Pacemaker (cont.)
What are the causes of slow heart rates?
Abnormally slow heart rates (bradycardias) can result from
diseases affecting the SA node, the conduction tissues, and the AV
node. Sick sinus syndrome is a disease wherein the SA node cannot
generate signals frequently enough to maintain adequate heart rate.
Heart blocks are conditions where diseases (such as heart attacks) or
degeneration (due to processes such as aging) of the AV node and/or
the conduction tissues impair the transmission of signals from the SA
node to the heart muscles.
Some medications can cause bradycardia. Examples of these
medications include calcium channel blockers such as verapamil
(Calan) and beta-blockers such as propanolol (Inderal) and digoxin
(Lanoxin). These medications can also aggravate bradycardias in
patients with existing diseases of the SA node, AV node, and other
parts of the heart's conduction system.
The most common cause of bradycardia is degeneration of the
conduction system that occurs as part of the aging process. Thus,
people are more likely to need a pacemaker as they get older, both as
part of the aging process and because older patients tend to have
more medical problems that can cause slow heartbeats.
What happens when the heart beats too
slowly?
When the heart beats too slowly, an insufficient amount of blood
reaches the organs. An insufficient supply of oxygen and nutrients
can lead to malfunction and failure of the organs. The organ most
affected by the lack of oxygen and glucose is the brain. Symptoms of
insufficient blood supply to the brain include lightheadedness,
forgetfulness, and loss of consciousness. Symptoms of inadequate
blood supply to the muscles include tiredness, malaise, and fatigue.
An insufficient blood supply to other organs can lead to heart,
kidney, and liver failure. When an abnormally slow heart rate causes
symptoms and/or organ failures, treatment for the slow heart rate
becomes necessary.
Highly trained athletes with efficient cardiovascular systems can
deliver all the oxygen and the nutrients the body needs with very
slow heart rates. They typically have abnormally slow heart rates
without any adverse symptoms or organ failures. Slow heart rates
because of physical fitness do not need treatment.
Next: How can slow heart rate be increased? »
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