Cardiac Anatomy takes on new importance when observed through the lens of Cardiac Electrophysiology (EP). There are several reasons for this – Most important is how the specialized pacemaker cells are interwoven throughout the myocardium to maintain normal cardiac conduction. If the myocardium containing the specialized pacing cells doesn’t form properly or becomes ‘stretched out’ there can be repercussions for the individual.
This blog feature discusses the posterior anatomy of the heart.
First, it’s important to keep in mind that the heart sits at an angle in the chest cavity. The left atrium is the most posterior chamber of the heart, extending from the posterior wall of the left atrium are the pulmonary veins. Typically, 2 pulmonary veins take off from each side of the left atrium. However, it doesn’t take many atrial fibrillation ablation procedures to see that the standard “4 pulmonary veins” come with numerous variations. The most anterior structure of the left atrium is the left atrial appendage (LAA). When mapping (or performing other procedures, such as LAA closure), keep in mind the LAA is anterior and therefore closer to the left ventricle and mitral annulus.
The coronary sinus (CS) is located on the posterior epicardial surface. In EP, the CS famously guides us along the AV groove, dividing atrial and ventricular electrograms. An EP catheter placed inside the CS allows us to record transmitted atrial and ventricular impulses, watch rhythm propagation across the heart and serves to pace the left ventricle in Bi-ventricular pacing (Cardiac Resynchronization Therapy- CRT). For more information about the coronary sinus, click here.
Another consideration in posterior cardiac anatomy is the esophagus, which comes into play significantly during radiofrequency atrial fibrillation ablation. The dynamic nature and proximity of the esophagus to the posterior left atrial wall must be carefully navigated during ablation procedures to prevent esophageal damage.
Finally, the posterior anatomy of the heart contains the inputs of the autonomic nervous system (ANS): the vagus and phrenic nerves. The Vagus nerve is a parasympathetic nerve and although not a cardiac structure is critical physiologically as a heart rate regulator. The second posterior nerve relevant to this feature is the phrenic nerve which controls the mechanical function of the diaphragm. During an atrial fibrillation ablation, it is imperative to avoid both nerves. The cardiac plexus ganglia can also vary in their exact location due to remodeling or the general nature of the ANS structure.
Cardiac anatomy is important in every specialty. In cardiac electrophysiology, it is necessary to also consider the heart's relationship to other vital structures such as the pulmonary veins, the interrelationship of the cardiac chambers and great vessels, the coronary sinus, and nervous inputs. For more information about cardiac electrophysiology, join the CHART Healthcare Academy website or take one of the many courses in various formats.