Patients that have valvular or some form of
congenital heart
disease have an excess strain situation that is particularly
susceptible
to the effects of increased exercise and blood shifting intoo the heart
and lungs due to water immersion.
The presence of an abnormality per se is not a
contraindication to
diving. In the case of intracardiac shunts due to holes in the walls,
and
in the presence of significant valve narrowing or widening inside the
heart,
diving is contraindicated.
Pathophysiological
Principles
In considering the pathophysiology of congenital and
valvular heart
disease one should be aware of the effect of the lesions on the heart
muscle.
Overload lesions of the heart can be classed as either pressure
or volume overload types.
Pressure overload lesions include the enlargement of
the
left ventricle
of the heart that results from blockage of the blood due to narrowing
of
the aortic valve (aortic stenosis), whereas volume overload of the left
side of the heart (ventricle) can occur from leaking aortic and mitral
valves (aortic or mitral regurgitation) or in the right side of the
heart
from a hole between the upper chambers (atria) or atrial septal defect.
The response of the heart muscle to these overload states depends on
whether
the overload is a pressure or volume type. The myocardium appears to
adapt
specifically to handle the type of load imposed.
The endocardium is the lining of the heart and is
the
first area
that is damaged by a reduction in blood supply (ischemia). This occurs
for several reasons: first, the forces in the subendocardial layers of
the myocardium are higher, thus requiring somewhat greater oxygen
demand
from the cells of the endocardial regions; second, the resistance
vessel
of the sub-endocardium are most distant from the supplying arteries
which
reside in the epicardium. Early enlargement and thickening, which may
even
be undetected by electrocardiogram, can be associated with evidence of
subendocardial ischemia detected by exercise stress testing.
Fortunately, the changes induced in the endocardium
by
maldistribution
of blood flow during exercise is often detected by the exercise stress
test, which can be used to evaluate the presence or absence of ischemia
in patients who have volume or pressure overloads due to acquired or
congenital
heart disease. Although there are specific contraindications, it is
possible
to allow selected patients with congenital or valvular heart disease to
dive (see table below).
Some circulatory abnormalities which are
present
in acquired
valvular and congenital heart disease need special consideration when
evaluating
diving candidates. Patients with circulatory obstruction such as aortic
stenosis, mitral stenosis, aortic coarctation, or pulmonic stenosis
have
limitations to exercise because of the narrowed segment of the
circulation.
Fainting with Exercise
When an imbalance occurs between the bodies' circulatory
demand
and cardiac output, blood pressure will fall and the patient will
develop
syncope (fainting). This is the probable mechanism for sudden death in
patients with narrowed aortic valve (aortic stenosis). These patients
should
not be approved for diving. This approach to the diving candidate is
similar
to that taken for competitive sports.
Patients with leaky valves or shunt lesions (holes
in the
wall between
the right and left sides of the heart) are generally less likely to
develop
syncope or low blood pressure (hypotension) with diving, but are more
likely
to develop heart failure with pulmonary congestion and associated
severe
shortness of breath from combined exercise
and
water immersion. Considerations mentioned above apply both
to
valvular regurgitation and to shunt lesions such as atrial and
ventricular
septal defect. In patients with minimal or no symptoms who have either
atrial or ventricular septal defects, if
pressures
in the central circulation are normal, the shunt will be
directed
from left to right and no arterial desaturation occurs. Any patient
with
a right to left shunt and low arterial oxygen levels (hypoxemia) will
normally
have severely limited exercise capacity.
In
diver candidates with atrial or
ventricular
septal defects, during decompression, there is a risk of venous bubbles
getting
into the arterial circulation without the filtering effect of the
lungs,
causing cerebral embolization. Since intra-atrial and intra-ventricular
shunts can be bidirectional at different phases of the cardiac cycle,
presence
of an atrial or ventricular septal defect is generally thought to be a
contraindication to
diving. Persons with atrial septal defects and patent foramen ovale
should have the defect repaired. However, ventricular pressures are
normally higher in the left ventricle and right to left shunts are
rare. The diver who is found to have a ventricular septal defect should
be studied with exercise stress testing and an echocardiogram. If the
shunt is small, there is no evidence of heart failure or strain and if
the shunt is left to right - the person should be advised of the risks
and allowed to continue diving.
Total Anomalous Pulmonary
Venous Return
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