The anatomy of the conduction system: implications for the clinical cardiologist.

It is just over 100 years since details emerged of the anatomical arrangement of the histologically specialised cardiomyocytes responsible for initiation and propagation of the cardiac impulse. Shortly thereafter, histological criteria were established to permit their location in autopsied human hearts. These criteria retain their value, but can now be enhanced by molecular and immunohistochemical findings. The new techniques have advanced our knowledge of the location and detailed structure of the sinus and atrioventricular nodes, along with the atrioventricular conduction axis. They also reveal the presence of additional areas of specialised myocardium, such as the paranodal area of the terminal crest, and the atrioventricular ring tissues. In contrast, they offer no support for the notion that the pulmonary venous sleeves are histologically specialised, but do provide insights to the substrates for outflow tract tachycardias. This article is part of a JCTR special issue on Cardiac Anatomy.