Drug Therapy
Once the specific arrhythmia is diagnosed, drug therapy is generally the first course of treatment considered. The existing drugs, however, often have limited usefulness-hence the need for newer agents. Because we are a nationally known testing center, our patients often have access to newer drugs not generally available. When patients cannot tolerate drugs due to side effects or the drug is not effective, other forms of treatment become the only realistic alternative.
ANTIARRHYTHMIC DRUGS
A wide range of drugs effective in the treatment of cardiac rhythm disturbances are currently available. These pharmacological agents are primarily used in the therapy of fast heart rhythms, or tachycardias, originating from either the upper chambers of the heart (atria) or the lower chambers (ventricles). Specific drug therapy is chosen based on the underlying arrhythmia, dosing schedule, side effects, and the presence of other cardiac, pulmonary, liver, or renal disease.
QUINIDINE
Quinidine, first described in 1848, is one of the oldest antiarrhythmic drugs. Originally used to treat malaria, its efficacy in treating cardiac rhythm disturbances was later discovered incidentally.
Quinidine is used to treat arrhythmias of both the upper and lower cardiac chambers. It has been used to treat atrial fibrillation, AV nodal reentrant tachycardia, Wolff-Parkinson-White syndrome, premature ventricular complexes, and ventricular tachycardia. Oral dosing of the relatively short-acting formulation quinidine sulfate is usually every 6 hours, while quinidine gluconate is available in a sustained-release preparation that allows dosing every 8 to 12 hours.
The side effect profile of quinidine has severely limited its use. About 1/3 of patients develop abdominal cramping and diarrhea. Rash, changes in hearing and altered vision are not uncommon. Most importantly, quinidine has the potential to cause serious heart rhythm disturbances, necessitating close monitoring during drug initiation.
PROCAINAMIDE
Procainamide has been in use since the mid 1900’s. Its use and efficacy are similar to that of quinidine. Long-term therapy may effectively control a variety of supraventricular and ventricular arrhythmias. Its use as an oral agent is limited in part by the need for frequent dosing. Standard short-acting preparations need to be dosed every 3-4 hours. Sustained release formulations require every 6-hour dosing.
Like quinidine, procainamide commonly causes gastrointestinal side effects. Additionally, a lupus-like syndrome with fever, joint and muscle pains, rash, lung and liver problems may occur in up to 30% of patients on long-term therapy. Like quinidine, procainamide may also produce serious cardiac rhythm disturbances.
DISOPYRAMIDE
Disopyramide belongs to the same class of drugs as quinidine and procainamide. Disopyramide’s side effect profile is notable for its potential to lessen the strength with which the heart muscle squeezes or contracts. As a result, it has found application not only in the treatment of supraventricular and ventricular arrhythmias, but also in the therapy of neurocardiogenic syncope, a condition triggered by increased contractility in the ventricles. Typical dosing is every 6 to 12 hours.
Significant side effects can occur in 1/3 of patients taking disopyramide, and are particularly bothersome in the elderly. These commonly include dry mouth, blurred vision, constipation, and difficulty with urination.
FLECAINIDE
Flecainide is a relatively well-tolerated agent that is effective in the therapy of many cardiac arrhythmias. It has a convenient dosing schedule, with usual dosing initiated every 12 hours. Side effects including blurred vision, headache, and difficulty with balance necessitate discontinuation in approximately 13% of patients.
The primary drawback of flec
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