Gams E, Schad H, Heimisch W
Klinik für Thorax- und Kardiovaskuläre Chirurgie, Heinrich-Heine-Universität Düsseldorf.
Herz. 1996 Jun;21(3):144-58.
Despite numerous improvement in cardiac surgery the results in mitral valve replacement are still not satisfactory, since impaired left ventricular function continues to be a problem during the postoperative course. In order to investigate the effect of mitral valve replacement on left ventricular function canine experiments were performed: During extracorporeal circulation bileaflet mitral valve prostheses were implanted preserving the ventriculo-annular continuity. Flexible wires were slung around the chordae of the subvalvular mitral apparatus and brought to the outside through the left ventricular wall. Left ventricular diameters were measured by sonomicrometry, left ventricular stroke volume, left ventricular enddiastolic volume and ejection fraction by dye dilution technique as well as left ventricular and aortic pressure by catheter tip manometers. After finishing cardiopulmonary bypass control values were registered and different preload values achieved by volume loading with blood transfusions to left ventricular enddiastolic pressures of 12 mm Hg. Subsequently under normovolumic conditions the chordae tendineae of the anterior and posterior papillary muscles of the mitral valve were cut from the outside, while the heart was beating, by application of electrocautery on the steel wires. Following severance of the ventriculo-annular continuity of the mitral valve again function curves of left ventricular hemodynamics were made during volume transfusions. When the chordae had been divided the left ventricular enddiastolic diameter increased by 10% in the major axis, while in the minor axis no significant changes occurred. The systolic shortening was impaired substantially by reduction of 43% during the ejection phase when the subvalvular mitral apparatus had been severed. Left ventricular enddiastolic volume was increased by 18% at any preload level, while left ventricular ejection fraction was reduced by 16%. Consequently left ventricular stroke volume was decreased by 24% at any left ventricular enddiastolic volume, when the chordae had been divided. It can be concluded that left ventricular geometry is changed when the annulo-ventricular continuity has been interrupted at mitral valve replacement: The major axis of the left ventricle is increased and the enddiastolic volume is augmented. The left ventricle is only able to eject the same stroke volume at higher preload levels when the chordae tendineae have been divided. The same cardiac performance can only be achieved by volume loading and at the expense of higher wall tension, which leads to unfavorable conditions in terms of cardiac muscle mechanics with reduced exercise tolerance. These data speak for preservation of the annulo-ventricular continuity in mitral valve replacement. Provided that these results from acute canine experiments can be transferred to humans, one would suggest that preservation of the mitral subvalvular apparatus is of importance in patients with dilated hearts and with impaired left ventricular function.
尽管心脏手术有了诸多改进，但二尖瓣置换术的结果仍不尽人意，因为左心室功能受损在术后过程中仍是一个问题。为了研究二尖瓣置换术对左心室功能的影响，进行了犬类实验：在体外循环期间，植入双叶二尖瓣假体，保留心室 - 瓣环连续性。将柔性线绕过二尖瓣瓣下装置的腱索，通过左心室壁引出到体外。通过超声测距法测量左心室直径，通过染料稀释技术测量左心室每搏量、左心室舒张末期容积和射血分数，以及通过导管尖端压力计测量左心室和主动脉压力。完成体外循环后记录对照值，并通过输血使左心室舒张末期压力达到12mmHg来实现不同的前负荷值。随后，在正常容积条件下，在心脏跳动时，通过对钢丝施加电灼从外部切断二尖瓣前后乳头肌的腱索。在二尖瓣瓣环 - 心室连续性中断后，再次在输血期间绘制左心室血流动力学功能曲线。当腱索被切断时，左心室舒张末期直径在长轴上增加了10%，而短轴上没有明显变化。当二尖瓣瓣下装置被切断时，射血期收缩期缩短显著受损，减少了43%。在任何前负荷水平下，左心室舒张末期容积增加了18%，而左心室射血分数降低了16%。因此，当腱索被切断时，在任何左心室舒张末期容积下，左心室每搏量减少了24%。可以得出结论，在二尖瓣置换术时，当瓣环 - 心室连续性中断时，左心室几何形状会发生改变：左心室长轴增加，舒张末期容积增大。当腱索被切断时，左心室只能在更高的前负荷水平下射出相同的每搏量。相同的心功能只能通过增加血容量来实现，且代价是更高的壁张力，这在心肌力学方面导致不利条件，运动耐力降低。这些数据支持在二尖瓣置换术中保留瓣环 - 心室连续性。如果急性犬类实验的这些结果能够应用于人类，那么可以认为保留二尖瓣瓣下装置对心脏扩大和左心室功能受损的患者很重要。
