quinta-feira, maio 23, 2013

PHT : Defeitos e limitações

Assunto já abordado no blog mas agora como Aula internacional:

Limitations Mitral

1) LV diastolic dysfunction: Left ventricle (LV) diastolic filling rate (reflected by the deceleration slope of the E-wave) depends on MVA but also on transmitral pressure gradient in early diastole, left atrial compliance and LV diastolic function (relaxation and compliance). For example, short PHT can be observed despite severe MS in case of associated severe aortic regurgitation. Early diastolic deceleration time tends to be shortened in case of decreased LV compliance and prolonged when LV relaxation is impaired. LV diastolic dysfunction makes PHT method to assess MVA less reliable, especially in older patients with degenerative calcific MS associated with aortic valve stenosis and hypertension.
2) PHT cannot be measured in tachycardic rhythms or first degree atrioventricular block, when E and A velocities are merged or the diastolic filling period is short.
3) Immediately after balloon mitral commissurotomy: in this situation, gradient and compliance are subject to important and abrupt changes. There may be important discrepancies between the decrease in mitral gradient and the increase in net compliance, making PHT method unsuitable for evaluating MS severity.
4) Prosthetic valves: PHT method overestimates the area of normal prosthetic mitral valves. However, a large rise in PHT on serial studies or a markedly prolonged single measurement (>200ms) may be a clue to the presence of prosthetic valve obstruction, because the PHT seldom exceeds 130 ms across a normally functioning mitral valve prosthesis.[4]
Os residentes adoram usar o PHT no refluxo aórtico...Mas estão equivocados ao ignorarem as limitações:

1) The PHT is influenced by chamber compliance in addition to chamber pressures. For a given severity of AR, pressure half-time is shortened with increasing left ventricular diastolic pressure, vasodilator therapy, and in patients with a dilated compliant aorta, or lengthened in chronic aortic regurgitation. Thus, this parameter serves only as a complementary finding for the assessment of AR severity.[6]
2) The assessment of PHT requires good Doppler beam alignment and an adequately dense spectral envelope of the regurgitant jet.
Importante saber as limitações!!!!!

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