An arrhythmia is an abnormal heart rhythm. This can mean an abnormal heart rate (the heart beats too fast or too slow), an irregular beat or pattern, or the electrical signal for the heart to beat is coming from an atypical site. Arrhythmias are most often seen in animals with heart disease, but can also arise because of another condition not related to the heart (such as pancreatitis or certain cancers). Arrhythmias can cause fainting, weakness, congestive heart failure, reduced blood flow to vital organs (such as the brain and kidneys) and even death. Arrhythmias are identified by analyzing the electrical activity of the heart on an electrocardiogram (ECG).
In order to treat an arrhythmia, the cause must first be identified. As mentioned above, the heart may be the cause and so an echocardiogram might be indicated, however conditions unrelated to the heart can cause these abnormal rhythms, and these should be checked for with blood work or other testing. There are many different types of arrhythmias (atrial fibrillation or atrioventricular block for example) that a pet can develop. Some are much more serious than others. The type of arrhythmia present, the clinical signs (if any) it is producing and the likely cause of the arrhythmia all contribute to determining the most appropriate and effective treatment. In general, the goal of therapy is to prevent the dangerous arrhythmias that can lead to sudden death and to eliminate the clinical signs (such as fainting or collapse) that are caused by these abnormal rhythms.
There are many different drugs (called
antiarrhythmics) used to treat arrhythmias. The drugs lidocaine, procainamide, mexiletine (Mexitil®), sotalol (Betapace®) and amiodarone (Cordarone®) are used to treat certain arrhythmias (called ventricular arrhythmias). Some arrhythmias that cause a very slow heart rate (such as third degree AV block and sick sinus syndrome) usually require a pacemaker to be implanted in the pet permanently. There are also drugs that may help slow heart rates as well—including probanthine, theophylline (Elixophyllin®) and terbutaline (Brethaire®)—but these have certain side effects and are often less reliably effective.