Anatomical EKG Heart
Description
I have wanted to create an effective model for some time to help teach EKG interpretation. I believe that beyond understanding rhythms and rates it is important to understand how those findings relate to the disease that the patient is presenting with. I have hopefully combined the historical and physiologic context of the EKG anatomy (Einthoven's Triangle) with more practical locations of of where those leads correlate on the reverse. The heart is has a very peculiar placement within the chest or mediastinum. It has multiple rotations from what we classically think of is the position and shape of the heart making visualization a problem. This is compounded by the fact that medical illustrations can only get us so far. To use this as a conceptual tool Think about that shape of the Einthoven Triangle as pointing toward the shoulders and then to the space between the feet. Look at the positioning of the heart and that is roughly how it is positioned in most people. Then looks at the blood vessels in relation to that position. You can see that the Left Anterior Descending artery is located directly in front of you or anterior left lateral if we were looking at a patient. Then look at how the precordial leads (V1-V6) relate to that anatomy (geography) of the heart. We can then appreciate the vectors of the limb leads and the augmented limb leads that are located on the Triangle. Where are those exiting the heart, which really corresponds with what kind of electrophysiologic dysfunction do they represent. Then you can relate that back to blood vessels that are adjacent to those regions and appreciate how they can represent some disease in the Right Coronary artery (marginal branch) and the Left Circumflex artery. On the reverse (ovoid) side then I placed labels next to the location of the heart muscle that best corresponds to those leads. This can help cement the the conceptual understanding that was hopefully gained on the obverse side. Lastly, the limitations of the EKG study is always important to discuss. As we can see there is much of the electrical activity of the heart that won't be captured by the 12-lead. It is primarily focused on capturing dysfunction (ischemia or infarction) related to the left ventrical. As this is the main function of the heart and responsible for the most severe disease and death that makes sense. But, by looking at the anatomy we can appreciate that there is a lot of the electrical activity of the heart that remains unknown with the standard 12-lead. That is the reason that the the 12-lead has such a limited sensitivity (30-70%), essentially you cannot use it to rule out a myocardial infarction. It does, however, have a very good specificity (70-100%). This specificity owes in part to the location of the location of the electrical conduction system (bundle of His, Purkinje fibers, etc) being in the sub-endocardial layer of the heart wall which is the most susceptible to decreased blood flow as the blood has to go through the major vessels and then penetrate all the way through the heart muscle to provide perfusion (oxygen and nutrients). Please let me know if you have any feedback or concerns with my model so that I can make it better.
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