Cardiac hypertrophy
and dilation
The heart may undergo compensatory enlargement in the form of
hypertrophy, dilation, or both, so as to prevent or postpone heart failure.
Compensatory hypertrophy
·
Hypertrophy of the heart is defined as an increase in
size and weight of the myocardium. It generally results from increased pressure
load while creased volume load (e.g. valvular incompetence) results in
hypertrophy with dilatation of the affected chamber due to regurgitation of the blood through incompetent
valve. The atria may also undergo compensatory changes due lo increased
workload.
·
It appears that stretching of myocardial fibers in response to stress induces the cells to
increase in length. The elongated fibers receive better nutrition and thus
increase in size.
Causes:
1. Left ventricular hypertrophy. The
common causes of left ventricular hypertrophy are:
a)
Systemic hypertension.
b)
Aortic stenosis and insufficiency.
c)
Mitral insufficiency.
d)
Coarctation of the aorta.
e)
Occlusive coronary artery disease.
f) Congenital anomalies
like septal defects and patent ductus arteriosus.
g) Conditions
with increased cardiac output: thyrotoxicosis, anemia, and arteriovenous
fistulae.
2. Right ventricular hypertrophy. Most
of the causes of right ventricular hypertrophy are due to pulmonary arterial
hypertension. These are:
a)
Pulmonary stenosis and insufficiency.
b)
Tricuspid insufficiency.
c) Mitral
stenosis and/or insufficiency.
d) Chronic lung
diseases: chronic emphysema, bronchiectasis, pneumoconiosis, pulmonary vascular
diseases, etc.
e)
Left ventricular hypertrophy.
Compensatory dilation. Quite
often, hypertrophy of the heart is accompanied by cardiac dilation.
·
Causes:
a)
Valvular
insufficiency (mitral and/or aortic insufficiency in left ventricular
dilatation, tricuspid and/or pulmonary insufficiency in right ventricular
dilatation).
b)
Conditions
with high cardiac output e.g. thyrotoxicosis, arteriovenous shunt.
c) Myocardial diseases:
cardiomyopathies, myocarditis.
d) Systemic
hypertension.
·
Hypertrophy of the myocardium without dilatation is
referred to as concentric, and when associated with dilatation is called
eccentric. The weight of the heart is increased above the normal, often over
500 gm.
·
Macroscopically, the thickness of the left ventricular wall above 15 mm is
indicative of significant hypertrophy. In concentric hypertrophy, the lumen of
the chamber is smaller than usual, while in eccentric hypertrophy the lumen is
dilated. In pure hypertrophy, the papillary muscles and trabeculae cameae are
rounded and enlarged, while in hypertrophy with dilatation these are flattened.
·
Microscopically, there is increase in size of individual muscle fibres.
There may be multiple minute foci of degenerative changes and necrosis in the
hypertrophied myocardium.
