Thoracic Imaging 2003 - Society of Thoracic Radiology

Cardiomyopathy
Martin J. Lipton, M.D.
Objectives
• Define cardiomyopathy
• Describe the classification
• Discuss etiology & pathophysiology
• Summarize the diagnostic approaches
• Describe the CT & MR Imaging characteristics
Cardiomyopathy is a difficult and confusing topic. There is a
great need to simplify the entity and explain the important role,
which cardiac CT and MRI can play in diagnosing and managing
this complex group of disorders. Once thought to be rare,
there is evidence that the incidence is greater than 1 in 500.
Cardiomyopathy was first used to describe a group of diseases
of the myocardium of unknown etiology [1]. The term
excludes patients with coronary atherosclerosis, valvular heart
disease, and arterial hypertension[2]. Three basic types of cardiomyopathy
have been described by the World Health
Organization (WHO) as illustrated in Table I.
Table I
Cardiomyopathy – Clinical Classification
• Hypertrophic or obstruction (HCM) – resembling aortic valve
stenosis
• Dilated (congestive) (DCM) – often resembling severe coronary
artery disease
• Restrictive (RCM) – resembling constrictive pericarditis
More recently arrythmogenic right ventricular dysplasia
(ARVD) is regarded as a fourth type. Each cardiomyopathy corresponds
to a basic type of functional abnormality, although
ARVD is difficult to fit into this classification.
Hypertrophic Cardiomyopathy
This disorder is characterized by an inappropriate myocardial
hypertrophy without any obvious cause, such as aortic valve
stenosis or hypertension.
The disease has been widely publicized as a cause of sudden
death in athletes[3, 4]. The disease is genetically linked in about
50% and it may skip generations. Histologically in HCM there
is severe disorganization of the myofibrils and the disorder classically
involves the superior part of the interventricular septum.
The left ventricle is not dilated, and may even be small. The
hypertrophy (LVH) is dues to increased wall thickness above
and beyond the upper normal limit of 12 mm in diastole in
adults. Although a symmetric (concentric) pattern of LVH may
occur, the distribution of the hypertrophy is almost always
asymmetric, i.e. segments of LV wall are thickened to different
degrees. The ventricular septum usually shows the greatest magnitude
of hypertrophy, furthermore the disease has been well
documented at nearly all ages from infancy to the elderly[5].
Asymmetric septal HCM, previously called, idiopathic
hypertrophic subaortic stenosis (IHSS), is the most common
subtype. LV outflow obstruction occurs due to the apposition of
the anterior mitral valve leaflet to the septum during systole, but
this varies in degree, and does not occur in all patients.
An apical variety of HCM also occurs and is seen most commonly
in Japan. The LV cavity has a ‘spade like’ appearance.
Diagnosis requires a detailed family history of cardiac illness,
chest radiographs, ECG, and echocardiography, which is
usually diagnostic. CT and MRI can demonstrate both morphology
and function. However, the majority of patients still undergo
cardiac catheterization with hemodynamic measurements
with angiocardiography. This also remains true for the other
types of cardiomyopathy, dilated and restrictive.
Pressure gradients occur in some patients, and can be severe.
These occur either in the outflow tract of the LV, or near the LV
apex during systole, when the cavity is obliterated at the mid
ventricular level.
A distorted LV cavity may be seen on left ventriculography
and has been described as resembling a ballerina’s shoe. This
appearance is due to the greatly thickened LV septum which
splints the chamber and produces angulation of the LV cavity.
LV wall thickness can be estimated from the distance between
the coronary vessels and LV cavity during coronary angiography.
Patient evaluation includes accurate measurements of the
degree of hemodynamic obstruction together with global and
regional LV wall mass and function. A major advantage of MRI
is its ability to select angled planes for more precise quantitation.
In some patients, abnormal LV diastolic dysfunction is the
dominant feature. MRI myocardial tagging has also been used
to study wall motion and strain patterns[6].
Gadolinium (Gd) – DTPA has value in two groups, those
patients suspected of a myocardial neoplasm which can mimic
myocardial hypertrophy, and patients with HCM in whom
ischemia or infarction is questioned. The later group demonstrates
increased MRI signal in ischemic areas. This does not
occur in non-hypertrophied normal myocardium[7].
Dilated Cardiomyopathy (DCM)
This syndrome involves dilatation of either the LV alone or
both ventricles. It is associated with myocardial hypertrophy
and severely depressed LV function. The degree of wall hypertrophy
is disproportionate for the degree of dilatation. Causes
include immunological, familial, toxic, metabolic, and infective
or it may be idiopathic. The final common pathway for all these
entities is often myocardial failure.
The symptoms are variable, often left heart failure is a presenting
feature, but some patients are minimally symptomatic or
have no symptoms. The chest radiograph reflects LVF often
with a normal sized heart. Imaging techniques may be non-specific
or demonstrate RV failure. LV thrombi may be present and
commonly there is global rather than regional impaired contractility.
This is an important feature, which distinguishes DCM
from coronary arterial occlusive disease.
MRI is an excellent technique to identify the morphological
and functional indices of both ventricles. RV mass is usually
normal while the LV mass is increased. The coronary arteries
are normal in all cardiomyopathies unless there is concomitant
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