Encyclopedia of Health and Medicine

myocarditis 87
also cannot conduct electrical impulses to reach
undamaged tissue. Myocardial infarction results in
“dead” areas of the heart MUSCLE that cannot participate
in the CARDIAC CYCLE, which often results
in ARRHYTHMIA as well as ineffective pumping ability.
The cellular structure of these areas changes,
initially becoming soft and subsequently becoming
fibrous (scarlike). New arteries are often able to
develop, through a process called angiogenesis, to
carry BLOOD around infarcted areas of the heart.
This helps the rest of the heart remain functional.
However, large infarctions may overcome the
heart, resulting in heart attack or CARDIAC ARREST.
ELECTROCARDIOGRAM (ECG) and ECHOCARDIOGRAM
are the diagnostic procedures that typically identify
myocardial infarction. Treatment includes
eliminating the cause of the infarction, such as
coronary artery occlusion, and stabilizing the
heart’s function to the best extent possible with
medications. Because CAD is nearly always the
culprit, ANGIOPLASTY or CORONARY ARTERY BYPASS
GRAFT (CABG) are nearly always among the treatment
options.
See also CARDIOVASCULAR DISEASE PREVENTION;
MEDICATIONS TO TREAT CARDIOVASCULAR DISEASE;
MICROINFARCTION; MYOCARDIAL PERFUSION IMAGING;
STROKE; SURGERY BENEFIT AND RISK ASSESSMENT; TRAN-
SIENT ISCHEMIC ATTACK (TIA).
myocardial perfusion imaging A radionuclide
procedure that allows cardiologists to observe the
flow of BLOOD from the CORONARY ARTERIES into the
tissues of the MYOCARDIUM (HEART MUSCLE). The test
usually involves a resting and an exercise component,
to provide a comprehensive picture of how
much blood the heart receives to assess the extent
to which CORONARY ARTERY DISEASE (CAD) is reducing
cardiac function. The procedure takes about an
hour and requires little preparation (namely,
abstaining from STIMULANTS such as CAFFEINE and
NICOTINE for 48 hours before the procedure).
The cardiologist administers a small amount of
a radioactive substance, called a radionuclide or
radioisotope (most commonly thallium), into a
VEIN in the back of the hand or in the arm. The
radionuclide is mixed in a solution, usually GLU-
COSE, that the blood carries to the cells. The
radionuclide rides along as a “tag” on the glucose
molecules, accompanying them into the cells. The
radionuclide rapidly disintegrates, releasing a pattern
of electromagnetic energy called gamma-rays.
A special device called a gamma camera detects
the gamma rays, and presents them as images.
The concentrations of energy tell cardiologists
where myocardial blood flow is strong and where
it is restricted, helping identify areas of ischemia
(oxygen-deprived tissue).
When actual physical exercise is not feasible,
the cardiologist may use a DRUG (often dipyridamole)
to chemically simulate the effects of exercise
on the heart. People who have ANGINA
PECTORIS or significant CAD may feel temporary
discomfort during this simulation. There are no
side effects from myocardial perfusion imaging.
The radionuclides cardiologists use emit minimal
radioactivity and are gone from the body within a
few hours.
See also COMPUTED TOMOGRAPHY (CT) SCAN;
ECHOCARDIOGRAM; MAGNETIC RESONANCE IMAGING
(MRI); POSITRON EMISSION TOMOGRAPHY (PET) SCAN;
SINGLE PHOTON EMISSION COMPUTED TOMOGRAPHY
(SPECT) SCAN.
myocarditis INFLAMMATION of the HEART MUSCLE,
often as a consequence of viral INFECTION that originates
elsewhere in the body (such as a cold).
Viruses known to cause myocarditis include
MEASLES, RUBELLA, coxsackie, and CYTOMEGALOVIRUS
(CMV). Myocarditis also may be bacterial, or the
consequence of cardiotoxic exposure (such as to
radiation or carbon monoxide). The autoimmune
processes of systemic inflammatory disorders such
as SYSTEMIC LUPUS ERYTHEMATOSUS (SLE), SARCOIDOSIS,
and RHEUMATOID ARTHRITIS also can involve the
myocardium. A rare and severe form of myocarditis
is giant cell myocarditis, an autoimmune disorder
that specifically attacks the heart.
Myocarditis may have few symptoms until
there is significant damage to the heart (commonly
in the form of CARDIOMYOPATHY and
ARRHYTHMIA), and often is life-threatening. Symptoms
of early or chronic myocarditis may mimic
those of INFLUENZA or of HEART ATTACK. Diagnosis is
by myocardial biopsy performed via CARDIAC
CATHETERIZATION, which reveals the infiltration of
lymphatic cells and other characteristic changes in
the myocardium that identify an inflammatory
process. Chronic or advanced myocarditis may