Intraventricular Conduction Defects
Twenty percent of patients with AMI have intraventricular conduction defects. Patients with AMI and intraventricular conduction defect with exception of left anterior fascicular block, have higher mortality, more advanced coronary artery disease and more impaired left ventricular function. ventolin inhalers
The following questions are of clinical significance in patients with ischemic chest pain and intraventricular conduction defects. First is the diagnosis of AMI. In patients with left anterior fascicular block, the diagnosis of AMI is not difficult because this conduction abnormality does not interfere with the ST-T wave changes of AMI. In contrast, old inferior and less frequently, old anterior MI may be more difficult to diagnose in patients with left anterior fascicular block.4<) The recognition of AMI in right bundle branch block is also easy with the exception of a true posterior myocardial infarction which is masked by the conduction defect. The ECG is least helpful in left bundle branch block because in the majority of these patients, the conduction defect prevents the development of Q waves in lead 1, aVL and V4-6 and causes ST-T wave changes which can imitate repolarization abnormalities of AMI. In addition, whether the Q waves in the inferior leads are diagnostic for inferior myocardial infarction remains controversial. From the many suggested ECG criteria for myocardial infarction in LBBB, only the following are highly specific: (a) evolutionary ST segment changes; (b) Q waves in the left precordial leads and in 1 and aVL; (c) late notching of the S wave in lead V, 5; (cl) primary T wave changes (T wave concordant with the QRS complex). However, the low sensitivity of these ECG findings (8 to 30 percent) limits their practical diagnostic value.