11 / 66
CARDIOVASCULAR JOURNAL OF AFRICA • Volume 30, No 6, November/December 2019
AFRICA
319
Overall, 16 of the patients had hospital admissions after valve
replacement surgery and the reasons included prosthetic valve
endocarditis in eight patients, stroke in five and miscellaneous
reasons in the rest.
Discussion
Our study showed that educational level of primary school or
less, distance from follow-up medical facility of more than 300
km, check-up visit once quarterly or less frequently, and free
drug supply from public institutions were significantly associated
with sub-optimal control of INR in this group of patients,
suggesting the need for interventions directed towards tackling
some of these factors.
Review of the existing literature shows a lower level of
knowledge consistently affects adherence to prescribed
medicines.
12
Multiple other factors including young age, level of
parental education, combination of warfarin and aspirin, and
missed anticoagulant doses also showed a tendency towards an
association, although not statistically significant, probably due
to the small sample size of our study. The number of major
bleeding/thrombotic events and mortalities in our study is also
unacceptably high considering the small number of patients we
are reporting on (Table 4).
A lower level of literacy may have influenced the patients’
understanding of the nature of the clinical condition they
are suffering from, the risks associated with sub-optimal
anticoagulation, and the importance of adhering to medications
and follow-up clinical visits, even when they do not have clinical
symptoms. Longer travel to follow-up clinics and INR test
facilities is even more important in sub-Saharan African settings
where transportation facilities are not readily available or are too
costly for most poor patients to afford, or travel is too difficult. It
may be surprising that free drug supply from public facilities was
associated with sub-optimal anticoagulation. However, the truth
is that warfarin was rarely available in the public institutions,
which means it was difficult for the patients to secure a regular
and sustainable supply.
Optimisation of anticoagulation in populations with
sub-optimal adherence to medication and follow up is a major
challenge.
13
Adherence to follow-up care and medication is a
challenge once patients are relieved of their cardiac symptoms.
14
Colleagues from Cameroon reported that their cohort of 233
patients with mechanical valves had freedom from neurological
events and anticoagulation-related bleeding of 93.1
±
2.1 and 78.9
±
3.7%, respectively, at six years.
9
While it is difficult to directly
compare our study with theirs due to the small number of patients
and differences in methodology, the number of major stroke and
bleeding events in our study was disproportionately high.
A study from Rwanda reported that no anticoagulation-
related events occurred,
15
but the number of patients with
valve replacement in that study was small and the follow up
was relatively short. The South African group that compared
adjusted-dose warfarin with pre-determined fixed-dose warfarin
also reported there were significant numbers of major thrombotic
and haemorrhagic events in their study population.
13
However,
this study was also significantly different in methodology and
cannot be compared with our study.
Our study has important limitations in methodology. We
included all patients we could acquire during the study period.
We did not know the exact number of patients with prosthetic
valves due to lack of records. We did not calculate our sample
size therefore our statistical tests should be taken with caution.
Besides the small size of the study population, the study
was cross-sectional with only one encounter with each patient
participant. We used medical records to determine the six-month
INR profile. Some of these patients may have had a single INR
determination within that period due to the compliance and
logistical problems already mentioned. The ideal study design
would have been a cohort study.
We only included patients who came for follow up during the
study period. Finally, recall bias may also have been a limitation
in our study. This study could prompt the hospital to re-organise
record keeping of patients.
It is worth mentioning the inherent drawbacks of warfarin
as an anticoagulant. Warfarin has marked individual variation
in its metabolism and hence varying dosage requirements and
the need for frequent monitoring.
16
However, there are no agreed
guidelines on how frequently one should monitor anticoagulation
in patients who are on chronic anticoagulation. Besides, warfarin
has wide dietary and drug interactions, making it difficult to
establish a desired level of anticoagulation. Fixed-dose warfarin
has been shown to be better than adjusted-dose warfarin. Future
studies may be required to determine the feasibility and safety of
this strategy in our patients. It may also be worth considering the
feasibility, affordability and effectiveness of novel anticoagulants
(NOACs) in our setting.
Finally, it may be better to opt for valve repair surgery
whenever possible,
14
although this strategy also has its own
drawbacks in this part of the world. Besides the significantly
high failure rate in advanced rheumatic heart disease, patients
usually fail to comply with their monthly benzathine penicillin
prophylaxis, putting themselves at risk of recurrence of acute
rheumatic fever. Ideally, development of prosthetic heart valves
that do not require anticoagulation may be a future solution to
tackle some of these complex problems.
Table 4. Description of patients with prosthetic heart valves and thrombo-embolic events
Age
(years) Gender Educational status
Age at
surgery
(years) Valve position
Duration of follow up
Type and number of events
Outcome
Bleeding
Thrombo-embolism
18
F
Secondary education
16 Aortic
2 years
1
2
Alive, no sequelae
14
M Primary education
14 Aortic and mitral
6 months
3
2
Alive, no sequelae
20
F Primary education
20 Aortic
8 months
1
1
Alive, neurological sequelae
12
M Primary education
11 Mitral
1 year
2
1
Deceased
15
F Primary education
15 Mitral
6 months
1
1
Deceased
20
F Primary
18 Mitral
2 years
1
1
Deceased
11
F Primary education
9 Aortic and mitral
2 years
2
1
Deceased