C H A P T E R 4 5
Antiarrhythmic agents
701
ANTIARRHYTHMIC AGENTS
Antiarrhythmics
affect the action potential of the
cardiac cells by altering their automaticity, conductiv-
ity or both. Because of this effect, antiarrhythmic drugs
can also produce new arrhythmias—that is, they are
proarrhythmic
. Antiarrhythmics are used in emergency
situations when the haemodynamics arising from the
person’s arrhythmia are severe and could potentially be
fatal. Box 45.2 contains information regarding use of
antiarrhythmic agents across the lifespan.
Antiarrhythmics were widely used on a long-term
basis to suppress any abnormal arrhythmia, until the
publication of the
Cardiac Arrhythmia Suppression
Trial (CAST)
in the early 1990s. This multicentre, ran-
domised, long-term study conducted by the US National
FIGURE 45.5
Ventricular fibrillation. Rhythm: irregular. Rate: not measurable. P–R interval: not measurable. QRS: not measurable, replaced by
an irregular wavy baseline. No coordinated electrical or mechanical activity in the ventricle, no cardiac output.
BOX 45.2
Drug therapy across the lifespan
Antiarrhythmic agents
CHILDREN
Antiarrhythmic agents are not used as often in children as
they are in adults. Children who do require these drugs,
after cardiac surgery or because of congenital heart
problems, need to be monitored very closely to deal with
the related adverse effects that can occur with these drugs.
Digoxin is approved for use in children to treat
arrhythmias and has an established recommended dose.
If other antiarrhythmics are used, the dose should be
carefully calculated using weight and age and should be
double-checked by another healthcare professional before
administration.
Adenosine, propranolol and digoxin have been
successfully used to treat supraventricular arrhythmias, with
propranolol and digoxin being the drugs of choice for long-
term management. Verapamil should be avoided in children.
Many arrhythmias in children are now treated by
ablation techniques to destroy the arrhythmia-producing
cells.This has been very successful in treatingWolff–
Parkinson–White and related syndromes in children. If
lignocaine is used for ventricular arrhythmias related to
cardiac surgery or digoxin toxicity, serum levels should
be monitored regularly to determine the appropriate dose
and to avoid the potential for serious proarrhythmias and
other adverse effects.The child should receive continuous
cardiac monitoring.
ADULTS
Adults receive these drugs most often as emergency
measures. Monitoring and careful evaluation of the total
drug regimen should be a routine procedure to ensure the
most effective treatment with the least chance of adverse
effects. Frequent monitoring and medical follow-up is very
important for these people.
PREGNANCY AND BREASTFEEDING
The safety for the use of these drugs during pregnancy
has not been established.They should not be used
in pregnancy unless the benefit to the mother clearly
outweighs the potential risk to the fetus.The drugs enter
breast milk, and some have been associated with adverse
effects on the neonate. Class I, III and IV agents should not
be used during breastfeeding; if they are needed, another
method of feeding the baby should be used.
OLDER ADULTS
Older adults frequently are prescribed one of these
drugs. Older adults are more likely to develop adverse
effects associated with the use of these drugs, including
arrhythmias, hypotension and congestive heart failure.
They are also more likely to have renal and/or hepatic
impairment related to underlying medical conditions,
which could interfere with the metabolism and excretion
of these drugs.
The dose for older adults should be started at a lower
level than that recommended for other adults.The person
should be monitored very closely and the dose adjusted
based on response. If other drugs are added to or removed
from the drug regimen, appropriate dose adjustments may
need to be made.
