Cardiac segmentation model

The American Heart Association (AHA) has published the nomenclature and segmentation of the left ventricular myocardium (the cardiac segmentation model), now widely used for the description of disease-affected myocardial territories and wall function.

There are 17 segments that have a reasonably consistent vascular supply from one of the three main coronary arteries (RCA, LAD and LCx), but significant anatomic variation does exist. This standard segmentation model can be used in cardiac nuclear tests, computed tomography, magnetic resonance imaging, echocardiography and coronary angiography.  Having a standard model optimises intra- and inter-modality comparison.

Myocardial segments

In the long axis, the left ventricle is divided into equal thirds named the basal, mid and apical thirds. The tip of the apex forms a separate final segment. When these thirds are viewed in short axis they form rings which can be further divided into equal sectors:

• the basal third has six 60° sectors
  • basal anterior (segment 1)
  • basal anteroseptal (segment 2)
  • basal inferoseptal (segment 3)
  • basal inferior (segment 4)
  • basal inferolateral (segment 5)
  • basal anterolateral (segment 6)
• the mid third has six 60° sectors
  • mid anterior (segment 7)
  • mid anteroseptal (segment 8)
  • mid inferoseptal (segment 9)
  • mid inferior (segment 10)
  • mid inferolateral (segment 11)
  • mid anterolateral (segment 12)
• the apical third has four 90° sectors
  • apical anterior (segment 13)
  • apical septal (segment 14)
  • apical inferior (segment 15)
  • apical lateral (segment 16)
• finally, the tip of the ventricular apex is its own segment
  • apex (segment 17)

Coronary artery territories

• LAD supplies segments 1, 2, 7, 8, 13, 14 and 17
• RCA supplies segments 3, 4, 9, 10 and 15
• LCx supplies segments 5, 6, 11, 12 and 16

Echocardiography

The inability to visualize the whole chamber often necessitates utilization of anatomical landmarks to delineate the thirds:

• basal: mitral annulus to the tips of the papillary muscles in end-diastole
• mid: along the length of the papillary muscles 

• apical: below the papillary muscles to the apex