Barron D J, Etherington P J, Winlove C P, Jarvis J C, Salmons S, Pepper J R
Department of Cardiac Surgery, National Heart and Lung Institute, London, United Kingdom.
Ann Thorac Surg. 2001 Mar;71(3):852-61. doi: 10.1016/s0003-4975(00)02445-0.
Atrophy and fibrosis of the distal part of the latissimus dorsi muscle (LDM) wrap is a recognized complication of cardiomyoplasty that has been attributed to ischemia. Failure of the muscle wrap contributes to the late attrition seen in clinical cardiomyoplasty. In this study we examined the role of two-staged mobilization and of preconditioning by electrical stimulation on the regional perfusion and oxygenation of the LDM.
In a rabbit model (n = 36) the LDM was preconditioned as follows: group A muscles received preconditioning in situ; group B muscles were partially mobilized by dividing the intercostal perforators and then preconditioned; and group C muscles were completely mobilized and wrapped around a silicone-rubber mandrel before conditioning. Controls received no conditioning. The preconditioning regimen consisted of 2 weeks of continuous stimulation at 2.5 Hz. At completion of preconditioning the muscles were fully mobilized and mounted on a muscle-testing apparatus. Purpose-built microelectrodes measured regional PO2 and perfusion using a diffusible gas tracer technique. Muscles were weighed and processed for fiber typing and capillary counting.
All preconditioned muscles demonstrated fiber transformation, with increased fatigue resistance. Perfusion of preconditioned muscles both at rest and during contraction was higher than control in the proximal part of the muscle. Distal regions of group B muscles had higher perfusion and capillary density than any other group (p < 0.05). Distal regions of group C had the lowest perfusion and capillary density, and showed muscle atrophy and histologic evidence of necrosis. During fatigue testing there was a decrease in the PO2 in the distal regions of the control and group C muscles (p < 0.05), whereas it was maintained at resting levels in both group A and B muscles.
Conditioning in situ improves perfusion of the distal LDM and prevents a fall in tissue PO2 during contraction. Two-stage mobilization further improves distal perfusion and capillary density. In contrast, shortterm elevation followed by conditioning produces impaired distal perfusion, decrease in PO2, and fiber necrosis in the distal muscle. The present study suggests that partial mobilization of the LDM performed at the same time as placement of electrodes for preconditioning may prepare the LDM better for the demands of cardiomyoplasty.
背阔肌（LDM）包绕远端的萎缩和纤维化是心脏成形术公认的并发症，其原因被认为是缺血。肌肉包绕失败导致了临床心脏成形术中出现的后期损耗。在本研究中，我们探讨了两阶段动员以及电刺激预处理对LDM局部灌注和氧合的作用。
在兔模型（n = 36）中，LDM的预处理如下：A组肌肉在原位进行预处理；B组肌肉通过切断肋间穿支血管进行部分动员，然后进行预处理；C组肌肉在预处理前完全动员并围绕硅胶芯棒进行包绕。对照组不进行预处理。预处理方案包括以2.5 Hz连续刺激2周。预处理完成后，将肌肉完全动员并安装在肌肉测试装置上。使用可扩散气体示踪技术，用特制的微电极测量局部PO2和灌注情况。对肌肉进行称重，并进行纤维类型分析和毛细血管计数。
所有预处理的肌肉均表现出纤维转化，抗疲劳能力增强。预处理肌肉在静息和收缩时的近端灌注均高于对照组。B组肌肉的远端区域灌注和毛细血管密度高于其他任何组（p < 0.05）。C组的远端区域灌注和毛细血管密度最低，表现出肌肉萎缩和坏死的组织学证据。在疲劳测试期间，对照组和C组肌肉远端区域的PO2下降（p < 0.05），而A组和B组肌肉的PO2维持在静息水平。
原位预处理可改善LDM远端的灌注，并防止收缩期间组织PO2下降。两阶段动员进一步改善远端灌注和毛细血管密度。相比之下，短期抬高后进行预处理会导致远端灌注受损、PO2降低以及远端肌肉纤维坏死。本研究表明，在放置电极进行预处理的同时对LDM进行部分动员，可能会使LDM更好地适应心脏成形术的需求。
