Assessment of Regional Wall Motion Abnormality

A critical occlusion of a coronary artery leads to myocardial ischemia which is manifested as regional wall motion abnormality (Abnormal motion and loss of systolic thickening) where is readily identified by 2D echocardiography.Decreased or cessation of myocardial contractility (systolic thickening) to the immediate manifestation of myocardial ischaemia, even before occurrence of ST changes or development of symptoms. Normally LV free wall thickness increases more than 1.5 times of the diastolic dimensions during systole. Ischemic muscle shows 3 discrete patterns of movement.

1) Hypokinesis: When the muscle shows systolic inward motion, however the amplitude of movement is less as compared to normal adjoining areas i.e.systolic wall thickness 1.2- 1.5 times the diastolic thickness.

2) Akinesis: When the muscle shows no perceptible systolic motion and systolic thickness is less than 1.1 times the diastolic dimensions.

3) Dyskinesis: Dyskinesis is defined as a myocardial segment moving'outward during systole, usually in association with systolic wall thinning.

In order to assess the wall motion, we have to concentrate on not only the movement of muscle but also the thickening during systole. This increases the specificity of wall motion study considerably.

Limitations

Inadequate visualization of the endocardium (may be present in 10-20 per cent of cases).

However, improved equipment, better transducer designs and imaging on digital platform have improved the visualization of the endocardium to a large extent.

Quantitative Analysis of Regional Wall Motions
Various attempts have been made in the past to try and quantify the ischaemic myocardium, however till date the best and most widely used is the 16 segment Echocardiography in Lscbaemic Heart DiseaseFundamentals of Echocardiography scoring system, which has also been approved by American society of Echocardiography. The system was devised keeping in mind the common pattern of coronary blood supply. The whole of the left ventricle muscle is divided into segments, which can be visualized in the conventional views. The whole length of the LV is divided into 3 segments. The apical, mid segment and basal segment. The circbmference of basal and mid myocardium is divided into 6 segments-Anterior Segment, Anterior wall, lateral wall, posterior wall, inferior wall and septum. Tbe apical portion however lacks anterior septum and posterior wall.

Schematic depresentation of LV divided into 16 segments in short axis
view at 3 leivels-basal, mid and apical

If the translate thesd segments into other conventional views, we find that parasternal long axiq Each segment is assigned a score based on its contractility as assessed visually:

Schematic reI)resentation of four conventional views showing various walls
visualized in different views

With variable degree of overlap the segments marked above denote coronary artery temtory. These can be plotted on a Bull's eye plot, which gives a better appreciation of the segments and the regions involved.

Bulls eye plot showing overlap of various segments and blood supply by
different coronary arteries

Each segment is assigned a score based on its contractility as assessed visually:
 

Normal- 1

Hypokinesis-2

On the basis of this wall motion analysis scheme, wall motion score index (WMSI) is calculated to semi-quantitate the extent of regional wall motion abnormalities.

WMSI= Sum of wall motion scores/Number of segment visualized

Normally contracting LV has a WMSI of 1 (each 16 segment receive a wall motion score of 1, hence total score of 16 and WMSI = 16/16 = 1).

Score is higher with larger infarcts, wall motion abnormalities become more severe.

Patients with WMSI greater than 1.7 had a perfusion defect greater than 20 per cent.

Wall motion score index