Platelet Dysfunction in Outpatients With Left Ventricular Assist Devices

Division of Cardiothoracic and Vascular Anesthesia and Intensive Care, Medical University of Vienna, Vienna, Austria.
The Annals of thoracic surgery (Impact Factor: 3.85). 01/2009; 87(1):131-7. DOI: 10.1016/j.athoracsur.2008.10.027
Source: PubMed
ABSTRACT
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.
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).
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.
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.

Full-text

Available from: Henrik Fischer, Jan 06, 2014
DOI: 10.1016/j.athoracsur.2008.10.027
2009;87:131-137 Ann Thorac Surg
Quehenberger and Bernd Jilma
Zeidler, Henrik Fischer, Ljubisa Milosevic, Georg Wieselthaler, Ernst Wolner, Peter
Barbara Steinlechner, Martin Dworschak, Beatrice Birkenberg, Monika Duris, Petra
Platelet Dysfunction in Outpatients With Left Ventricular Assist Devices
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Print ISSN: 0003-4975; eISSN: 1552-6259.
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is the official journal of The Society of Thoracic Surgeons and theThe Annals of Thoracic Surgery
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Page 1
Platelet Dysfunction in Outpatients With Left
Ventricular Assist Devices
Barbara Steinlechner, MD, Martin Dworschak, MD, MBA, Beatrice Birkenberg, MD,
Monika Duris, MD, Petra Zeidler, MD, Henrik Fischer, MD, Ljubisa Milosevic, RN,
Georg Wieselthaler, MD, Ernst Wolner, MD, Peter Quehenberger, MD, and
Bernd Jilma,
MD
Division of Cardiothoracic and Vascular Anesthesia and Intensive Care, Division of Cardiothoracic Surgery, Institute of Medical
and Chemical Laboratory Diagnostics, and Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria
Background. Thromboembolic and bleeding complica-
tions in outpatients with a left ventricular assist device
are common and can be detrimental. A meticulous bal-
ance between anticoagulant and procoagulant factors is
therefore crucial. However, in contrast to routinely per-
formed plasmatic coagulation tests, platelet function is
hardly ever monitored although recent reports indicated
platelet dysfunction. We therefore differentially evalu-
ated 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 func-
tional 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 Wille-
brand factor activity. These findings resemble the ac-
quired von Willebrand syndrome that is associated with
microaggregate formation and enhanced bleeding.
(Ann Thorac Surg 2009;87:131– 8)
© 2009 by The Society of Thoracic Surgeons
T
he need for mechanical circulatory devices to mini-
mize end-organ damage and to provide rehabilita-
tion potential for individuals awaiting heart transplanta-
tion becomes more important as the incidence of heart
failure is still rising on account of refined medication [1].
Furthermore, heart transplantation still remains a limited
treatment option for patients with end-stage heart failure
because of the scarcity of donor organs [2]. In these
instances, and when heart transplantation is not consid-
ered opportune, left ventricular assist devices (LVADs)
are increasingly implanted as destination therapy.
Foreign surfaces of LVADs, altered rheologic condi-
tions, and blood stasis within the chambers of the native
heart induce activation of coagulation [3] and require
adequate anticoagulation to prevent thromboembolic
events [4]. Most often, a combination of platelet inhibi-
tors and a vitamin K antagonist is prescribed for this
purpose [5]. Whereas clinicians routinely measure the
effect of warfarin (Coumadin) derivatives on plasmatic
coagulation, they rarely measure the effect of platelet
inhibitors on platelet function. Severe perioperative
bleeding and also spontaneous hemorrhage have been
reported in LVAD patients that cannot completely be
explained by the anticoagulation regimen alone. It has
been suspected that platelet dysfunction does play a role
here. We thus hypothesized that platelet dysfunction
may be present in LVAD patients owing to high shear
forces at the artificial surfaces. Shear stress, ie, stress,
which is applied parallel or tangential to the face of a
material, is sensed by ligand-bound extracellular do-
mains of integrins and converted to functional cellular
responses such as the activation of platelets. Hereby,
high shear–induced platelet plug formation is dependent
on a functioning von Willebrand factor–glycoprotein Ib
(vWF–GpIb) axis.
To date, however, there is no routine monitoring
procedure for platelet inhibition, and platelet function
Accepted for publication Oct 14, 2008.
Address correspondence to Dr Steinlechner, Division of Cardiothoracic
and Vascular Anesthesia and Intensive Care, Medical University of
Vienna, Waehringer Guertel 18-20, Vienna, A-1090, Austria; e-mail:
barbara.steinlechner@meduniwien.ac.at.
© 2009 by The Society of Thoracic Surgeons 0003-4975/09/$36.00
Published by Elsevier Inc doi:10.1016/j.athoracsur.2008.10.027
ADULT CARDIAC
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Page 2
has not even been systematically evaluated in this
patient population. Different platelet function tests
currently on the market (ie, thrombelastography
[TEG], rotation thromboelastometry, and the platelet
function analyzer-100) have been used for this purpose
to a variable extent by centers that have an active
LVAD program. The three devices mentioned above
use whole blood, which is a more physiologic approach
as compared with studying platelet suspensions. The
complementary use of these point-of-care tests allows
assessment of the underlying pathophysiology of
platelet dysfunction. However, with the exception of
single case reports they have not been used simulta-
neously and test results have not been compared with
each other. We therefore determined platelet function
in LVAD outpatients with the help of the above men-
tioned and widely used four point-of-care tests includ-
ing the newly developed Multiplate, a whole blood
aggregometer. In addition, we also tried to elucidate
the cause of the suspected dysfunction.
Material and Methods
Study Design
After institutional review board approval, written in-
formed consent was obtained from all subjects. In this
observational study platelet function of 12 outpatients
after elective LVAD implantation was evaluated by the
following frequently used point-of-care tests: TEG, rota-
tion thromboelastometry, platelet function analyzer-100,
and Multiplate. Additionally, blood from healthy volun-
teers without a history of previous bleeding or thrombo-
sis recruited from hospital staff, matched for age and sex,
was analyzed to define laboratory specific ranges for
normal values. Blood samples were taken from fasting
patients and volunteers during the morning hours. All
measurements were done within 4 hours after blood
sampling. All LVAD outpatients were anticoagulated
with 100 mg of aspirin orally (Aspirin; Bayer, Vienna,
Austria) once daily and phenprocoumon (Marcoumar;
Roche, Basel, Switzerland; desired international normal-
ized ratio, 2.5 to 3.5).
Thrombelastography Platelet Mapping Assay
Thrombelastography (Haemoscope, Skokie, IL) enables
monitoring of hemostasis as a whole dynamic process,
rather than isolated end points. Global assessment of
hemostatic function is made from whole blood, docu-
menting the interaction of platelets with the protein
coagulation cascade from the time of the initial platelet–
fibrin interaction, through platelet aggregation, clot
strengthening, and fibrin cross linkage to eventual clot
lysis. The “signature” of generated tracings can give
information on clotting factor activity, platelet function,
and any clinically significant fibrinolytic process within
20 to 30 minutes. The platelet-mapping assay that mea-
sures the presence of aspirin requires heparin to sup-
press thrombin and 10 L of ActivatorF (Haemoscope) to
replace thrombin in converting fibrinogen into fibrin and
arachidonic acid as platelet agonist [6, 7]. ActivatorF
consists of the snake venom reptilase that converts fibrin-
ogen to des-A-fibrin and activated factor XIII, which
crosslinks the fibrin monomers. Heparinized blood as
well as ActivatorF is also necessary for the determination
of fibrin to clot strength. In contrast, when kaolin is used
as an activator, citrated blood is needed.
For quantification of TEG variables, the time from
sample placement in the cuvette until the tracing ampli-
tude reaches 2 mm represents the rate of initial fibrin
formation and is related to plasma clotting factor and
circulating inhibitor activity (intrinsic coagulation); the
greatest amplitude on the TEG trace is a reflection of the
absolute strength of the fibrin clot—a direct function of
the maximum dynamic properties of fibrin and platelets.
Rotation Thromboelastometry
Rotation thromboelastometry (Pentapharm, Munich,
Germany) is related to, but in some aspects different
from, classical TEG. In rotation thromboelastometry a
ball bearing guides the firmness sensor, which makes the
analysis less susceptible to mechanical stress, movement,
and vibration. Just before running the assay, citrated
blood samples were recalcified with 20 L of CaCl
2
0.2
mol/L. To assess activation and inhibition of coagulation
sensitively we did not add an exogenous agonist to the
test system (no agonist thromboelastometry) [8]. The
following variables were analyzed: coagulation time, clot
formation time, and maximum clot firmness. To function-
ally assess the fibrinogen of the samples, the clotting was
determined using tissue factor activation of clotting after
addition of an unknown amount of platelet inhibitor
cytochalasin D, which the company would not disclose
(fibrinogen thromboelastometry). Both tests, no agonist
and fibrinogen thromboelastometry, were performed in
samples from both patients and volunteers.
The Platelet Function Analyzer-100
The platelet function analyzer-100 (Dade Behring, Mar-
burg, Germany) measures in vitro platelet plug forma-
tion in whole blood under high shear stress. It deter-
mines the closure time needed for a platelet plug to form
after activation of platelets by pathophysiologically rele-
Abbreviations and Acronyms
ASPItest aspirin test
CADP-CT collagen adenosine diphosphate
closure time
CEPI-CT collagen epinephrine closure time
GpIb glycoprotein receptor Ib
LVAD left ventricular assist devices
PFA-100 platelet function analyzer-100
TEG thrombelastography
vWF von Willebrand factor
vWF:Ag von Willebrand factor antigen
vWF:RiCO von Willebrand factor ristocetin
132 STEINLECHNER ET AL Ann Thorac Surg
PLATELET DYSFUNCTION WITH LVAD 2009;87:131–8
ADULT CARDIAC
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vant stimuli (eg, collagen adenosine diphosphate or col-
lagen epinephrine). Aspirin prolongs the collagen epi-
nephrine closure time [CEPI-CT] of activated blood,
whereas the collagen adenosine diphosphate closure
time [CADP-CT] is only minimally affected [9, 10].
The Multiplate Analyzer
The Multiplate analyzer (Dynabyte Medical, Munich,
Germany) uses whole blood [10 –12]. Test cells incorpo-
rate two independent sensor units, each consisting of two
silver-coated 3.2-mm-long copper wires. The instrument
detects the impedance change (aggregation) of each
sensor separately. The most important variable is the
area under the curve. Its unit is AU · min (as the y axis
is the aggregation, expressed in aggregation units [AU],
and the x axis is the time, expressed in minutes). One unit
corresponds to 10 AU · min. As an anticoagulant, which
does not affect the free calcium concentration in the
sample, hirudin (a direct thrombin inhibitor) is preferred
because heparin has some platelet-activating properties.
In the ristocetin test (triggered by 0.77 mg/mL ristoce-
tin) the binding of ristocetin–vWF complexes leads to
activation and aggregation of platelets, which relies on
the binding of vWF to the GpIb receptor.
In the collagen test (triggered by 3.2 g collagen/mL)
platelets are activated by means of the collagen receptor.
For appropriate platelet activation, release of endoge-
Table 1. Demographic Characteristics
a
Characteristic
Patients
(n 12)
Volunteers
(n 12)
Sex (female/male) 2/10 2/10
Age (y) 48 (15) 45 (6)
Weight (kg) 81 (11) 77 (9)
Height (cm) 174 (7) 175 (9)
Underlying heart disease (n)
Ischemic heart failure 4 0
Dilated CMP 4 0
Acute myocarditis 3 0
Cytostatic-induced CMP 1 0
NYHA class all class IV all 0
Type of LVAD (n)
De Bakey 9 NA
HeartWare 2 NA
Incor 1 NA
Mean duration of support at day of
blood sampling (mean SD)
253 (81) NA
Incidence of bleeding (n) 0 NA
Thromboembolic cerebrovascular
events (n)
0NA
a
Data are given as either absolute values or mean SD.
CMP cardiomyopathy; LVAD left ventricular assist de-
vice; NA not available; NYHA New York Heart Associa-
tion; SD standard deviation.
Table 2. Laboratory Tests
a
Variable Patients Volunteers
Reference
Value
VWF:Ag (%) 194 (48)
b
117 (29) (60–180)
VWF:RiCO (%) 71 (32) 81 (35) (60–180)
F VIII (%) 205 (38)
b
125 (30) (60–230)
INR 3.5 (0.6)
b
1.0 (0.1) (1.0)
ProBNP (pg/mL) 1688 (834)
b
28 (16) (0–125)
Hemoglobin (g/dL) 12.3 (1.7)
b
14.9 (0.8) (12.0–16.0)
Platelets (G/L) 216 (33) 246 (35) (150–350)
Leukocytes (G/L) 7.3 (1.4) 5.1 (1.2) (4.0–10.0)
CRP (mg/dL) 1.4 (1.2)
b
0.1 (0.1) (1)
Fibrinogen (mg/dL) 423 (63)
b
339 (54) (180–390)
fHb (mg/dL) 6.3 (1.8)
b
4.4 (1.7) (0.2–1.0)
LDH (U/L) 525 (186)
b
189 (27) (247)
a
Data are given as mean ⫽⫾standard deviation or, for reference values,
absolute values, or ranges.
b
p 0.05 versus volunteers (Mann-
Whitney U test).
CRP C-reactive protein; F VIII factor VIII; fHb free hemoglo-
bin; INR international normalized ratio; LDH lactate dehydro-
genase; ProBNP pro–brain natriuretic peptide; vWF:Ag von
Willebrand factor antigen; vWF:RiCO von Willebrand factor
ristocetin.
Table 3. Platelet Function Monitoring
a
Variable Patients Volunteers
Reference
Value
TEG
R-CK (min) 12 (2) 8 (2) (3–6)
MA-CK (mm) 67 (3) 64 (5)
MA-Fibrin (mm) 11 (4)
b
21 (22)
MA-AA (mm) 21 (14)
b
60 (5)
MA reduction (%) 81 (25)
b
11 (10) (0–20)
ROTEM (na-TEM)
CT (s) 2019 (1701)
b
664 (109) (300–999)
CFT (s) 338 (144)
b
237 (51) (150–700)
Mean alpha angle (°) 51 (8) 51 (6) (50–60)
MCF (mm) 58 (6)
b
48 (6) (40–65)
MA 30 (mm) 59 (5) 52 (0) (40–65)
fib-TEM
MCF (mm) 23 (5)
b
13 (2) (9–25)
PFA-100
CADP-CT (s) 267 (29)
b
104 (19) (60–120)
CEPI-CT (s) 272 (32)
b
125 (33) (80–170)
Multiplate analyzer
AUC (RISTOtest) (U) 57 (20)
b
142 (20) (90–201)
AUC (ASPItest) (U) 25 (15)
b
94 (12) (74–136)
AUC (ADPtest) (U) 56 (24) 54 (30) (53–122)
a
Data are given as means ⫽⫾standard deviation or, for reference values,
absolute values or ranges.
b
p 0.05 versus volunteers (Mann-Whit-
ney U test).
ADPtest adenosine diphosphate test; ASPItest aspirin test;
AUC area under curve; CADP-CT collagen adenosine diphos-
phate closure time; CEPI-CT collagen epinephrine closure time;
CFT clot formation time; CT coagulation time; fib
fibrinogen; MA maximum amplitude; MA-AA maximum
amplitude arachidonic acid; MA-CK maximum amplitude citrate
kaolin; MCF maximum clot firmness; PFA-100 platelet func-
tion analyzer-100; R-CK reaction time for citrate kaolin; RIS-
TOtest ristocetin test; ROTEM rotation thromboelastometry;
TEG thrombelastography; TEM thromboelastometry.
133Ann Thorac Surg STEINLECHNER ET AL
2009;87:131–8 PLATELET DYSFUNCTION WITH LVAD
ADULT CARDIAC
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