that would challenge even someone in peak car-
diovascular function. Neither extreme is healthy
and can result in further health problems. A per-
son who has not been physically active for years
to decades often benefits from the advice and sug-
gestions of a health expert who can help deter-
mine an appropriate entry point for returning to
an active lifestyle.
Recent studies affirm that cardiac rehabilitation
has therapeutic value for people who have
chronic cardiovascular conditions such as conges-
tive HEART FAILURE, improving symptoms and QUAL-
ITY OF LIFE. Many people will begin cardiac
rehabilitation before leaving the hospital after
treatment or surgery, starting with an exercise
STRESS TESTto determine cardiopulmonary capac-
ity, and continue in a structured way for 3 to 6
months. Under ideal circumstances the activities
of rehabilitation, including EATING HABITS and
nutrition, become elements of routine daily living
and foster a lifestyle that supports cardiovascular
health.
See alsoDIET AND HEALTH; EXERCISE AND HEALTH;
LIFESTYLE AND CARDIOVASCULAR HEALTH; NUTRITIONAL
ASSESSMENT; NUTRITIONAL NEEDS; PHYSICAL EXERCISE
AND CARDIOVASCULAR HEALTH; SEXUAL ACTIVITY AND
CARDIOVASCULAR DISEASE.
cardiac resynchronization therapy (CRT) A
method of biventricular pacing in which an
implanted device regulates and coordinates the
contractions of both ventricles, typically to treat
severe HEART FAILURE. SUDDEN CARDIAC DEATHas a
result of ARRHYTHMIAis a significant risk in HEART
failure, particularly heart failure resulting from
dilated CARDIOMYOPATHY. Certain BUNDLE BRANCH
BLOCKarrhythmias also benefit from CRT.
Conventional pacing therapy stimulates only
the right ventricle, which in an otherwise healthy
heart results in contraction of both ventricles as
the electrical impulse spreads simultaneously
across them. In severe heart failure, however,
both ventricles are extensively damaged and do
not function in synchronization. Conventional
pacing therapy ends up being counterproductive
by further extending the dysfunction between the
two ventricles. A biventricular PACEMAKERhas two
leads (wires that conduct electrical impulses), one
of which the cardiologist inserts in each ventricle.
The pacemaker’s discharge sends impulses simul-
taneously to each lead.
The risks of CRT are similar to those of conven-
tional pacing therapy and include possible INFEC-
TIONor blood clots from the inserted leads. These
risks are minimal, however, and CRT provides
substantial benefit for people whose arrhythmias
due to heart failure do not respond to other treat-
ments.
See also IMPLANTABLE CARDIOVERTER DEFIBRILLATOR.cardiomyopathy Weakness and loss of pumping
effectiveness of the HEART, usually with changes to
the structure of the heart and in particular the left
ventricle. Cardiomyopathy is as likely to affect
people under age 40 as people over age 60 and is a
leading cause of HEART FAILUREresulting in HEART
TRANSPLANTATION. Genetic factors can play a role in
cardiomyopathy, especially in younger people,
though lifestyle factors such as nutrition and ALCO-
HOLconsumption are also significant. Viral and
bacterial infections of the heart (MYOCARDITITIS) can
leave the heart MUSCLEdamaged. In many situa-
tions, however, doctors do not know what causes
the structural and functional changes in myocar-
dial (heart muscle) cells that result in primary car-
diomyopathy. Secondary cardiomyopathy may
also develop as a consequence of other CARDIOVAS-
CULAR DISEASE(CVD), such as ISCHEMIC HEART DISEASE
(IHD) and HYPERTENSION(high BLOOD PRESSURE).
The five major types of cardiomyopathy are- Dilated cardiomyopathy, in which the heart
enlarges in an attempt to compensate for dam-
age to myocardial cells that limits the heart’s
ability to efficiently pump BLOOD. Long-term
ALCOHOLabuse accounts for the dilated car-
diomyopathy in about a third of the people
who develop it. Deficiency of vitamin B 1 also
damages the heart. Though uncommon in the
general US population, vitamin B 1 deficiency
can occur with long-term, heavy alcohol con-
sumption as well as with long-term EATING
DISORDERS such as anorexia nervosa. Dilated
cardiomyopathy is more common in people
over age 60. - Hypertrophic cardiomyopathy, in which
the walls of the heart, particularly the ventri-
cles, thicken. Some doctors may refer to this
cardiomyopathy 31