Das Reizleitungssystem des Säugetierherzens (English: "The Conduction System of the Mammalian Heart") is a scientific monograph published in 1906 by Sunao Tawara. It has been recognized by cardiologists as a monumental discovery, and a milestone in cardiac electrophysiology".
The monograph revealed the existence of the atrioventricular node and the function of Purkinje cells. It was used by Arthur Keith and Martin Flack as a detailed guide in their attempts to verify the existence of the Bundle of His, which subsequently led to their discovery of the sinoatrial node. Throughout the beginning of the 20th century, Tawara's monograph influenced the work of many cardiologists and it was later cited by Willem Einthoven in his anatomical interpretation of the electrocardiogram.
Background
Prior to Tawara's discoveries, it was assumed that electrical conduction through the Bundle of His was slow, because of the long interval between atrial and ventricular contractions. The Swiss cardiologist Wilhelm His, Jr. assumed that the heart bundle was connected directly to the base of the ventricle, and physiologists incorrectly taught that the base of the ventricle contracted first, followed by the apex.
However, Tawara postulated that ventricular contraction occurs in the opposite manner, with the apex contracting earlier than the base. He also believed that the heart's electrical conduction was not slow but rapid. Working under the guidance of his mentor, Ludwig Aschoff, Tawara performed a histological examination of 150 hearts with myocarditis (which led to the discovery of Aschoff bodies), and he began examining the atrioventricular bundle before embarking on a comprehensive study of the anatomy and histology of the heart's conduction system.
The implications of his work were immediately recognized by Aschoff, who arranged for it to be published in the form of a monograph.
Discoveries
Tawara's monograph, titled "Das Reizleitungssystem des Säugetierherzens" (English: "The Conduction System of the Mammalian Heart") was published in 1906. The most important discoveries are listed below:
The Bundle of His is divided into 2 bundle branches that are connected with a fanlike group of “subendocardially scattered characteristic muscular bundles”. Purkinje cells act as a pathway for the "atrioventricular connecting system". The atrioventricular connecting system starts in the atrioventricular node, moves into the fibrocartilaginous portion of the septum (Bundle of His), divides into defined left and right bundle branches, and descends into the terminal ends of the Purkinje fibers.
Tawara commented that the system represents a transporting or conducting pathway, and "because the pathway is not a ductal, but a continuously related protoplasmic cord, conduction of excitation impulses surely must take place there."
Influences
On 26 September 1905, shortly before the monograph was due to be published, Ludwig Aschoff wrote an article about Tawara's work. It was subsequently read by the Scottish cardiologist James Mackenzie and forwarded to anatomist Arthur Keith, who was attempting to confirm the existence of the Bundle of His. Despite putting in his best efforts, he failed to locate the structure. On 15 January 1906, Keith wrote a letter to Mackenzie and acknowledged his skepticism about its existence: "I have given up the search for His' bundle—having come to the conclusion that there is not and never was any such thing.”
Verification of the Bundle of His (1906) In response to Arthur Keith's skepticism, Mackenzie forwarded Aschoff's article about Tawara's findings, which stimulated Keith's renewal of his studies on the cardiac conduction system. Despite having written a letter to The Lancet about his failure to locate the Bundle of His and his increasing doubts about its existence, Keith (with his student Martin Flack) later reported that they had succeeded in locating the structure by following the detailed descriptions and figures in Tawara's monograph. In a paper published in The Lancet on 11 August 1906, they acknowledged the monograph's high degree of accuracy:
"We take this opportunity of clearly stating that although some of our observations are new our work is in the main but a verification of the accurate and complete monograph published recently by Tawara, a Japanese working in the laboratory of Professor Aschoff of Marburg."
Discovery of the sinoatrial node (1907)