1) Granted, the first targeted market for most VAD's is bridge to
transplant, hopefully followed by bridge-to-recovery (permanent
implant). This is a logical sequence. I cannot imagine the Heart Saver
would not be used as a bridge-to-transplant first. Anything else would
be foolish and over-confident. It would be like trying to run a marathon
before you could walk. Jarvik tried this with the Jarvik-7. The results
were less than inspiring. Whoever dominates the bridge-to-transplant
market will have a huge advantage in the permanent implant market.
This assumes the device is capable of doing both. Clinical data is
showing that the DeBakey VAD has a high probability of achieving this.
whoever dominates the bridge-to-transplant market will have a huge advantage in the permanent implant market.
I don't necessarily agree. Bridge to transplant may very well be dominated by one device and permanent implant by another. The recipients will probably determine that! In the case of a bridge to transplant, the less intrusive device would probably be the better unit, assuming both perform equally well. Whereas the longterm longevity and reliabilty of the device will dominate the decision for permanent implantation. They very well may be the same unit in the end, but only time will tell.
2) Cell damage and clotting are no more of an issue with the DeBakey
VAD than a pulsatile pump. Cell damage levels for the DeBakey VAD are
lower than some people even believe. Clotting is proving to be less of an
issue with the DeBakey VAD than with pulsatile pumps. It's all in the
design. Blood gets in and out of an axial pump so much faster than a
pulsatile pump. Residence time seems to be an important factor.
Actually the clotting issue is a concern, I have been told. The rotating impeller in the blood stream apparently creates the same problems that any rotating device causes in a liquid solution. Apparently the rotating impeller creates (for ease of explanation and my understanding) the equivalent of a "magnetic field" that attracts a film to the surface of the impeller and clotting is a concern. (Appreciate this is all hear-say, and is based on no fact, but also appreciate there is little information available on the deBakey unit at this point) The other issue that is of major concern is if the impeller stops! Apparently the path of the blood instead of "thru the body" is lessened because the "path of lesser resistance" is thru the stalled impeller. I am told that this is of such concern that the deBakey unit will be modified and fitted with valves (hear-say).
3) As for changing flowrate in response to physical exertion, we're not
talking about taking a bedridden person and turning them into an
Olympic athlete. Adding an additional 5 liters/minute will allow the
patient to do all but the most strenuous tasks. When someone is able to
go from complete lethargy to active walking, traveling, and normal
social activities, it's a huge improvement in their quality of life.
Actually, this is one of the disadvantages of the deBakey unit at the moment, the user has no control over the variance of impeller speed, nor does the bodies demand cause the impeller to change speed. You state it wouldn't take much to produce a variance of impeller speed to "create a pulse"! That is very true, however, you must now "electronically control the device" to mimic the pulsatile rate of the recipients heart. This is to ensure that the heart and deBakey unit stay in "sync" with each other....that the pulse created by the flushing heart, occurs at the sametime as the pulsating deBakey!
4)Organ damage from a continuous flow vs. pulse? Don't know much
about that one. I do know if the patient has a pulse at all, the DeBakey
VAD will follow it and in fact amplify the pulse. Will it do this as
strongly as a pulsatile pump? Certainly not. Now we're talking about
degrees of pulsatility. What's sufficient for long term organ health.
(140/60,120/80, etc...) Keep in mind that the speed of an extremely
lightweight impeller can be changed rapidly. You don't need much of
speed change to make a pulse. It's easily done. Also, it's well known that
after a VAD is implanted, the patient's own heart improves, sometimes
dramatically. This would result in improving pulsatility over the long
term. This is not conjecture, but actual proven fact.
Add in all the features of a tiny, lightweight, low power, reliable pump
and the competitive advantage gets pretty compelling.
The volume of blood that the debakey unit can pump is also not an argument for allowing the patient to exert himself, the volume of blood must be variable based on the bodies needs at the time, the deBakey unit does not, in its present form, allow for this.
All the things you describe, now raise the complexity of the deBakey unit to the level of the Heartsaver, which as originally touted was the saving grace of the deBakey....its simplicity! Couple this with the fact that the deBakey unit, as it exists right now, must have wires leaving the body to an electrical power supply and you really are talking about two totally different devices. To ensure the "variance of fan speed, to ensure its asynchronous function with the heart, to ensure its total body cavity integrity, to ensure it is "not" the path of lesser resistance....you have to build a non-pulsatile Heartsaver...which deBakeys unit is not.
The things you describe can be added to the deBakey unit...but in doing so I then challenge its "description of being "tiny, compact etc. etc....it then becomes a "Heartsaver like" non-pulsatile unit.
Disclaimer
I have not one clue..of what I speak! I have literally no idea how difficult it would be to do the work described, the information I have compiled is thru reading the Ottawa Citizen as opposed to any reputable medical journal. The "shortfalls" I have outlined in the debakey unit are my perception and may be a long way from "reality"! And for God's sake don't invest in either unit based on my ramblings!!
just trying to motivate a discussion!
the Chief
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