Electrocardiographic Patterns Evoked by Venom of the Stingray.

Intravenous injection of stingray venom produced various changes in the ECG patterns of cats. The extent of the change depends, for the most part, on the amount of venom injected. Small amounts of the venom produce bradycardia with an increase in the PR interval giving a first, second or third degree auriculo-ventricular block. The second degree block is usually followed by sinus arrest. Reversal of the small dose effects occurs within 30 seconds following the end of the injection. Cats receiving larger amounts of the venom show, in addition to the PR interval change, almost immediate ST, T wave change indicative of ischemia and in some animals true muscle injury. These changes often persist for 10 minutes before reverting to normal. When fatal amounts of the venom are injected the pattern is abnormal and unpredictable. All degrees of auriculo-ventricular block, sinus arrest, inter-ventricular block, decreased amplitude of QRS complex, and various degrees of ischemia and injury are seen. The rapid alteration of auriculo-ventricular conduction suggests that the venom has a direct effect on the auricles. The alteration in the ST, T wave suggests that the venom also has a direct effect on the ventricles. These experiments support previous observations (1).