also cannot conduct electrical impulses to reach
undamaged tissue. Myocardial infarction results in
“dead” areas of the heart MUSCLEthat cannot par-
ticipate in the CARDIAC CYCLE, which often results
in ARRHYTHMIAas well as ineffective pumping abil-
ity. 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 BLOODaround 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) andECHOCARDIOGRAM
are the diagnostic procedures that typically iden-
tify 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 treat-
ment 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 BLOODfrom the CORONARY ARTERIESinto the
tissues of the MYOCARDIUM(HEART MUSCLE). The test
usually involves a resting and an exercise compo-
nent, to provide a comprehensive picture of how
much blood the heart receives to assess the extent
to which CORONARY ARTERY DISEASE(CAD) is reduc-
ing cardiac function. The procedure takes about an
hour and requires little preparation (namely,
abstaining from STIMULANTSsuch as CAFFEINEand
NICOTINEfor 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
VEINin 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 pat-
tern 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 dipyri-
damole) to chemically simulate the effects of exer-
cise on the heart. People who have ANGINA
PECTORISor 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 INFLAMMATIONof the HEART MUSCLE,
often as a consequence of viral INFECTIONthat orig-
inates 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 myocardi-
tis is giant cell myocarditis, an autoimmune disor-
der that specifically attacks the heart.
Myocarditis may have few symptoms until
there is significant damage to the heart (com-
monly in the form of CARDIOMYOPATHY and
ARRHYTHMIA), and often is life-threatening. Symp-
toms of early or chronic myocarditis may mimic
those of INFLUENZAor 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 maymyocarditis 87