470
U N I T 5
Circulatory Function
The heart is enlarged (two to three times its normal
weight) and flabby with dilation of all four chambers
(Fig. 19-19). Because of wall thinning that accompa-
nies dilation, the ventricular thickness may be less than,
equal to, or greater than normal. The histologic abnor-
malities in DCM are nonspecific. Microscopically, most
myocytes are hypertrophied with enlarged nuclei, but
many are thinned, stretched, and irregular or atrophied.
Clinical Manifestations.
The most common clinical
manifestations of DCM are those related to heart fail-
ure, such as dyspnea, orthopnea, and reduced exercise
capacity. In the end stages, persons with DCM often
have ejection fractions of less than 25% (normal ejec-
tion fraction 50% to 65%).
6
As the disease progresses,
stasis of blood in the walls of the heart chambers can
lead to thrombus formation and systemic emboli.
Secondary mitral valve regurgitation and abnormal car-
diac rhythms are common. Death is usually due to heart
failure or arrhythmias and can occur suddenly.
Treatment.
The treatment of DCM is directed toward
relieving the symptoms of heart failure, reducing the
work of the heart, and preventing atrial and ventricular
dysrhythmias. Pharmacologic agents include diuretics to
reduce preload, beta blockers to reduce heart rate and
myocardial oxygen demand, afterload-reducing agents
to decrease left ventricular filling pressures, and angio-
tensin converting enzyme (ACE) inhibitors to prevent
vasoconstriction. Anticoagulant and antiarrhythmic
drugs (e.g., amiodarone for atrial fibrillation) may be
used. Other treatments may include a biventricular
pacemaker, an implantable cardioverter–defibrillator
for chronic symptomatic DCM with reduced systolic
function, and in cases that are refractory to treatment,
cardiac transplantation. The prognosis for patients with
DCM who do not undergo cardiac transplantation is
poor with the average 5-year survival rate being less
than 50%. Removing or avoiding causative agents (if
identified); avoiding myocardial depressants, including
alcohol; and spacing rest with asymptomatic levels of
exercise or activity are also important.
Primary Restrictive Cardiomyopathy
Restrictive cardiomyopathy is a rare form of heart
muscle disease in which ventricular filling is restricted
because of excessive rigidity (but not necessarily thick-
ening) of the ventricular walls, although the contractile
properties or systolic function of the heart remain rela-
tively normal.
6
Restrictive cardiomyopathy can be idio-
pathic or associated with other conditions that affect the
myocardium, principally radiation fibrosis, amyloidosis,
sarcoidosis, or metastatic tumors. Genetics may also
play a role because familial forms of restrictive cardio-
myopathy have been reported.
46
Symptoms of restrictive cardiomyopathy include
dyspnea, PND, orthopnea, peripheral edema, ascites,
fatigue, and weakness. The manifestations of restrictive
cardiomyopathy resemble those of constrictive pericar-
ditis. In the advanced form of the disease, all the signs of
heart failure are present except cardiomegaly.
Myocarditis
Myocarditis, or inflammatory cardiomyopathy, can be
defined as an inflammation of the heart.
6,51,52
The clinical
spectrum of the disease is broad: at one end, the disease
is asymptomatic with full recovery, and at the other end
it has a precipitous onset of heart failure or arrhythmias,
occasionally with sudden cardiac death.
An acquired cardiomyopathy, myocarditis is associ-
ated with a number of etiologies; however, it is usually
caused by a viral infection, most commonly an entero-
virus (coxsackievirus group B).
6,52–54
In young children
adenovirus and parvovirus are the most likely causative
agents. Other etiologies include bacterial or fungal
infections, hypersensitivity to certain drugs, and auto-
immune diseases, such as systemic lupus erythematosus.
Myocarditis is a frequent pathologic cardiac finding
in persons with acquired immunodeficiency syndrome
(AIDS), although it is unclear whether it is due to the
human immunodeficiency virus infection itself or to sec-
ondary infections.
The pathogenesis of myocarditis is one of cardiac
injury, followed by an immunologic response.Myocardial
injury due to infectious agents is thought to result from
necrosis caused by direct invasion of the offending organ-
ism, toxic effects of exotoxins or endotoxins produced
by a systemic pathogen, or destruction of cardiac tissue
by immunologic mechanisms initiated by the infectious
agent. The immunologic response may be directed at for-
eign antigens of the infectious agent that share molecular
characteristics with those of the host cardiac myocytes
(i.e., molecular mimicry; see Chapter 16), providing a
continuous stimulus for the immune response even after
the infectious agent has been cleared from the body.
FIGURE 19-19.
Idiopathic dilated cardiomyopathy. A
transverse section of the enlarged heart reveals conspicuous
dilation of both ventricles. Although the ventricular wall
appears thinned, the increased mass of the heart indicates
considerable hypertrophy. (From Saffitz JE.The heart. In:
Rubin E, Strayer DS, eds. Rubin’s Pathology: Clinicopathologic
Foundations of Medicine., 6th ed. Philadelphia, PA: Wolters
Kluwer Health | Lippincott Williams &Wilkins; 2012:525.)
