.
Undoubtedly massive PE, we all agree the patient gets a bolus of systemic tPA, weight based, but more and more we are doing thrombectomy for clot reduction in spite of patients on a full-dose of tPA. [In a large vessel occlusion] tPA may or may not effectively decrease the clot burden. So we are supplementing that in massive patients with thrombectomy and the results are promising so far. When we move onto the sub-massive population toward what Tom was saying, as well as catheter directed therapy (CDT) versus mechanical thrombectomy, I do favor mechanical thrombectomy with avoiding the risk of intracranial hemorrhage that goes with CDT… On the other hand, the clot location helps me decide in ways which ones I want to be aggressive with thrombectomy versus CDT. The central, the huge clot burden favor mechanical versus something very segmental or subsegmental PE with the right indication to treat, then that might be something I would consider CDT.
Yeah, I would second that completely.
Mechanical Thrombectomy for Pulmonary Embolism: What Lies Ahead
Dr. Tu and Dr. Tummala give their thoughts on the future of endovascular treatment and mechanical thrombectomy’s role in pulmonary embolism therapy. Dr. Tu discusses the implications of mechanical thrombectomy. Aside from reduction in short-term mortality, he highlights the potential role of non-lytic therapies like thrombectomy in decreasing short-term acuity and potential for chronic thromboembolic pulmonary hypertension (CTEPH). Meanwhile, Dr. Tummala comments on the effectiveness of mechanical thrombectomy in targeting an organized thrombus and emphasizes positive patient feedback with the procedure.
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.
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.
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.
Dr. Venkat Tummala is a practicing interventional radiologist with Lakeland Vascular Institute in Florida.
Dr. Thomas Tu is an interventional cardiologist and chief medical officer of Inari Medical. Until recently, Dr. Tu was the director of the cardiac cath lab at Louisville Cardiology in Kentucky.
Host Dr. Michael Barraza is a practicing interventional radiologist with Radiology Alliance in Nashville.
Cite this Podcast:
BackTable, LLC (Producer). (2020, March 11). Ep 58 – Endovascular Treatment of Pulmonary Embolism [Audio podcast]. Retrieved from https://www.backtable.com/podcasts
The Materials available on the BackTable Blog are for informational and educational purposes only and are not a substitute for the professional judgment of a healthcare professional in diagnosing and treating patients. The opinions expressed by participants of the BackTable Podcast belong solely to the participants, and do not necessarily reflect the views of BackTable.
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