Pulmonary embolism (PE) is the third most common cause of cardiovascular death in the United States of America. It is one of the most common causes of death worldwide. Most patients die within the first few hours of presentation, making an early diagnosis and treatment paramount to survival. Pulmonary embolism is categorized as small (low risk), sub-massive (intermediate risk) and massive (high risk). Catheter-directed thrombolysis (CDT) is one of the newest treatment options for pulmonary embolism. The SEATLE II study was a prospective multicenter study which revealed that ultrasound-guided catheter-directed, low-dose thrombolysis decreased right ventricular dilation, lessened pulmonary hypertension, reduced clot burden, and minimized intracranial bleeding in acute massive and submassive PE. This chapter will review the anatomy involved with pulmonary embolism, indications for CDT, contraindications for CDT, procedural technique, possible complications, and the clinical significance of CDT for PE.
Pulmonary embolism usually arises from deep veins of the lower extremities and/or pelvis. Dislodgement of the DVT or parts of the DVT can result in the blood clot traveling up the venous system through the right heart and lodging in the pulmonary vasculature. The pulmonary trunk, main pulmonary artery, segmental or sub-segmental branches are all common locations for a pulmonary embolus to lodge. Once lodged in the pulmonary vasculature depending on the size and location of the PE, this can cause heart strain and decreased oxygenation. The most serious consequence of pulmonary embolus is when the clot blocks the right and left pulmonary artery, blocking the right heart outflow tract. This is called a saddle embolus. Saddle embolus usually results in death, but in the event of survival immediate medical therapy should be administered to reduce adverse events. CDT was developed to provide direct thrombolytic therapy to the site of the pulmonary embolus.
Currently CDT for the management of PE is only suggested for massive PE as a class IIa and level B recommendation according to the ACC/AHA. While the use of systemic thrombolytic therapy in patients with submassive PE is not recommended by the guidelines, cardiopulmonary collapse or the development of critical hypotension is the only case exemption. CDT has a considerable advantage over systemic thrombolytic therapy due to the lower the risk of bleeding. Some centers divide the category of submassive PE into intermediate high risk and intermediate low risk. At these facilities, those patients who fall into the intermediate high risk are considered for CDT. Those patients determined to be in the intermediate low risk are not considered for thrombolytic therapy. All patients considered for thrombolytic therapy should have a low bleeding risk.
Though thrombolysis is administered locally during CDT for PE, the thrombolysis disperses systemically. Systemic dispersion of thrombolytic therapy is the cause for many of the severe complications of CDT. Therefore, contraindications to CDT are a prior ischemic stroke, cerebral bleed, cerebral mass, vascular deformation, recent ulcer in the gastrointestinal tract, recent brain/spine surgery, major abdominal or pelvic surgery, or any source of active hemorrhage. Those with contraindications to CDT therapy are usually contraindicated for systemic thrombolytic. These patient are treated with anticoagulant therapy, antiplatelet therapy, or supportive care.
The equipment required for catheter-directed thrombolysis for pulmonary embolism includes an introducer needle or sheath, multiple-sized guide-wires, CDT catheter, ultrasonic core, thrombolysis therapy, and a closure compression device.
The new guidelines recommend a pulmonary embolism response team (PERT) approach. This is an interprofessional team that is alerted in the event of submassive or massive pulmonary embolism diagnosis. The team members job is to determine the best course of action to treat critically ill patients with massive PE. The PERF team usually consists of a pulmonologist and cardiologist. Other healthcare professionals who may be on the team include a cardiac nurse, pulmonary nurse, cardiac pharmacist, and pulmonary pharmacist. To perform CDT, a trained professional familiar with the chosen catheter system to perform the CDT procedure must be present.
Before initiation of the procedure, the practitioner should inspect the thrombolysis catheter delivery system thoroughly to ensure all pieces are present. They may administer intravenous antibiotics before the procedure to prevent infection. This procedure requires a fully operating catheterization laboratory. Healthcare professionals should use proper sterile techniques including sterile drapes, gloves, and gowns.
CDT procedure begins by obtaining vascular access. Insertion of the introducer needle into the desired venous system is the first step. Then one threads a guide-wire through the needle and up through the right heart into the pulmonary system close to the thrombus. Using fluoroscopic guidance, the infusion catheter is passed over the guide-wire and across the treatment site. Note that radiopaque marker bands can be found at each end of the catheter to enhance catheter placement. Once positioned correctly, remove the guide-wire. Gently insert the ultrasonic core into the catheter until the fittings lock into place. Thrombolysis can now be administered. The thrombolysis exits the catheter through side holes while saline exits through the distal tip. Activating the ultrasonic waves enhances the dispersion of the thrombolysis medication. When the therapy is complete, remove the ultrasonic core and replace the guide-wire inside the catheter. Next, remove the catheter leaving the guide-wire in place. Finally, remove the guide-wire and apply a compression device to the access site.
There are several possible complications from CDT for pulmonary embolus. One of the most common and most feared complications being hemorrhagic stroke which can be debilitating. Other common complications include vascular access related injury, pulmonary hemorrhage, retroperitoneal hemorrhage, cardiogenic shock, perforation or dissection of the pulmonary artery, arrhythmias, right-sided valvular regurgitation, pericardial tamponade, and contrast-induced nephropathy.
Catheter-directed thrombolysis (CDT) is an alternative revascularization procedure to systemic thrombolysis and surgical embolectomy for PE. It is associated with some risks, but overall it reduces the systemic risk of thrombolytic therapy in patients with severe submassive or massive PE. The use of this therapy is on the rise in the United States as more healthcare professionals are becoming trained in the art of CDT. Overall, it saves lives and reduces the burden of pulmonary embolism (PE).
Catheter-directed thrombolysis is a minor procedure but just like all procedures it can have devastating complications if not done correctly. The current guidelines recommend all hospitals treating PEs to setup a pulmonary embolism response team (PERT). The PERT team is a multidisciplinary team made up of cardiologist and pulmonologist specialized. They work together to treat PE and to determine the best treatment plan and achieve the best outcomes. Once CDT is chosen as a management course, the practitioners should counsel the patient regarding the risk and benefits of the procedure. A trained physician knowledgeable in the risk and benefits should have this discussion. The patient should give consent. An anesthesiologist should evaluate the patient to determine the need, mode, and safety of anesthetic delivery. An imaging specialist or structuralist may consult for further recommendations on the size and burden of pulmonary embolism. It is a level I recommendation to utilize this multidisciplinary approach. Studies have shown the PERF team can reduce adverse events. A swift and early diagnosis followed by early treatment is the key to successful thrombolysis of pulmonary embolism.