arrhythmias (= dysrhythmias) - abnormal cardiac rhythm. They may be abnormalities of impulse formation, conduction, rate or regularity and arise from delayed after-depolarisation or re-entry.
Arrhythmias may not affect the heart's efficiency as a pump and require no treatment, eg sinus arrhythmia which is normal in fit animals. Other arrhythmias eg ventricular fibrillation are immediately life threatening. Most arrhythmias fall between these extremes. (nb, all antiarrhythmic drugs decrease cardiac output to some extent, and may also cause arrhythmias, so you have to be sure that the presenting arrhythmia is worse for the animal than the treatment.) Treat the animal, not the ECG!!!
other heart disease
hereditary
autonomic system
metabolic diseasehypoxia
acidosis
electrolyte imbalance (particularly K+)drug toxicity (including antiarrhythmics!)
A variety of mechanisms can give rise to arrythmias.
Vaughan Williams classification of antiarrhythmic drugs
diagram
