Heart Rhythm Disorders (cont.)
Premature atrial contractions (PACs) and premature ventricular contractions (PVCs)
Every person experiences the occasional
palpitation, where the atrium or the ventricle beats early. These PACs (premature atrial contractions) or PVCs (premature ventricular contractions) are normal variations and most people are unaware of their occurrence, however, some patients report palpitations in the chest and neck. PACs and PVCs in healthy individuals generally do not pose any health risks.
Sinus tachycardia
The heart, its cells, and its electricity may come under many outside
influences where it may beat more quickly. Sinus tachycardia - (sinus=from the SA node + tachy=rapid + cardia + heart) or
a rapid regular heartbeat - is a common rhythm issue. It occurs when the body
asks the heart to pump more blood, or when the electrical system is stimulated
by chemicals.
The body needs increased cardiac output in time of
physiologic stress.
Cardiac output is the amount of blood the heart pumps in the course of one minute.
It can be calculated by the amount of blood that the heart pumps with each beat
(stroke volume) multiplied by the
heart rate. Since the stroke volume tends not
to change too much, it is the heart rate that has to increase to meet the body's
needs. Examples include exercise,
in which the muscles have greater oxygen requirements and the heart rate speeds
up to pump more blood to meet that need,
dehydration, in which the stroke volume may fall a little since there
is less fluid in the body and the heart rate has to speed up to compensate, or
with acute blood loss such as after an accident.
The electrical system can be stimulated in a variety of ways to make the
heart beat faster. In times of stress, the body generates adrenaline, and among
other symptoms it produces, it can make the heart beat faster. Think of being
frightened and feeling your heart race. Increased thyroid hormone levels in the
body can also cause a tachycardia. Ingestion of a variety of drugs can also
cause the heart to race, including caffeine,
alcohol, and
over-the-counter cold
medications that include drugs like phenylephrine. These compounds get
metabolized by the body to act like adrenaline on the heart. Illegal drugs like
methamphetamine and
cocaine can also cause a sinus tachycardia.
Next: Sinus bradycardia »
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