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C H A P T E R 4 5 Antiarrhythmic agents

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.

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

Drug therapy across the lifespan

BOX 45.2

Antiarrhythmic agents CHILDREN

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.

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