Importance of haemodynamic, metabolic and electrocardiographic alterations in the detection of coronary failure.

Haemodynamic, metabolic and ECG alterations due to a "critical" stenosis of the left anterior descending coronary artery (LAD) with and without additional work load induced by pacing and the changes due to a total obstruction of the artery have been investigated in anaesthetized open-thorax dogs. Direct ECG recording was done from the epicardial surface of the area perfused by the constricted coronary artery; blood samples were collected from the same area for estimation of metabolites. It was shown that ischaemic biochemical changes (decrease of myocardial lactate uptake and of the ratio myocardial O2 supply/myocardial O2 demand) can be detected along with a reduction of flow in the constricted artery long before the appearance of ischaemic ST-segment elevation in the epicardial ECG. This change can be evoked by an additional work load induced by pacing but even at the stage of manifest ischaemia, left ventricular end-diastolic pressure (LVEDP) is unaffected. It increases only after complete obstruction of the LAD. Accordingly, ischaemic metabolic changes in the area with restricted blood supply seem to be the most sensitive indicator of an incipient coronary insufficiency. ECG and particularly LVEDP changes are limited value, since they only appear if the ischaemic damage and/or the ischaemic area is sufficiently large.