Sinus Rhythm Disturbances
Some rhythm disturbances are due to a malfunction of the heart's pacemaker cells. These commonly occur
in one of two forms: bradycardia, in which the heart beats at an abnormally slow rate, and tachycardia,
in which it pulsates at 100 or more beats per minute. In itself, neither condition is particularly
worrisome. In fact, a slow heart rate is often found in highly trained athletes whose hearts have been
conditioned to beat more slowly, pumping a greater volume of blood per beat. In some older people, however,
an abnormally slow beat may be a sign of an underlying disease. In such cases, there is usually a telltale
rhythm of fast beats followed by slow ones. And while this pattern is not necessarily a cause for concern,
in some individuals it can lead to loss of consciousness or dizziness due to poor output of blood from the
heart. In these cases, an artificial pacemaker may stabilize the heartbeat.
Tachycardia arising in the pacemaker cells also may be harmless. The exceptions include an accelerated rapid
heartbeat, which may indicate congestive heart failure, or conditions in which there is both a rapid beat and
some other problem involving the heart and blood vessels.
Atrial Rhythm Disturbances
Though the relay cells in the atrium chamber are designed to pass on beat impulses sent out by the pacemaker
cells, sometimes they acquire the ability to produce a beat on their own. Since such beats occur just before
the "true" heartbeat, they are known as atrial premature beats. Commonly associated with the heavy use of
tobacco, alcohol and coffee, these beats disappear once the stimulants are removed. However, when they are
accompanied by palpitation, fluttering in the chest, rapid heartbeat, dizziness or shortness of breath, they
may indicate underlying heart disease. In such cases, treatment with drugs may be indicated.
Potentially far more serious is atrial fibrillation, a condition in which the muscles of he atrium contract
in an erratic, uncoordinated fashion. In most instances, it can be corrected by drugs; at times, it may be
necessary to employ a technique called cardioversion, a type of electrical shock designed to restore normal
rhythm. One major complication of atrial fibrillation is blood clotting. Usually, these clots from in the left
atrium and then move out into the general circulatory system, where they can produce a potentially serious
blockage. Anti-clotting drugs are therefore often prescribed for people with this condition.
