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Graft Resistance Difference after HVAD to HeartMate 3 Left Ventricular Assist Device Exchange
Kevin Bourque1, Matthew J Martin1, Daniel I Harjes1
1Heart Failure Division, Abbott, Burlington, Massachusetts.
Insights
Replacing the HeartWare Ventricular Assist Device (HVAD) with the HeartMate 3 may require higher pump speeds if the old HVAD outflow graft is retained. Complete conversion to the HeartMate 3 graft is preferred for optimal performance.
Area of Science:
- Cardiovascular Engineering
- Medical Device Technology
Background:
- The discontinuation of the HeartWare Ventricular Assist Device (HVAD) necessitates increased use of the HeartMate 3 for left ventricular assist device replacements.
- Retaining parts of the HVAD's 10-mm outflow graft during HeartMate 3 implantation may require higher device operating speeds compared to using the standard 14-mm HeartMate 3 graft.
Purpose of the Study:
- To evaluate the hemodynamic impact of using a remnant HVAD outflow graft with the HeartMate 3 left ventricular assist device.
- To determine the effects of partial HVAD graft retention on HeartMate 3 performance parameters, including rotor speed and power consumption.
Main Methods:
- An in vitro study was conducted using steady-state flow conditions.
- Samples included HeartWare Ventricular Assist Device (HVAD), HeartMate 3, and hybrid HVAD/HeartMate 3 grafts of varying lengths (125-375 mm).
- Flow rates from 3.0 to 6.0 L/min were applied to simulate clinical scenarios.
Main Results:
- At clinically relevant flow rates (4.3 and 6.0 L/min), HeartMate 3 rotor speeds increased from 5350 to 5700 rpm and 6350 to 6900 rpm, respectively, when using the full HVAD graft compared to the HeartMate 3 graft.
- Corresponding power consumption increased by 16% (3.7 to 4.3 W) and 24% (5.5 to 6.8 W) at these flow rates.
Conclusions:
- While no severe immediate consequences were identified, using a remnant HVAD graft necessitates higher HeartMate 3 rotor speeds.
- This can lead to reduced patient battery runtime and increased power consumption.
- Complete replacement with the HeartMate 3 graft is the preferred approach from an engineering perspective for optimal device function and patient benefit.
Background:
A likely consequence of the discontinued distribution and sale of the HVAD System (Medtronic, Minneapolis, MN) will be an increase in replacement with the HeartMate 3 (Abbott, Chicago, IL) left ventricular assist device when device exchange is necessary. If part or all of the HVAD 10-mm-diameter outflow graft is retained during replacement, the HeartMate 3 will have to run at a higher speed than it would with its 14-mm-diameter graft.
Methods:
A steady-state, in vitro study was run with 250-mm-long samples of HVAD, HeartMate 3, and half-HVAD/half-HeartMate 3 grafts and additionally 125- and 375-mm-long samples of the HVAD graft. Flows of 3.0, 3.9, 4.3, 4.7, and 6.0 L/min were applied to encompass expected clinical conditions.
Results:
At typical and high flow rates of 4.3 and 6.0 L/min, HeartMate 3 rotor speeds with the full HVAD graft had to be increased relative to those with the HeartMate 3 graft from 5350 to 5700 and 6350 to 6900 rpm, respectively, with power consumption increases from 3.7 to 4.3 W (16%) and 5.5 to 6.8 W (24%), respectively.
Conclusions:
The study did not elucidate a severe consequence of using a remnant HVAD graft during pump exchange, but the incremental risks of a higher rotor speed, disadvantage to the patient in battery runtime, and the general benefit of complete conversion to the HeartMate 3 graft should be balanced against other procedural considerations. Complete graft replacement during HVAD-to-HeartMate 3 conversion remains the preferred approach from an engineering point of view.
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