Regional Perfusion of the LV
To simplify this challenging topic we go over understanding what segments are and corresponding coronary perfusion territories. We then need to understand the geometric views and their corresponding segments since we need to be able to locate these regional wall abnormalities in at least 2 cardiac windows. Then we can finally analyze a segment and determine the degree in which it appears compromised.
To assess regional wall motion of the LV, we divide it into segments. These segments reflect coronary perfusion territories. This result in segments with comparable myocardial mass, and allow standardized communication within echocardiography and with other imaging modalities. Regional myocardial function is assessed on the basis of the observed wall thickening and endocardial motion of the myocardial segment.
There are various segmentation models availabe and we will be looking at the 17 segments used in regional wall assessment and out of the scope for FoCUS interrogation since multiple chamber views are needed. However they are mentioned here for illustration purposes
As a reminder, the objectives of FoCUS here is to do semiquantification of ranges of function (e.g., the left ventricle is hyperkinetic, normokinetic, hypokinetic, or severely hypokinetic).
1A. Coronary perfusion model: 3D overview
The right coronary artery (RCA) originates from the right aspect of the aortic bulb. The RCA gives of the Right Marginal Artery (RMA) which supplies the entire right ventricle. The RCA gives off the Posterior Descending Artery (PDA).
The left main coronary artery branches into the left anterior descending artery (LAD) and the left circumflex coronary artery (Cx). The LAD gives off the Diagonal (D1) branches which supply the anterior and anterolateral walls of the left ventricle. The Cx give off the obtuse marginal arteries (M1) which supply the lateral wall of the left ventricle
3D model showing major coronary arteries. Images created with the use of Z-anatomy.
1B. Coronary perfusion territories
Although certain variability exists in the coronary artery blood supply to myocardial segments, segments are usually attributed to the three major coronary arteries. The LV is divided into base mid and apex while on the parasternal short axis view. The following images represent our current model of perfusion.
Coronary perfusion territories. On the right, the cuts obtained depending on the level of the short axis; base, mid or apex. We will concern ourselves with the midventricular walls for a focused cardiac assessment. Notice that the anterolateral (AL) papillary muscle is perfused by two vessels while the posteromedial (PM) is only perfused by one in this model. RCA is the right coronary artery, the LAD is the Left anterior descending artery and the Circ or Cx is the Circumflex artery.
2. Segmentation model and Orientation
The LV is divided into base, mid and apex while on the parasternal short axis view. Regional wall can thus occur at each of the segments walls.
The full 17 segmentation model is seen here. For the purposes of FoCUS we will be concerned on the base and mid segment of the 2D cut here depicted in gray and red. On the right, a mid pap short axis view and their corresponding segments. You will not have to memorize the numeration of the segments but their relative location to each other so you can correlate patterns of prefusion and segments.
Lets look at the perfusion of the segments that can be analyzed with the Apical 4 chamber view and Parasternal long axis for completness:
Parasternal long axis and apical 4 chamber view with labeled segments. 1, Parasternal long axis and 2, Apical 4 chamber view. Inf sep; infero septal, Ant lat; anterolateral; Ant sep: antero septal and Inf lat, inferolateral wall.
Remembering the segments on the parasternal short axis model appears easier to do when compared with the other two views so lets make a side by side comparison of the short axis with those others so we can have spatial awareness of their perfusion segments. Lets start with the Apical 4 chamber view.