468
U N I T 5
Circulatory Function
Cardiomyopathies
Cardiomyopathies are disorders of the heart muscle.
They are usually associated with disorders of myocar-
dial performance, which may be mechanical (e.g., heart
failure) or electrical (e.g., life-threatening arrhythmias).
The definition and classification of the cardiomyopathies
have evolved tremendously with the advance of molecu-
lar genetics. The American Heart Association’s classifica-
tion system divides the cardiomyopathies into two major
groups: primary cardiomyopathies, which are confined
to the myocardium, and secondary cardiomyopathies,
which are associated with other disease conditions.
45
Primary Cardiomyopathies
The primary cardiomyopathies are classified as genetic,
mixed, or acquired, based on their etiology.
45
The genetic
cardiomyopathies include hypertrophic cardiomyopathy
and arrhythmogenic right ventricular dysplasia. The
mixed cardiomyopathies, which include dilated and
restrictive cardiomyopathy, are of both genetic and non-
genetic origin. Acquired cardiomyopathies include those
that have their origin in the inflammatory process (e.g.,
myocarditis), pregnancy (peripartum cardiomyopathy),
and stress (takotsubo cardiomyopathy). In many cases
the cause is unknown, and in these cases it is referred to
as an idiopathic cardiomyopathy.
Hypertrophic Cardiomyopathy
Hypertrophic cardiomyopathy (HCM) is character-
ized by unexplained left ventricular hypertrophy with
disproportionate thickening of the ventricular septum,
abnormal diastolic filling, cardiac arrhythmias, and, in
some cases, intermittent left ventricular outflow obstruc-
tion (Fig. 19-18). It is one of the most common types of
cardiomyopathy, occurring in approximately 1 out of
500 persons in the general population.
46
Hypertrophic
cardiomyopathy is the most common cause of sudden
cardiac death in young athletes.
47
Hypertrophic cardiomyopathy is an autosomal dom-
inant disorder caused by mutations in genes encoding
proteins of the cardiac sarcomere (i.e., muscle fibers).
Histologically, HCM specimens have myocyte hypertro-
phy with myofibril disarray and increased cardiac fibro-
sis. More than 400 mutations have been identified in
11 sarcomeric genes.
46–48
Although HCM is inherited,
it may present at any time from early childhood to late
adulthood with a broad category of manifestations and
a variable clinical course.
Clinically, HCM is characterized by a massively
hypertrophied left ventricle with a reduced chamber size
and a paradoxical decrease in stroke volume that results
from impaired diastolic filling; in about 25% of cases,
dynamic obstruction of left ventricular outflow occurs
due to disproportionate thickening of the interventricu-
lar septum.
6
Hypertrophic cardiomyopathy is frequently
associated with the development of left ventricular
or exudate, how quickly it accumulates, and the
elasticity of the pericardium determine the effect
the effusion has on cardiac function.
■■
Cardiac tamponade represents a life-threatening
compression of the heart resulting from excess
fluid in the pericardial sac. It may be caused
by bleeding into the pericardial sac due to
conditions such as chest trauma or rupture of the
heart following myocardial infarction.
■■
In constrictive pericarditis, scar tissue develops
between the visceral and parietal layers of the
serous pericardium. In time, the scar tissue
contracts and interferes with cardiac filling.
SUMMARY CONCEPTS
(continued)
FIGURE 19-18.
Normal heart
(A)
and
hypertrophic cardiomyopathy
(B)
in
which disproportionate thickening of the
intraventicular septum causes intermittent left
ventricular outflow obstruction.
A
B
