Kadem Lyes, Pibarot Philippe, Dumesnil Jean G, Mouret Frédéric, Garitey Vincent, Durand Louis-Gilles, Rieu Régis
Quebec Heart Institute/Laval Hospital, Laval University, Sainte-Foy, Canada.
J Heart Valve Dis. 2002 Sep;11(5):615-23.
Transvalvular mean pressure gradients (MPG) are important in the evaluation of aortic stenosis, but surprisingly they often differ in patients having similar valve effective orifice area (EOA) and stroke volume (SV). The study aim was to determine if these differences could be explained by variations in left ventricular ejection time (LVET).
A pulse duplicator system with a constant SV of 75 ml and incremental increases of LVET from 250 to 450 ms was used to measure MPG by Doppler echocardiography in three fixed stenoses (0.5, 1.0 and 1.5 cm2). The same variables were also measured at rest in 192 patients with isolated aortic stenosis (EOA <1.5 cm2) as well as during stress in a subgroup of 24 patients.
In vitro, the increase in LVET produced marked decreases of MPG ranging from -40 mmHg (-45%) for the 0.5-cm2 stenosis to -22 mmHg (-61%) for the 1.5-cm2 stenosis. In vivo, MPG measured by Doppler correlated strongly (R2 = 0.83) with the MPG predicted by the formula: MPGpred [SV/(50xEOAxLVET)]2, and on this basis the relative contributions of EOA, SV and LVET to the variance of MPG were found to be 36, 34 and 13%, respectively. During stress, the contribution of LVET to the increase in MPG was variable, but was sometimes as important as that of SV.
LVET may significantly and independently influence MPG in aortic stenosis. Clinically, variations of up to 15 mmHg in MPG may be observed uniquely on the basis of a change in duration of LVET, and hence the MPG cannot be used as a stand-alone parameter for serial evaluations or for comparisons of aortic stenosis severity between patients. A correction of MPG for LVET (in ms) such as MPGc = MPGx(LVET/300)2 might be helpful for rendering comparisons of MPG more meaningful in patients with aortic stenosis.
跨瓣平均压力阶差（MPG）在评估主动脉瓣狭窄中很重要，但令人惊讶的是，在具有相似瓣膜有效瓣口面积（EOA）和每搏量（SV）的患者中，MPG常常存在差异。本研究的目的是确定这些差异是否可以用左心室射血时间（LVET）的变化来解释。
使用一个每搏量恒定为75 ml且LVET从250 ms逐步增加至450 ms的脉搏复制器系统，通过多普勒超声心动图测量三个固定狭窄（0.5、1.0和1.5 cm²）时的MPG。还在192例单纯主动脉瓣狭窄患者（EOA < 1.5 cm²）静息状态下以及24例患者亚组的应激状态下测量了相同变量。
在体外，LVET增加导致MPG显著降低，0.5 cm²狭窄时从 - 40 mmHg（- 45%）到1.5 cm²狭窄时 - 22 mmHg（- 61%）。在体内，通过多普勒测量的MPG与公式MPGpred [SV/(50×EOA×LVET)]²预测的MPG高度相关（R² = 0.83），在此基础上，发现EOA、SV和LVET对MPG方差的相对贡献分别为36%、34%和13%。在应激期间，LVET对MPG增加的贡献是可变的，但有时与SV的贡献一样重要。
LVET可能显著且独立地影响主动脉瓣狭窄中的MPG。临床上，仅基于LVET持续时间的变化，MPG可能会出现高达15 mmHg的差异，因此MPG不能作为连续评估或患者间主动脉瓣狭窄严重程度比较的独立参数。对LVET（以ms为单位）进行MPG校正，如MPGc = MPG×(LVET/300)²可能有助于使主动脉瓣狭窄患者的MPG比较更有意义。
