Non-uniform recovery of performance in stunned myocardium evaluated by two-dimensional sonomicrometry

The objective of the present study was to assess the uniformity of contraction in reperfused myocardium. Regional function was measured by two pairs of piezo-electric crystals oriented in the circumferential and longitudinal axis of the left ventricular anterior midwall in 10 open-chest pentobarbitone-anaesthetized cats. The left anterior descending coronary artery was occluded for 10 min followed by 60 min of reperfusion. Myocardial blood flow was measured four times by radioactive labelled microspheres: at pre-occlusion, occlusion and after 30 and 60 min of reperfusion. There was a severe and transmural homogenous ischaemia during coronary occlusion. The recovery of ejection shortening was on average 76% at 30 min and 77% at 60 min of reperfusion in circumferential segments versus 25 and 44% in longitudinal segments (P < 0.05). Diastolic function was deranged in longitudinal segments; at 60 min of reperfusion the end diastolic pressure-length relation was still shifted rightwards in longitudinal segments, whereas it was normalized in circumferential segments. In conclusion, systolic and diastolic dysfunction in stunned myocardium were more severe in the longitudinal axis than in the circumferential axis of the feline heart. This indicates that stunning was more pronounced in longitudinally oriented sub-endocardial fibres which were reflected by the longitudinal segment, despite transmural homogenous ischaemia during coronary artery occlusion.