Regional dysfunction of the interventircular septum during acute coronary artery occlusion

To compare the effects of local myocardial ischaemia on the dynamics of different portions of the interventricular septum (IVS), pairs of miniature ultrasonic crystals were implanted across the anterior and posterior portion of the IVS and the left ventricular free wall (LVFW) to measure wall thickness changes in open chest dogs. Following left anterior descending coronary artery (LAD) occlusion, the end-diastolic wall thickness decreased in all areas indicating significant chamber dilation. Systolic thickening was reduced from 19.2% to 0.8% in the anterior LVFW and from 16.0% to 4.1% in the anterior IVS, while a significant increase in thickening occurred in the posterior LVFW (from 17.1% to 21.0%) and in the posterior IVS (from 13.6% to 16.5%). Left circumflex artery (LCx) occlusion produced a greater distension of the ischaemic free wall and the magnitude of responses tended to be less in the IVS than in the free wall (percentage thickening being reduced from 15.3% to 7.2% in the posterior IVS, and from 17.4% to -4.4% in the posterior LVFW). Enhancement of the systolic thickening of the normal perfused area was more marked with LCx occlusion than with LAD occlusion. Percentage thickening increased from 19.0% to 26.9% in the anterior LVFW and from 17.2% to 28.6% in the anterior IVS. These findings indicate that the ischaemic responses of the IVS, as induced by ischaemia differed in the anterior and posterior portion of the septum. Thus, when attempting to assess clinical echocardiographic findings of an ischaemic septum, one should take into account these regional differences with regard to which area of the septum the ultrasonic beam had passed.