Case Report
A 53 year old male with a past medical history of high-grade glioma and recent brain surgery presented to ED after a syncopal episode. His head computed tomography (CT) was negative for intracranial hemorrhage or infarct. Simultaneous Chest CT- PE protocol (2 mm slices) noted large saddle pulmonary embolism with significant clot burden (Figure 1a, b). It revealed a “snake like” thrombus in the right atrium suggesting free floating clot with significant right heart (RH) strain (Figure 2a, b). The N-terminal pro-B-type natriuretic peptide (NT-proBNP) was 832 pg/mL (Ref Range: <=300 pg/mL), and Troponin I 0.91 ng/mL (Ref Range: 0.00 - 0.03 ng/mL). Bilateral lower extremities venous Doppler’s reported acute vein thrombosis in the left popliteal vein. The patient was transferred to the intensive care unit (ICU) with a heart rate (HR) of 127 beats/min, systolic blood pressure of 120 mmHg, and peripheral capillary oxygen saturation (SpO2) of 92% on 6 liters of oxygen in a non-rebreather. Full anticoagulation with unfractionated Heparin was started. The use of thrombolysis was precluded given his neurological status. Interventional radiology and cardiothoracic surgery (CTS) were consulted for possible mechanical thrombectomy of pulmonary embolism and clot in the right atrium (RA).
The patient was sedated and monitored by cardiovascular anesthesia. Additional venous and arterial 6 Fr vascular sheaths were inserted to anticipate any urgent transition to extracorporeal membrane oxygenation (ECMO). Through a right common femoral vein approach, a catheter was advanced into the inferior vena cava (IVC). IVCgram demonstrated clot extending from the IVC into the RA (Figure 3a, b). Given the potential risk of dislodging clot that could increase the PA pressure, the Triever20 catheter (Inari Medical Inc., Irvine, CA, USA) was inserted for mechanical thrombectomy. Suction thrombectomy was performed at the level of the IVC confluence and RA under fluoroscopic guidance. Moderate amount of clot was aspirated (Figure 4) and resolution was confirmed with a follow up cavogram. The main PA was accessed using a 6 Fr, 100 cm Vert catheter. The initial main PA pressure was elevated (46/13 mmHg, mean of 38 mmHg). Pulmonary angiography demonstrated extensive saddle embolism (Figure 5a, b, c). Next, the Triever20 catheter was advanced to the left PA and a large amount of clot was retrieved from the segmental branches with minimal residual thrombus. The self-expanding nitinol disks of the device were not required given the results obtained with aspiration. The same intervention was repeated in the main and right PA with improvement of PA pressures (28/ 9 mmHg, mean 14mmHg) and oxygen demand. The blood loss was approximately 150 cc and there was no change in the hemoglobin monitored throughout and after the procedure.
Follow-up chest CT-PE protocol demonstrated decreased clot burden in the RA and PA without visualization of right heart strain (Figure 6a, b). Subsequent TTE reported no definite RA thrombus. Walking oxygen assessment showed resting Sp02 of 96% and walking Sp02 100% on room air. Four days later after the procedure, the patient was discharged on long term Apixaban.
Discussion
RiHT are classified as type A Thrombi, those serpiginous, highly mobile, and with high mortality. Type B Thrombi are less mobile, pedunculated, broad base, and have better prognosis. And type C is an intermediate in all characteristics. (7). The association of free floating-right heart thrombi and massive pulmonary embolism (PE) has an incidence of 4-18% (1). It is a life-threatening condition that requires emergent diagnosis and treatment with reported fatal outcomes up to 21% in 14 days (8). Thrombi that are adherent to the RA or right ventricle (RV) wall usually have a more benign prognosis (8). However, free-floating, “snake-like” thrombi are uncommon and usually associated with massive unstable pulmonary embolism (9, 10). Some studies have reported the clot in transit as a predictor of poor outcome (11). There are no evidence-based guidelines for treatment of pulmonary embolism complicated by free-floating RH thrombus (12).
In a retrospective analysis of 177 cases of right heart thromboembolism and pulmonary embolism in 98% of the cases, the mortality rate associated with no therapy, anticoagulation therapy, surgical embolectomy, and thrombolysis was 100.0%, 28.6%, 23.8%, and 11.3%, respectively (13). One year later the European Cooperative Study reported a mortality rate of 60% for anticoagulated patients; 40% for those treated with thrombolytics; and 27% for those submitted to surgical procedures, which suggested the surgical approach to be the most effective (8). Although, some small case series of RiHT type A showed thrombolytic therapy with a favorable outcome in relation to mortality (7), some controversy has arisen with systemic thrombolysis in the treatment of giant right atrial thrombosis and clot fragmentation, with subsequent fatal results related to the development of cardiogenic shock (14). Until 2017, there was no studies that clearly determined which patients with PE and RiHT would benefit from reperfusion treatment (15). With this purpose, the Registro Informatizado de la Enfermedad Trombo Embolica (RIETE) Registry compared the outcome during the first month after treatment of standard anticoagulation therapy (heparin) against reperfusion treatment (including thrombolysis or cardiac surgery). The study did not show differences in survival among patients who received standard anticoagulation compared with the reperfusion therapy (15). They concluded that reperfusion therapies might be reserved for patients who have acute symptomatic pulmonary embolism, associated hypotension, or shock irrespective of the presence or absence of coexisting RiHT (15).
Few reports of percutaneous treatment of free-floating thrombus in the right atrium and PE has been published, and their results have been promising. In these cases, several types of catheters were used in which they also included direct AngioVac and IVC filters, or a Cook intravascular retrieval. (16, 17, 18, 19).
FlowTriever System, an FDA approved device for treatment of PE, allows it to be maneuvered into the pulmonary segmental branches and to aspirate central and more distal pulmonary clot. It permits the use of contrast injections through a coaxial system which enables us to monitor the progress of the intervention. In the multicenter single-arm FLARE (FlowTriever Pulmonary Embolectomy Clinical Study), presented in 2018 on 106 patients with intermediate-risk PE who underwent catheter embolectomy using the FlowTriever catheter, they found the system safe and effective. There was a significant improvement in RV/LV ratio and minimal major bleeding. Potential advantages included immediate thrombus removal, absence of thrombolytic complications, and reduced need for post-procedural critical care (20).
This report highlights the effectiveness of FlowTriver for mechanical thrombectomy of RiHT and PE in this case. Limitations described for AngioJet or AngioVac as dysrhythmias, or difficult maneuverability were not found (6). Additionally, its use showed a rapid normalization of PA pressure and Sp02. This method allowed removal of the clot in a high risk patient who exhibited contraindications to thrombolysis.  Indigo CAT (Penumbra) device has been evolving to larger diameters which can be manipulated at a more segmental level and it is a very useful alternative for pulmonary embolism however, the use on Right, has not been reported.