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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 31, No 4, July/August 2020
AFRICA
185
Incidence and risk factors for thromboembolism and
major bleeding in patients with mechanical heart valves:
a tertiary hospital-based study in Botswana
Elizabeth Botsile, Julius Chacha Mwita
Abstract
Introduction:
Mechanical heart valve (MHV) prostheses increase
the risk of thromboembolic complications. While warfarin
anticoagulation reduces this risk, its use increases the risk of
bleeding. We sought to estimate the rate of thromboembolic
and bleeding complications among patients with MHVs at a
tertiary hospital in Botswana. Factors associated with bleeding
and thromboembolic complications are also described.
Methods:
This retrospective cohort study involved a cohort
of patients with MHV at Princess Marina Hospital who were
operated on before September 2017. The study documented
bleeding and thromboembolic events since the valve replace-
ment, patients’ demographic information, co-existing medical
conditions, drug history and details of valve replacement.
Using the recent international normalised ratio (INR) results,
each patient’s time in therapeutic range (TTR) was calculated
to assess the level of anticoagulation control.
Results:
The study enrolled 142 patients with a mean (SD)
age of 42 (12) years and a median (IQR) duration since valve
replacement of four years (1.8–10.0). The median (IQR) TTR
was 29.8% (14.1–51.0) and only 14.8% of the patients had an
optimal anticoagulation control. The rates of major bleeding
and thromboembolic complications were 1.5 per 100 person-
years and 2.80 per 100 person-years, respectively. A longer
duration of warfarin use was associated with an increased risk
of both bleeding (
p
= 0.008) and thromboembolic complica-
tions (
p
= 0.01).
Conclusion:
Bleeding and thromboembolic complications
were common in MHV prosthesis patients in this study. Long
duration of anticoagulation, albeit sub-optimal control, was
a risk factor for bleeding and thromboembolic complications
in these patients. Therefore, long-term efforts are necessary to
address these complications and possibly improve the quality
of life of these patients.
Submitted 17/9/18, accepted 23/2/20
Published online 16/3/20
Cardiovasc J Afr
2020;
31
: 185–189
www.cvja.co.zaDOI: 10.5830/CVJA-2020-006
Rheumatic heart disease (RHD) remains the leading cause
of cardiovascular disease in developing countries, including
Botswana.
1-4
The disease affects young people and has been the
main reason for valve replacement in sub-Saharan Africa.
5
Because of their longevity, mechanical heart valves (MHVs)
are preferred to bio-prostheses in most patients with RHD.
6
As MHVs increase the risk of thromboembolic complications,
these patients require life-long warfarin anticoagulation.
7,8
While warfarin is effective and the only anticoagulant used for
thromboembolic prophylaxis in patients with MHVs, it has
a narrow therapeutic window.
9
It may be difficult to achieve
the desired anticoagulation without excess risk of bleeding.
9
Therefore, patients with MHVs are at increased risk of both
bleeding and thromboembolic complications.
10,11
Theratesof majorbleedingandthromboemboliccomplications
after implantation of MHVs are 1–3.9 per 100 patient-years and
1.3–1.6 per 100 patient-years, respectively.
7-9,12-14,16
Generally,
the rates of bleeding and thromboembolic complications vary
across settings, due to differences in the levels of anticoagulation
control and the population studied.
12,13,17
A combination of both
non-genetic and genetic factors influence the inter-individual
and ethnic variability in warfarin responses and the quality of
anticoagulation.
18
Differences in the two genes responsible for
warfarin pharmacokinetics and pharmacodynamics, cytochrome
P450 2C9 (
CYP2C9
) and vitamin K epoxide reductase complex
1 (
VKORC1
) account for up to 30% of the variability in warfarin
dose among Caucasians and 10% among blacks.
The quality of anticoagulation is often measured by the
patient’s average time in therapeutic range (TTR), which correlates
with bleeding and thromboembolic complications.
20-22
Achieving
optimal anticoagulation control has been a challenge, especially
in developing countries, due to system-related problems.
17,21
Unsustainable availability of medications, including warfarin,
long distance to the centralised international normalised ratio
(INR) testing centres, and underfunded health systems in
developing countries are some of the problems.
23,25
A recent study reported optimal anticoagulation control
in only 15% of warfarin-treated patients in our setting.
17
Consequently, the majority of our patients have an elevated
risk of warfarin-related complications.
15
However, there is a
lack of data on the frequency of bleeding and thromboembolic
complications among patients with MHVs in our setting. This
information is imperative in managing our increasing number of
patients with MHV prostheses. As a result, this study sought to
determine the rate of both major bleeding and thromboembolic
complications and associated factors among patients withMHVs
at a tertiary hospital in Botswana.
Methods
This retrospective cohort study was conducted at the warfarin
clinic of Princess Marina Hospital (PMH). PMH is a tertiary
Princess Marina Hospital, Gaborone, Botswana
Elizabeth Botsile, FCP,
litz_b@yahoo.comUniversity of Botswana, Gaborone, Botswana
Julius Chacha Mwita, MD, MMed, MSc