Wall motion score index (echocardiography)

Calculation of the left ventricular wall motion score index (WMSI) with transthoracic echocardiography allows the semi-quantification of left ventricular ejection fraction (LVEF). Calculation of the LVEF with a WMSI demonstrates stronger agreement with measures obtained by cardiac MRI, the gold standard, than the traditional Simpson's biplane method.

Radiographic features

Echocardiography

Using a standard transthoracic echocardiography sequence, each myocardial segment is assigned a score from 1 to 4. The 16 segment model of myocardial segmentation is recommended, as the apical cap of the 17 segment model is acontractile and therefore more appropriate for perfusion imaging. The left ventricle is divided as follows ¹:

• basal segments
  • six segments, each encompassing 60 degrees of the left ventricular short axis
  • basal anterior, basal anterolateral, basal inferolateral, basal inferior, basal inferoseptal
• mid segments
  • divided into six segments in a similar manner to the base
• apical segments
  • divided into 4 90 degree segments
  • apical anterior, apical lateral, apical inferior, apical septum

Each segment is then scored, using the following criteria:

• normokinesia (1 point)
  • normal wall thickening and endocardial excursion
• hypokinesia (2 points)
  • reduced wall thickening, reduced endocardial excursion
• akinesia (3 points)
  • absence of either wall thickening or endocardial excursion
• dyskinesia (4 points)
  • systolic outward stretching or thinning
  • includes "aneurysmal" wall motion, which bulges eccentrically during both systole and diastole

The wall motion score index is then calculated by dividing the sum of the aforementioned segmental values by the number of myocardial segments (16). A WMSI of 1.0 (16/16) is considered normokinetic, and correlates with a CMRI calculated ejection fraction of 64%, whereas a WMSI of 3.0 correlates with an ejection fraction of 12% and is considered akinetic. WMSIs of 1.5, 2.0, and 2.5 are designated mild hypokinesia, hypokinesia, and severe hypokinesia respectively ².

A regression equation is sometimes used to convert the calculated WMSI to an equivalent ejection fraction calculated by cardiac MRI as follows ³:

• left ventricular ejection fraction (LVEF) = 0.93 − (0.26 × WMSI)

Differential Diagnosis

An abnormal wall motion score index may imply one of the following pathological entities:

• myocardial ischemia/myocardial infarction
  • results in a segmental (or "regional") distribution of wall motion abnormalities
  • affected region correlates with the affected coronary artery
    • left anterior descending artery
    • right coronary artery
    • left circumflex artery
• myocarditis
• takotsubo cardiomyopathy
• sarcoidosis
• conduction abnormalities
  • may result in dyssynchronous contraction, simulating a true decrease in the contractile function of the myocardium
  • left bundle branch block