On-X Proact - Plavix and Aspirin Response

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Well-known member
Jun 26, 2011
Atlanta, GA
On-X posted this last week, authored by the PROACT Lead Investigator (John Puskas - Emory) among others. The numbers are pretty astonishing:

Dennis Nichols MD of Tacoma, Washington, USA will present, “Prevalence of Risk Factors and Low Response to Antiplatelet Medications in the Prospective Randomized On-X Anticoagulation Clinical Trial (PROACT)” at the Society for Heart Valve Disease 7th Biennial Congress in Venice, Italy, June 22-25, 2013

*The occurrence of risk factors for thromboembolism and antiplatelet response in valve patients has not been reported prior to now.
*The PROACT trial examines these risk factors and antiplatelet response in patients to screen them for participation in the Low Risk Treatment Group of patients—those taking aspirin and clopidogrel (Plavix).
*The nonresponse rate of patients for the Low Risk Treatment Group for clopidogrel was 47.1% and for aspirin was 80.4%.
*Therefore, enrollment in the High Risk Patient Treatment Group of the PROACT trial was rapidly completed.

The PROACT trial is innovative and unique for producing the never before seen data related to valve implant. Countless valve studies have reviewed simple clinical or hemodynamic results but have not examined these important data points.


An excerpt from the link:

Results – The study enrolled 425 high risk patients of which 375 were randomized to either test (185 at INR target of 1.5-2.0) or control (190 at INR target of 2.0-3.0). Atrial fibrillation was uncommon (4.5% – 19). The most common clinical factor was history of vascular pathology (14.1% – 60) which is similar to the occurrence of LDL (18.5% – 44/237) and indicative of the prevalence of obesity in NA. Reduced antithrombin III activity was the most common hypercoagulability factor (22.5% – 55/244). The degree to which there was a poor response to antiplatelet medication, clopidogrel (47.1% – 106/225) and aspirin (80.4% – 164/204), was astonishing.

Conclusion – The number of patients randomized to the high risk AVR arm of the trial because of poor antiplatelet therapy response alone was surprising. Antiplatelet drug response is important to consider for safe alternate drug therapy in a mechanical valve patient population because of the prevalence of poor responders.

So, IF these numbers are really true, only a pretty small percentage of patients are actually even eligible to be classified as Low Risk, meaning the Plavix/Aspirin protocol (study results still several years down the road) would not even be an option for most, even if it did happen to be proven effective and one day get FDA approval. Now, I intentionally said "IF"...I'm actually wondering a little about these percentages quoted. The PROACT data presented a year or two earlier seemed to indicate inadequate response percentages that were only about half as much (25% Plavix and 39% Aspirin): http://my.americanheart.org/idc/groups/ahamah-public/@wcm/@sop/@scon/documents/downloadable/ucm_425310.pdf. It appears to be two different denominators, not sure, but obviously one would expect the Lead Investigator to have the numbers right.