Anesthesia was introduced with sodium thiopental and maintained with halothane in cats and dogs. Comparative studies were made on these animals to clarify what extent irregular pulse (IP) was induced to in the routine clinical practice, when IP appeared in the period of anesthesia, how long IP continued, and the type and cause of occurrence of IP.
Irregular pulse in the period of anesthesia, except tachycardia induced by sodium thiopental, was found in 71 of 886 cats (8.0%) and 20 of 652 dogs (3.1%) . Therefore, the rate of occurrence of IP was higher in the cats than in the dogs.
The types of IP induced in the period of anesthesia were various, including upper ventricular early beat, ventricular early beat, multiple ventricular heterotopic beat, atrioventricular block of the first, second, and third degree, atrioventricular dissociation, atrial standstill, alternating pulse, sinus bradycardia, and sinus standstill.
The type of IP of frequent occurrence was ventricular early bea t in the dogs and multiple ventricular heterotopic beat in the cats. It was induced by the drug in nearly half of all the cases 10 minutes after the introduction of anesthesia. IP noticed in the maintenance of anesthesia was induced by artificial causes, such as visceral traction and ligation, in many cases. Animals showing IP during anesthesia extending from introduction to wakin were almost always suffering from the side effects of some auxiliary drugs, bad general conditions with serious anemia and hypothermia, and abnormality in serum electrolytes.
Particular attention had to be paid to IP which was accompanied with the extension of QT, sinus bradycardia, and the descent of ST.