**3.4.6 Clinical results**

Of the 49 total patients in this series, 27 patients were male, and 22 female. The average age of the male patients was 53 years with a range between 27 and 88 years, and the average age of the female patients was 51 years, with a range between 19 and 82 years. Twelve of the procedures were performed in a totally percutaneous manner, while thirty-seven procedures were performed via surgical exposure of the femoral veins. Success of an extraction procedure is defined as removal of occluding material, fluoroscopic or echocardiographic evidence of venous patency, and stabilization of patient hemodynamic parameters. Forty of the forty-nine procedures resulted in removal of intravascular material for an 80% overall success rate. In 9 cases, minimal or no material was removed. In one case, spontaneous fragmentation and distal embolization of the thrombus occurred prior to initiation of the suction embolectomy procedure. One perioperative death occurred in a hemodialysis patient with a right atrial mass and an inferior vena cava occlusion. Hemothorax from a suspected guidewire perforation of the right atrium was noted during the procedure. The patient was brought to the operating room, and surgical exploration found a substantial fibrotic mass encasing the right atrium and inferior vena cava, preventing cannulation for cardiopulmonary bypass. The patient survived the surgery, but succumbed within 48 hours in the intensive care unit. No hemolysis or thrombocytopenia was observed in any of the patients in this study, and the patients' hematocrit values remained stable post procedure.

Application of a Novel Venous Cannula for

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En-Bloc Removal of Undesirable Intravascular Material 141

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### **3.4.7 Discussion**

The propensity for clot to propagate as well as to organize renders treatment of thromboembolic disease difficult. Anticoagulation addresses further propagation of thrombus; however, once a patient presents with a significant mass of clot, vascular recanalization becomes a formidable task. Complete occlusions in major or great venous vessels tend to be unresponsive to thrombolytic therapy, as circulating thrombolytic agents are unable to access the inner mass of a substantial body of clot that typifies massive pulmonary embolism or total vena cava occlusion. Thrombolytic dissolution occurs at the periphery of the occlusion, proceeding progressively inwards with time. Hemodynamic instability may curtail the opportunity window for therapeutic intervention, and immediate bulk extraction of occlusive material is warranted. Percutaneous interventional devices utilizing mechanical or rheolytic fragmentation of clot increase the rate of thrombolysis. Dissolution is a function of the amount of interaction achieved by the device with the clot. Higher surface contact area between the active components of the device and resident clot yields greater thrombolytic activity. Presently available percutaneous devices are limited by their size relative to clot in the great vessels. The luminal cross-sectional area of a 7F catheter is equal to 3 mm2, which encompasses 0.5% of the surface area of a 30 mm diameter inferior vena cava or pulmonary artery with a luminal cross-sectional area of 615 mm2. This means that a 7F catheter approaching an occluding thrombus in the vena cava contacts only 0.5% of the cross-sectional area of a clot on a single pass. An impractical number of catheter passes would be required to clear a total occlusion in the great vessels.

The large bore of the funnel cannula facilitates material removal from the great vessels. The large conduit size also minimizes the potential for hemolysis during vacuum extraction. Suction therapy is conducted by a centrifugal pump which generates typical flow rates up to 5 liters per minute via the 22 F cannula. At this flow rate and cannula size, laminar flow is maintained in the extracorporeal circuit, providing atraumatic passage for circulating erythrocytes.

### **4. Conclusion**

Removal of undesirable intravascular material using extracorporeal recirculation with a funnel venous drainage cannula seeks to mimic surgical removal of massive emboli, by maximizing physical contact with the leading edge of the occlusion, and conducting en bloc removal of substantial embolic masses. The significant flow rates (on the order of 4 or 5 liters per minute) established in the drainage cannula while extracting major emboli, are matched by simultaneous reinfusion to maintain hemodynamic stability during the embolectomy process. A funnel cannula tip that matches the size of the occluded vessel and a high circulating flow rate are necessary elements to facilitate embolectomy. Bench top tests indicate that backflow must be present to support the level of pump flow rate that generates vacuum sufficient to remove large masses. In some of the procedures that yielded little or no material extraction, it is possible that a lack of backflow was exhibited due to absent or severely limited retrograde collateralization. Guidewire or angiographic catheter passage through the thrombotic substrate may yield partial recanalization that provides the requisite degree of retrograde flow for successful embolic removal. Another cause of unsuccessful extraction may be an advanced degree of fibrotic attachment associated with aged thrombus that is not amenable to vacuum dislodgment. Further clinical experience will delineate additional associated techniques and define best patient selection criteria for optimal application of vacuum extraction with the funnel cannula. The experience to date generates a sense of optimism that suction embolectomy with associated extracorporeal recirculation has potential as a functional therapeutic component in the battle against thromboembolic disease. Continued research into this and other approaches is certainly warranted.
