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Cerebrovascular disease and risk of stroke
Submitted by Dr. Yasser
Mokhtar, MD. Dept. of internal medicine. School of
medicine, University of South Dakota.
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Stroke is a loss of cerebral
function with symptoms lasting >24 hrs or death due to vascular
disease |
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Causes of stroke
Ib. Embolism from the heart:
There is no doubt that emboli arising from within the heart or passing
through it from the venous system can reach the brain to cause ischemic stroke
and TIAs (Cerebral Embolism Task Force 1989).
Although there are a large number of potential cardiac sources of embolism,
most can be diagnosed easily using modern non-invasive technology. The much
greater difficulty is deciding whether an identified potential embolic source is
the source of embolism (Bogousslavsky et al 1990).
In developed countries, about twenty per cent of ischemic strokes and TIAs
are due to embolism from the heart, the most common cause being non-rheumatic AF
with presumed, but seldom proven, thrombus in the left atrium (Kittner et al.,
1990 and Petersen 1990).
1. Coronary artery disease: Left ventricular mural thrombus diagnosed
echocardiographically occurs within days of an acute myocardial infarction in
about twenty per cent of the patients. Those with anterior infarcts are at
higher risk than those with inferior infarcts, large infarcts and a dyskinetic
wall segment are also risk factors. A chronic left ventricular aneurysm often
contains thrombus but embolization does not seem to be at all common (Meltzer et
al., 1986).
2. Mitral valve prolapse (MVP) is a common echocardiographic and even
clinical finding in asymptomatic people (Levy and Savage 1987). It is found in
5-7 per cent of adult population and in 6-17 per cent of normal adult women
(Jackson et al., 1984). Estimates of its prevalence are bedevilled by lack of
diagnostic standardization (Devereux et al., 1987). MVP is more common in young
ischemic stroke patients than expected (Barnett et al., 1980) but a cause and
effect relationship between the two is not universally accepted.
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3. Paradoxical embolism from the venous system (or exceptionally from
thrombus in the right side of the heart) is a well accepted concept. However,
certain diagnosis is almost impossible because a PFO can be found not only in
about twenty five per cent of unselected postmortems but with modern
non-invasive technology (TEE with IV contrast) in about fifteen per cent of
normal people (Gautier et al., 1991).
4. Atrial septal aneurysm (ASA) is increasingly recognized and some
evidence is emerging that it may be complicated by thrombosis and embolism to
the brain (Belkin et al., 1987). Multiple recent reports have suggested that
patients with ASA are at increased risk for embolic events (DiPasquale et al.,
1988 and Schneider et al., 1990). In 1991, Pearson et al. reported that with the
advent of TEE, ASA was documented in 15-20 per cent of stroke population
(Pearson et al., 1991). Also in 1991, Herrera et al. stated that ASA should be
considered in patients suspected of having embolic arterial event without an
obvious cardiac source (Herrera et al., 1991). However, it is often associated
with other cardiac conditions which have embolic potential particularly PFO.
5. Infective endocarditis is complicated by ischemic stroke as a
result of embolism of infected vegetations in about twenty per cent of cases.
Mycotic aneurysms may form at sites of embolic occlusion and some rupture to
cause intracerebral or subarachnoid hemorrhage (Kenter and Hart 1990, Hart et
al., 1990 and Salgado 1991).
6. Cardiac myxomas can arise in any heart chamber but seventy five per
cent are found in the left atrium (Markell et al., 1987). Tumor material may
embolize to the brain and very often there are additional cardiac symptoms (e.g.
syncope) and constitutional aspect (e.g. malaise, weight loss,
anemia) (Reichman
et al., 1992). Valvular fibroelastoma is an even rarer example of an embolic
cardiac tumor (Kasarskis et al., 1988).
7. Prosthetic heart valves particularly mechanical ones have been
known to be complicated by thrombosis with embolic potential. Those in the
mitral position are more prone to thrombosis than those in the aortic position (DeBono
1982). The overall risk of embolism is about two per cent per annum even on
anticoagulants (Bloomfield et al., 1991).
8. Pulmonary arteriovenous fistula often visible on the chest X-ray is
a very rare route by which emboli may reach the brain from the venous system
(Dennis 1985).
9. Dilated cardiomyopathies are well recognized to be complicated by
intracardiac thrombus but this seems to be a rare cause of embolic stroke
(Meltzer et al., 1986).
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