The second question is localization of myocardial infarction. Patients with new right bundle branch block usually have an extensive anterior myocardial infarction in comparison to those with LBBB who can have either anterior or inferior one. The third question is whether the intraventricular conduction defect is new or old. According to Ross, in 20 to 50 percent of patients, this question remains unanswered.
Figure 4 illustrates the difficulties in differentiating between acute and old myocardial infarction. Upper ECG shows an extensive acute anterior mvocardial infarction. Center ECG, which was recorded 14 month later, reveals a left anterior fascicular block with pathologic Q waves in lead 1 and aVL, QRS in V2 and QS with ST segment elevation in which is consistent with old extensive anterior MI and possible ventricular aneurysm. Finally in the lower ECG, 3.5 years later, there is a LBBB with Q waves in lead 1 and aVL, ST segment elevation in leads V,.4, and a notch in the ascending limb of the S wave in lead V4. While the rS and ST segment elevation in lead V13 can be explained by the LBBB, the RSR and ST segment elevation in lead V4 raises the possibility of an AMI. The ST segment elevation present on ECG A and B argues against an AMI. buy ampicillin
Figure 4. Upper ECG shows acute extensive anterior myocardial infarction; center ECG, 14 months later left anterior fascicular block, abnormal Q waves in 1 and aVL and QS with persistent ST segment elevation in leads V^; and lower ECG after 2V-2 years a LBBB with Q waves in lead 1 and aVL, ST segment elevation in lead V, 4 and a notch on the ascending limb of the S wave in lead V4 suggestive of AMI (see text for details).