Progressive epicardial coronary blood flow reduction fails to produce ST-segment depression at normal heart rates.

ST-segment depression is commonly seen in patients with acute coronary syndromes. Most authors have attributed it to transient reductions in coronary blood flow due to nonocclusive thrombus formation on a disrupted atherosclerotic plaque and dynamic focal vasospasm at the site of coronary artery stenosis. However, ST-segment depression was never reproduced in classic animal models of coronary stenosis without the presence of tachycardia. We hypothesized that ST-segment depression occurring during acute coronary syndromes is not entirely explained by changes in epicardial coronary artery resistance and thus evaluated the effect of a slow, progressive epicardial coronary artery occlusion on the ECG and regional myocardial blood flow in anesthetized pigs. Slow, progressive occlusion over 72 min (SD 27) of the left anterior descending coronary artery in 20 anesthetized pigs led to a 90% decrease in coronary blood flow and the development of ST-segment elevation associated with homogeneous and transmural myocardial blood flow reductions, confirmed by microspheres and myocardial contrast echocardiography. ST-segment depression was not observed in any ECG lead before the development of ST-segment elevation. At normal heart rates, progressive epicardial stenosis of a coronary artery results in myocardial ischemia associated with homogeneous, transmural reduction in regional myocardial blood flow and ST-segment elevation, without preceding ST-segment depression. Thus, in coronary syndromes with ST-segment depression and predominant subendocardial ischemia, factors other than mere increases in epicardial coronary resistance must be invoked to explain the heterogeneous parietal distribution of flow and associated ECG changes.

Simple, quantitative body surface potential map parameters in the diagnosis of remote Q wave and non-Q wave myocardial infarction.

BACKGROUND: Body surface potential mapping has been shown to be a useful tool in the diagnosis and localization of remote non-Q wave and Q wave myocardial infarction, but human expertise is required to interpret the maps. OBJECTIVE: To identify quantitative body surface potential mapping parameters that could enable a computer-based diagnosis. METHODS: Body surface isopotential maps (63 unipolar leads) were recorded in 86 patients with remote Q wave and 71 patients with remote non-Q wave myocardial infarction. Twenty-four healthy adults served as control subjects. Myocardial infarctions were classified using standard electrocardiogram leads in the acute and chronic phases, and were validated by coronary angiography, ventriculography and thallium scintigraphy. RESULTS: Two simple quantitative parameters with high diagnostic power were identified: the time interval between the peak minimum and the peak maximum potentials (time-shift), and the ratio of these potentials (maximum to minimum ratio [max/min]). Both parameters showed significant differences between infarction patients and normal control subjects, and optimum cut-off values were determined using receiver operating characteristic curves (anterior infarction: time-shift of -4 ms or less, max/min of 0.6 or less; posterior infarction: time-shift of 8 ms or greater, max/min of 1.25 or greater). The sensitivities of the two parameters were 100% and 97%, and the specificities were 99% and 100%, respectively, in the anterior Q wave infarction group, compared with sensitivities of 88% and 100%, and specificities of 94% and 95%, respectively, in the posterior Q wave infarction group. In the anterior non-Q wave infarction group, sensitivity was 35% for both parameters, specificity was 100% for both parameters, and only infarctions associated with a low ejection fraction were detected, indicating that infarction size may influence the power of the tests. CONCLUSIONS: Time-shift and max/min are two new, simple, powerful parameters for infarction diagnosis and may also be suitable for automated, computer-based processing.

Distinction between myocardial ischemia and postural changes in continuous ECG monitoring based on ST-segment amplitude and vector orientation--preliminary results.

BACKGROUND: Myocardial ischemia, commonly defined as ST-segment elevation or depression on the electrocardiogram (ECG), is plagued by a large number of false positive events. OBJECTIVES: To present a new method that attempts to distinguish between 'highly probable ischemia' and positional changes. METHODS: Continuous three-lead orthogonal ECG monitoring was performed in three groups of subjects: 16 healthy volunteers undergoing a body position change protocol, 22 patients undergoing percutaneous transluminal coronary angioplasty (PTCA) and 17 patients with acute coronary syndromes (ACS). For each event (ischemic or postural), the change in ST-segment amplitude was calculated, as well as the angle between the ST-segment vector of the reference beat and the beats demonstrating ST-segment elevation or depression. Angles and ST-segment amplitude changes from well-documented ischemic events obtained from the PTCA patients and from the healthy volunteers in six different body positions were compared. RESULTS: Using both ST-segment amplitude and vector angle changes, ischemic events could be detected and differentiated from a postural change with a sensitivity of 91% and a specificity of 96%. Finally, the approach was blindly applied to continuous ECG recordings of ACS patients. The method allowed the classification of 37% of all ST-segment changes detected as highly probable ischemic events as opposed to only 7% using the standard 100 microV threshold. CONCLUSION: The current approach showed that highly probable ischemic events could be better distinguished from positional changes with objective criteria using ST-segment amplitude and vector orientation.