Medical Terminology Daily - Est. 2012

Medical Terminology Daily (MTD) is a blog sponsored by Clinical Anatomy Associates, Inc. as a service to the medical community. We post anatomical, medical or surgical terms, their meaning and usage, as well as biographical notes on anatomists, surgeons, and researchers through the ages. Be warned that some of the images used depict human anatomical specimens.

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A Moment in History

Jean George Bachman

Jean George Bachmann
(1877 – 1959)

French physician–physiologist whose experimental work in the early twentieth century provided the first clear functional description of a preferential interatrial conduction pathway. This structure, eponymically named “Bachmann’s bundle”, plays a central role in normal atrial activation and in the pathophysiology of interatrial block and atrial arrhythmias.

As a young man, Bachmann served as a merchant sailor, crossing the Atlantic multiple times. He emigrated to the United States in 1902 and earned his medical degree at the top of his class from Jefferson Medical College in Philadelphia in 1907. He stayed at this Medical College as a demonstrator and physiologist. In 1910, he joined Emory University in Atlanta. Between 1917 -1918 he served as a medical officer in the US Army. He retired from Emory in 1947 and continued his private medical practice until his death in 1959.

On the personal side, Bachmann was a man of many talents: a polyglot, he was fluent in German, French, Spanish and English. He was a chef in his own right and occasionally worked as a chef in international hotels. In fact, he paid his tuition at Jefferson Medical College, working both as a chef and as a language tutor.

The intrinsic cardiac conduction system was a major focus of cardiovascular research in the late nineteenth and early twentieth centuries. The atrioventricular (AV) node was discovered and described by Sunao Tawara and Karl Albert Aschoff in 1906, and the sinoatrial node by Arthur Keith and Martin Flack in 1907.

While the connections that distribute the electrical impulse from the AV node to the ventricles were known through the works of Wilhelm His Jr, in 1893 and Jan Evangelista Purkinje in 1839, the mechanism by which electrical impulses spread between the atria remained uncertain.

In 1916 Bachmann published a paper titled “The Inter-Auricular Time Interval” in the American Journal of Physiology. Bachmann measured activation times between the right and left atria and demonstrated that interruption of a distinct anterior interatrial muscular band resulted in delayed left atrial activation. He concluded that this band constituted the principal route for rapid interatrial conduction.

Subsequent anatomical and electrophysiological studies confirmed the importance of the structure described by Bachmann, which came to bear his name. Bachmann’s bundle is now recognized as a key determinant of atrial activation patterns, and its dysfunction is associated with interatrial block, atrial fibrillation, and abnormal P-wave morphology. His work remains foundational in both basic cardiac anatomy and clinical electrophysiology.

Sources and references
1. Bachmann G. “The inter-auricular time interval”. Am J Physiol. 1916;41:309–320.
2. Hurst JW. “Profiles in Cardiology: Jean George Bachmann (1877–1959)”. Clin Cardiol. 1987;10:185–187.
3. Lemery R, Guiraudon G, Veinot JP. “Anatomic description of Bachmann’s bundle and its relation to the atrial septum”. Am J Cardiol. 2003;91:148–152.
4. "Remembering the canonical discoverers of the core components of the mammalian cardiac conduction system: Keith and Flack, Aschoff and Tawara, His, and Purkinje" Icilio Cavero and Henry Holzgrefe Advances in Physiology Education 2022 46:4, 549-579.
5. Knol WG, de Vos CB, Crijns HJGM, et al. “The Bachmann bundle and interatrial conduction” Heart Rhythm. 2019;16:127–133.
6. “Iatrogenic biatrial flutter. The role of the Bachmann’s bundle” Constán E.; García F., Linde, A.. Complejo Hospitalario de Jaén, Jaén. Spain
7. Keith A, Flack M. The form and nature of the muscular connections between the primary divisions of the vertebrate heart. J Anat Physiol 41: 172–189, 1907.


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AV node as depicted by Sunao Tawara
Figure 1: AV node as depicted by Sunao Tawara

The atrioventricular (AV) node is a critical component of the conduction system of the heart, serving as the only (normal) electrical connection between the atria and the ventricles. By delaying atrioventricular transmission by 1/10th of a second, the AV node allows the heart to work as a pump.

The AV node is situated in the inferior portion of the interatrial septum. It was discovered in 1906 by Sunao Tawara, who identified it as a discrete small structure located at the atrioventricular junction and demonstrated continuity of the AV node with the His–Purkinje system (see image 1).

The AV node is a located in the “Triangle of Koch” (see note), a region bound by the tendon of Todaro, the septal leaflet of the tricuspid valve, and the ostium of the coronary sinus (see image 2). Its blood supply is by way of the AV node artery, a branch of the right coronary artery (RCA) that arises usually at the crux cordis, the point of division of the RCA into the posterior descending artery and posterolateral artery.

Triangle of Koch, location of the AV node

Image 2: SVC: Superior vena cava, RPA: Right pulmonary artery, RSPV: Right superior pulmonary vein, RIPV: Right inferior pulmonary vein, IVC: Inferior vena cava, RAA: Right atrial appendage, FO: Foramen ovale, TV: Septal leaflet of the tricuspid valve. The yellow line shows the location of the "Tendon of Todaro". The complete triangle is the triangle of Koch.  

The ventricles are isolated from the atria by connective tissue that forms an electrical barrier between. This barrier is sometimes called the “skeleton of the heart” a misnomer that does not explain the reason for its presence. If there was no barrier, the atria and ventricles would all contract at the same time and the pumping action of the heart would not exist.

The only place where the electrical impulse can pass from the atria to the ventricles is through the AV node. Because of the specialized cardiomyocytes that form the node, the transmission of the impulse is delayed by one tenth of a second, enough that the ventricles will contract after the atria contract, causing blood flow through the heart.

Note: The "triangle of Koch" is eponymically named after Walter Eduard Carl Koch (1880 - 1962) a German physician and pathologist.

Sources and References:
1. Markowitz, MM; Lerman BL. A contemporary view of atrioventricular nodal physiology. J Interv Card Electrophysiol. 2018 Aug;52(3):271-279.
2. Efimov IR, Nikolski VP, Rothenberg F, Greener ID, Li J, Dobrzynski H, Boyett M. Structure-function relationship in the AV junction. Anat Rec A Discov Mol Cell Evol Biol. 2004 Oct;280(2):952-65.
3.Fumarulo I, Salerno ENM, De Prisco A, Ravenna SE, Grimaldi MC, Burzotta F, Aspromonte N. Atrioventricular Node Dysfunction in Heart Failure: New Horizons from Pathophysiology to Therapeutic Perspectives. J Cardiovasc Dev Dis. 2025 Aug 15;12(8):310.
4. Anderson RH, Sánchez-Quintana D, Nevado-Medina J, Spicer DE, Tretter JT, Lamers WH, Hu Z, Cook AC, Sternick EB, Katritsis DG. The Anatomy of the Atrioventricular Node. J of Cardiovasc Development and Disease. 2025; 12(7):245.
5. Tawara, S.  Das Reizleitungenssystem des Säugetierherzens : eine anatomisch-histologische Studie über das Atrioventrikularbündel und die Purkinjeschen Fäden 1906 J Fischer pub. courtesy of archive.org
6. "Tratado de Anatomia Humana" Testut et Latarjet 8th Ed. 1931 Salvat Editores, Spain
7. Anderson, Robert H. MD; Becker, Anton E. MD. "Slide Atlas of Cardiac Anatomy" 10 volumes London: Gower Medical Publishing, 1985. (out of print)