PMT devices are designed to achieve rapid clearance of occlusions in large arteries, veins and bypass grafts. In massive PE the rationale behind PMT is the rapid relief of central pulmonary obstruction. PMT devices form a heterogeneous group and vary in terms of mechanism of action, efficacy, safety, and costs. Essentially, however, there are currently three available catheter thrombectomy techniques: aspiration thrombectomy, fragmentation thrombectomy, and rheolytic thrombectomy. A detailed description of each technique along with their corresponding catheters is beyond the scope of this case study and has already been clearly documented in the literature. Our choice of PMT device in this particular scenario owed mainly to a specific recollection of its application in massive PE from the literature as opposed to any previous experience using it.
The AngioJet rheolytic thrombectomy catheter removes thrombus by use of the Bernoulli principle. It has a double-lumen shaft; one lumen for high-pressure saline delivery which loops back re-directing flow through a gap into the effluent lumen. This creates a localised low pressure area which aspirates thrombus for fragmentation into small particles. The fragmented debris then pass into a collection bag. There are disadvantages to the AngioJet system that include a significant risk of fluid overload, haemolysis, bradyarrhythmias, and the actual cost of the pump-drive set.
Rheolytic thrombectomy to treat massive PE was first described by Koning et al in 1997. Despite their success the use of PMT for massive PE in clinical practice has not become widespread in the United Kingdom. This, in part, can be attributed to a lack of expertise in this area and also a lack of awareness as to the availability of this treatment modality. The former statement can be misleading, however, since this was the first time our team had attempted this procedure. In addition cases of massive PE are rare and so it is difficult to ascertain what is best practice in terms of local protocols.
The alternative to PMT is surgical embolectomy. This, however, carries with it a high mortality and can be associated with complications such as acute respiratory distress syndrome, acute renal failure, mediastinitis and severe neurological sequelae. An experienced cardiac surgical team is required and careful patient selection is necessary for mortality and morbidity benefits to be borne out.
Despite a lack of good quality randomised trials pointing to mortality benefit thrombolysis remains the mainstay of treatment for severe PE; either administered intravenously or via catheter-directed means. When this is contraindicated pulmonary catheterisation or surgical embolectomy should be considered. This recommendation remains anecdotal, however, since no trial evidence for PMT exists and no randomised trial of medical versus surgical therapy has ever taken place.[9, 10] Hence the decision to go with either alternative to thrombolysis has to be made on a case-by-case basis and will depend on local availability and expertise.
We have demonstrated that PMT via a rheolytic thrombectomy catheter can be relatively straightforward in the hands of a clinician experienced in endovascular procedures. It can be a safe and effective means of clearing significant thrombus burden from the pulmonary arterial tree and can be considered a possible alternative to pulmonary embolectomy when thrombolysis is relatively or absolutely contraindicated. PMT can also be used as an adjuvant therapy prior to thrombolysis since fragmentation of the thrombus increases surface area making thrombolytic infusion more successful. In the future further evaluation involving a larger cohort of subjects is necessary to determine whether this treatment is superior to surgical embolectomy when thrombolysis cannot be performed.