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Eur J Cardiothorac Surg 2004;26:1174-1179
© 2004 Elsevier Science NL
a Department of Cardiovascular Surgery, Graduate school of Medicine, Kyoto University, Kyoto, Japan
b Hayama Heart Center, Hayama, Japan
Received 18 November 2003; received in revised form 11 June 2004; accepted 16 June 2004.
* Corresponding author. Tel.: +81 75 751 3781; fax: +81 75 751 3098. (E-mail: masakom{at}kuhp.kyoto-u.ac.jp).
| Abstract |
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| 1. Introduction |
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PLV works very well in some patients, but not so well or even worse in others. The reason why the effect of PLV is inconsistent remains unclear so far.
In our clinical practice, we noticed that the left ventricle of DCM was not always homogeneously affected as pointed out previously [3,4]. Some patients have inhomogeneous left ventricular (LV) wall property, and others have diffusely and homogeneously damaged LV wall [5,6].
The hypothesis is that the surgical benefit does not last long if fibrosis was prominent in the retained myocardium after PLV. The main purpose of PLV is to reduce the diameter and the volume of the left ventricle, and therefore we perform LV volume reduction surgery (LVR) as an alternative to PLV in this study. We have focused attention to the LV wall property as assessed by the amount of myocardial fibrosis and evaluated the relationship between the residual fibrosis of the retained myocardium and the surgical result of LV volume reduction surgery in a rat DCM model.
| 2. Materials and methods |
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All animals received humane care in compliance with Principles of Laboratory Animal Care formulated by the National Society for Medical Research and the Guide for the Care and Use of Laboratory Animals prepared by the Institute Council and published by the National Academy Press.
2.2. DCM model
Six weeks old Lewis rats were autoimmunized with purified cardiac myosin and later on developed DCM as reported elsewhere [7,8]. Animals have suffered from sort of acute myocarditis for 45 weeks and such inflammatory reaction almost disappeared within 8 weeks after autoimmunization [9].
Ten weeks after autoimmunization all animals were evaluated by means of echocardiography. Rats with dilated LV and severely depressed LV function confirmed by echocardiography were provided for this study. After all, 18 rats completed the study, among which 12 rats underwent surgical intervention and the rest were served as controls.
2.3. Echocardiographic study
Rats were anesthetized with ether and LV function was assessed by means of echocardiography with a 12MHz phased-array transducer (SONOS 5500, Philips Medical Systems, Bothell, WA, USA) [1012]. The following parameters were measured from B- and M-mode tracing: LV end-diastolic dimension (LV Dd, mm), LV end-systolic dimension (LV Ds, mm), fractional shortening (FS, %), and fractional area change (FAC, %). All parameters were measured by the American Society for Echocardiography leading-edge method from at least three consecutive cardiac cycles.
Echocardiography was performed before and immediately after surgery, following 2 and 4 weeks after surgery serially.
2.4. LV volume reduction surgery
Animals were orally intubated with ethyl ether gas and anesthesia was maintained with 1% isoflurane under control ventilation during operation. LV volume reduction surgery (LVR) was carried out by placation of the posterolateral wall. LV was gently pulled out from the pericardial cavity via left thoracotomy and the posterolateral wall of the left ventricle was plicated with several horizontal mattress sutures of 4-0 prolene without any kind of cardiac support. Surgical technique performed in this study was similar with the technique adapted to a large animal model, apex-preserving LVR [13]. Before and after surgery, echocardiography and cardiac catheterization were performed simultaneously and the efficacy of the surgical technique was evaluated.
2.5. Cardiac catheterization
A 2 French micromanometer-tipped catheter (Millar Instruments Inc, Houston, TX) was introduced from the right carotid artery to measure LV pressure and a 3 French occlusion balloon catheter was introduced from the right femoral vein to occlude the inferior vena cava. At the stable state, LV pressure and its first time derivative (dp/dt) were continuously monitored through the arterial catheter by using a multiple recording system during temporary caval occlusion. Simultaneously LV dimension was measured by echocardiography. The maximum time-varying elastance (LV Emax, mmHg/µl) and the time constant of isovolumic relaxation (Tau
, ms) was calculated as an index of global systolic and diastolic function, respectively [1012].
2.6. Histological study
At 4 weeks after surgery, final echocardiography was performed and all rats were sacrificed. Hearts were removed and transected at the base of the papillary muscles. The transverse sections were fixed with 10% formalin and stained with hematoxylin eosin and Masson's trichrome staining. In the same manner six DCM rats without LVR were served as control group.
The heart sections were divided into four parts: anterior, septal, posterior, and lateral part. Masson's trichrome stained sections were subjected to quantitative evaluation of the severity of interstitial fibrosis (percent fibrosis) using the point counting method.
2.7. Statistical analysis
Data were expressed as means±SD. Statistical analysis was performed by using StatView (SAS Institute Inc, Cary, NC). Differences between two groups were assessed by the non-parametric test, Wilcoxon test and MannWhitney U-test. Correlation trends were assessed by Spearman rank correlation coefficient r. Values of P less than 0.05 were considered statistically significant.
| 3. Result |
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Table 1 summarized echocardiographic data at baseline. LV Dd and LV Ds of DCM rats became bigger than those of health Lewis rats of the same age (normal control). FS and FAC of DCM rats were lower than those of normal control.
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3.2. Cardiac catheterization before and after surgery
Emax and the maximal LV dp/dt increased after surgery. The LV end-diastolic pressure, minimum LV dp/dt, and
decreased after surgery. The values measured by the catheterization were summarized in Table 2 and there was a significant difference between values before and after surgery.
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3.3. Serial echocardiographic change after surgery
Thirty-five rats underwent LV volume reduction surgery and 24 rats survived surgery. In 16 rats LVR was properly carried out and the efficacy of the surgery was confirmed by echocardiography and cardiac catheterization. Among them, 12 rats survived 4 weeks after surgery and were subjected to serial echocardiographic follow-up completely.
Comparing LV dimensions at 4 weeks after surgery with those at baseline, rats were divided into two groups as follows. One was Good result group, of which LV dimension at 4 weeks after surgery remained smaller than that at baseline. The other was Poor result group, of which LV dimension at 4 weeks after surgery became larger than that at baseline. LV Dd of Poor result group increased quicker and more severely than that of Good result group, as shown in Fig. 1.
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Comparing the relationship between the ratio of LV redilatation (delta redilatation) and percent fibrosis of the septum, there was a strong correlation recognized between them (r=0.951, P<0.001) as shown in Fig. 3.
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| 4. Discussion |
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In 1996 we started performing PLV for DCM and achieved good initial results, following unpredictable mid-term result as occurred similarly around the world. We examined LV wall motion thoroughly by echocardiography with utilizing color kinetic method before surgery and intraoperatively and we noticed some patients had abnormal regional wall motion [5,6]. Abnormal LV wall motion and heterogeneity of LV wall property in DCM was pointed out previously [3,4]. According to the echocardiographic findings, we started SAVE operation, septal anterior ventricular exclusion, instead of PLV when LV wall motion of the anteroseptal part was worse than that of the posterolateral part [15,16]. Then left ventriculoplasty for DCM by careful selection of PLV and SAVE improved a mid-tem result. Four year survival rate of 61 elective operations was 69.3% [17].
In the present study, we adopted a DCM model created by means of autoimmunization with cardiac myosin because this model type is mimicked with humane DCM without hypertension [7,8]. Histological study showed that localized fibrosis scattered in the left ventricle and location of fibrosis differed individually. This means that the LV wall in this DCM model has inhomogeneous histology, and that the model is suitable for evaluating the relationship between LV wall property and the surgical result.
The findings of the present study are summarized as follows. Echocardiography and cardiac catheterization confirmed the efficacy of the surgery, but LV diameter which had been reduced right after the surgery had gradually enlarged as time passed. The ratio of LV redilatation differed in two groups. Half of animals remained in good shape with smaller LV dimension than baseline, and the other half deteriorated in bad shape with larger LV dimension. Histological study showed the fraction of residual fibrosis in Good result group was significantly less than that in Bad result group. There was a strong correlation between the ratio of LV redilatation and the relative amount of residual fibrosis.
This study infers that localization of fibrosis affects the long-term result of PLV. Decreasing number of heart transplantation around the world, there seeks a possibility of non-transplant surgery for end-stage heart failure. Initial experience of PLV has left a fact that PLV could salvage some candidates for heart transplantation to a considerable extent in spite of denying the almightiness of PLV [2]. We must consider not only resecting the posterolateral wall like PLV but also some intervention to the anteroseptal wall such as SAVE operation depending on the patients' LV wall property. Such a strategic approach as a combination of resecting damaged myocardium and retaining sound muscle can improve a long-term result of LV restoration surgery for DCM.
In conclusion, a long-term result of LV volume reduction surgery for DCM rats was affected by the amount of residual fibrosis. This information suggests that proper selection of the surgical site is important to achieve a good result of LV restoration surgery for DCM.
| 5. Study limitations |
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Further development of the technology may help to detect the LV wall property exactly and predict the result of the surgery prospectively.
| Appendix A. Conference discussion |
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Dr Horii: I don't follow you.
Dr Poston: It is possible that there is just overall more myocardial inflammation and fibrosis that also included the septum in the hearts that did bad which was not necessarily specific to the septum. If that's the case, it could just be that in your model a bad heart outcome is due mainly to a more intense inflammatory response from the autoimmune stimulus. Irregardless of the ventricular surgery, the inflammatory response led to the hearts dilating back out.
Dr Horii: Unfortunately, I don't have a good answer for you, because I cannot tell you if such a fibrosis is the reason or is the cause.
Regarding myocardial fibrosis, the septum was the least damaged by surgery itself and the least fibrotic portion as shown in my presentation. And even in the clinical setting and also in this experimental setting, there was localized fibrosis and heterogeneity of LV wall in DCM hearts. And so, LV surgery can be performed in an appropriate way to treat DCM hearts.
| Footnotes |
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| References |
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