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https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2794462/
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When the blood flow contracts to pass through a stenotic orifice, a portion of the potential energy (ie, blood pressure) is converted into kinetic energy, thus resulting in a pressure drop and acceleration of flow (Figure 1) (19,20). Downstream of the vena contracta, the flow jet re-expands, which causes flow turbulences. As a result of these turbulences, a large part of the kinetic energy is irreversibly lost as heat. Nonetheless, a portion of the kinetic energy is reconverted back to potential energy (pressure). The extent of this pressure recovery essentially depends on the relationship between the size of the valve orifice and the size of the aorta (Figure 1) (19). The smaller the valve orifice relative to the size of the aorta, the more flow turbulence will occur and the less energy will be available to be recovered as pressure.
Doppler measurements rely on the maximum velocity or gradient measured across the aortic valve at the level of the vena contracta. On the other hand, catheterization measurements are generally performed a few centimeters downstream of the valve, where the pressure is fully recovered. As a result, the pressure gradient recorded by catheterization, which corresponds to the ‘recovered’ or net pressure gradient, tends to be lower than the Doppler gradient, especially in patients with smaller aortas (ie, aortic diameter at the sinotubular junction less than 30 mm). Consistently, catheter measurements will also yield larger values for EOA, compared with measurements derived from Doppler. In this context, it should be emphasized that the American College of Cardiology/American Heart Association guidelines were first established based on data obtained from catheter measurements (12). The same cut-point values (eg, EOA less than 1.0 cm2 for severe AS) were then extended to echocardiographic data on the assumption that Doppler EOA and catheter EOA were equivalent parameters and indeed, the guidelines make no distinction between catheter and Doppler measurements of EOA. However, these parameters are not, in fact, equivalent, and differences in results of up to 50% may be observed depending on the size of the aorta and the severity of the stenosis
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Texto muito bom e explicativo das diferenças entre os gradientes obtidos ao CATETERISMO e ao ECOCARDIOGRAMA.
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A energia que ele afirma ser “perdida” na forma de calor, pode ser a responsável por dilatar a raiz da aorta?
Sendo assim, estenose grave só deveria ser encontrada em paciente com raiz da aorta dilatada.
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Então as dimensões da raiz da aorta deveriam entrar na avaliação da gravidade da estenose.
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