arteries, disease, sophiahayes

The Normal Interventricular Septum
CT scan in the Axial plane of a healthy 24 year old male reveals a straightened RV side of the septum while there is a slight bulge on the LV side 
Ashley Davidoff MD

The Common Vein Copyright 2019

Ganesh Athappan MD Ashley Davidoff MD

Definition:

The inter ventricular septum is a fibromuscular obliquely placed partition between the right and left ventricular cavities. Structurally it is composed of membranous and muscular parts and ,takes a  gentle convex curvature toward the right ventricle.  Functionally it serves to disconnect the right and left ventricular outflow tracts from one another .

Diseases of the ventricular septum are predominantly congenital with ventricular septal defect being the most common congenital heart disease .

Diagnosis of a VSD, is suspected in the presence of a thrill and a loud, harsh, or blowing holosystolic murmur  over the lower left sternal border in the third or fourth intercostal space . The most common symptoms depending on the size of the defect are dyspnea, feeding difficulties, poor growth, profuse perspiration, recurrent pulmonary infections, and cardiac failure. The ECG shows  equiphasic RS complexes in the mid precordial leads  representing biventricular hypertrophy (Katz-Wachtel phenomenon ).  The CXR may show RV enlargement and pulmonary plethora. Transthoracic echo by two-dimensional and Doppler color flow mapping identifies the type of defect in the ventricular septum in most cases. Cardiac catheterization may be used to determine the hemodynamic characteristics of the VSD.

Medical therapy for congestive heart failure or infective endocarditis, minimally invasive techniques and surgical options are available .

Structural Considerations

The infrastructure of the heart is built on  cross, and the limbs of the cross reflect the septa of the heart.  The upper septum called the atrial or interatrial septum divides the right and left atrium while the lower “vertical” septum divides the ventricles into right and left ventricles and is called the interventricular septum or simply the ventricular septum.  The horizontal septum called the atrioventricular septum divides the atria from the ventricles.  A third septum called the conal septum forms part of the interventricular septum as well as part of the septum at the base of the great vessels.  The heart is tipped on its side with the apex pointing leftward and inferiorly while the right sided structures are tipped anteriorly and so the positional relationship of the structures are not orthogonal.

 

The Basic Scaffolding of the Heart
The infrastructure of the heart is a cross resulting conceptually in a box with four chambers. The upper chambers are the receiving chambers and the lower chambers are the pumping chambers. Between the two atria is the interatrial septum, and between the two ventricles is the interventricular septum.
This diagram shows perfect symmetry. The heart although having the same infrastructure has a beautiful asymmetric symmetry, similar to the painting of a Girl Before the Mirror by Picasso.
Ashley Davidoff MD

 

 

 


Atrial Septum, Ventricular Septum, and Conal Septum
The orientation of the basic scaffolding is not vertical but oriented with the cross tipped to it’s right side (as seen in the person) so that the atrial septum is rightward of the ventricular septum.  The atria and atrial septum thus  lie superior and relatively rightward to the ventricles and also lie posterior to the ventricles.  The apex of the scaffolding points toward the left of the patient..
The interatrial septum has 3 components.  Superiorly it arises embryologically from the sinus venosus (purple).  The middle portion (green) arises from the septum primum, and the inferior portion (pink) arises from the  endocardial cushions, which also contribute to the horizontal part of the scaffolding in the atrioventricular part of the scaffolding.  The tricuspid valve to the right and the mitral valve to the left are formed in part from the endocardial cushions.  The most superior portion of the interventricular septum also arises from the endocardial cushions (pink).
The rest of the interventricular portion of the vertical part of the scaffolding (interventricular septum) has a  small portion forming the membranous septum (white), and a large portion (red) that forms the muscular septum.  
At the crossroads (AKA crux of the heart) where the horizontal portion of the scaffolding and the vertical portion meet, the conal septum (orange) arises and lies between the aortic  valve and pulmonary valve.
key words
 heart cardiac embryology conal septum line drawing right atrium left atrium left ventricle right ventricle interatrial septum interventricular septum atrioventricular septum crux of the heart embryology anatomy
Ashley  Davidoff MD
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The  atrial septum has  three independent embryologic origins .

The upper portion arises from sinus venosus , the middle portion arises from the muscle itself (mesoderm), while the lower portion arises from the endocardial tissue.

 

Atrial Septum, Ventricular Septum, and Conal Septum
and the Chambers Attached to and Surrounding the Scaffolding
In this diagram the interatrial,  atrioventricular, and interventricular parts of the scaffolding are enhanced, and the surrounding attached chambers are also shown.
 In this diagram the crux (crossroads of the vertical limb and horizontal limb of the cross) of the heart is colored in pink and represents the endocardial cushion contribution to the heart. The interatrial septum consists of the sinus venosus component (purple), the septum primum (green) and the portion contributed by the the endocardial cushions (pink) The interventricular septum consists of a muscular portion (red), and a endocardial cushion component (pink). The conal septum is part of the conus arteriosus, lies between the pulmonary artery and aorta and is colored in orange.
The heart chambers do not lie in a vertical orientation. The atria are relatively posteriorly placed and the ventricles tend to be anterior. The atria also tend to be rightwardly placed while the ventricles tend to be leftward. The right sided structures tend to be anteriorly placed while the left are posteriorly placed.
key words
heart cardiac embryology conal septum line drawing right atrium left atrium left ventricle right ventricle interatrial septum interventricular septum atrioventricular septum crux of the heart embryology anatomy
Ashley Davidoff MD 01669b03
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The strong ventricular septum, made up of a small membranous and large muscular portion  is directed obliquely backwards and to the right, and is curved with the convexity towards the right ventricle.  This septal  geometry , subsequent to  elevated LV pressures  can be appreciated on imaging and is important as changes may signify either  abnormalities of the septal myocardium  or  abnormal pressure differences between the LV and RV.  Flattening of the interventricular septum may strongly correlate with RV overload.

 

The heart has a left and right arterial system. The vessels are formed around the cross of the heart, “vertically” along the interventricular septum and interatrial septum, and “horizontally” in the atrioventricular (A-V) grooves. The left coronary artery arises from the left coronary ostium and supplies one branch, the left anterior descending artery, that travels anteriorly on the anterior aspect of the interventricular septum, and one branch that travels in the atrioventricular groove (left circumflex). The right coronary artery has a branch that courses along the right atrioventricular groove and usually continues as the posterior descending artery on the posterior aspect of the interventricular groove, and commonly gives rise to the A-V nodal branch, at the back of the crux of the heart, which travels in the vertical axis in the interatrial septum.
Courtesy of: Ashley Davidoff, M.D.

 

LAD Defines the Position of the Interventricular Septum   The frontal view of the heart is a normal post mortem specimen with contrast in the coronary arteries delineating the large central left anterior descending artery that separates the right side of the heart from the left.
15009c cardiac heart coronary artery normal anatomy gross pathology LAD diagonal artery acute marginal artery conal artery arc of Vieussens Courtesy Ashley Davidoff MD
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LAD Marks the Position of the Interventricular Septum
This is an anterior view of the heart showing the long LAD travelling within the expected course of the interventricular septum.
This post mortem angiogram in the LAO projection shows normal LAD overlaid in red with the PDA as the main vessels slightly to the hearts lt side.   The septal branches from the PDA are well seen and the interventricular septum can be seen as a faint blush.
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cardiac heart coronary artery LAD diagonal conal infundibulum RVOT anatomy normal
Ashley Davidoff MD
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PDA Marks the Position of the Interventricular Septum Posteriorly
This is a look at the back of the heart, really looking at the inferior (diaphragmatic) surface. The triangular RV noted toward the left of the image dominates this inferior surface. The posterior descending artery can be seen outlined in white. 
key words
cardiac heart coronary artery PDA posterior left ventricular artery LV RV anatomy normal circumflex artery obtuse marginal PDA
Courtesy of Ashley Davidoff M.D.
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Posterior Descending Artery
Both coronary arteries have been injected with barium in this post mortem angiogram taken in shallow left anterior oblique projection. The PDA is shown in red as it takes a 90 degree turn off the right coronary artery. Note the acute marginal artery (AM) reflects the edge of the right side of the heart, and the obtuse marginal off the LCA and circumflex reflects the left edge of the heart. The PDA reflects the inferior border of the heart. The septal perforators supply the posterior and inferior 1/3 of the ventricular septum and arise at right angles off the PDA.
Courtesy: Ashley Davidoff, M.D.

 

Internal View of the Left ventricle (LV) 
In this post mortem image the left ventricle is opened along the LAD anteriorly and PDA posteriorly so that the ventricular septum is displayed to the left and the free wall, mitral valve and papillary muscles to the right. The aortic valve is seen to the top of the image in fibrous continuity with the anterior leaflet of the mitral valve. Note the conical shape of the left ventricle, the relatively smooth septal wall that has fine muscle bundles, the two major groups of papillary muscles, and the relatively thick muscular wall.
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heart LV left ventricle mitral valve MV ventricular septum free wall anterolateral papillary muscle posteromedial papillary muscle aortic valve fibrous continuity normal anatomy gross anatomy
Ashley Davidoff MD
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Interventricular Septum                                                                                                                                                                                                                                                                                        Short axis of an anatomic specimen showing the tricuspid valve within the right ventricle and the mitral valve within the left ventricle. the anterior leaflet of the mitral valve is in fibrous continuity with the aortic valve
Ashley Davidoff MD
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Imaging the Septum

The Normal Interventricular Septum
CT scan in the Axial plane of a healthy 24 year old male reveals a straightened RV side of the septum while there is a slight bulge on the LV side 
Ashley Davidoff MD

RV aspect :

Interventricular portion of the membranous septum: Part of the membranous septum that  is overhung by the septal leaflet of the tricuspid valve.

Atrioventricular membranous septum: The part of the membranous septum that  lies superior to the tricuspid valve and forms the floor of the right atrium.

Right ventricular Infundibulum : part of the right ventricle which lies between the pulmonary valve above  and an imaginary line through the papillary muscle of the conus and upper edge of the membranous septum.

Crista supraventricularis : The crista supraventricularis if oversimplified can be considered synonymous with the infundibular (or conus) ventricular septum.

The appreciation of these terms is essential to  understand the various classifications of ventricular septal defects which are discussed in the disease section of the cardiac module.

Interventricular Septum as seen from the Right Ventricle
The view of the septum from the right ventricle is very different and is difficult to define.  the most obvious and consistent structure is the septal band (pink) pink = septal band  purple = conal septum aka infundibular septum blue = trabeculated portion of the muscular septum
key words  heart cardiac RV RVOT IVS tricuspid valve interventricular septum papillary muscle of Lancisi Y of septal band normal anatomy right ventricular outflow tract pulmonary valve normal anatomy gross anatomy
Ashley Davidoff MD
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Position of the Chambers and the Atrioventricular Valves and the septa  of the Heart on CT scan
The cross-sectional images from a CT scan through all 4 chambers reveals the relative position of the chambers and A-V valves. In general “blue” chambers are both anterior to and superior to the “red” chambers so that both the right atrium (RA) and right ventricle (RV) are anterior to the LA and LV. The tricuspid valve (blue valve) follows the rule and is slightly anterior to the mitral valve as well. Not shown here is that the fact that the right sided structures are slightly superiorly positioned.
Ashley Davidoff, M.D.
27531cd01.8s aka heart-anatomy-P-070

 

Interventricular Septum As Seen on a Coronal CT Examination
key words right atrium heart cardiac RA tricuspid valve TV left atrium LA MV mitral valve RV right ventricle anterolateral papillary muscle interventricular septum left ventricle LV CTscan
Ashley Davidoff MD
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Interventricular Septum As Seen In CT examination
27531b01 right atrium heart cardiac RA tricuspid valve TV left atrium LA MV mitralvalve RV right ventricle anterolateral papillary muscle interventricular septum left ventricle LV CTscan Davidoff MD

Gentle Curve of the Septum
The anterior cut of this T1 weighted MRI sequence shows that the dominant anterior chamber is the right ventricle with a portion of the thicker walled left ventricle toward its left. The right ventricle in this instance is dilated. Courtesy of Ashley Davidoff M.D. 32069

 Septum Using Tissue Doppler Imaging
This tissue doppler echo of the heart using a left apical 4-chamber view, and demonstrating a normal heart.

Courtesy Philips Medical Systems 33179 code cardiac heart echo tissue doppler LV RV RA LA

 

 

 

 

The diastolic inter ventricular septal  (IVS)thickness as measured by echo ranges from 0.7-1.1 cm.  Increased IVS thickness is seen early in hypertension and may signify a diastolic abnormality. HOCM which is a genetically determined disease characteristically produces an asymmetrical septal hypertrophy .

Change in Septal Size During Systole (right) and Diastole (left)
The heart is not static in size and has volume changes every heart beat. The ejection volume is about 70ccs per heart beat. Thus in a normal heart, the diastolic volume of each ventricle is larger than the systolic volume by 70 ccs. In this image of the normal heart, the difference in size is perceptible, with the left image showing contracting ventricles and the right image showing the dilated diastolic ventricles. Courtesy of Philips Medical Systems. 32073 heart normal systole diastole RV LV MV TV LV RV cardiac imaging radiology MRI

 

 

 

Septal motion during the cardiac cycle is posterior during systole and anterior during diastole. Right ventricular volume overload produces an abnormal systolic interventricular septal motion on echocardiography.

Aging

There is a clinically relevant disproportionate  increase in the ventricular septal thickness  with age,   regardless of gender and in the absence of a history of hypertension. The ratio of ventricular septal to left ventricular free-wall thickness may exceed 1.3 in patients older than 60 years of age, normal being < …”

Parts

LV aspect:

Membranous septum:  The fibrous membrane occupying the basal portion of the septum and anteriorly leveled below the mid portion of the right aortic cusp.

Anterior septum (conoventricularis septum, infundibular, supracristal, outlet): A small portion that lies between the anterior LV wall and membranous septum.

Posterior smooth septum(Inlet) :  superior 1/3rd to ½ of the muscular part of the septum. It is devoid of trabeculations which differentiate it from the trabecular septum.

Posterior trabeculated septum:  Septal wall of the apical ½ to 2/3rd of the ventricle.

RV aspect :

Interventricular portion of the membranous septum: Part of the membranous septum that  is overhung by the septal leaflet of the tricuspid valve.

Atrioventricular membranous septum: The part of the membranous septum that  lies superior to the tricuspid valve and forms the floor of the right atrium.

Right ventricular Infundibulum : part of the right ventricle which lies between the pulmonary valve above  and an imaginary line through the papillary muscle of the conus and upper edge of the membranous septum.

Crista supraventricularis : The crista supraventricularis if oversimplified can be considered synonymous with the infundibular (or conus) ventricular septum.

The appreciation of these terms is essential to  understand the various classifications of ventricular septal defects which are discussed in the disease section of the cardiac module.

Calcification of the LAD
This CTscan with contrast through the heart shows heavy calcification of the LAD as well as the circumflex coronary artery as well as calcification of the aortic annulus. Courtesy Ashley Davidoff MD. 15401 code cardiac heart artery coronary calcification calcium calcified CAD atherosclerosis aortic sclerosis annulus imaging radiology CTscan AO aorta

 

Anemia –Normal Thickness left and Thin (Right
19730 31675b01 heart pleural calcification cardiac interventricular septum IVS LV mitral valve calcification rheumatic heart disease probable chronic hemothorax or empyema anemia fx relatively dense interventricular septum due to anemia CTscan Courtesy Ashley Davidoff MD

VSD

Defects in the Septa of the Heart
06570e heart cardiac atrial septum ventricular septum IVS sepatal defects ASD of primum type secundum ASD membranous VSD ventricular septal defect muscular VSD VSD of the conal septal conal VSD supracristal VSD subpulmonic VSD ASD of the AV canal type Davidoff art drawing Courtesy Ashley Davidoff MD

Membranous VSD
This is a series of angiograms of the left ventricle in LAO projection showing a puff of contrast into the right ventricle through the interventricular septum. A similar collection of contrast is noted in the the main pulmonary artery just to the left of the aorta. This high VSD is in the position of the membranous septum and thus represents a mebranous ventricular septal defect.. Courtesy Ashley Davidoff MD. 00250 code cardiac heart LV RV VSD membranous MPA aorta AO congenital imaging radiology angiography

Muscular Ventricular Septal Defect
10230b01 right ventricle septal band VSD muscular ventricular septal defect congenital heart disease grosspathology Davidoff MD

Conoventricular Defect – Single Ventricle
16933 heart cardiac interventricular septum heart dx single ventricle dx ILR dx pulmonary atresia congenital heart disease MRI T1 weighted Courtesy Ashley Davidoff MD

VSD of the A-V canal type – Complete Endocardial Cushion Defect
01863b01 heart cardiac LV left ventricle IVS interventricular septum mitral valve endocardial cushions complete AVC canal defect cleft mtral valve VSD endocardial cushion defect congenital heart disease grosspathology Courtesy Ashley Davidoff MD

High VSD
11992b03 heart LV left ventricle interventricular septum ventricular septum VSD ventricular septal defect subaortic grosspathology Courtesy Ashley Davidoff MD

Abnormal Axis of the Septum – Mesocardia
This is a CT scan through the chest in which the apex of the heart points forward. The left ventricle (LV) is left sided and the right ventricle is right sided. There is situs solitus of the atria. This is a case of mesocardia ie neither right nor leftwad pointing apex. Courtesy Ashley Davidoff MD. 19689 code heart mesocardia cardiac imaging radiology CTscan

Normal and IHSS
This series of CTscans shows a normal Left ventricular outflow tract overlayed in bright red in a, with normal septum in green (c) contrasted to a patient with IHSS, where the LVOT is narrowed (b and bright red in d) with a thickened septum with overlay in green (d). Courtesy Ashley DAvidoff MD 39208c01 code cardiac heart CTscan interventricular septum thickened IHSS imaging radiology CTscan

 

Dacron Graft Repair of a Membranous VSD
07932c01 heart LV cardiac defect left ventricle membranous septum ventricular septum interventricular septum VSD dacron graft repair of a membranous VSD papillary muscles grosspathology Courtesy Ashley Davidoff MD

 

 

Septal and Apical Thinning post MI
26334b heart cardiac interventricular septum IVS apical thinning LV aneurysm apical and septal thinning myocardial infarction CTscan Couresy Ashley Davidoff

Concentric Hypertrophy
08028b06 heart cardiac LV left ventricle papillary muscles RV right ventricle LVH left ventricular hypertrophy thickened LV concentric hypertrophy interventricular septum thickened enlarged grosspathology Courtesy Ashley Davidoff MD

IHSS Asymmetric Septal Hypertrophy
This is a case of focal thickening (bright red overlay) in the region of the septum, which causes obstruction of the LV outflow tract during systole. This condition is known as asymmetric septal hypertrophy – also known as idiopathic hypertrophic sub-aortic stenosis -IHSS. Courtesy of Philips Medical Systems, Ultrasound, and modified by Ashley Davidoff M.D. 32133

 

References

Kitzman D, Edwards WD. Minireview: age-related changes in the anatomy of the normal human heart. J Gerontol Med Sci. 1990;45:M33