Premature Ventricular Contractions (cont.)
What are the dangers of premature ventricular contractions?
Premature ventricular contractions in healthy
individuals without high blood pressure and heart diseases do not pose any
health risks. Premature ventricular contractions in patients with heart diseases
(heart attacks, heart failure, diseases of the heart valves)
may be associated with
increased risks of developing ventricular tachycardia. Ventricular tachycardia
is a sustained run of rapid ventricular contractions. Ventricular tachycardia is
life-threatening because: 1) it occurs suddenly with no prior warning, and 2) it
frequently develops into ventricular fibrillation. Ventricular fibrillation is a chaotic rhythm where the
ventricles quiver rapidly in a purposeless fashion. The heart with ventricular
fibrillation cannot pump blood effectively to the brain
and the rest of the body. If untreated, ventricular fibrillation can be fatal
within minutes. An estimated 250,000 Americans die in this way each year.
Many doctors believe that premature ventricular contractions do not necessarily cause ventricular tachycardias or ventricular fibrillations. Instead, premature ventricular contractions may be merely indicators (symptoms) of serious heart diseases or other serious conditions
such as hypokalemia, hypoxia, and on-going heart damage from heart attacks, or
medications such as digoxin
and
aminophylline toxicity. It must be emphasized that many
premature ventricular contractions are harmless (benign) and not associated with structural heart disease. If the work up for underlying heart disease is unrevealing, the patient can be assured that their prognosis is excellent.
How is premature ventricular contraction diagnosed?
There are two aspects in the diagnosis of premature
ventricular contractions; detecting them, and diagnosing the underlying causes.
Electrocardiograms (ECG EKG) and Holter monitors are used to diagnose premature ventricular
contractions. EKGs, blood tests, echocardiograms,
and cardiac stress tests are used to
determine the underling causes of premature ventricular contractions.
Electrocardiogram (EKG, ECG)
An electrocardiogram (EKG,
ECG) is a brief recording of the
heart's electrical discharges. EKGs can be performed in the doctors' offices,
clinics, and hospital emergency rooms. Doctors frequently ask for a rhythm strip
(a prolonged EKG recording) to be performed at the same time as EKG to increase
the chances of detecting premature ventricular contractions and other abnormal rhythms. The premature ventricular contractions are easy to recognize on EKG
and rhythms strips, provided premature ventricular contractions occur during the recording. EKG may also
demonstrate other problems such as heart attacks, hypokalemia, digoxin toxicity,
heart muscle thickening (hypertrophy) due to long term high blood pressure.
Holter monitor
A standard EKG and a rhythm strip performed at the time
of a visit to the doctor's office may not detect the premature ventricular
contractions because they may not be occurring at that moment.
Holter monitoring is then
necessary to detect the premature ventricular contractions in these patients with heart palpitations. A Holter
monitor is a continuous recording of the heart's rhythm for 24 hours. Holter
monitoring can be used diagnose premature ventricular contractions as well as other
heart rhythm abnormalities
such as atrial fibrillation, atrial flutter, and ventricular tachycardias.
Since more than 50% of middle aged men
can have premature ventricular contractions during Holter monitoring, not all
premature ventricular contractions found during Holter
monitoring are clinically important. Doctors interpreting the Holter monitoring
studies must take into account the patient's medical history in determining the
importance of Holter monitor findings.
In patients with infrequent symptoms an event marker may be used in lieu of a Holter monitor as this can be worn for up to 30 days.
Echocardiography
Echocardiography uses
ultrasound waves to produce images of the heart's
chambers and valves and the lining around the heart (pericardium).
Echocardiography is useful in measuring the size of the heart chambers, the
forcefulness of heart ventricle contractions, the thickness of the heart
muscles, and the functioning of the heart valves. Echocardiography is therefore
useful in diagnosing conditions that can cause premature ventricular
contractions such as:
- Mitral valve prolapse: Echocardiography can detect and measure the severity
of mitral valve prolapse
and other valvular diseases.
- Muscle hypertrophy: Echocardiography can detect heart muscle hypertrophy
(thickening of heart muscle) as a result of long term high blood pressure.
- Heart muscle damage: Echocardiography can measure the extent of heart
muscle damage from heart attacks or cardiomyopathy.
- Ejection fraction: Echocardiography can be
used to calculate the ejection fraction of the left ventricle. Ejection fraction
is a measure (estimate) of the amount of blood pumped during each contraction of
the ventricle. Heart ventricles extensively weakened by heart attacks or
cardiomyopathy will have low ejection fractions. Patients with low ejection
fractions have higher risks of developing life threatening ventricular
tachycardias and fibrillations than patients with normal ejection fractions.
Exercise cardiac stress test
(treadmill stress test)
Exercise cardiac stress testing (ECST) is the most
widely used cardiac stress test. The patient exercises on a treadmill according
to a standardized protocol with progressive increases in the speed and elevation of the treadmill
(typically changing at three minute intervals). During the ECST, the patient's
electrocardiogram (EKG), heart rate, heart
rhythm, and blood pressure are continuously monitored. If a coronary arterial
blockage results in decreased blood flow to a part of the heart during exercise,
certain changes may be observed in the EKG, including increase in premature
ventricular contractions and development of ventricular
tachycardias.
Adjuncts to ECST (stress echo and nuclear imaging)
Another supplement to the routine ECST is stress
echocardiography. During stress echocardiography, the sound waves of ultrasound
are used to produce images of the heart at rest and at the peak of exercise. In
a heart with normal blood supply, all segments of the left ventricle (the major
pumping chamber of
the heart) exhibit enhanced contractions of the heart muscle during peak
exercise. Conversely, in the setting of cardiovascular disease, if a segment of the left ventricle does not receive optimal blood
flow during exercise, that segment will demonstrate reduced contractions of
heart muscle relative to the rest of the heart on the exercise echocardiogram.
Stress echocardiography is very useful in enhancing the interpretation of the
ECST, and can be used to exclude the presence of significant cardiovascular
disease in patients suspected of having a "false-positive" ECST. Alternatively, nuclear imaging may be used as an adjunct to ECST and may be even more sensitive in noninvasively detecting underlying coronary artery disease.
Blood tests in diagnosing causes of premature ventricular contractions
Blood tests for diagnosing
conditions that can cause premature ventricular contractions include:
- blood electrolyte levels can be performed to detect low potassium or magnesium levels (hypokalemia and hypomagnesemia);
- blood drug levels can be performed to detect digoxin
and aminophylline drug toxicity
or thyroid levels, for example, an
overactive thyroid may
result in premature ventricular contractions;
- blood oxygenation
(oximetry) can be measured to detect hypoxia;
- blood tests can be performed to detect illicit drugs,
such as amphetamine abuse; and
- blood levels of cardiac enzymes [creatine phosphokinase (CPK), troponins
(regulatory proteins)] can be performed to assess for heart muscle
damage as a result of heart attacks.
Next: What are the treatments for premature ventricular contractions? »
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