Effect of ischemic anoxia on transmural electrical activity in the intact canine heart

An intact canine myocardial pedicle preparation was created by a transmural cut and suture technique yielding a well defined area served by a single branch of the LAD artery and completely free of all collaterals, The pedicle volume was sufficiently small to avoid systemic effects due to impaired cardiac pump function during occlusion of this arterial branch. A 23 gauge needle electrode of the Sher type containing 15 tungsten tips with 1 mm spacing was plunged transmurally into the pedicle from epicardial to endocardial surface. After 15 min of anoxia, which abolished the contractile response, the propagation velocity was reduced to an average of 33% of control value with a concomitant broadening of the equivalent dipole separation. Monopolar signal strength averaged 40% of preocclusion control and there was significant ST segment elevation or depression in all regions. In all cases, the earliest and most profound changes occurred subendocardially. On revascularization, the parameters all returned to control levels. After 30 min of ischemic anoxia (corresponding to borderline irreversibility of the ischemic damage as determined by electron microscopy) changes in the activation sequence within the muscle were also observed, though the Purkinje network was unaffected. On revascularization electrical activity returned toward control though the changed activation sequence within the pedicle persisted.