The Atrioventricular Region of the Teleost Heart. A Distinct Heart Segment

Abstract

This article reports the morphological characteristics of the atrioventricular (AV) region of the teleost heart. A total of 29 teleost species belonging to 19 families and 10 orders were analyzed. The study includes hearts with entirely trabeculated ventricles and hearts possessing a ventricular compacta. In all cases, the AV region is formed by a ring of compact myocardium surrounded by a connective tissue ring. The myocardium contains vessels in most species having entirely trabeculated ventricles, and in all species possessing a compacta. The ring of connective tissue is rich in collagen and elastin, partially isolating the AV muscle from the surrounding musculature. Continuity between the AV muscle and the atrial and ventricular musculature is always observed. The AV muscle supports the AV valves, which are formed by two leaflets, lack papillary muscles, show a collagenous fibrosa on the atrial side, and present a variable number of cells and a variable amount of extracellular material. Ventricular trabeculae attach to the AV muscle. These trabeculae may help to bear the stress generated by ventricular contraction and may constitute a preferential pathway for the conduction of electrical impulses. In all teleosts studied, the AV region can be recognized as a distinct morphological segment interposed between the atrium and the ventricle. The morphological characteristics of the AV segment appear to be species specific. Anat Rec, 294:236-242, 2011. V V C 2010 Wiley-Liss, Inc.

The Teleost Heart: A Morphological Approach

“…Areas of continuity with the atrial and ventricular muscle are always observed (Fig. 2.7 ) (Icardo and Colvee 2011 ) . From a morphological point of view, the AV region constitutes a distinct segment of the adult teleost heart.…”

“…Strikingly, this feature is not restricted to temperate teleosts. Coronaries are also observed in the Antarctic species Dissostichus mawsoni (Icardo and Colvee 2011 ) and Nothotenia angustata (Eastman 1993 ) . Overall, ventricular subepicardial vessels are not very numerous, and they do not appear to form a very rich plexus.…”

“…This succinct description, together with several references to the presence of a delay in the electrical conduction in the heart (Satchell 1991 ;Sedmera et al 2003 ) , sums up most of our knowledge of this part of the heart. However, recent morphological analyses show a more complex picture (Icardo and Colvee 2011 ) . When the heart of teleosts with completely trabeculated ventricles is examined, the AV region appears formed by a distinct ring of myocardium ( Fig.…”

“…2.7a, b ). This myocardium is compacted, shows vascular pro fi les in most of the species, and contains variable amounts of collagen and elastin (Icardo and Colvee 2011 ) . These three characteristics differentiate clearly the AV area from the ventricular and atrial chambers.…”

“…Recent studies indicate that, in addition to those four chambers, all teleosts contain a conus arteriosus (Schib et al 2002 ;Grimes et al 2006 ;Icardo 2006 ) and a distinct atrioventricular segment (Icardo and Colvee 2011 ) . Accordingly, the morphology of the heart is reviewed to include these two segments.…”