week later, 3 weeks later, and finally 1 year later. From this electrocardiogram, one can see that the injury potential is strong immediately after the acute attack (T-P segment displaced positively from the S-T segment). However, after about 1 week, the injury potential has diminished considerably, and after 3 weeks, it is gone. After that, the electrocardiogram does not change greatly during the next year. This is the usual recovery pattern after acute cardiac infarction of moderate degree, showing that the new collateral coronary blood flow develops enough to re-establish appropriate nutrition to most of the infarcted area.
Conversely, in some patients with coronary infarction, the infarcted area never redevelops adequate coronary blood supply. Often, some of the heart muscle dies, but if the muscle does not die, it will continue to show an injury potential as long as the ischemia exists, particularly during bouts of exercise when the heart is overloaded.
Old Recovered Myocardial Infarction. Figure 12-22 shows leads I and III after anterior infarction and leads I and III after posterior infarction about 1 year after the acute heart attack. The records show what might be called the "ideal" configurations of the QRS complex in these types of recovered myocardial infarction. Usually a Q wave has developed at the beginning of the QRS complex in lead I in anterior infarction because of loss of muscle mass in the anterior wall of the left ventricle, but in posterior infarction, a Q wave has developed at the beginning of the QRS complex in lead III because of loss of muscle in the posterior apical part of the ventricle.
These configurations are certainly not found in all cases of old cardiac infarction. Local loss of muscle and local points of cardiac signal conduction block can cause very bizarre QRS patterns (especially prominent Q waves, for instance), decreased voltage, and QRS prolongation.
Electrocardiograms of anterior and posterior wall infarctions that occurred about 1 year previously, showing a Q wave in lead I in anterior wall infarction and a Q wave in lead III in posterior wall infarction.
Current of Injury in Angina Pectoris. "Angina pectoris" means pain from the heart felt in the pectoral regions of the upper chest. This pain usually also radiates into the left neck area and down the left arm. The pain typically is caused by moderate ischemia of the heart. Usually, no pain is felt as long as the person is quiet, but as soon as he or she overworks the heart, the pain appears.
An injury potential sometimes appears in the electrocardiogram during an attack of severe angina pec-toris, because the coronary insufficiency becomes great enough to prevent adequate repolarization of some areas of the heart during diastole.
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