Pathology of Cardiomyopathy and Heart
Failure
Pathology of Cardiomyopathy
Cardiomyopathies
(Cardiomyopathy) are causes of congestive heart
failure (Congestive Heart Failure). Heart failure is a
common end result of many different diseases
affecting the heart’s ability to function.
Cardiomyopathy literally means “disease of heart
muscle.” Dr. Cleveland’s definition of
Cardiomyopathy is disease of the heart muscle
intrinsically. It is a primary disease of
the myocardium, leading to dysfunction. It
excludes disease of the myocardium and resulting
dysfunction related to ischemic heart disease (IHD),
hypertension, or valve disorders; changes in the
myocardium are secondary to those pathologies.
Etiologies, pathophysiology, and pathogenesis of
dilated, hypertrophic, and restrictive Cardiomyopathy
were discussed by Dr. Klapholz. Dr. Cleveland stressed
the important points below, sorry if it’s repetitive.
Dilated Cardiomyopathy
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Most common form of Cardiomyopathy.
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Morphology:
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Cardiomegaly is due to cardiac myocyte hypertrophy.
Heart can enlarge up to 800g! (Normal weight of
adult heart is 275-325g.)
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Progressive 4 chamber dilation.
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Thinning of the all the walls and the
interventricular septum.
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Leads to a weak, hypocontracting heart.
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Ischemic changes of the heart are seen.
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Genetic: inherited as autosomal dominant, autosomal
recessive, or X-linked.
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Histology: enlarged, skinny cardiac myocytes
compared to myocyte changes seen in other
cardiomyopathies. Normal transverse diameter
of a cardiac myocyte is 15 microns while that of
HCardiomyopathy is 20-25 microns.
Hypertrophic Cardiomyopathy
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Associated with early death in athletes.
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Morphology:
-
Massive cardiac hypertrophy
involving almost all the myocardium. Hearts can get
up to 1000g!!
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Dramatic thickening of the walls.
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Resistance to filling.
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Left atrial dilation.
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Muscular, strong, hypercontracting heart.
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Histology: Trichrome stain highlights collagen,
showing some interstitial fibrosis. More importantly,
there is a disorganized (non-longitudinal)
appearance of the cardiac myocytes and they are very
enlarged (up to 40 microns). This is known as
cardiac myocyte disarray and sarcomeric
disorganization.
Restrictive Cardiomyopathy
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Due to some infiltrative disease like amyloidosis,
sarcoidosis, or radiation fibrosis.
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Morphology:
-
Modest thickening of walls.
-
Not much dilation
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Stiff, inelastic walls and chambers.
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This consists of a process that infiltrates the
myocardium, replaces it, and stiffens the walls.
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Histology: Between the cardiac myocytes is a pale,
homogenous, structure-less substance which in this
case is amyloid. However, you cannot make a diagnosis
of amyloidosis on an H&E stain. You must use the
Congo Red stain and submit it to polarization
microscopy
à
the amyloid will light up as a green bifringence.
Pathology of Heart Failure
Heart failure (Heart Failure) is the common end result
of other diseases that affect the heart’s ability to
function (Hypertension, ischemia, valve disease,
Cardiomyopathy). It is not a disease in and of itself.
It
is a multisystem, metabolic derangement in which CO is
inadequate to meet the oxygen requirements of the
tissues and organs of the body. It’s a supply and
demand problem. Because heart failure is usually
accompanied by organ congestion due to failure of the
heart to keep pace with the venous return of the lungs
or systemic circulation, it is called congestive
heart failure (Congestive Heart Failure).
Pathogenesis:
-
Heart Failure results from a stress imposed on the
heart, which causes it to work harder to maintain CO
and tissue perfusion.
-
Stresses = Hypertension, ischemia, valve disease,
Cardiomyopathy
-
When the stress is imposed initially, there are
compensatory mechanisms which help to maintain CO and
perfusion.
-
With persistence and chronicity of the stress, there
is cardiac myocyte hypertrophy.
-
In
pathologic hypertrophy, other structural and
deleterious changes take place. They are irreversible
and progressively cause systolic and diastolic
dysfunction.
-
With persistence of the stress and sufficient
dysfunction, there are manifestations of diseases that
are remote from the heart.
-
As
long as the heart can meet the body’s metabolic
demands, all you will see is a large heart. Once it
can’t any longer, you will see peripheral edema,
pulmonary congestion edema, and other clinical
manifestations discussed earlier.
Cardiac hypertrophy
(675g in the picture she showed us) is a very
important early milestone end marker (morbidity and
mortality). Hypertrophic hearts and cardiac
myocytes look different based on the disease that’s
causing heart failure. Physiologic hypertrophy due to
exercise leads to proportionate enlargement of cardiac
myocytes. You won’t see additional deleterious
structural abnormalities of the heart in this case.
Now
we’ll discuss the pathological manifestations of Heart
Failure. It is classified according to right or left
sided Heart Failure depending on the predominant side of
the heart that’s affected. Most patients present
with left-sided or biventricular Heart Failure. The
most common cause of right-sided Heart Failure is NOT
cor pulmonale but left-sided Heart Failure because the
heart is a closed circuit; over time it affects the
opposite side of the heart. In cor pulmonale, there
is right-sided Heart Failure
Left-Sided or Biventricular Heart Failure
-
You will see pulmonary congestion and edema
because the left heart cannot keep pace with the blood
being emptied into it from the lungs.
-
The lungs get big, wet, and heavy. The normal weight
is 300-400g while these lungs are 700-800g. They are
full of fluid due to the increase in intervascular
hydrostatic pressure in the pulmonary vascular system
– it’s like a soapy sponge.
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Histology: Congestion is seen as redness in the
alveolar septae. Edema is the pink, tinged material
within the alveolar spaces.
-
Sometimes the blood vessels can burst and RBCs gain
access to alveolar space. The pigment of Hb (hemosiderin)
is ingested by phagocytes in the alveolar spaces.
These pigmented cells are called “heart failure cells”
but they can also be seen in pneumonia.
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Affects on the CNS were discussed by Dr. Klapholz.
-
You will see cyanosis of the fingers and lips on the
patient.
Right-Sided or Biventricular Heart Failure
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Principal effects are on liver-portal system drainage
and subcutaneous tissues.
·
There’s a backup of blood which leads to congestive
hepatomegaly and splenomegaly.
·
Liver morphology: Red brown pattern = nutmeg liver
due to chronic passive congestion.
·
Liver histology: Congestion occurs around central veins
of liver. Sinusoids are congested. Hypoxic hepatocytes
are located around the central vein, demonstrating
coagulative necrosis. Over time this will organize
and fibrose.
·
Subcutaneous edema is caused by increased central venous
and capillary hydrostatic pressures. According to
Starling’s forces, fluid will exude out of those vessels
and collect as a transexudate within the subcutaneous
tissues.
o
If
you’re ambulatory, gravity forces the fluid down to your
legs = dependent edema. Pedal edema affects the
feet. Pitting edema is caused by pushing into the
swollen tissues and creating a depression.
o
Generalized, severe edema (aka sarca) can cause fluid
collection within body cavities.
·
In
Congestive Heart Failure, you will have venous stasis
so thrombi can develop and travel to the lungs
causing a pulmonary thromboembolism.
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