What is the optimal anticoagulation strategy for a patient with a mechanical aortic valve who needs to undergo a bone marrow biopsy?
In thinking about bridging anticoagulation, I always start with this table to help me figure out who even needs it. My patient falls into the moderate risk category, and while there's not a clear right answer, I generally do err on the side of bridging these patients. Both unfractionated and low molecular weight heparin (LMWH) are viable options, and practically we know that one is much easier to administer than the other. I was curious to see if we had any good evidence to guide which one we should choose, and I found two articles that might help us answer this question.
The first AJC paper observationally looked at unfractionated heparin versus LMWH bridging in patients with mechanical heart valves and found no difference in terms of major adverse events nor major bleeds. The LMWH group did have more bileaflet valves, and I wonder if this could be a confounding issue in terms of this group having presumably newer valves/lower thrombosis risk. The LMWH group was also less likely to undergo major surgery - it's hard to say if that means anything in terms of patient acuity, as the baseline characteristics between the two groups were similar. Unsurprisingly, LMWH patients had shorter hospital stays. Here is the complete table of outcomes:
Table 3. Adverse events within 30 days of procedures
Basically, no evidence that LMWH was worse. I like that this group overall seemed reflective of true clinical practice - about half had a mechanical mitral valve, almost half had atrial fibrillation, and roughly a quarter were also on some anti-platelet therapy. The authors point out that unfractionated heparin may have been the anticoagulant of choice for higher bleeding risk procedures (given its reversibility), always a consideration.
The other AJC paper retrospectively looked at patients with mechanical heart valves who had been bridged with enoxaparin and compared them to patients with atrial fibrillation who had been bridged with enoxaparin. They make the point that patients in the mechanical heart valve group were at high risk for thromboembolism, while patients in the afib group were mostly at low to moderate risk for thromboembolism, but that they [both groups] had similar rates of embolic events (namely zero) as well as similar rates of bleeding:
Figure 3.
The second study is much more limited: retrospective, heterogenous, and frankly it doesn't address the question of enoxaparin versus unfractionated heparin. Plus, the fact that the thromboembolic rate was zero raises some questions in my mind about the acuity of this patient group, even accounting for the small sample size. That said, it is some more data that suggests that enoxaparin is a safe alternative for bridging anticoagulation.
I'd like to see more studies, but I suspect that we will not. Reviewing these two papers makes me conclude that enoxaparin is indeed a reasonable alternative, especially considering the benefit of saving a patient from a prolonged hospital stay. I'd perhaps be more cautious if the surgery bleeding risk was particularly high, but in this case, for a bone marrow biopsy, I believe enoxaparin is fine.
Bridging Anticoagulation. Circulation. 2012;125(12). doi:https://doi.org/10.1161/circulationaha.111.084517
Bui HT, Krisnaswami A, Le CU, Chan J, Shenoy BN. Comparison of Safety of Subcutaneous Enoxaparin as Outpatient Anticoagulation Bridging Therapy in Patients With a Mechanical Heart Valve Versus Patients With Nonvalvular Atrial Fibrillation. The American Journal of Cardiology. 2009;104(10):1429-1433. doi:https://doi.org/10.1016/j.amjcard.2009.06.065
Spyropoulos AC, Turpie AGG, Dunn AS, et al. Perioperative Bridging Therapy With Unfractionated Heparin or Low-Molecular-Weight Heparin in Patients With Mechanical Prosthetic Heart Valves on Long-Term Oral Anticoagulants (from the REGIMEN Registry). The American Journal of Cardiology. 2008;102(7):883-889. doi:https://doi.org/10.1016/j.amjcard.2008.05.042
