R Wave

R-wave amplitude changes have been reported in many settings, including exercise testing and sponta­neous angina associated with ST depressions and coronary spasm and myocardial infarction associated with ST elevations. The mechanisms proposed to explain R-wave changes and other alterations of the QRS complex seen with myocardial ischemia are many and include changes in intracellular/extracellular ions in the ischemic area, QRS-axis shifts, changes in LV cavity size (the Brody effect), changes in LV contrac­tility, and alterations in intramyocardial conduction time. Not only is there disagreement on the mechanisms involved, but many investigators question the consistency of R-wave changes with ischemia as well as the actual direction of the changes. Experi­mental evidence suggests that R waves decrease with ST depressions and increase with ST elevations. Clinical investigators, however, have generally found R waves to increase or not to be significantly changed with ST depressions, with no reports suggesting consistent reductions in R-wave ampli­tudes.

In previous studies evaluating R-wave changes with transmural ischemia during coronary angioplasty, R-wave changes have also been variable and small, but generally downward. This compares with the small increases in R waves seen in our study. An important distinction between our study and previous investiga­tions is the duration of ischemia at the time of ECG analysis. While in the other studies the mean time of coronary occlusion at time of ECG analysis ranged from 40 to 78 s, in our study the mean time was 169 s with no ECG examined at less than 75 s. In several dog studies, it has been shown that increases in R waves are often not seen until after 60 to 120 s of myocardial ischemia and that reductions in R waves may be seen in the first 60 s. The importance in the timing of ECG analysis may simply be a reflection of the need for more severe myocardial ischemia. Our patients also appear to have had the highest magnitude of ST elevations.
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Greenberg et al found that R-wave changes with exercise correlated with changes in ejection fraction and systolic volume but not with changes in diastolic volume. Others have found no relationship be­tween exercise-induced changes in R waves and changes in ST segment, ejection fraction, or thallium 201 imaging. We believe that our study is the first to examine the relationship between R-wave changes during transmural ischemia and changes in ischemic parameters. We found a fair to good correlation to exiit between R-wave changes and ST elevations. Only fairly generally insignificant correlations between R- wave changes and increases in LV filling pressures were found, but as a group, patients with the largest increases in R waves had the highest rises in PW.

S Wave

Although initially described together with R-wave changes, the presence of S-wave changes during ischemic ST deviation is less generally recognized and studied. Glazier et al evaluated the behavior of the S wave during ischemic ST depression seen with exercise testing and ambulatory ECG monitoring. S waves increased in 49 of 50 patients during exercise testing and in 169 of 170 episodes of ST depression on ambulatory monitoring. Wagner et al demonstrated that S waves tended to decrease during coronary angioplasty and ST elevations. The apparent conflict­ing results of these studies appear to relate to whether ST elevation or depression was present. Ekmekci et al demonstrated in the early 1960s that receding S waves are found with ST elevations while S-wave increases are seen with ST depressions. In our study, S waves were almost uniformly reduced in the precor­dial leads where only ST elevations were evident. In lead V5, where ST depressions or minimal ST devia­tions were also seen, S waves increased in four patients, including two who developed new S waves. canada viagra online

We found significant correlations between changes in S waves and ST deviations. However, the correla­tions between changes in S wave and PW were only fair to poor. Still, the patients with the largest S-wave reductions tended to have the largest increases in PW. The potential value of monitoring S-wave changes in transmural ischemia appears limited in that the S waves can only regress to the extent they are present. They are also not present in all leads.