The Conducting System of the Vertebrate Heart

Does the right muscular atrioventricular valve in the avian heart perform two functions?

“…Indirectly, the argument in favor of this opinion is the fact that thickening of the MV occurs when RV hypertrophy is developed in birds (Pees et al, 2001;Stedman and Brown, 2002;Pees et al, 2006). One more reason for this opinion is the presence of conducting myocytes in the MV (Davies, 1930;Prosheva, 1986;Lu et al, 1993;Parto et al, 2013). As it is known, mainly the conduction system is responsible for the excitation pattern in the heart of endothermic animals.…”

“…The muscular AV valve has neither chordae tendinae nor papillary muscles (Davies, 1930;Prosheva and Rapota, 1989;Lu et al, 1993;Pees et al, 2006;Alsafy et al, 2009;Yoldas and Dayan, 2012). Light microscopy showed that the muscular valve (MV) in the avian heart is a two-layered structure, formed by an outer layer of inverted ventricular muscle and an inner layer of downwardly projecting atrial muscle (Vassall-Adams, 1982).…”

“…Histological studies showed that the feature of the topography of the ventricular conduction system in the avian heart is a small special branch (formed by conducting fibers), which runs just from the right limb of the AV bundle (not from the AV node), and enters the MV (Davies, 1930). Later, the presence of conducting myocytes in the avian MV was proved by electrophysiology and electron microscopy (Prosheva, 1986;Lu et al, 1993;Parto et al, 2013).…”

‘The electrical spiral of the heart’: its role in the helical continuum.The hypothesis of the anisotropic conducting matrix

“…The His-Purkinje conducting system is a neomorphic development limited to birds and mammals [16,17] whose heartbeat requires rapid dissemination of the impulse. In man it is only subendocardial.…”

“…The His bundle penetrates the septum and soon divides into a right and left bundle that course subendocardially and send fibers that penetrate the entire thickness of the ventricular myocardium. This allows a hummingbird to have 1500 instantly coordinated ventricular contractions per minute required by its flight pattern, and the canary to have a heart rate of 1000 bpm [16,17]. Larger birds with comparatively less cardiac output requirement such as the peregrine falcon have a heart rate of 347 bpm [18].…”