Regional Perfusion of LV
The ventricle is divided into segments for regional wall assessment. Segmentation schemes reflect coronary perfusion territories result in segments with comparable myocardial mass, and allow standardized communication within echocardiography and with other imaging modalities. Currently there are 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).
1. Coronary perfusion model
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
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.
Mid papillary walls and corresponding apical 4 chamber segments. The colors on these clips correspond to the same walls. Red, mid papillary inferoseptal wall and in white, mid papillary anterolateral wall. Notice that the bisecting purple line is actually the cut that the ultrasound probe displays on the apical 4 chamber view. Based on the current model the Red colored wall is perfused by the RCA and LAD while the white wall, LAD and Cx.
Now a side by side of the short axis view with the long axis view:
Mid papillary walls and corresponding parasternal long axis segments. The colors on these clips correspond to the same walls. Purple, mid papillary anteroseptal wall and in white, mid papillary inferolateral wall. Notice that the bisecting red line is actually the cut that the ultrasound probe displays on the parasternal long axis view. Based on the current perfusion model the Purple colored wall is perfused by the LAD only while the white wall, the RCA and Cx.
For the purpose of FoCUS we will only be using 3 views which severely limits our ability to look at all the segments of the wall and we focus on visualizing major abnormalities i.e. severely hypokinetic or dyskinesis.
The recommendation is that each segment be analyzed individually in multiple views. A semiquantitative wall motion score can be assigned to each segment to calculate the LV wall motion score index as the average of the scores of all segments visualized. Regional myocardial function is assessed on the basis of the observed wall thickening and endocardial motion of the myocardial segment. Regional deformation such as thickening and shortening should be the focus of the analysis.
(1) normal or hyperkinetic,
(2) hypokinetic(reduced thickening); here segments can be mildly, moderate or severely hypokinetic.
(3) akinetic (absent or negligible thickening, e.g.,scar),
(4) dyskinetic (systolic thinning or stretching, e.g., aneurysm)
3. Major perfusion defects
In an effort to recognize major wall abnormalities the following are comparisons to a normal wall motion.
Severe hypokinesis of inferior wall
Moderate hypokinesis of inferior septal wall
Modw hypokinesis of inferior lat wall