Circulation
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Randomized Controlled Trial Clinical Trial
Truncated biphasic pulses for transthoracic defibrillation.
Early defibrillation is the single most important factor for improving out-of-hospital ventricular fibrillation resuscitation rates. To achieve the earlier response times required for survival, typically < 6 minutes from time of collapse, it will be necessary to equip a far wider network of first responders (firefighters, police, and other individuals with responsibility for public safety) with small, lightweight, and inexpensive automatic external defibrillators (AEDs). An important step in reducing the size and cost of AEDs will be to improve defibrillation efficacy. Because biphasic waveform defibrillation has had a favorable impact on implantable cardioverter-defibrillators (ICDs), there are reasons to believe that biphasic waveforms would also improve transthoracic defibrillators. Our purpose, therefore, was to examine the efficacy of two different low-energy biphasic truncated waveforms referenced to a standard damped sine waveform for transthoracic defibrillation in humans. ⋯ The results of this study suggest that biphasic truncated transthoracic shocks of low energy (115 and 130 J) are as effective as 200-J damped sine wave shocks used in standard transthoracic defibrillators. This finding may contribute significantly to the miniaturization and cost reduction of transthoracic defibrillators, which could enable the development of a new generation of AEDs appropriate for an expanded group of out-of-hospital first responders and, eventually, layperson use.
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Continuous positive airway pressure (CPAP) can improve cardiac function in patients with congestive heart failure (CHF). We hypothesized that this effect might be related to CPAP-induced increases in intrathoracic pressure, which would reduce left ventricular transmural pressure (LVPtm) during systole, thereby decreasing left ventricular afterload. ⋯ In patients with CHF, the inspiratory muscles generate greater force per breath and systolic Pes contributes more to LVPtm than in healthy subjects. By increasing intrathoracic pressure in patients with CHF, CPAP unloaded inspiratory muscles and reduced left ventricular afterload without compromising CI.
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Active compression-decompression (ACD) cardiopulmonary resuscitation (CPR) has recently been demonstrated to provide significantly more blood flow to vital organs during cardiac arrest. To further enhance the effectiveness of this technique, we tested the hypothesis that intermittent impedance to inspiratory gas exchange during the decompression phase of ACD CPR enhances vital organ blood flow. ⋯ Intermittent impedance to inspiratory flow of respiratory gases during ACD CPR significantly improves coronary perfusion pressures and vital organ blood flow and lowers defibrillation energy requirements in a porcine model of VF.
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Comparative Study Clinical Trial
Comparative real-time effects on platelet adhesion and aggregation under flowing conditions of in vivo aspirin, heparin, and monoclonal antibody fragment against glycoprotein IIb-IIIa.
A real-time in vitro system of human platelet thrombosis under arterylike flowing conditions similar to those produced in vivo by angioplasty would be useful for the evaluation of potential antiarterial thrombotic agents in association with in vivo trials. Aspirin, heparin, and the chimeric monoclonal antibody antigen-binding fragment 7E3 (c7E3 Fab) directed against platelet glycoprotein (GP) IIb-IIIa have been used in attempts to delay or prevent thrombotic reocclusion of coronary arteries after angioplasty. We compared the effects of these agents administered in vivo on GPIb-mediated platelet adhesion to von Willebrand factor (vWF)/collagen type I (as in atherosclerotic subendothelium) and on subsequent GPIIb-IIIa-fibrinogen/vWF-mediated platelet aggregation under flowing conditions analogous to those in constricted coronary arteries. ⋯ In contrast to aspirin or heparin, the in vivo injection of c7E3 Fab considerably reduces platelet aggregate formation mediated by the binding of fibrinogen, vWF, or some other ligand to platelet GPIIb-IIIa under conditions of abnormally increased shear stress analogous to those in narrowed coronary arteries. Platelet adherence to collagen I/vWF is not affected. This study describes an in vitro model of arterial injury (similar to angioplasty) that uses human blood to compare directly, in real time, the precise relative effects of aspirin, heparin, and c7E3 Fab on platelet adhesion and subsequent aggregation.
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Ischemia of the myocardium surviving an infarction induces ST segment elevation in infarct-related ECG leads. In cases with no viable tissues, ischemia adjacent to the infarction could induce a similar ECG pattern if there is ST segment potential transmission through the necrotic scar. We analyzed whether acute ischemia adjacent to a healed infarction with no viable tissue may induce ST segment elevation on the surface of the necrotic scar. ⋯ Acute ischemia adjacent to a chronic infarction induces ST segment elevation at the surface of the scar despite the virtual absence of viable tissue within the infarction. Data suggest a passive ST segment potential transmission through the infarction. Moreover, ischemia adjacent to a chronic infarction induces lower ST segment elevation than ischemia not adjacent to a necrosis. The mechanisms accounting for these regional differences are probably independent of collateral myocardial perfusion and ischemia extension.