Relationship between regional contractile function and S-T segment elevation after experimental coronary artery occlusion in the dog

The relationship between regional contractile function (ultrasonic crystals) and S-T segment elevation recorded from both endocardial and epicardial electrodes was examined at thoracotomy in dogs with sudden or graded coronary artery occlusion. After sudden occlusion of the left anterior descending artery in 5 dogs, hypokinetic changes were apparent within 10 s. However. S-T segment elevation was first observed in both endocardial and epicardial electrograms at 30 s, synchronous with the onset of dyskinesia. By 5 min after occulsion, endocardial S-T segment elevation (8.6 ± 1.3 mV) and epicardial S-T segment elevation (7.6 ± l.4mV) were essentially identical. In 6 dogs, a carotid-to-coronary shunt was created to perfuse the LAD. A significant reduction in normalised velocity of contraction over the first ⅓ of systole ⅓ (Vn; from 10.1 ± 1.0 to 3.7± 2.5 mm·s−1 cm−1; P < 0.05) was first observed after reduction of coronary perfusion pressure (CPP) to 5.3 kPa (40 mmHg) (P 0.05). Both the end-diastolic segment length and the mean systolic segment length were significantly increased at CPP = 4.0 kPa (30 mmHg). Significant endocardial S-T segment elevation (11.7 ±3.8 mV; P < 0.05) was observed after graded occlusion and reduction of CPP to 6.7 kPa (50 mmHg). Epicardial S-T segment elevation was less than endocardial S-T segment elevation at all levels of CPP and was only significantly increased after reduction of CPP to 4.0 kPa (30 mmHg) (9.0; 1.2 mV; P < 0.05). These data suggest that endocardial S-T segment elevation may be a slightly more sensitive index of ischaemia than is depression of contractile function which, in turn, is more sensitive than epicardial S-T segment elevation.