7.5 Principles of the treatment of arrhythmias
A limited range of antidysrhythmic drugs is licensed for use in animals. In small animal medicine, the pharmacology of a range of drugs, designed for use in humans, is understood. However, little is known about the pharmacology of most of these drugs in the horse. The number of drugs which can be safely used in horses is therefore very limited. Some have to be used on the presumption that their pharmacology and action is similar to that in other species. It is advisable first to obtain informed consent from owners prior to treatment because these drugs are unlicensed for use in horses in the UK.
Fortunately, the incidence of arrhythmias which require treatment in the horse is relatively low compared with small animals and humans. Atrial fibrillation (AF) is the most common arrhythmia which requires treatment. Although other arrhythmias are quite common, they are often intermittent and do not require treatment. Severe bradydysrhythmias are rare and tachydysrhythmias are relauncommon, perhaps as a result of the relatively low incidence of myodisease. An additional problem is that drugs are not always as effective at reducing the deleterious effects of arrhythmias as might be hoped. Even in human and small animal medicine, it is increasingly recognised that antidrugs may themselves cause arrhythmias and that they may not be as beneficial as was once thought. They may also have side-effects. As a general rule, therefore, drugs should be avoided except in cases where underlying disease cannot be controlled and the condition is life threatening, or when an arrhythmia is persistent and limits athletic performance.
The most important principles of treatment of arrhythmias are to:
- Identify the arrhythmia and determine whether it is physiological or abnormal.
- Identify any underlying heart disease.
- Identify any underlying systemic disease.
- Decide on the significance of the arrhythmia and perform any further diagtests which may be required.
- Decide what treatment, if any, is required.