Atrial Fibrillation (cont.)
What are the risk factors for developing atrial fibrillation?
There are many risk factors for developing atrial fibrillation. These risk
factors are:
- Increased age (1% of people over 60 years of age have
atrial fibrillation)
- Coronary heart disease (including heart attack)
- High blood pressure
- Abnormal heart muscle function (including congestive
heart failure)
- Disease of the mitral valve
between the left and right ventricle
- An overactive thyroid gland (hyperthyroidism
)or
overdose of thyroid medication
- Low amounts of oxygen in the blood, for example, as
occurs with lung diseases such as emphysema or chronic obstructive pulmonary
disease (COPD)
- Inflammation of the lining surrounding the heart
(pericarditis)
- Blood clots in the lung (pulmonary embolism)
- Chronic lung diseases (emphysema, asthma, COPD)
- Excessive intake of alcohol (alcoholism)
- Stimulant drug use such as cocaine or
decongestants
- Recent heart or lung surgery
- Abnormal heart structure from the time of birth
(congenital heart
disease)
About 1 in 10,000 otherwise healthy, young adults have AF without any
apparent cause or underlying heart disease. AF in these individuals usually is
intermittent, but can become chronic in 25%. This condition is referred to as
lone AF. Stress, alcohol, tobacco, or use of stimulants may play a role in
causing lone AF.
How is atrial fibrillation diagnosed?
AF can be chronic and sustained, or brief and intermittent (paroxysmal).
Paroxysmal AF refers to intermittent episodes of AF lasting, for example,
minutes to hours. The heart rate reverts to normal between episodes. In chronic,
sustained AF, the atria fibrillate all of the time. Chronic, sustained AF is not
difficult to diagnose. Doctors can hear the rapid and irregular heartbeats using
a stethoscope. Abnormal heartbeats also can be felt by taking a patient's pulse.
EKG (electrocardiogram)
An electrocardiogram (EKG) is a brief recording of the heart's
electrical discharges. The irregular EKG tracings of AF are easy to recognize
provided AF occurs during the EKG.
Holter monitor
If episodes of AF occur intermittently, a standard EKG performed at the
time of a visit to the doctor's office may not show AF. Therefore, a Holter
monitor, a continuous recording of the heart's rhythm for 24 hours, often is
used to diagnose intermittent episodes of AF.
Patient-activated event recorder
If the episodes of AF are infrequent, a 24-hour Holter recording may not
capture these sporadic episodes. In this situation, the patient can wear a
patient-activated event recorder for 1 to 4 weeks. The patient presses a button
to start the recording when he or she senses the onset of irregular heartbeats
or symptoms possibly possible caused by AF. The doctor then analyzes the
recordings at a later date.
Echocardiography
Echocardiography uses ultrasound waves to produce images of the heart's chambers and valves and the lining
around the heart (pericardium). Conditions that may accompany AF such as
mitral valve prolapse, rheumatic valve diseases, and pericarditis (inflammation of
the "sack" surrounding the heart) can be detected with echocardiography.
Echocardiography also is useful in measuring the size of the atrial chambers.
Atrial size is an important factor in determining how a patient responds to
treatment for AF. For instance, it is more difficult to achieve and maintain a
normal heart rhythm in patients with enlarged atria.
Transesophageal echocardiography (TEE)
Transesophageal echocardiography
(TEE) is a special echocardiographic technique that involves taking pictures of
the atria using sound waves. A special probe that generates sound
waves is placed in the esophagus (the food pipe connecting the mouth to the stomach).
The probe is located at the end of a long flexible tube that
is inserted through the mouth into the esophagus. This technique brings the probe very
close to the heart (which lies just in front of the esophagus). Sound waves generated by
the probe are bounced off of the structures within the heart, and the reflected
sound waves are used to form a picture of the heart. TEE is very accurate for
detecting blood clots in the atria as well as for measuring the size of the atria.
As previously discussed, blood may clot in the atria during AF, and pieces of
the clot may dislodge and travel to the brain, causing a stroke. Doctors are
especially concerned about blood clots dislodging during or after cardioversion
(the conversion of AF back into a normal heart rhythm with either drugs or
electrical shocks). Moreover, doctors believe that resumption of atrial
contractions after successful cardioversion increases the likelihood that pieces of
clot will dislodge. For these reasons, anticoagulation (thinning) of blood
usually is done prior to cardioversion. This prevents new clot from forming
while the old clot dissolves or solidifies so that pieces cannot break off. If
no clots are detected in the atria by TEE, the risk of stoke after cardioversion
is believed to be lower. Thus, some doctors use TEE to determine the risk of
stroke following cardioversion. Studies are underway to determine whether
patients with a normal TEE (no blood clots) need to have their blood thinned prior
to cardioversion.
Other tests
High blood pressure and signs of heart failure can be ascertained
(determined) during a physical examination of the patient. Blood tests are
performed to detect abnormalities in blood oxygen and carbon dioxide levels,
electrolytes, and thyroid hormone levels. Chest x-rays reveal enlargement of the
heart, heart failure, and other diseases of the lung. Exercise treadmill testing
(a continuous recording of the EKG during exercise) is a useful screening study
for detecting severe coronary artery disease.
Next: How is atrial fibrillation treated? »
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