Encyclopedia of Health and Medicine

74 The Cardiovascular System
cardiovascular care typically sponsor support
groups where people can share their worries and
fears.
Outlook
In the course of 40 years—the span of a generation—cardiovascular
disease shifted from harbinger
of restricted living and early death to a
plethora of treatment options. For many people,
living with cardiovascular disease is little different
from living without cardiovascular disease. Operations,
medications, and lifestyle interventions can
mitigate many forms of cardiovascular disease.
With the intensified focus on preventive measures
and interventions, the generation born at the turn
of the 21st century could be the first that does not
have the experience of living with cardiovascular
disease.
See also CARDIOVASCULAR DISEASE PREVENTION;
LIFESTYLE AND CARDIOVASCULAR HEALTH; RISK FACTORS
FOR CARDIOVASCULAR DISEASE.
long QT syndrome (LQTS) An ARRHYTHMIA disorder
in which an electrical conduction defect in
the HEART results in delayed repolarization of
myocardial cells. Repolarization is the process by
which myocardial cells restore themselves to
receive another electrical impulse. With LQTS, the
myocardial cells hold a positive charge much
longer than normal, preventing the heart from
recharging for the next CARDIAC CYCLE. Most LQTS
is hereditary, and researchers have isolated a
number of GENE mutations that affect the heart’s
ion channels (conductive pathways), usually
potassium channels though sometimes sodium
channels. The condition can also develop as a consequence
of STROKE or as a medication SIDE EFFECT,
notably with antiarrhythmia and ANTIDEPRESSANT
MEDICATIONS though numerous drugs affect the QT
interval.
The points Q and T on the ELECTROCARDIOGRAM
(ECG) identify polarization or discharge of electrical
activity (the Q wave) and repolarization (the T
wave). Doctors call the amount of time it takes for
this phase to complete the QT interval. The longer
the QT interval, the greater the risk for a dangerous
arrhythmia called TORSADE DE POINTES, a form
of highly unstable ventricular tachycardia (rapid
though regular contractions of the ventricles, typically
exceeding 100 contractions a minute). Torsade
de pointes can quickly lead to VENTRICULAR
FIBRILLATION, in which the ventricular contractions
are rapid, irregular, and nonfunctional. Ventricular
fibrillation quickly becomes life-threatening and
may require emergency DEFIBRILLATION. LQTS is a
common cause of SUDDEN CARDIAC DEATH in young
people who are apparently healthy.
Symptoms and Diagnostic Path
Often, people who have LQTS do not have symptoms,
and doctors detect the condition during ECG
done for other reasons. The most common symptom
that does occur is unexplained syncope (fainting),
especially with intense exercise or emotional
response (such as anger or fear). ECG generally
provides the diagnosis, though the cardiologist
may do an exercise STRESS TEST to evaluate the
heart’s electrical response with increased physical
activity.
Treatment Options and Outlook
The standard medical treatment for LQTS is a beta
blocker medication, which helps slow and stabilize
the HEART RATE. The beta blockers most commonly
prescribed for LQTS are propanolol (Inderal),
metoprolol (Lopressor or Toprol), nadolol (Corgard),
and atenolol (Tenormin). Beta blockers control
LQTS in about 70 percent of people who have
the condition. When medications fail to prevent
arrhythmias, the next level of treatment is an
IMPLANTABLE CARDIOVERTER DEFIBRILLATOR (ICD), an
electronic device similar to a PACEMAKER. The ICD
monitors the heart’s rhythm and can deliver an
electrical shock to return the heart to a normal
rhythm should dangerous arrhythmias occur.
Because a prolonged QT interval is most likely
to occur during intense physical exercise that puts
high demand on the heart LQTS may require
lifestyle modifications, especially for people who
participate in competitive sports. Most people are
able to enjoy recreational athletic and physical
activities, however.
Risk Factors and Preventive Measures
Gene mutations establish the foundation for
LQTS, probably even in secondary LQTS (LQTS