Relationship between potassium administration, hyperkalaemia and the electrocardiogram: an experimental study.

Hyperkalaemia affected the equine myocardium. The minimum plasma potassium concentration required to induce electrocardiographic changes was 6.2 mmol/litre and severe cardiotoxic effects were observed at levels of 8.0 to 10.1 mmol/litre in this experimental situation. The most consistent sign of hyperkalaemia was broadening and flattening of the P wave, which was generally associated with a change in T waves in the chest lead from negative to positive. The more pronounced the hyperkalaemia, the less pronounced the P wave and the more peaked positive the T wave. Severe hyperkalaemia was associated with various arrhythmias invariably associated with the presence of broad flat or absent P waves and upright T waves in chest leads. Caution against extrapolation from the experimental to the clinical situation must be exercised because of many complex interacting factors. Hyperkalaemia is difficult to induce experimentally and, unless associated with disease, is unlikely to occur in the horse.