Diagnosis of multiple infarcts from complex electrocardiograms during normal rhythm, left bundle-branch block, and ventricular pacing

IntroductionBecause of better treatment of chronic coronary artery disease, patients with multiple ischemic insults are living longer and requiring long-term management. Electrocardiograms (ECGs) in patients with multiple myocardial infarctions (MMIs) are a challenge to the clinician or cardiologist. This is because second myocardial infarctions (MIs) often modify or obscure the ECG effects of the first MI and vice versa. This can result in complex tracings, which are difficult to interpret and predict the locations of damaged regions. It is important to identify MMI because, additively, they can result in poor ventricular function.MethodsNew criteria for the diagnosis of MMI were derived from studies in which ECGs and body surface potential distribution maps were correlated with epicardial and intramural depolarization in animal studies of MI and in patients at the time of coronary artery bypass graft and with the pathologic anatomy in a few patients. The initial criteria were fine tuned by correlations between ECGs and independent data obtained from catheterization and other imaging modalities (ultrasound and radionuclide single photon emission computed tomography).ResultsOften 2 or more MIs are concealed according to classical Q- and R-wave criteria. Myocardial infarctions located in opposing walls (180°), that is, inferior-superior, anterior-posterior, are the most difficult to identify. Two MIs that are not opposing (90°) are usually readily detectable. The pathologic Q waves produced by each separate MI, when opposing, are replaced by multiple QRS deflections or baseline crossings, which are referred to as M and W complexes. These waveforms replace Q waves and are equally weighted in a scoring system to improve diagnostic accuracy of ECG interpretation. These new criteria can also be used to predict MIs in left bundle-branch block, intraventricular conduction delay, and ventricular pacing.ConclusionMultiple myocardial infarctions modify the ECG because they eliminate Q waves and result in confusing, splintered QRS waveforms, referred to as M and W complexes. New criteria are presented to diagnose the presence and locations of these MMIs, which predict reduced left ventricular function, in normal sinus rhythm, left bundle-branch block, and ventricular pacing.