clots, such as with myocardial infarction or stroke,
the doctor injects the agent into a vein for distri-
bution throughout the circulation. Thrombolytic
agents remain active in the bloodstream for 15 to
90 minutes, depending on the agent. With prompt
initiation of thrombolytic therapy, the agent dis-
solves the clot and the person experiences little or
no adverse effects as a consequence of the throm-
bolytic event.
See also ANTICOAGULANT THERAPY; IMMUNE
RESPONSE.
torsade de pointes A life-threatening ventricu-
lar tachycardia (rapid contractions of the ventri-
cles) that is the most serious complication of the
ARRHYTHMIAdisorder LONG QT SYNDROME(LQTS). Tor-
sade de pointes is a distinctive pattern of QRS
complex electrical activity, QRS being the points
on the ELECTROCARDIOGRAM(ECG) that identify ven-
tricular contraction.
The term “torsade de pointes” means “twisting
around the points.” In ballet, the term’s origination,
the term identifies a movement in which multiple
steps rotate the dancer around an imaginary axis.
On the ECG, the QRS complex appears to twist
around the electrical baseline with a continuously
changing point of origin, reminiscent of the ballet
movement. The pattern represents a progressive
change in myocardial cell polarity (abnormal shifts
in the cell’s electrical charge), a marked dysfunc-
tion of the heart’s electrical pacing and conduction
mechanisms. Unless interrupted, torsades de
pointes results in SUDDEN CARDIAC DEATH.
The ECG provides definitive diagnosis. Torsade
de pointes may stop spontaneously or may require
emergency medical intervention such as DEFIBRIL-
LATION(electrical shock to restore normal rhythm)
or a temporary PACEMAKER. Numerous medications
can cause acquired LQTS and consequently tor-
sade de pointes, including the commonly pre-
scribed antibiotic erythromycin, ANTIPSYCHOTIC
MEDICATIONSsuch as the phenothiazines, and most
drugs that affect the heart’s function such as those
to treat arrhythmias, HEART FAILURE, and HYPERTEN-
SION(high BLOOD PRESSURE). COCAINEalso can cause
torsade de pointes. Stopping the causative DRUG
typically ends the torsade de pointes.
See also HEART; HYPOCALCEMIA; HYPOKALEMIA;
MEDICATIONS TO TREAT CARDIOVASCULAR DISEASE.
transient ischemic attack (TIA) A brief, episodic
interruption of the flow of BLOODto the BRAIN,
often called a mini-STROKE. The most common
cause of a TIA is a fragment of ATHEROSCLEROTIC
PLAQUEor a BLOODclot that breaks free and travels
through the blood circulation until it lodges in an
ARTERYor arteriole. TIAs also can be hemorrhagic,
the result of small ruptures in the tiny arteries in
the brain, often a consequence of untreated HYPER-
TENSION(high BLOOD PRESSURE) and CAROTID STENOSIS
(narrowing and occlusion of the carotid artery in
the neck). ATRIAL FIBRILLATIONand VALVULAR HEART
DISEASEare other common sources of clots.
Symptoms of TIA are brief and temporary and
may include- episodes of SYNCOPE(loss of CONSCIOUSNESS) or
“freezing,” in which the person appears con-
scious and alert but does not respond - episodes of tingling or numbness affecting the
face or parts of the body such as the fingers or
hand, typically only on one side of the body - temporary inability to use the arm or leg, or
both, on one side of the body - lapses in cognitive function or memory
TIAs are more common in people over age 70.
Doctors generally consider them to be warning
signs of impending stroke. Early diagnosis and
therapeutic intervention can help avert full-
fledged stroke. The diagnostic path typically
includes imaging procedures such as COMPUTED
TOMOGRAPHY(CT) SCANor MAGNETIC RESONANCE IMAG-
ING(MRI). Treatment may include ANTICOAGULA-
TION THERAPYto reduce the blood’s tendency to clot
as well as medications to treat arrhythmias
(notably atrial fibrillation), hypertension, and
HYPERLIPIDEMIA(elevated blood lipid levels), if these
conditions are present. The cardiologist may rec-
ommend carotid ENDARTERECTOMY when carotid
stenosis is a causative factor.
See also ARRHYTHMIA; CARDIOVASCULAR DISEASE
PREVENTION; COGNITIVE FUNCTION AND DYSFUNCTION;
MICROINFARCTION.transmyocardial laser revascularization (TMLR)
A treatment for ANGINA PECTORISand ISCHEMIC HEART
DISEASE(IHD) in which the cardiovascular surgeontransmyocardial laser revascularization (TMLR) 111