C H A P T E R 4 5
Antiarrhythmic agents
711
CHAPTER SUMMARY
■■
Disruptions in the normal rate or rhythm of the heart
are called arrhythmias (also known as dysrhythmias).
■■
Electrolyte disturbances, decreases in the oxygen
delivered to the cells leading to hypoxia or anoxia,
structural damage that changes the conduction
pathway, acidosis or the accumulation of waste
products or drug effects can lead to disruptions in the
automaticity of the cells or in the conduction of the
impulse that result in arrhythmias. The result can be
changes in heart rate (tachycardias or bradycardias);
stimulation from ectopic foci in the atria or ventricles
that cause an uncoordinated muscle contraction;
or blocks in the conduction system (e.g. AV heart
block, bundle-branch blocks) that alter the normal
movement of the impulse through the system.
■■
Arrhythmias cause problems because they alter the
haemodynamics of the cardiovascular system. They
can cause a decrease in cardiac output related to
the uncoordinated pumping action of the irregular
rhythm, leading to lack of filling time for the
ventricles. Any of these effects can interfere with the
delivery of blood to the brain, to other tissues or to
the heart muscle.
■■
Antiarrhythmics are drugs that alter the action
potential of the heart cells and interrupt arrhythmias.
The CAST study found that the long-term treatment
of arrhythmias may actually cause cardiac death, so
these drugs are now indicated only for the short-term
treatment of potentially life-threatening ventricular
arrhythmias.
■■
Class I antiarrhythmics block sodium channels,
depress phase 0 of the action potential and generally
prolong the action potential, leading to a slowing of
conduction and automaticity.
■■
Class II antiarrhythmics are beta-adrenergic receptor
blockers that prevent sympathetic stimulation.
■■
Class III antiarrhythmics block potassium channels
and prolong phase 3 of the action potential.
■■
Class IV antiarrhythmics are calcium channel
blockers that shorten the action potential, disrupting
ineffective rhythms and rates.
■■
A person receiving an antiarrhythmic drug needs
to be constantly monitored while being stabilised
and throughout the course of therapy to detect the
development of arrhythmias or other adverse effects
associated with alteration of the action potentials of
other muscles or nerves.
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• Report any of the following to your healthcare provider:
chest pain, difficulty breathing, palpitations, numbness or
tingling
.
• Tell any doctor, nurse or other health provider involved in
your care that you are taking this drug.
• Keep this drug, and all medications, out of the reach of
children.
• Schedule regular medical appointments while you are
on this drug to evaluate your heart rhythm and your
response to the drug and to monitor your blood levels
of important electrolytes that affect heart function.
• Do not stop taking this medication. If you have to
stop the medication, contact your healthcare provider
immediately.
