The Supernormal Period in the Mammalian Ventricle1

Exploration of the excitability during recovery from previous response of various nerve and muscle preparations has revealed a period of heightened excitability following the relatively refractory period. Since the threshold at this time is found to be lower than subsequently or at rest, this phase has been designated as the supernormal period. This period of enhanced excitability may exist normally or may be produced by such agents as fatigue, acid, or veratrine. In the frog ventricle a supernormal period was found by Adrian (1921) when the fluid bathing the tissue was acidified, and Wastl (1922) detected supernormality in fatigued preparations. Eccles and Hoff (1934) noticed occasional supernormality in the pacemaker of decerebrate cats, while Lewis and Master (1924) and later Rothberger and Goldenberg (1936) presented evidence for its existence in the conduction system. The object of this study has been to determine 1, whether a supernormal period exists in the mammalian ventricle; 2, what its position is in respect to the ventricular electrocardiogram, and 3, what factors may influence its occurrence.