Regional wall motion abnormalities in coronary artery disease
Echocardiography is one of the simplest investigations to assess the myocardial regional wall motion abnormalities in coronary artery disease. Regional wall motion abnormalities can also be assessed by nuclear imaging and cine CT (computerised tomography) scan / MRI (magnetic resonance imaging). The wall motion is scored from 1 to 4 depending on whether it is normal wall motion, hypokinesia, akinesia or dyskinesia. Hypokinesia means reduced contraction, akinesia means absence of contraction and dyskinesia means bulging out in systole. In order to standardise the reporting of wall motion abnormalities, American Society of Echocardiography has brought out a 17 segment model for left ventricular wall motion abnormalities. The segments are analysed from 6 views: parasternal long axis, apical four chamber, apical two chamber and parasternal short axis view at the levels of mitral valve, papillary muscles and apex. Wall motion scores assigned to all the segments are added to get the total wall motion score.
Left ventricular segments for assessing wall motion abnormalities in parasternal long axis view
Segments in parasternal long axis view are basal anteroseptal and mid anteroseptal on the septum; and basal posterior and mid posterior in the posterior wall. The echocardiogram video at the end of this post shows hypokinesia of the mid anteroseptal region in the parasternal long axis view. Both basal anteroseptal and mid anteroseptal territories are supplied by the left anterior descending coronary artery (LAD). Basal posterior and mid posterior segments can be supplied either by the right coronary artery (RCA) or the left circumflex coronary artery (LCX). The parasternal long axis view thus gives information about four segments and two coronary territories.
Apical four chamber view
Apical four chamber view (apical 4C view) gives information about 7 segments: Apex, apical lateral, apical septal, mid septal, mid lateral, basal septal and basal lateral. Of these, the apical segment can be supplied either by the LAD or LCX. Apical septal and mid septal segments are supplied by the LAD. Basal septal segment belongs to the RCA territory while the apical lateral, mid lateral and basal lateral segments are in the LCX territory. The echo video at the end of the post shows almost akinesia of apical septal segment and dyskinesia of apex and apical lateral segments. The apical septal segment appears thin as well. Over a period of time, when fibrosis ensues, a dyskinetic segment can become akinetic causing improvement in the wall motion score. Wall motion score can also improve when areas of stunned myocardium regain contractility. Similar recovery can also occur after revascularisation of hibernating myocardium.
Apical two chamber view (apical 2C view) also shows seven segments: basal inferior, mid inferior and apical inferior segments on one side and basal anterior, mid anterior and apical anterior segments on the other side. In addition there is the apcial segment at the apex. Basal inferior and mid inferior segments are supplied by the right coronary artery while the apical anterior could be either by the RCA or LAD. All the other segments in this view are in the LAD territory.
Parasternal short axis view at papillary muscle level for wall motion analysis
Parasternal short axis view (PSAX view) can be taken at three levels for assessing wall motion scores: mitral valve level (six segments), papillary muscle level (six segments) and apical level (four segments). The segments at the apical level are apical septal, apical anterior, apical lateral and apical inferior. The segments at papillary muscle level are mid septal, mid anteroseptal, mid anterior, mid lateral, mid posterior and mid inferior. The segments at the mitral valve level are basal septal, basal anteroseptal, basal anterior, basal lateral, basal posterior and basal inferior. Mid inferior segment is supplied by the RCA while mid posterior segment could be either by the RCA or the LCX. Mid septal and mid anteroseptal segments are in the LAD territory while the mid anterior could be in the LAD or LCX territory. Mid lateral segment is in the LCX territory. In the video below, the PSAX view at the papillary muscle level shows mid septal and mid anteroseptal hypokinesia. These segments belong to the LAD territory.