CARDIOVASCULAR JOURNAL OF AFRICA • Vol 23, No 10, November 2012
554
AFRICA
made before arrhythmogenic right ventricular dysplasia was
characterised and identified as a separate disease in the literature,
hence its omission in the classification.
The reaction of clinicians/researchers to this classification
was mixed. While everyone agreed with the designation of
these diseases as cardiomyopathies, not everyone agreed with
its classification. Several classifications followed thereafter
but, in so doing, many of them again extended the definition of
cardiomyopathies to include any disorder of the myocardium.
The report of another task force, set up by the WHO in 1995
16
to update the 1980 classification, defined the cardiomyopathies
as any disease of the myocardium with cardiac dysfunction,
although it retained the original three types of cardiomyopathies:
hypertrophic, dilated and restrictive. It added a fourth one,
arrhythmogenic right ventricular cardiomyopathy (formerly
known as arrhythmogenic right ventricular dysplasia). But while
it recognised that dilated cardiomyopathy may derive its origin
from conditions such as viral myocarditis, it created, under
specific cardiomyopathies, an entity known as inflammatory
cardiomyopathy, which it defined as ‘myocarditis in association
with cardiac dysfunction’.
Similarly it also created another entity, known as alcoholic
cardiomyopathy, under specific cardiomyopathies after it had
agreed that dilated cardiomyopathy may be caused by the
consumption of alcohol. Moreover, ischaemic cardiomyopathy
was recognised in the report as a separate entity under specific
cardiomyopathies, although the same disease was earlier said to
be a variety of dilated cardiomyopathy. Finally, the document
introduced new names for well-recognised diseases. For example,
hypertensive cardiomyopathy was substituted for the well-known
and more specific terms, hypertensive heart disease/hypertensive
heart failure.
The latest classification, sponsored by the American Heart
Association,
17
agreed to classify the cardiomyopathies in line
with ‘the molecular era of cardiovascular disease’. It also
agreed that cardiomyopathies should include any disorder of the
myocardium and therefore defined them as ‘a heterogeneous
group of diseases of the myocardium associated with mechanical
and/or electrical dysfunction that usually (but not invariably)
exhibit inappropriate ventricular hypertrophy or dilatation and
are due to a variety of causes that are frequently genetic.
Cardiomyopathies either are confined to the heart or are part of
generalised systemic disorders, often leading to cardiovascular
death or progressive heart failure-related disability’
.
The panel made a case for inclusion of the ion channelopathies
in the classification of the cardiomyopathies, although it agreed
that they are primary electrical diseases with no gross or
histopathological abnormalities. As in the 1980 classification,
it excluded from the list of cardiomyopathies ‘pathological
myocardial processes and dysfunction that are a direct consequence
of other cardiovascular abnormalities, such as that which occurs
with valvular heart disease, systemic hypertension, congenital
heart disease, and atherosclerotic coronary artery disease
producing damage secondary to impairment in coronary flow’.
The report went further to classify the cardiomyopathies into
two major groups ‘based on predominant organ involvement’.
These were primary and secondary cardiomyopathies. Primary
cardiomyopathies, whichmay be genetic, non-genetic or acquired,
were defined as ‘those solely or predominantly confined to
heart muscle and are relatively few in number’. The genetic
forms included hypertrophic cardiomyopathy, arrhythmogenic
right ventricular cardiomyopathy (ARVC), left ventricular
non-compaction, conduction system disease, glycogen storage
disorders, mitochondrial myopathies, and ion-channel disorders.
The mixed forms were dilated cardiomyopathies and the
restrictive (non-hypertrophied and non-dilated) types.
In the report, secondary cardiomyopathies were diseases that
were associated with systemic illnesses. These were similar to
those listed under specific heart muscle disease and specific
cardiomyopathies by the 1980 and 1996 reports, respectively.
Classification of the cardiomyopathies in Africa
For clinicians working in Africa where the cardiomyopathies
are most prevalent, the question that follows is which of these
classifications is appropriate for Africa? Before we answer this
question, let us briefly review what is currently known about the
cardiomyopathies in Africa.
Hypertrophic cardiomyopathy
In the pre-echocardiography era, hypertrophic cardiomyopathy
(
HCM) was hardly diagnosed in Africa. All abnormal
electrocardiographs (ECGs) suggestive of left ventricular
hypertrophy (LVH) were attributed by clinicians to hypertensive
heart disease since hypertension was the dominant cardiovascular
disease among Africans and was extremely common in
African populations. The widespread use of echocardiographic
examination all over Africa changed all this as it showed that
HCM indeed occurs among Africans.
For instance, HCM was found in 0.2% of 6 680 unselected
echocardiograms in Tanzania
18
and in 2% of 712 echocardiograms
in Lagos, Nigeria.
19
Similar reports have also come from South
Africa where extensively genetic investigations have confirmed
similar findings with other parts of the world.
20
In Ghana,
21
1.15%
of 572 patients referred for echocardiography at the Ghana
National Cardiac reference centre had HCM, while Abegaz in
Ethiopia discovered that 53 out of 1 240 abnormal echocardiograms
performed at the Armed Forces General Hospital had HCM.
22
The
prevalence rate among populations outside Africa ranged from 0.2
to 0.5%. Interestingly, Maron
et al.
17
found in their CARDIA study
that the prevalence of HCM in blacks was twice that of whites,
while more African-Americans performing competitive sports
died suddenly compared with their white counterparts.
The aetiology of HCM has similarly been sorted out.
Investigations all over the world have conclusively shown that
HCM is inherited as an autosomal dominant genetic disorder
that is caused by mutations in at least 10 different genes that
code for sarcomeric proteins.
2,15
Mutations in the
β
-
myosin heavy
chain gene, myosin-binding protein C and troponin T account
for 70 to 80% of all the cases. The total number of mutations is
well over 100, and new mutations are being discovered. HCM
is therefore no longer a heart muscle disease of unknown cause
and this implies that the 1980 report on the cardiomyopathies is
no longer valid.
Arrythmogenic right ventricular cardiomyopathy
(
ARVC)
Reports from Africa about this disease have come from only
South Africa.
20,23
There are familial cases of ARVC as well as
