Atrial Standstill in a Horse with Cardiac Glycoside Intoxication

Atrial standstill is described in human and veterinary medicine. Among causes are atrial myocarditis, hyperkalemia and cardiac glycosides.

To describe atrial standstill in a horse due to cardiac glycosides intoxication.

A 6-year-old horse was presented with symptoms of weakness, sweating and trembling.
A general clinical examination, ultrasonography of lungs, abdomen and heart, continuous electrocardiography and repeated blood exams were performed. Treatment was initiated.

The horse had an increased temperature (38.9°C) and respiration rate. Ultrasound of thorax and abdomen revealed no abnormalities. An irregular heart rhythm was present. Electrocardiography showed periods of atrial standstill resulting in a sinoventricular rhythm. On echocardiography, tissue Doppler imaging showed a complete loss of atrial contraction. Left ventricular fractional shortening was ±50%. Blood exams revealed a PCV of 60%, a ureum of 15.8mmol/l, a creatinine of 10.3μg/dl, a potassium of 8.9mmol/l and a digoxin concentration of 6.7ng/ml. Following intensive treatment with saline perfusions, glucose, insulin, antibiotics, anti-inflammatory drugs and diuretics low amplitude P waves with long PQ intervals re-appeared. Subsequently, the horse developed atrial flutter with tachycardia. Atrial flutter could be terminated by lidocaine treatment. However, thirty-two hours later, the horse became recumbent, excited and was euthanized.

During atrial standstill a sinoventricular rhythm is present because the cells of the sinus node and internodal tracts are more resistant to inexcitability than atrial myocytes.

To our knowledge this is the first case of atrial standstill in a horse due to hyperkalemia associated with digitalis intoxication.