Local Pump Thrombus Lysis: First In vitro Results with the VAD Maintenance System

Objectives: Ventricular assist devices (VAD) are an established therapy for end stage heart failure patients. Although, pump thrombosis is a major complication in VAD patients, conventionally treated with systemic lysis therapy. If unsuccessful, a surgical pump exchange is the last option. To improve lysis therapy and prevent pump exchange procedures, ReliantHeart, Inc. is developing a new catheter-based tool (VAD maintenance system, VMS), which separates the VAD´s inner rotor area from the patient´s circulation and allows for directed local lysis, flushing through the inner lumen of the balloon catheters. We conducted an in vitro study to evaluate handling of the VMS as well as lysis behavior, and to assess clinically relevant issue.

Methods: We developed an in vitro set up including a mock circulation with catheter insertion ports, artificial thrombus (colored gelatin, 1:10), and corresponding lysis (water, 90–100°C). Handling pretests were conducted to find detailed sequences for catheter positioning and blocking. For lysis testing thrombus was placed on HVAD rotor blade in typical position (10 µl) and in outflow channel (⅛, ¼, ½ obstruction). Measurements were conducted without and with thrombus. Test procedure included 5 phases: unblocked pump, balloon-placement/blocking, lysis, unblocking, unblocked pump. Pressure, real flow, calculated flow, and power consumption were recorded.

Results: In pretests a detailed blocking/unblocking sequence could be developed for successful and safe balloon placement and blocking/unblocking procedure. Unsuccessful blocking/unblocking may result for example in unwanted downstream carried balloons. In lysis tests, pump could be completely separated from circulation with successful balloon placement/blocking in any measurement. No lysis fluid entered the circulation. Lysis was successful in each case within several minutes (visual control). Lysis success could not be predicted with pump parameters.

Conclusion: The VMS is a promising tool for local pump thrombus lysis improving patient treatment. Currently ongoing studies are including lysis success evaluation methods (e.g., acoustics) and a real thrombus/lysis model to develop a clinically relevant lysis protocol.

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