Platelet dysfunction in outpatients with left ventricular assist devices.
BACKGROUND
Thromboembolic and bleeding complications in outpatients with a left ventricular assist device are common and can be detrimental. A meticulous balance between anticoagulant and procoagulant factors is therefore crucial. However, in contrast to routinely performed plasmatic coagulation tests, platelet function is hardly ever monitored although recent reports indicated platelet dysfunction. We therefore differentially evaluated platelet function with four commonly used point-of-care devices.


METHODS
In a cross-sectional design platelet function was assessed in 12 outpatients and 12 healthy matched volunteers using thrombelastography platelet mapping, thromboelastometry, platelet function analyzer, and a new whole blood aggregometer (Multiplate).


RESULTS
Phenprocoumon produced an international normalized ratio of 3.5. It was associated with a twofold prolongation in the thromboelastometry clotting time (p < 0.001). Platelet function under high shear was severely compromised: collagen adenosine diphosphate closure times were 2.5-fold longer in patients than in volunteers (p < 0.001), and 50% of patients had maximal collagen adenosine diphosphate closure time values. Although antigen levels of von Willebrand factor were 80% higher in patients (p < 0.001), von Willebrand factor-ristocetin was subnormal in 5 of 12 patients. Ristocetin-induced aggregation was also threefold higher in volunteers (p < 0.001), indicating an additional functional defect of platelets affecting the glycoprotein Ib-von Willebrand factor axis. The von Willebrand factor multimer pattern in patients also appeared abnormal.


CONCLUSIONS
Multimodal antiplatelet monitoring showed markedly impaired platelet function in patients with a left ventricular assist device. Platelet dysfunction under high shear rates and abnormal ristocetin-induced aggregation is only partly attributable to low von Willebrand factor activity. These findings resemble the acquired von Willebrand syndrome that is associated with microaggregate formation and enhanced bleeding.
Steinlechner
Barbara
B
Division of Cardiothoracic and Vascular Anesthesia and Intensive Care, Medical University of Vienna, Vienna, Austria. barbara.steinlechner@meduniwien.ac.at
Dworschak
Martin
M
Birkenberg
Beatrice
B
Duris
Monika
M
Zeidler
Petra
P
Fischer
Henrik
H
Milosevic
Ljubisa
L
Wieselthaler
Georg
G
Wolner
Ernst
E
Quehenberger
Peter
P
Jilma
Bernd
B
D000328:Adult; D000553:Ambulatory Care; D001780:Blood Coagulation Tests; D001791:Blood Platelet Disorders / Q000175:diagnosis* / Q000453:epidemiology / Q000209:etiology*; D003430:Cross-Sectional Studies; D005260:Female; D005500:Follow-Up Studies; D006353:Heart-Assist Devices / Q000009:adverse effects*; D006801:Humans; D015994:Incidence; D019934:International Normalized Ratio; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000379:methods; D010045:Outpatients / Q000706:statistics & numerical data; D010976:Platelet Count; D010979:Platelet Function Tests; D019106:Postoperative Hemorrhage / Q000175:diagnosis / Q000453:epidemiology / Q000209:etiology*; D011336:Probability; D012016:Reference Values; D018570:Risk Assessment; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D013916:Thrombelastography / Q000379:methods; D014914:Whole Blood Coagulation Time; D014841:von Willebrand Factor / Q000378:metabolism*
D014841:von Willebrand Factor