The atria and the ventricles are separated by a ring of fibrous tissue, and the only conduction pathway between the two sets of chambers is the atrioventricular node, which is located at the base of the right atrium. Once the action potential is initiated in the sino-atrial node, it propagates to the rest of the heart, resulting in the heart beat. The sino-atrial node, located in the right atrium, is the pacemaker of the heart it is responsible for the initiation of the cardiac action potential. The three main parts of the system are the sino-atrial node, the atrioventricular node and the His–Purkinje system ( Fig.
#Conducdtion system of the heart pdf basics series
The cardiac conduction system (CCS) is a series of specialized tissues in the heart responsible for the initiation and co-ordination of the heart beat. William Shakespeare in ‘ Measure for Measure’ (Act 2, Scene II) ‘ Knock there, and ask your heart what it doth know’ During embryological development, all parts of the CCS have been shown to develop from the primary myocardium of the linear heart tube, partly under the influence of the transcription factor, Tbx3. These additional tissues do not participate in the initiation and co-ordination of the heart beat and instead they are likely to be the source of various life-threatening arrhythmias. Recent work has highlighted less well-known components of the CCS, including tricuspid, mitral and aortic rings and even a third (retro-aortic) node. Differences in ion channel expression may even be responsible for the bradycardia in the athlete and differences in heart rate among different species (such as humans and mice). Dysfunction of the CCS has previously been attributed to fibrosis, but it is now clear that remodelling of ion channels plays an important role in dysfunction during ageing, heart failure and atrial fibrillation. Ion channel expression in the CCS has been shown to be fundamentally different from that in the working myocardium. Immunohistochemistry, used in conjunction with anatomical techniques, has transformed our understanding of its anatomy arguably, we now understand the position of the sino-atrial node (not the same as in medical textbooks), and our new understanding of the atrioventricular node anatomy means that we can compute its physiological and pathophysiological behaviour. In the last decade, our understanding of the CCS has been transformed. The cardiac conduction system (CCS), consisting of the sino-atrial node, atrioventricular node and His–Purkinje system, is responsible for the initiation and co-ordination of the heart beat.
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