Remembering the canonical discoverers of the core components of the mammalian cardiac conduction system: Keith and Flack, Aschoff and Tawara, His, and Purkinje.

The mammalian cardiac conduction system (CCS) is a multifaceted continuum of electrically distinct, interconnected constructs within the myocardial mass. The key components are the sinus node (SAN), the atrioventricular node (AVN), the His bundle (HB), and the Purkinje fiber network (PF), the latter serendipitously discovered by Jan Evangelista Purkinje in 1839 in the sheep ventricle. In 1893, Wilhelm His, Jr. described a ventricular muscular tract conveying SAN-generated action potentials from the AVN (discovered by Sunao Tawara and Karl Albert Aschoff in 1906) to the PF. In 1906, Keith and Flack completed these explorations by localizing the SAN, the of CCS, which functions as a biologic oscillator emitting cadenced impulses that travel via the Bachmann bundle to the atrial myocytes and, via internodal pathways, to the AVN. Here these impulses are briefly delayed, enabling atrial systole before continuing via the AVN and the high-speed His-Purkinje conduction axis to signal ventricular contraction. The CCS canonical discoverers (Keith and Flack, Aschoff and Tawara, His, and Purkinje), historical controversies, fundamental notions of anatomy, physiology, and pathology, and therapeutic interventions pertaining to the CCS are the main themes of this review. Any scientist mentioned or unmentioned in this report who contributed directly or indirectly, with correct or inaccurate hypotheses, to the characterization of the CCS deserves our deepest gratitude for the long and painstaking hours spent microscopically scrutinizing heart specimens from multiple mammalian species, including humans. This report presents the first comprehensive summary of the factors enabling the discovery of the cardiac conduction system (CCS). Biographical highlights and achievements of the CCS canonical discoverers, hypotheses concerning mechanisms underlying sinus node (SAN) automaticity, use of eponyms to denominate a discovery, famous controversies, possible reproachable behavior (e.g., intellectual support for eugenics in post-World War I Germany) by two of the discoverers, and examples of historical mentor-pupil relationships are discussed.