Pulsus alternans during halothane anesthesia in a dog.

An adult dog with pyloric obstruction was anesthetized with thiamylal and halothane for surgical revision. When an ECG was attached, the QRS-complex rate was noted to differ dramatically from the peripheral pulse rate. A dorsal pedal arterial catheter was introduced, and direct arterial pressure measurements revealed a blood pressure waveform that alternated in amplitude. Blood pressure and ECG traces were recorded, and the condition was diagnosed as pulsus alternans. The inhalation anesthetic was changed to isoflurane, and the condition was resolved.