Yun K L, Niczyporuk M A, Sarris G E, Fann J I, Miller D C
Department of Cardiovascular Surgery, Stanford University School of Medicine, California 94305.
J Clin Invest. 1991 Jan;87(1):247-54. doi: 10.1172/JCI114978.
To assess the importance of the intact mitral subvalvular apparatus for left ventricular (LV) energetics, data from nine open-chest ejecting canine hearts were analyzed using piezoelectric crystals to measure LV volume. After mitral valve replacement with preservation of all chordae tendineae, baseline LV function was assessed during transient caval occlusion: A quadratic fit of the LV end-systolic pressure-volume data was used to determine the curvilinear end-systolic pressure-volume relationship (ESPVR). All chordae were then divided with exteriorized snares. Reassessment revealed deterioration of global LV pump function: (a) the coefficient of nonlinearity, decreased (less negative) by 90% (P = 0.06); (b) slope of the curvilinear ESPVR at the volume axis intercept, decreased by 75% (P = 0.01); and V100, end-systolic volume at 100 mmHg end-systolic pressure, increased by 42% (P less than 0.02). Similarly, preload recruitable stroke work fell significantly (-14%) and Vw1,000 (end-diastolic volume [EDV] at stroke work [SW] of 1,000 mmHg.ml) rose by 17% (P less than 0.04). With respect to LV energetics, the total mechanical energy generated by the ventricle decreased, as indicated by a decline in the slope of the pressure volume area (PVA)-EDV relationship (120 +/- 13 [mean +/- SD] vs. 105 +/- 13 mmHg, P less than 0.001). Additionally, comparison of LV SW and PVA from single beats with matched EDV showed that the efficiency of converting mechanical energy to external work (SW/PVA) declined by 14% (0.65 +/- 0.13 vs. 0.56 +/- 0.08, P less than 0.03) after chordal division. While effective systemic arterial elastance, Ea, also fell significantly (P = 0.03) after the chordae were severed, the Ea/Ees ratio (Ees = slope of the linear ESPVR) increased by 124% (0.91 +/- 0.53 vs. 2.04 +/- 0.87, P = 0.001) due to a proportionally greater decline in Ees. This indicates a mismatch in ventriculo-arterial interaction, deviating from that required for maximal external output (viz., Ea/Ees = 1). These adverse effects of chordal division may be related to the observed changes in LV geometry (i.e., eccentricity). We conclude that the intact mitral subvalvular apparatus is important in optimizing LV energetics and ventriculo-vascular coupling in addition to the enhancement of LV systolic performance.
为评估完整的二尖瓣瓣下结构对左心室（LV）能量代谢的重要性，使用压电晶体测量左心室容积，对9只开胸射血犬心脏的数据进行了分析。在保留所有腱索进行二尖瓣置换后，在短暂腔静脉闭塞期间评估基线左心室功能：使用左心室收缩末期压力 - 容积数据的二次拟合来确定曲线收缩末期压力 - 容积关系（ESPVR）。然后用外置圈套器将所有腱索分开。重新评估显示左心室整体泵功能恶化：（a）非线性系数降低（负值减小）90%（P = 0.06）；（b）曲线ESPVR在容积轴截距处的斜率降低75%（P = 0.01）；以及V100，即收缩末期压力为100 mmHg时的收缩末期容积，增加42%（P < 0.02）。同样，可招募的前负荷搏功显著下降（-14%），Vw1,000（搏功为1,000 mmHg·ml时的舒张末期容积[EDV]）增加17%（P < 0.04）。关于左心室能量代谢，心室产生的总机械能下降，压力 - 容积面积（PVA）与EDV关系的斜率下降表明了这一点（120±13[平均值±标准差] vs. 105±13 mmHg，P < 0.001）。此外，对具有匹配EDV的单搏左心室搏功和PVA进行比较表明，腱索分开后，机械能转化为外部功的效率（SW/PVA）下降了14%（0.65±0.13 vs. 0.56±0.08，P < 0.03）。虽然在腱索切断后有效体循环动脉弹性Ea也显著下降（P = 0.03），但Ea/Ees比值（Ees = 线性ESPVR的斜率）增加了124%（0.91±0.53 vs. 2.04±0.87，P = 0.001），这是因为Ees下降幅度更大。这表明心室 - 动脉相互作用不匹配，偏离了最大外部输出所需的状态（即Ea/Ees = 1）。腱索分开的这些不利影响可能与观察到的左心室几何形状变化（即偏心度）有关。我们得出结论，完整的二尖瓣瓣下结构除了增强左心室收缩性能外，对优化左心室能量代谢和心室 - 血管耦合也很重要。
