VAD's & antiplatelet protocol?

[Toby's mum]

Just curious as to what you find is the typical antiplatelet protocol for ventricular assist devices.

Are your VAD patients getting heparin gtt's or do they get a plavix/ASA type regimen?

Also, what is the min. hemeglobin level for your VAD patient's prior to transfusing.

Thanks,

[augigi, CNS]

darn, i just wrote out the longest answer and the cybergods vanished it! eeeek. here goes again.

regime depends on:

- patient comorbidities (a/fib, any issues leading to hypercoagulability etc)

- device being used

- bleeding status

certain devices are prone to stasis thrombosis ("red clots"). these include external devices (abiomed bvs5000, thoratec pvad, abiomed ab5000 ventricle, berlin heart excor), internal devices such as the novacor, thoratec ivad. the risk is due to potential incomplete ejection and filling of the blood sac which may lead to thrombosis.

certain patients susceptible to stasis thrombosis are those with arrhythmias (esp af) who may have incomplete ejection of their own cardiac chambers, also potentially leading to stasis thrombosis which may be ejected via the pump.

this type of thrombosis risk is mitigated by an anticoagulation regime such as postop heparin iv infusion in the acute phase until bleeding is acceptable (2.5 (usually) for the remainder of the implant duration.

devices which are based on continuous flow (heartmate ii, incor, micromed debakey, jarvik 2000, ventrassist) are more susceptible to “high shear” damage to blood cells (esp platelets). this can lead to platelet/fibrin clots (“white clot”). as such, antiplatelet therapies are key. common regimes are aspirin +/- persantine +/- plavix. these therapies should ideally be guided by tests such as thromboelastography (teg) to judge platelet response, as many people can be resistant to aspirin and/or plavix. some of these devices have bearings which generate heat and can also be a risk for red clots. given that many vad patients also suffer from arrhythmias, these patients usually also are on an anticoagulation regime to target inr >2.5.

the exception is the heartmate i device, which has a pseudointimal layer inside the blood sac which encourages incorporation of tissue so that the blood sees a “native” surface. as such, only antiplatelet therapies are required in general, although many patients also have concomitant arrhythmias and also need coumadin.

most of the vad manufacturers have recommendations for anticoagulation/antiplatelet therapies in their manuals, or on their websites.

sorry for the long answer, this is my day job and i find it fascinating!

language edited per tos

[augigi, CNS]

Re transfusions, it's a delicate balance, as many patients are waiting for transplant and so transfusions should be minimized to prevent increasing antibodies and leading to potential rejection. However, as a general rule, keep the HCT > 30%.

[Toby's mum]

Augigi,

Thank you for taking the time to provide such a thorough/comprehensive response! I really appreciate it, especially since this is all relatively new to me and I want to learn more.

The particular LVAD I was thinking of was the Heartmate II. There was some discussion about whether the pt should have been on the heparin gtt or rather the ASA/plavix protocol. You mentioned both options above with good explanations as to the rationale for either one. It makes a lot of sense and I have a better understanding of the patho underlying the decisions as to which way to go--thanks to you. Regards,

[augigi, CNS]

you're most welcome, i love the area and am glad to share. i have got hundreds of articles about vads if you ever need anything. there is actually a specific article about heartmate ii anticoagulation used in one case which may be helpful: amir et al. (2005). a successful anticoagulation protocol for the first heartmate ii implantation in the united states. tex heart inst j. 32:3 p.399-401.

the protocol they used was:

• 10% low-molecular-weight dextran at 25 ml/hr until chest tube drainage reached
• intravenous heparin to attain a target aptt of 45 to 55 seconds.
  
• aspirin (100 mg) daily and dipyridamole (75 mg) 3 times a day.
  
• warfarin to achieve a target inr of 2.5 to 3.5 (upon removal of chest tubes and no evidence of bleeding).
  
• heparin discontinuation after overlap with warfarin and achievement of the target inr for 2 to 3 consecutive days.

this does seem quite excessive though, but this was the first patient so they may have overcompensated :)

the thought these days is that antiplatelets are definitely most important for continuous flow devices. my company makes one, and we have cetainly seen that you can support patients (without af) for over a year on only antiplatelet therapy (asa and plavix) with no neurological/thombotic adverse events.

what happened to your patient?