Circulation
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Comparative Study
Body surface potential mapping of ST segment changes in acute myocardial infarction. Implications for ECG enrollment criteria for thrombolytic therapy.
Several large, randomized clinical trials have shown that early thrombolytic therapy substantially reduces early mortality after acute myocardial infarction (MI). In most trials, eligibility criteria include typical chest pain and diagnostic ST segment elevation in two or more contiguous leads of the standard 12-lead ECG. Unfortunately, large areas of the thoracic surface are left unexplored by the standard electrode positions. As a consequence, acute MI patients with ST elevation in regions not interrogated by the conventional electrodes may not receive reperfusion therapy and its attendant benefits. ⋯ Analysis of BSPM identifies areas on the torso where the most significant ST changes most frequently occur in acute MI. Two leads from areas with the most abnormal ST changes achieve optimal classification in each MI class. Of these six leads, five are outside the standard precordial lead positions. ST depression is the most potent discriminator for each MI group and contains information independent from ST elevation. Quantitative analysis of ST magnitude at each electrode site allows determination of best thresholds for ECG criteria. Appropriate selection of ECG leads may help remove inconsistencies in current ECG selection criteria and improve comparability of treatment results.
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Autonomic modulation, especially increased sympathetic activity may play a role in the genesis of ventricular arrhythmias. The purpose of this study was to determine whether beta-sympathetic stimulation with isoproterenol would alter sustained ventricular tachycardia (VT) circuits similarly during the drug-free and antiarrhythmic drug-treated states. ⋯ Isoproterenol affects presumed reentrant sustained VT circuits less in the absence of antiarrhythmic drugs but markedly attenuates the antiarrhythmic drug-induced slowing of sustained VT. To the extent that the change in QRS duration reflects a change in conduction within the VT circuit, these data imply that the attenuation of drug-induced slowing of VT by isoproterenol is due to a greater change in conduction rather than refractoriness.
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One or more brief episodes of coronary artery occlusion protect or "precondition" the myocardium perfused by that artery from a subsequent episode of sustained ischemia. We sought to determine whether ischemic preconditioning protects only those myocytes subjected to brief coronary occlusion or whether brief occlusions in one vascular bed also limit infarct size and/or attenuate contractile dysfunction in remote virgin myocardium subjected to subsequent sustained coronary occlusion. ⋯ Brief episodes of ischemia in one vascular bed protect remote, virgin myocardium from subsequent sustained coronary artery occlusion in this canine model. These data imply that preconditioning may be mediated by factor(s) activated, produced, or transported throughout the heart during brief ischemia/reperfusion.
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Several studies performed before the advent of thrombolysis have shown that the presence of ventricular arrhythmias is an independent risk factor for subsequent mortality in patients recovering from acute myocardial infarction. Since fibrinolysis affects the natural history of infarction and may alter the clinical relevance of different risk factors, the aim of the present study was to establish the prevalence and prognostic value of ventricular arrhythmias in post-myocardial infarction patients treated with fibrinolytic agents during the acute phase. ⋯ This study shows that approximately 36% of patients recovering from acute myocardial infarction presented with less than one premature ventricular beat per hour in Holter recordings obtained before discharge from the hospital, whereas almost 20% of patients showed frequent (more than 10 premature ventricular beats per hour) ventricular arrhythmias. Due to the large size of the population of this study, these figures may be used as a reliable estimate of the prevalence of arrhythmias in postinfarction patients treated with fibrinolytic agents during the acute phase. Frequent premature ventricular beats are confirmed as independent risk factors of total and sudden death in the first 6 months following the acute event; the significance of nonsustained ventricular tachycardia in this population appears more controversial.
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Arrhythmias are a significant source of morbidity and mortality in patients with congenital heart defects. ⋯ The prevalence of arrhythmias (especially ventricular arrhythmias) was higher for patients with aortic stenosis, pulmonary stenosis, or ventricular septal defect than for an historical control population. "Serious arrhythmias" were most frequently noted in patients with aortic stenosis who also had a higher incidence of sudden death. The prevalence of "serious arrhythmias" was second highest for patients with ventricular septal defect who had the second highest incidence of sudden death.