Circulation
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Multicenter Study
Sudden cardiac death and the use of implantable cardioverter-defibrillators in pediatric patients. The Pediatric Electrophysiology Society.
During the past decade, the implantable cardioverter-defibrillator (ICD) has emerged as the primary therapeutic option for survivors of sudden cardiac death (SCD). Investigation of the clinical efficacy of these devices has primarily assessed outcome in adults with coronary artery disease. The purpose of this cooperative, international study was to evaluate the impact of ICDs on the pediatric population of SCD survivors, based on an analysis of the clinical characteristics and outcomes of young patients who underwent ICD implantation following an episode of life-threatening ventricular tachycardia or resuscitation from SCD. ⋯ Pediatric patients resuscitated from SCD appear to remain at risk for recurrence of life-threatening tachyarrhythmias. During a mean follow-up of 31 months, the ICD provided an effective therapy for such arrhythmias in the majority of patients in this study. Following ICD implant, impaired ventricular function was the primary factor correlated with mortality. The patterns of ICD discharge observed in young patients and, thus, inferred risk of recurrent life threatening arrhythmias are similar to those of adult survivors of SCD. Thus, the use of ICDs in pediatric patients, with implant selection criteria similar to adults, appears valid.
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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.