The Common Vein
Copyright 2009
Introduction
The “twist” in the story is long and complicated, with important implications in congenital heart disease – beyond the scope and need of this anatomy text. In the normal setting we make the following observations: The blue-blooded chambers tend to be rightward, anterior, and slightly superior in position. One of the main structural differences between the right and left sides is that the right ventricle has a separate and distinct outflow chamber – the RVOT or infundibulum. There is an oblique and leftward pointing orientation of the outflow chamber , so that the pulmonary valve lies to the left and superior to its counterpart, the aortic valve. During embryological development, the RVOT, MPA (Main Pulmonary Artery), and aorta twist around each other to result in the structural positioning and relationships of the valves. It always seemed odd that the pulmonary valve coming from the right sided chambers lay to the left of the aortic valve. Under-twisting or over-twisting results in mispositioning of the great vessels in relation to their ventricles with consequent drastic hemodynamic results. Transposition of the great vessels is one such example. The left ventricle arises from the mesodermal germ layer. By the 22nd day of development there is a single heart tube made of an inner endocardial tube and a surrounding myocardial mantle. Starting at the 4th week, the interventricular septum develops to form the distinct left ventricle. This is formed by the inferior endocardial atrioventricular cushion and left conus swelling.
Straight Tube
Straight Tube The heart starts as a straight tube. In this stick diagram inflow is through the sinus venosus (maroon) which will evolve into the atria. Blood then passes through the single common atrioventricular valve (short pink horizontal region) which will evolve into the tricuspid and mitral valves. The next vertical limb (red) represents the portion of the tube that will develop into the ventricles. The horizontal orange bar represents the conus ? or muscular bundle that lies under the truncus arteriosus. (royal blue). The truncus arteriosus will evolve into the aorta and pulmonary artery. 01477b03 heart cardiac straight tube primitive heart embryology Ashley Davidoff MD TheCommonVein.net
The Single Tube Phase Blood enters the sinus venosus and into the developing atria (maroon), after which it traverses the region of the developing A-V canal (pink) and into the developing ventricles (red) The blood passes through the conus (yellow) and via the truncus (blue)into the aortic sac and branchial arch arteries Ashley Davidoff MD TheCommonVein.net
D Loop
Genetic Instruction for the D-Loop Ashley Davidoff MD TheCommonVein.net
Looping of the RV The developing RV in most hearts starts out by looping to the right and also evolves anteriorly because there is room anteriorly in the chest for development since the tube starts out abutting the spine keywords heart cardiac straight tube d loop D loop primitive heart embryology right ventricle RV sinus venosus atria atrium A-V cushions conus arteriosus truncus arteriosus drawing Ashley Davidoff Davidoff MD 01488b02
DORV phase without Septation
DORV phase without Septation The heart in double outlet right ventricle phase prior to septation, so blood flows into the common ventricular chamber, and out into the conus (infundibulum) and into the truncus prior to entering the aortic sac Ashley Davidoff MD TheCommonVein.net
DORV phase with Septation The heart in double outlet right ventricle phase prior to septation, so blood flows intot the common ventricular chamber, and out into the conus (infundibulum) and into the truncus prior to entering the aortic sac Ashley Davidoff MD TheCommonVein.net
Stage of Embryology of the Heart Prior to Septation At this stage the heart consists of un-septated atria, ventricles and great vessels, with atria situated posteriorly connected to the ventricles by the AV canal, and the ventricles have a common outlet over the right ventricle to the conus arteriosus, which is connected to the truncus arteriosus Key words heart cardiac right atrium left atrium right ventricle, left ventricle atrioventricular canal conus arteriosus truncus arteriosus aortic arches RA LA RV LV AVC embryology 01492b04L Ashley Davidoff MD TheCommonVein.net
Septation
Septation of the Heart Septation occurs at all levels of the heart, including the atria, A-V valves, ventricles, conus, truncal valves, truncus and aortic sac A D loop will result in positioning the aorta to the right of the pulmonary artery, but at this stage the conus still arises from the developing right ventricle (DORV). During septation the conus will be divided into a right sided portion that will be subaortic, and a left sided portion that will be subpulmonary Key words heart cardiac d loop left ventricle is born to the left septation truncus arteriosus conus arteriosus ventricles atrium atria primitive heart embryology 01477e03 Ashley Davidoff MD TheCommonVein.net TheCommonVein.net
Septa of the Heart
Septa of the Heart The atrial septum consists of 3 parts; The most superior is the septum derived from the sinus venosus (purple), the middle is the septum primum (green) and the most inferior is derived from the endocardial cushions (pink) The endocardial cushions also contribute to the formation of the of the membranous component of the interventricular septum. The interventricular septum consists of the membranous septum and the muscular septum (red). The great vessels are separated by a muscular conal septum (orange) and the membranous aorticopulmonary septum (light pink). Ashley Davidoff MD TheCommonVein.net
Septation of the A-V Valves
Septation of the endocardial cushions to form the A-V Valves Septation occurs at all levels of the heart, including the atria, A-V valves, ventricles, conus, truncal valves, truncus and aortic sac The 4 endocardial cushions are separated into 2 evolving valves. On the right side 3 leaflets form ? the tricuspid valve and on the left side 2 leaflets of the mitral valve Key words 01492b12 heart cardiac left atrium right atrium mitral valve tricuspid valve coronary arteries coronary ostia A-V canal atrioventricular canal conus arteriosus truccus arteriosus D loop left ventricle right ventricle embryology RV LV MV TV LA RA aorta pulmonary artery normal drawing Davidoff art Davidoff MD 01492b11 01492b06b 01492b05b01 01492b1201492b14 Ashley Davidoff MD TheCommonVein.net
Septation of the endocardial cushions to form the A-V Valves Septation occurs at all levels of the heart, including the atria, A-V valves, ventricles, conus, truncal valves, truncus and aortic sac The 4 endocardial cushions are separated into 2 evolving valves. On the right side 3 leaflets form ? the tricuspid valve and on the left side 2 leaflets of the mitral valve Key words heart cardiac left atrium right atrium mitral valve tricuspid valve coronary arteries coronary ostia A-V canal atrioventricular canal conus arteriosus truncus arteriosus D loop left ventricle right ventricle embryology RV LV MV TV LA RA aorta pulmonary artery normal drawing 01492b14 Ashley Davidoff MD TheCommonVein.net
Cono-Truncal Septation
The Conotruncal Region The conus (gold exterior consists of a single muscular tube prior to septation. Theorigin of the truncus contains 4 truncal cushions which are going to develop into the aortic and pulmonary valve following septation. Ashley Davidoff MD TheCommonVein.net
Septation A D loop will result in positioning the aorta to the right of the pulmonary artery, but at this stage the conus still arises from the developing right ventricle (DORV). The truncus after it divides will have two valves consisting of 3 leaflets each During septation the conus will be divided into a right side portion that will be subaortic, and a left sided portion that will be subpulmonary Ashley Davidoff MD TheCommonVein.net
Result of Septation of the Conotrucus The conus now consists of muscle bould tubes, and the aortic valve and pulmonary valve are well formed. Double outlet right ventricle persistsresulting in both great vessels receiving blood from the single ventricle. Ashley Davidoff MD TheCommonVein.net
Result of Septation of the Conotruncus The conus consists of muscle bound tubes, separated by the conal septum, and the aorta and pulmonary artery are separated by the aorticopulmonary septum. The morphology and physiology are consistent with a double outlet right ventricle state. Both great vessels receive mixed blood from the “single” ventricle. Ashley Davidoff MD TheCommonVein.net
Connecting with Growth and Resorption
Ready to Connect At this stage the heart is close to totally septating but before this happens the left ventricle and aorta have to connect in order to create a systemic circulation that is separate from the pulmonary circulation. The aorta lies to right of the pulmonary artery and still has a subaortic conus. In order to connect with the left ventricle and mitral valve, the subaortic conus has to resorb. Mr Aorta has a his eyes set on Ms Mitral Valve Ashley Davidoff MD TheCommonVein.net
Aorta and Pulmonary Artery Side by Side with Bilateral Conus 2018 01806 Ashley Davidoff MD TheCommonVein.net
Ready to Connect At this stage the heart is close to totally septating but before this happens the left ventricle and aorta have to connect in order to create a systemic circulation that is separate from the pulmonary circulation. The aorta lies to right of the pulmonary artery and still has a subaortic conus. In order to connect with the left ventricle and mitral valve, the subaortic conus has to resorb. Mr Aorta has a his eyes set on Ms Mitral Valve Ashley Davidoff MD TheCommonVein.net
A Poem of the Love Affair
A Match Made in Heaven
Ready to Connect At this stage the heart is close to totally septating but before this happens the left ventricle and aorta have to connect in order to create a systemic circulation that is separate from the pulmonary circulation. The aorta lies to right of the pulmonary artery and still has a subaortic conus. In order to connect with the left ventricle and mitral valve, the subaortic conus has to resorb. Mr Aorta has a his eyes set on Ms Mitral Valve Ashley Davidoff MD TheCommonVein.net
Immediate Attraction Mr Aorta only has eyes for Ms Mitral How is Mr Aorta going to reach her? Double Outlet RV Morphology Ashley Davidoff MD 07427b10 TheCommonVein.net
Resorption of the subaortic conus brings Mr Aorta (the aortic valve) toward Ms Mitral (the mitral valve) keywords 06370b04 heart cardiac bilateral conus outflow tract infundibulum aorta pulmonary artery D-loop RV LV cono-ventricular defect bilateral conus atrioventricular endocardial cushion mitral valve anatomy embryology subaortic conus sub-pulmonary conus fibrous continuity mitral valve MV 06370b04 Ashley Davidoff MD TheCommonVein.net
Aortic Valve and Mitral Valve Bond in Fibrous Union 07427b02 Ashley Davidoff MD TheCommonVein.net
Mitral Valve and Aortic Valve Working Together to Keep Flow Moving Forward Ashley Davidoff MD 34814c01.800 TheCommonVein.net
Working Together to Form an Inflow and an Outflow to teh Left Ventricle The mitral valve participates in the inflow as well as the outflow of the LV. The LV does not have an infundibular chamber like the RV. It is the anterior leaflet of the MV that has this dual function. The first drawing represents LV diastole, showing the open anterior leaflet acting as the anterior, medial and rightward border of the inflow to the LV. The second drawing is the systolic phase where this same anterior leaflet acts as the leftward and lateral border of the outflow tract. Ashley Davidoff MD TheCommonVein.net
Sagittal view of the Fibrous Continuity Between the Anterior Leaflet of Mitral Valve and the Aortic Valve Note how the aorta is tucked facing posteriorly (“heels of the patient”) as a result of the conal resorption 06373b05 heart cardiac aorta mitral valve anatomy embryology resorption of subaortic conus fibrous continuity mitral valve with aortic valve position shape of aorta MV Ashley Davidoff TheCommonVein.net
Septation of the Heart with an L Loop Septation occurs at all levels of the heart, including the atria, A-V valves, ventricles, conus, truncal valves, truncus and aortic sac An L loop will result in positioning the aorta to the left of the pulmonary artery, but at this stage the conus still arises from the developing right ventricle (DORV). During septation the conus will be divided into a left sided portion that will be subaortic, and a right sided portion that will be subpulmonary Key words heart cardiac d loop left ventricle is born to the left septation truncus arteriosus conus arteriosus ventricles atrium atria primitive heart embryology 01477e03 Courtesy Ashley Davidoff MD TheCommonVein.net
Diagram of the Embryological origins and Consequences of Conotruncal Malformations in an L Loop
embryology bilateral conus DORV growth resorption normal mitral to aortic continuity transposition D transposition double outlet right ventricle
Ashley Davidoff
06394c02L01s
TheCommonVein.net
Summary
Common Conotruncal Abnormalities The image reflects the relationship of the aorta and pulmonary arteries in the normal patient, in DTGA, LTGA and DORV. In the normal patient with D loop the aorta (Ao) is posterior and to the right, and the pulmonary artery (PA) is anterior and to the right. In the patient with DTGA, the Ao is anterior and to the right and the PA is posterior and to the left. In an L loop the Ao is anterior and to the left and the PA is posterior and to the right. In double outlet right ventricle (DORV) the great vessels lie side by side and in DORV with a D loop the aorta is to the right and with an L loop the aorta is to the left 86778 01639 01639d02 01639d04 01639f03.jpg Anterior aorta = Transposition Ashley Davidoff MD TheCommonVein.net
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