Cardiac anatomy is bizarre, the heart is the only organ, which for no obvious reason has been described as though it were outside of the body, standing on its apex in the shape of a Valentine heart. Despite extensive publications by the likes of McAlpine, Anderson and Hill on the attitudinal correct orientation of the human heart, many organisations, books and other anatomical resources have been either slow or limited in adopting anatomical accurate descriptions of the heart based on the normal anatomical position.
The Valentine orientation has clinical implications, consider deciphering any form of cross-sectional imaging of the heart, the anatomy of the heart on CT makes no sense using the Valentine model, the chambers, except the right atrium, are not topographically congruent with their outdated nomenclature. Procedures such as angiography and ablation make little sense when describing the position of the catheter in relation to the Valentine orientation. During the performance of ablation of the atrioventricular node, the node is identified by finding the apex of the Triangle of Koch, see Figure 1. Using the Valentine orientation, a catheter advanced through the inferior vena cava into the right atrium was traditionally described as travelling posterior to anterior, which makes no sense at all, a catheter moving in that direction would end up perforating the IVC! In actual fact, the catheter is being advanced from inferior (feet) to superior (head). The position of the AV node means, a clinician would advance the catheter in a superior direction and then once in the right atrium, the catheter is moved in a superior and slightly anterior direction to get to the apex of the Triangle of Koch (AV node).
Figure 1, Right atrium opened up to show the boundaries of the Triangle of Koch: Tendon of Todaro, coronary sinus and the septal leaflet of the tricuspid valve.
The heart as it develops indeed does have a have a right and left side, however, during development twisting and folding results in the heart sitting obliquely with the right-sided structures finally lying anteriorly and left-sided structures lying posteriorly. The conventions of right and left thus become anatomically redundant for most of the relevant structures. As a student, it’s important to appreciate the correct orientation early on in your careers. Remember that the heart is a dynamic structure, its morphology changes during diastole and systole, as well as this the heart moves with the diaphragm. The heart sits mainly over the central tendon of the diaphragm and slightly on the left muscular region. The following paragraphs will discuss the attitudinally correct nomenclature of the coronary arteries, and cardiac chambers, the valve leaflets and papillary muscles are beyond the scope of this post.
Figure 2, Casts made by Professor Anderson, heart shown in attitudinally correct orientation, adapted from Gray’s Anatomy, the Anatomical Basis Of Clinical Practice.
The right and left coronary arteries arise from their respective right and left coronary ostia (in the aortic root), however, from there on the naming of some of the key vessels make little sense. The name of the posterior interventricular coronary artery would suggest that the artery is sitting in its sulcus (interventricular) facing the vertebral column, with the posterior aspect of each ventricle on either side. The reality does not match the convention. The artery and its sulcus actually face the diaphragm on the inferior surface of the heart and travel in an oblique direction from posterior to anterior to reach the apex on the left side of the thorax, see Figure 3. Interestingly when the “posterior” interventricular artery becomes blocked by a thrombus the resulting infarct is described correctly as an inferior infarct, would it not make more sense, therefore, to correctly name the artery inferior in the first place? Next time you are in the prosectorium or looking at a photographic atlas, it should be obvious. The correct name for this artery is the inferior interventricular artery, see Figure 3 below.
Figure 3, Lateral view of the thorax illustrating the positions of the interventricular arteries, adapted from adapted from Gray’s Anatomy, the Anatomical Basis Of Clinical Practice.
So where does this leave the anterior descending artery? The artery lies in the “anterior” interventricular groove. The anterior interventricular groove is certainly not on the anterior surface of the heart. Instead, it is located superiorly (see Figure 3 above) and divides the two ventricles and heads towards the cardiac apex, again an oblique direction from posterior to anterior. The artery should be more accurately referred to as the superior interventricular coronary artery.
The anterior chambers
Let’s start with the right ventricle, the term right implies that the ventricle should be on the right side of the midsagittal line, facing the right hilum of the lung. Surprise surprise, it’s not the case in the cadaver, or on echocardiography, MRI or CT. The right ventricle actually forms the sternal face of the heart, it faces anteriorly. Therefore it would be more accurate to refer to it as the anterior ventricle. The right atrium also faces anteriorly, though a significant portion of it faces the right hilum of the lung, thus making it the only truly right facing chamber. Summarising, the right border of the heart is the right atrium. The anterior (sternal) surface is the right ventricle. Figure 4 shows how the right ventricular chamber and its myocardium form the entire anterior surface, note the asterisk marks the apex (the tip of the left ventricle) of the heart.
The “left” atrium forms the posterior surface of the heart, the surface which faces the vertebral column, see Figure 4. Some sources refer to this as the base. However, this can sometimes be confused with the diaphragm and hence is best avoided. Behind the “left” atrium are the oblique sinus, oesophagus and vertebral column. Thus the “left” atrium in the cadaver and on radiological imaging is clearly located posteriorly, it couldn’t be any less left. Yet the term left atrium persists. The correct descriptor should be the posterior atrium, this would finally describe the location of the chamber in line with the anatomical position.
Figure 4, showing a cross-sectional perspective of the cardiac chambers, adapted from Master Medicine, Clinical Anatomy
So what about the left ventricle? Where is it? Well, let us consider once again the so-called posterior interventricular coronary artery, as discussed above a more accurate name would be the inferior interventricular coronary artery, already this term is far more useful. It tells us that this artery is facing the diaphragm and it is interventricular. So, I know the right ventricle is actually front facing, some of it is also in contact with the diaphragm, as the inferior interventricular artery separates the two ventricles, posterior to the artery, therefore, is the “left” ventricle, see Figure 4. So the so-called left ventricle actually forms the greater part of the inferior surface of the heart, it faces posteriorly and also makes up the left border of the heart. Note the apex of the heart does not point inferiorly in the mid-line as in the Valentine orientation, but rather towards the left.
What do I write in exams?
If you are asked to write about the topographic anatomy of the heart, in my opinion, this should be done in an attitudinally correct manner, if your MCQs are set using old terms, you have no choice but to stick to the old nomenclature. Textbooks are changing, the 41st edition of Gray’s Anatomy, The Anatomical Basis Of Clinical Practice, does reflect the current literature. Remember you will come across clinicians and academics who continue to use the Valentine model nomenclature, you don’t have to agree, just be tactful when you decide to disagree.
- Attitudinally correct nomenclature, Heart BMJ, A C Cook and R H Anderson
- Gray’s Anatomy, The Anatomical Basis Of Clinical Practice, Susan Stranding