Non-uniform recovery of segment shortening during reperfusion following regional myocardial ischaemia despite uniform recovery of ATP

Objective: This study focused on transmural postischaemic recovery of ATP and regional contractile function related to reversible and irreversible tissue injury. Methods: Fifty anaesthetised open-chest cats were randomised into two groups. Group I: 10 min of LAD occlusion ( n = 10) and 10 min of LAD occlusion followed by 180 min of reperfusion ( n = 15). Group II: 40 min of LAD occlusion ( n = 10) and 40 min of LAD occlusion followed by 180 min of reperfusion ( n = 15). Histochemical staining (TTC) was performed in hearts from 5 additional cats subjected to 40 min of LAD occlusion and 180 min of reperfusion. Regional function was measured by sonomicrometry in the circumferential (CIRC) and longitudinal (LONG) axis of the anterior left ventricular midwall. Myocardial blood flow was measured with radiolabelled microspheres. Adenine nucleotides in the subepi- and subendocardium were measured with high-pressure liquid chromatography after LAD occlusion and after reperfusion. Results: Ten minutes of ischaemia induced a transmurally uniform ATP depletion. Repletion of ATP following reperfusion was transmurally uniform. Recovery of regional shortening was non-uniform with better recovery in CIRC (76 ± 8% vs. LONG;46 ± 10%, P < 0.05). Forty minutes of ischaemia induced a more severe ATP depletion in the subendocardium compared to the subepicardium. A slight recovery of ATP following reperfusion was transmurally uniform. Recovery of function was present only in CIRC (48 ± 6%). Tissue blood flow showed a transmurally homogenous flow restriction during ischaemia and uniform recovery following reperfusion. TTC staining demonstrated predominantly subendocardial infarctions following 40 min of regional ischaemia. Conclusions: Postischaemic recovery of regional function is non-uniform and independent of ATP repletion and collateral blood flow during ischaemia. Absence of functional recovery in LONG is associated with development of infarction.