Inferior pyramidal space

The inferior pyramidal space of the heart is occupied by the fibro-adipose tissue of the inferior atrioventricular groove, which fills the space between the atrial floor of the atrioventricular nodal triangle (triangle of Koch) and the crest of the muscular interventricular septum.[1]

The inferior pyramidal space of the heart is bounded by the atrial and ventricular septa, the attachments of the mitral and tricuspid valves, and the membranous septum. This space is extracardiac, lying outside the myocardium but within the cardiac contour, and is filled with fat and connective tissue.

In cardiology routine, the content of the inferior pyramidal space of the heart is extended the coronary sinus, the atrioventricular (AV) node, the AV nodal artery, the membranous septum, and the proximal His bundle. The right atrial aspect of this space is known as the atrioventrioventricular triangle (triangle of Koch), which is a key landmark for electrophysiological procedures.

The fibroadipose tissue of the inferior pyramidal space separates the atrial wall from the crest of the muscular interventricular septum, forming what is sometimes called the "atrioventricular muscular sandwich".

Understanding the three-dimensional anatomy of the inferior pyramidal space is essential for interventions involving the AV conduction system, catheter ablation, and for appreciating the potential for procedural complications in this region.