CARDIOVASCULAR JOURNAL OF AFRICA • Vol 21, No 6, November/December 2010
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AFRICA
offers promise in assessing dabigatran anti-coagulation, but is
not yet available on the market.
‘The discussion is, however, ongoing with regard to the most
useful tests and we are encouraging manufacturers to develop
appropriate safety tests for their therapies’, Prof Haas stressed.
Currently the chromagenic assays will give the most accurate
reflection of rivaroxaban or dabigatran levels and anti-coagulant
status’, Prof Haas pointed out.
7
At a pragmatic level, a pocket
card with the
t
-max and
t
-half-life of these agents can be useful
to assess the coagulation state if the time and dose of last medi-
cation is known.
D-dimers – how do we use this test clinically?
Prof Harry Buller, Amsterdam, Netherlands
It is essential to assess the clinical probability of either deep-
vein thrombosis or pulmonary embolism in an individual patient
before initiating and interpreting a D-dimer test, Prof Buller
advised. ‘The D-dimer is a valuable test to identify fibrin-derived
products. Although the ELISA version is highly sensitive,
clinical urgency does not often allow time for this test. Instead,
latex-based tests are used; they are sensitive and rapid, but have
a lower specificity.’
In an evaluation of published trials that determined the preva-
lence of DVT using clinical prediction rules for the diagnosis
of DVT, Wells and colleagues
8
determined the likelihood ratios
of DVT in low, moderate and high clinical probability-assessed
groups. ‘Patients with a low clinical probability of DVT, using
the Wells predictive rule, and a subsequent negative D-dimer test
can be excluded from ultrasound evaluation’, Prof Buller noted.
‘Patients in the moderate-risk category with a raised D-dimer
value should undergo compression ultrasound for confirmation
of DVT. In high-risk VTE patients, one should rather ignore
the need to do the D-dimer test and go directly to compression
ultrasound’, Prof Buller advised.
A useful diagnostic management protocol to determine the
probability of pulmonary embolism has been developed and
prospectively tested by the so-called Christopher study group.
9
Prof Buller commented; ‘this option is attractive in that 30% of
patients with clinically suspected pulmonary embolism can be
excluded by using the clinical probability score in combination
with a normal D-dimer test result. In all other patients, computed
tomography (CT) scans effectively rule out pulmonary embo-
lism without using other imaging tests. In fact, there was only
a 1.3% incidence of VTE in the subsequent three months in
patients with a negative CT scan.’
In conclusion, Prof Buller referred to new data indicating
that the cut-off values for D-dimer tests may well be higher in
the elderly, and a prospective study is currently underway to
determine normal values in this patient population. With regard
to using D-dimer tests to determine optional length of anti-
coagulation therapy, Prof Buller noted that the normal D-dimer
test has little value in this situation, as the sensitivity is very low
(43%). ‘We would harm the majority of patients if we used this
parameter and stopped anti-coagulation therapy too early’, he
added. In cancer patients, D-dimer tests can be predictive and
prognostic to some extent, but this is still at a research stage.
Thrombolytics in stroke patients
Dr Jody Pearl, Sunninghill Hospital, Johannesburg
Facing a lack of therapeutic innovation in the treatment of stroke,
Dr Pearl referred to the successful stroke intervention protocol
set up at the Vergelegen Medi-Clinic, Somerset West. This unit
provides a 24-hour intervention service similar to the acute
stroke units in London, which have successfully intervened to
significantly drop the mortality from stroke. The concept is that
‘time is brain’ and the patient needs to get to the appropriate
centre quickly, where neurologists and interventional radi-
ologists or cardiologists are on call and available to provide a
24-hour support service. Fibrinolytic therapy and/or percutane-
ous thrombosis aspiration devices are the current options avail-
able, depending on the patient characteristics. This approach
should be adopted more widely in South Africa.
Minimally invasive surgery for carotid disease –
where are we?
Prof TalibAbdul Carrim, University of Kwazulu-Natal, Durban
While the debate continues as to whether carotid artery stenting
(CAS) or carotid endarterectomy (CAE) is the preferred strategy
for carotid disease, two issues remain: (1) what are the indica-
tions in 2010 for each procedure; and (2) is treating asympto-
matic patients with significant stenoses – CAS – unethical as
the procedure itself may be associated with a 6.9% increased
risk. Prof Carrim indicated that some clarity was emerging as to
which procedure best suits which patient and when one should
submit a patient.
After the CREST study,
10
which showed no difference in over-
all short- and long-term outcomes of these two techniques, new
analyses are beginning to identify appropriate patient selection.
In CREST, it was shown that outcomes with CAS were better
than CEA for patients less than 70 years of age. In two recent
meta-analyses,
11,12
CEA was shown to be better than CAS; but
both reviews acknowledge that the treatment strategy chosen
should best meet the individual patient’s risk.
‘At this juncture we can conclude that CAS is not indicated
in the elderly, in those with disease situated in difficult-to-reach
sites of the carotid artery, and those with echolucent plaques that
are more liable to rupture.
continued on p. 337…
Summary of CAS and CEA characteristics
CAS • increased peri-operative stroke incidence
• higher restenosis rates
• poor outcomes in those older than 70 years
• higher death rates in the elderly and in high-risk sites (difficult
to reach and echolucent plague)
• longer term outcome equal to CEA
CEA • remains the gold standard
• periprocedural MI and cranial nerve injury higher than in CAS
• better for patients with unstable plaque
Monitoring of direct coagulation inhibitors
• There is no need for routine monitoring, as a standard dose of the
new anti-coagulants is used.
• New anti-coagulant agents affect conventional clotting tests.
• Do not routinely measure PTT/PT when using these agents.
• Use the specific tests, as advocated by the manufacturers, for
suspected over- or under-dosing.
