A dom inant tenet in physio logy for m .ore t han half a century h as been the principle of homeostasis. The term was coined by W. B. Cannon (2) to describe the observation that physiological systems normally operate to reduce variability and to maintain a constancy of internal function. Accordingly, one might expect most any physiological variable, including heart rate, to return to its normal...

Specialized fiber electrograms were recorded from selected sites along the His bundle and bundle branches during open-heart surgery in 26 patients. The heart was then paced from the same recording sites. Stimuli applied to the proximal His bundle recording site always resulted in His bundle pacing, which was characterized by a stimulus artifact-to-QRS interval which equaled or very nearly equal...

His bundle electrograms were repeatedly recorded in two patients with complex arrhythmias. In the first case the pacemaker was located in the lower part of the left bundle-branch, retrogradely activating the His bundle. Atrial standstill was associated with this mechanism. Afterfour days, His bundle tachycardia occurred, with constant retrograde activation of the atria, and anterograde block. I...

Specialized fiber electrograms were recorded from selected sites along the His bundle and bundle branches during open-heart surgery in 26 patients. The heart was then paced from the same recording sites. Stimuli applied to the proximal His bundle recording site always resulted in His bundle pacing, which was characterized by a stimulus artifact-to-QRS interval which equaled or very nearly equal...

SUMMARY Four patients are described with different degrees of conduction disturbance within the His bundle. In one patient with a Mobitz type II atrioventricular (A-V) block with normal QRS complexes the blocked atrial beats were followed by a His potential. Since the QRS complexes of the conducted beats were completely normal, the site of the block was thought to be in the distal part of the H...

The mechanism of atrioventricular delay has been studied in isolated rabbit hearts. Multiple intracellular microelectrodes have been employed to obtain simultaneous records from single fibers of atrium, A-V node and His bundle. An appreciable delay in the transmission of excitation has been found only in the atrial portion of the A-V node. Action potentials recorded from single fibers in this a...

To investigate the electrophysiological properties of ventricular impulse formation after His-bundle ablation in 11 patients, incremental ventricular overdrive stimulation studies were performed. The studies, which were spread over a follow-up period of up to 601 days, were carried out invasively with temporary leads as well as noninvasively with the implanted pacemakers and chest wall inhibiti...