Circulation
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Comparative Study Clinical Trial Controlled Clinical Trial
Defibrillation efficacy of commercially available biphasic impulses in humans. Importance of negative-phase peak voltage.
Recent studies have shown that specifically shaped biphasic waveforms can lower energy requirements for ventricular defibrillation. We prospectively compared the defibrillation efficacy of three different biphasic wave shapes incorporated in three commercially available implantable defibrillators. The results led to the development of a second protocol in which the importance of negative-phase peak voltage and duration was investigated. ⋯ Our results suggest that specifically shaped biphasic waveforms delivered from commercially available devices can affect energy requirements for defibrillation. More importantly, the amplitude of the P2 peak voltage may be a more critical determinant than the P2 duration for defibrillation success of biphasic waveforms in humans.
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Central aortic pressures and waveform convey important information about cardiovascular status, but direct measurements are invasive. Peripheral pressures can be measured noninvasively, and although they often differ substantially from central pressures, they may be mathematically transformed to approximate the latter. We tested this approach, examining intersubject and intrasubject variability and the validity of using a single averaged transformation, which would enhance its applicability. ⋯ Central aortic pressures can be accurately estimated from radial tonometry with the use of a generalized TF. The reconstructed waveform can provide arterial compliance estimates but may underestimate the augmentation index because the latter requires greater fidelity reproduction of the wave contour.
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Relations between organs and body size are not linear but rather follow allometric (growth) relations characterized by their powers (exponents). ⋯ Indices of SV and cardiac output for BSA are pertinent when the effect of obesity needs to be removed, because these indices obscure the impact of obesity. To detect the effect of obesity on LV pump function, normalization of SV and cardiac output for ideal BSA or for height to its age-specific allometric power should be practiced.