Two hundred and forty patients with recent inferior myocardial infarction were studied by a symptom-limited ergometric test with haemodynamic monitoring (triple lumen tip-thermistor Swan-Ganz catheter) in order to investigate and quantify the haemodynamic effects of exercise-induced myocardial ischaemia in post-infarct patients and to assess whether the ST-segment changes give any indication of the degree of ventricular impairment. One hundred and thirteen patients showed no ST-segment changes during excercise; ST-segment elevation in leads with abnormal Q wave occurred in 14 patients, ST-segment depression was recorded in 88 subjects, and both ST-segment elevation and depression were found in 27 patients. In subjects with no ST-segment shift, as well as in those with exercise-induced ST-segment elevation, the resting and exertional haemodynamic patterns were normal or nearly normal. In subjects showing ST-segment depression or both ST-segment elevation and depression during exercise the mean pulmonary wedge pressure was abnormally elevated (at peak exercise 25 +/- 8 and 24 +/- 7 mm Hg, respectively). However, 31% of these showed a normal haemodynamic pattern either at rest or during exercise. The number of leads with ST-segment depression and the sum of ST-segment depressions in standard ECG does not reliably indicate the degree of ischaemia-dependent left ventricular impairment. In contrast, in patients grouped on the basis of time of ST depression appearance, the lower the ischaemic threshold the more severe was the left ventricular impairment. Finally, to assess the relative role of both scar and ischaemia in producing left ventricular dysfunction, the haemodynamic patterns of patients with and without exercise-induced ST-segment depression were compared in subsets with similar echocardiographic wall asynergy extent (inferior, infero-apical, infero-septo-apical). Among patients with small or medium-sized scar, the exertional left ventricular filling pressure was normal in patients with no ST-segment depression and abnormally elevated in those with ST-segment depression. In patients with large infarct, the exercise pulmonary wedge pressure was similarly elevated in both the ischaemic and non-ischaemic group, but in the latter cardiac output increase during exercise was limited.
In conclusion: in patients with recent inferior myocardial infarction exercise-induced ST-segment depression is a marker of left ventricular impairment when the ischaemic threshold is low. The impairment consists of an abnormal elevation of left ventricular filling pressure in all subjects, associated with a reduced increase in cardiac output in patients with large infarct.