Outcomes of long storage times for cryopreserved vascular grafts in outflow reconstruction in living donor liver transplantation

Authors


  • This study was not funded by any foundation or organization.

  • The authors of this article have no conflicts of interest to disclose.

Abstract

The outflow reconstruction of the right anterior sector in a right liver graft (RLG) with cryopreserved vascular grafts (CVGs) is crucial for preventing graft congestion in living donor liver transplantation (LDLT). The impact of the duration of cryopreservation has not been evaluated so far. From 2006 to 2009, 250 LDLT were performed: 47 of these patients (group 1) received CVGs stored for ≦1 year, and 33 patients (group 2) received CVGs stored for >1 year. Single or multiple segment 8 hepatic veins were reconstructed. The number of anastomoses did not affect vascular graft patency (P = 0.21). The length of the cryopreservation time did not affect the histological findings for CVGs. The preoperative and postoperative liver graft volumes were 783.8 ± 129.7 and 1102 ± 194.7 cc, respectively, for group 1 and 753.7 ± 158.5 and 1097.2 ± 178.7 cc, respectively, for group 2. The regeneration indices for liver grafts in the whole patient group, group 1, and group 2 were 48.9%, 47.4%, and 51.05%, respectively. In conclusion, the storage duration has no impact on the patency of CVGs in outflow reconstruction or on the regeneration of RLGs in LDLT. CVGs stored for >1 year can be safely used for the outflow reconstruction of RLGs in LDLT. Liver Transpl 20:173-181, 2014. © 2013 AASLD.

Abbreviations
ACR

acute cellular rejection

CTA

computed tomography angiography

CVG

cryopreserved vascular graft

DMSO

dimethyl sulfoxide

GRWR

graft-to-recipient weight ratio

LDLT

living donor liver transplantation

LT

liver transplantation

MHV

middle hepatic vein

RLG

right liver graft

RPMI-1640

Roswell Park Memorial Institute 1640

V5

segment 5 hepatic vein

V8

segment 8 hepatic vein

VG

vascular graft

Living donor liver transplantation (LDLT) has been used to overcome the shortage of deceased donor organs. For right liver graft (RLG) procurement, surgical options include harvesting the graft without the middle hepatic vein (MHV) in order to guarantee donor safety[1-3] and harvesting the graft with the MHV in order to improve the graft outcome.[4-6] Outflow reconstruction of RLGs in LDLT has been advocated to prevent the congestion of the right anterior sector of the liver and after sinusoidal injury[3] and graft failure.[7]

Different types of vascular grafts (VGs), such as cryopreserved vascular grafts (CVGs),[2] autologous saphenous and femoral vein grafts,[8, 9] and even artificial grafts,[10] have been used to drain the segment 5 hepatic vein (V5) and the segment 8 hepatic vein (V8). Although autologous grafts have been rated the best choice, CVGs are used most frequently for logistical reasons.[11] Already in 1979, Starzl et al.[12] proposed storing vascular homografts from cadaveric organ donors in order to deal with unexpected vascular problems during different abdominal transplant procedures. Those vessels, preserved in sterile plastic containers containing cold normal saline solution or lactated Ringer's solution, were stored in commercial refrigerators at 4°C. Nowadays, cryopreserved grafts are frequently stored for a long time. The impact of such prolonged storage on graft patency has not been thoroughly investigated; this is the reason that storage has been limited by some authors to 30 days.[13] The histological examination of CVGs has been reported only for animal models with preservation for up to 30 days.[14, 15]

The aim of this study was to evaluate the impact of the duration of cryopreservation on graft patency and eventual liver regeneration in adult-to-adult RLG LDLT.

PATIENTS AND METHODS

Between April 2006 and December 2009, 80 of 250 patients receiving an RLG (32%) needed an interposition CVG for right anterior sector outflow reconstruction in adult-to-adult RLG LDLT. All transplants were reviewed retrospectively.

During the study period, 47 of the 80 patients (58.8%) received CVGs stored for ≦1 year (group 1), and 33 (41.2%) received CVGs stored for >1 year (group 2). CVGs from grafts with a cryopreservation time > 5 years were discarded according to protocol regulations of the Kaohsiung Chang Gung Memorial Hospital CVG tissue bank.

Intraoperative Doppler ultrasound was performed with an Acuson 128 (Acuson, Mountain View, CA) using a 7.0 scanner in the imaging and Doppler modes daily after graft implantation until the 14th postoperative day and once a week afterwards until discharge. Then, vascular velocities were controlled monthly for the first 6 months and every 3 months thereafter. Computed tomography angiography (CTA) was performed 6 months after liver transplantation (LT) so that the vascular anatomy and volume of each graft could be studied after hepatic regeneration.[16, 17] A measurable velocity flow on Doppler ultrasound was considered an indicator of patency; when this was absent, a CVG was considered to be occluded. Preoperative and postoperative analyses of graft volumetry were performed in order to determine differences between the 2 patient groups through measurements of graft regeneration with a modification of the Scatton formula.[6]

Criteria for the Reconstruction of the MHVand Hepatic Veins Other Than the Right Hepatic Vein

The volume of the liver drained by MHV tributaries was estimated by the degree of congestion induced by simultaneous clamping of the right hepatic artery and MHV tributaries during donor hepatectomy. Our criteria for MHV reconstruction included a larger portion of the graft drained by MHV tributaries, a small right graft, large V5 and V8 tributaries (>5 mm in diameter), a graft size < 40% of the recipient's estimated standard liver volume, and an advanced state of sickness and/or the presence of severe portal hypertension.[18] Right inferior hepatic veins with a diameter > 5 mm were always preserved and reconstructed to the recipient inferior vena cava.

Selection of Interposition CVGs

All VGs were provided by the Kaohsiung Chang Gung Memorial Hospital tissue bank. The selection criteria for using CVG interposition to reconstruct the allograft outflow included ABO compatibility, length, and side branches. A short CVG segment was excised after thawing for histological evaluation.

Cryopreservation and Thawing Techniques

Each procured VG was preserved in histidine-tryptophan-ketoglutarate solution for less than 24 hours at 4°C; after tissue culturing, the graft was placed in a Roswell Park Memorial Institute 1640 (RPMI-1640) solution (BioLife Solutions, Inc., Bothell, WA) enriched with cefepime (240 mg/L) and vancomycin (50 mg/L) for another 24 hours at the same temperature. Before cryopreservation, the VG was placed in a 10% dimethyl sulfoxide (DMSO) solution (OriGen Biomedical Austin, TX) in an ice bath. The VG was then put into a bag that was sealed, and a controlled-rate freezer was programmed to a −1°C/minute rate until the temperature of −80°C was reached. The VG was than stored at −100°C in vapor-phase nitrogen.

For the thawing procedure, each VG was placed in a laminar-flow cabinet at room temperature for 7 minutes.[19] The outer bag was opened, and the inner bag was placed within a warm (37°C) and sterile normal saline solution for 10 to 15 minutes to allow the bag's contents to melt. The bag was next cut after sterilization with povidone-iodine for 5 minutes. Afterwards, the inner bag was opened, and the VG was placed in 30 mL of a 5% DMSO/RPMI-1640 solution; the medium was removed, and 30 mL of Ringer's lactate solution was added and removed twice. Another 60 mL of Ringer's lactate solution was added in 2 different steps before a new tissue sample was taken for culturing and histological study; the VG was then ready to be trimmed on the back table according to the request of the transplant surgeon.

Outflow Reconstruction

The outflow reconstruction technique has been described in detail previously.[2, 7, 20]

Statistical Analysis

All data are reported as means and standard deviations, means, and ranges. Incidence rates were compared with a 1-way analysis of variance test and Spearman correlations; survival and patency rates were estimated with the Kaplan-Meier method and were compared with a log-rank test. A P value < 0.05 was considered statistically significant. The analyses were performed with SPSS 20 for Windows (SPSS, Inc., Chicago, IL).

The institutional review board of Kaohsiung Chang Gung Memorial Hospital in Taiwan approved this study (101-0930B).

RESULTS

The types of CVGs included iliac veins (n = 48 or 60%), iliac arteries (n = 29 or 36.2%), and others (n = 3 or 3.8%). The demographic characteristics are listed in Table 1. The mean liver graft weight was 749.7 g for group 1 and 705.2 g for group 2 (P = 0.10), and the overall graft-to-recipient weight ratio (GRWR) was 1.07%; there was no statistical difference in the latter between the 2 groups (P = 0.53). The mean storage duration was 140.9 days for group 1 and 719.7 days for group 2 (P < 0.001; Table 2).

Table 1. Recipient Characteristics for RLGs Undergoing MHV Reconstruction With CVGs
 Overall (n = 80)CVG Storage for ≦1 Year (n = 47)CVG Storage for >1 Year (n = 33)P Value
  1. a

    The data are presented as means and standard deviations with ranges in parentheses.

  2. b

    The numbers include venous and arterial VGs.

Age (years)a54 ± 8 (16-68)55 ± 8 (16-68)53 ± 6 (36-67)0.36
Sex: male/female (n/n)66/1439/827/60.89
Model for End-Stage Liver Disease scorea25 ± 10 (7-40)24 ± 10 (7-40)26 ± 10 (7-40)0.43
Body weight (kg)a69 ± 10 (48-99)70 ± 10 (53-98)67 ± 11 (47.6-97.2)0.35
Height (cm)a165 ± 7 (150-181)165 ± 7 (152-181)164 ± 7 (150-179)0.81
Diagnosis [n (%)]   0.76
Hepatitis B virus49 (61.2)28 (59.6)21 (63.6) 
Hepatitis C virus19 (23.8)14 (29.8)5 (15.2) 
Hepatitis B virus + hepatitis C virus5 (6.25)3 (6.4)2 (6.1) 
Other7 (8.75)2 (4.3)5 (15.2) 
Hepatocellular carcinoma48 (60)29 (61.7)19 (57.6)0.68
CVG type [n (%)]   0.008
Iliac vein48 (60)32 (68.1)16 (48.5) 
Iliac artery29 (36.2)12 (25.5)17 (51.5) 
Inferior vena cava1 (1.25)1 (2.1)0 
Jugular vein1 (1.25)1 (2.1)0 
Portal vein1 (1.25)1 (2.1)0 
CVG histology [n (%)]    
All grafts: normal [n (%)]b69 (86.2)45 (95.7)24 (72.7) 
Arterial CVGs [n (%)]    
Intimal thickening5 (6.2)1 (2.1)4 (12.1) 
Mild atherosclerosis5 (6.2)1 (2.1)4 (12.1) 
Moderate atherosclerosis1 (1.2)1 (2.1)0 
Overall patient survival (%)    
1 year97.595.71000.23
3 years93.895.790.70.40
5 years9093.684.60.16
Table 2. Demographics of CVGs, liver graft regeneration, and outflow reconstruction
 Overall (n = 80)CVG Storage for ≦1 Year (n = 47)CVG Storage for >1 Year (n = 33)P Valuea
  1. a

    Comparison of CVG storage for <1 year and CVG storage for >1 year.

  2. b

    The data are presented as means and standard deviations with ranges in parentheses.

  3. c

    Graft regeneration (%) = (Volume of postoperative RLG measured by CTA − Volume of preoperative RLG)/Volume of preoperative RLG × 100.

Graft weight (g)b731.42 ± 121.1 (512-1038)749.7 ± 115.7 (554-1034)705.2 ± 125.5 (512-1038)0.10
Recipient standard liver volume (cc)b1254.6 ± 122.2 (998.1-1709.7)1274.8 ± 120.3 (1084.2-1709.7)1225.8 ± 121 (998.16-1468.6)0.07
Preoperative RLG volume (cc)771.4 ± 142.1 (446-1226)783.8 ± 129.7 (446-1030)753.7 ± 158.5 (509-1226)0.35
Postoperative RLG volume (cc)1100 ± 186.7 (662-1677)1102 ± 194.7 (673-1677)1097.2 ± 178.7 (662-1484)0.91
Graft standard liver volume (%)b58.8 ± 9.2 (40.9-81.8)59.3 ± 9 (40.9-81.5)58.2 ± 9.6 (44.3-81.8)0.63
GRWR (%)b1.1 ± 0.2 (0.6-1.5)1.1 ± 0.2 (0.7-1.4)1.1 ± 0.2 (0.6-1.5)0.53
Graft regeneration (%)bc48.9 ± 34.2 (1.6-168)47.4 ± 35.2 (11.5-168)51.1 ± 33.3 (1.6-166.6)0.66
CVG preservation (days)b379.6 ± 346.4 (2-1529)140.9 ± 102 (2-358)719.7 ± 279.8 (377-1529)<0.001
CVG length (mm)b112 ± 21.7 (60-170)111.4 ± 21.8 (60-170)112.7 ± 21.9 (70-150)0.80
CVG diameter (mm)b13.8 ± 4.5 (4-30)14.2 ± 4.1 (8-30)13.2 ± 5 (4-30)0.33
Outflow anastomosis [n (%)]    
1 vessel28 (35)14 (29.8)14 (42.4)0.21
2 vessels42 (52.5)26 (55.3)16 (48.5) 
3 vessels10 (12.5)7 (14.9)3 (9.1) 
Type of CVG [n (%)]   0.64
Bifurcated15 (18.8)8 (17)7 (21.2) 
Not bifurcated65 (81.2)39 (83)26 (78.8) 

By the end of follow-up (range = 18.2-1964 days, mean = 780.9 days), 8 patients (10%) had died. One patient presented with secondary biliary cirrhosis after LDLT and required retransplantation; he died of uncontrolled ascites due to liver failure after deceased donor liver transplantation (n = 1). The causes of mortality included veno-occlusive disease (n = 1), sepsis (n = 1), hepatocellular carcinoma recurrence (n = 1), and de novo extrahepatic tumor development [peritoneal carcinomatosis (n = 1), squamous cell carcinoma (n = 1), leiomyosarcoma (n = 1), and malignant mesenchymoma (n = 1)]. None of these deaths were related to the procedure. Postoperative complications are listed in Table 3. Nine of the 17 acute cellular rejection (ACR) episodes (52.9%) were associated with VG occlusion. Patients with ACR were categorized according to the period of CVG occlusion: early or ≤14 days (n = 2 or 11.8%) and late or >14 days (n = 7 or 41.2%). Eight of the patients with ACR (47.1%) had a patent CVG. The 1-, 3-, and 5-year overall survival rates were 97.5%, 93.8%, and 90%, respectively. The 1-, 3-, and 5-year overall survival rates for patients receiving CVGs stored for <1 year were 95.7%, 95.7%, and 93.6%, respectively, and the rates for patients receiving CVGs stored for >1 year were 100%, 90.7%, and 84.6%, respectively (P = 0.23, P = 0.40, and P = 0.16).

Table 3. Morbidity and Mortality After LDLT With Respect to the Length of CVG Storage
ParameterOverall (n = 80)CVG Storage for ≦1 Year (n = 47)CVG Storage for >1 Year (n = 33)P Value
ACR [n (%)]17 (21.2)12 (25.5)5 (15.2)0.26
Portal vein complications [n (%)]    
Portal vein stenosis3 (3.8)3 (6.4)00.26
Portal vein thrombosis1 (1.2)1 (2.1)0>0.99
Veno-occlusive disease1 (1.2)1 (2.1)0>0.99
Biliary complications [n (%)]    
Biliary fistula1 (1.2)1 (2.1)00.26
Secondary biliary cirrhosis1 (1.2)1 (2.1)0>0.99
Sepsis [n (%)]2 (2.5)1 (2.1)1 (3)>0.99
Retransplantation [n (%)]1 (1.2)1 (2.1)0>0.99
Recurrent disease [n (%)]    
Recurrent viral disease2 (2.5)02 (6.1)0.69
Recurrent tumor7 (8.8)2 (4.3)5 (15.2) 
Mortality [n (%)]8 (10)3 (6.4)5 (15.2)0.48

Histology and Patency Rates of CVGs

The cryopreserved veins were usually well preserved, had good viability, and showed no remarkable changes; the cryopreserved arteries had good viability at the time of LDLT despite the presence of various degrees of atherosclerotic change (Fig. 1). Eighteen of the 29 arterial CVGs had normal histology or minimal intimal thickening; 5 VGs showed mild fibrous intimal thickening; and 5 VGs showed fibrous intimal thickening, foam cell infiltration, degeneration, and microcalcification on histology. One VG showed atherosclerotic plaque with marked fibrous and thickened intima as well as a necrotic core with degeneration, macrophage foam cells, an accumulation of extracellular lipid particles, and calcification on histology.

Figure 1.

Histological findings and storage times for CVGs after thawing. (A) Normal histology and minimal focal intimal thickening (arrow). The storage time was 244 days. (B) A VG showed mild fibrous intimal thickening. The storage time was 181 days. (C) A CVG showed fibrous intimal thickening with degeneration, foam cell infiltration, and microcalcification. The storage time was 90 days. (D) A VG showed atherosclerotic plaque with marked fibrous intimal thickening and a necrotic core with degeneration, macrophage foam cells, an accumulation of extracellular lipid particles, and calcification (NC indicates the necrotic core, and C indicates the calcification). The storage time was 155 days.

The number of anastomoses performed between the MHV tributaries and CVGs is shown in Table 2. The patency rates at 2 weeks were 90% and 94% for groups 1 and 2, respectively. The CVG patency rates 2 years after LDLT were 61.7% and 54.5% for groups 1 and 2, respectively (P = 0.46; Fig. 2). The changes in the CVG velocity rates are shown in Table 4.

Figure 2.

Overall patency rate of CVGs in patients with outflow reconstruction after RLG LDLT.

Table 4. Velocity Rates of CVGs After RLG LDLT
 Velocity Rate (cm/Second)a 
TimeCVG Storage for ≦1 Year (n = 47)CVG Storage for >1 Year (n = 33)P Value
  1. NOTE: The normal velocity for an MHV is >10 cm/second.

  2. a

    The data are presented as means and standard deviations with ranges in parentheses.

Intraoperative28.8 ± 14.8 (8-66)31.6 ± 15.4 (6-73)0.42
Follow-up   
Postoperative week 128 ± 16.4 (0-71)28 ± 14.5 (0-52)0.99
Postoperative week 223.4 ± 14.5 (0-70)27.04 ± 18.4 (0-95)0.35
Postoperative week 423.4 ± 14.5 (0-53)23.1 ± 126 (0-54)0.92
Postoperative week 2412.2 ± 11.5 (0-39)11.9 ± 10.6 (0-33)0.93
Postoperative week 7212.1 ± 9.7 (0-36)12.1 ± 13.3 (0-51)0.99
Postoperative week 9611.2 ± 11.8 (0-52)9.04 ± 10.4 (0-42)0.41

The mean preservation durations for arterial and venous CVGs were 536.3 ± 417.2 and 294.3 ± 269.7 days, respectively (P = 0.008). The intraoperative velocity rates for arterial and venous CVGs were 23.9 ± 10.3 and 34.3 ± 16.2 cm/second, respectively (P = 0.001). Twenty-seven of 29 arterial CVGs (93.1%) and 44 of 48 venous CVGs (91.7%) were patent 2 weeks after LDLT. The patency rates at 96 weeks for arterial and venous CVGs were 58.6% (17/29) and 58.3% (28/48), respectively (P = 0.70; Table 5).

Table 5. Long-Term Outcomes and Velocity Rates for Arterial and Venous CVGs
TimeArteries (n = 29)Veins (n = 48)P Value
  1. a

    The data are presented as means and standard deviations with ranges in parentheses.

GRWR (%)a1.1 ± 0.2 (0.6-1.4)1.1 ± 0.2 (0.7-1.5)0.76
CVG preservation (days)a536 ± 417 (39-1529)294 ± 270 (2-985)0.008
Overall patient survival (%)   
1 year10095.80.52
3 years93.193.8>0.99
5 years93.187.50.70
Intraoperative velocity (cm/second)a23.9 ± 10.3 (8-59)34.3 ± 16.2 (6-73)0.001
Follow-up velocity (cm/second)a   
Postoperative week 2a23.5 ± 19.1 (0-95)27.0 ± 14.6 (0-70)0.39
Postoperative week 24a13.5 ± 11.5 (0-39)11.3 ± 10.9 (0-33)0.51
Postoperative week 72a11.7 ± 10.3 (0-41)12.5 ± 12.1 (0-51)0.78
Postoperative week 96a9.6 ± 10.1 (0-30.1)10.7 ± 12.2 (0-52)0.70

As for surgical outcomes, 2 of 29 patients with arterial CVGs (6.9%) and 6 of 48 patients with venous CVGs (12.5%) died after LDLT; there was no statistical significance (P = 0.70). The overall patient survival rates at 1, 3, and 5 years with arterial and venous CVGs are shown in Table 5.

Impact on Liver Regeneration

The mean volumes before LDLT and 6 months after LDLT (as measured by CTA) were 783.8 ± 129.7 and 1102 ± 194.7 cc, respectively, for group 1 and 753.7 ± 158.5 and 1097.2 ± 178.7 cc, respectively, for group 2 (Table 2). The rate of graft regeneration for grafts presenting with late CVG occlusion was 46.0% ± 32.5%; for livers with patent CVGs, the rate of graft regeneration was 51% ± 36.3%. For grafts with early occlusion of CVGs, the rate of graft regeneration was 47.5% ± 29.7% (Table 6).

Table 6. Comparison of the Graft Regeneration Percentages for Liver Grafts and the Periods of Occlusion for CVGs
 Graft Regeneration (%)aP Value
Overall (n = 80)CVG Storage for ≦1 Year (n = 47)CVG Storage for >1 Year (n = 33)
  1. a

    The data are presented as means and standard deviations with ranges in parentheses.

  2. b

    Early occlusion was defined as a CVG with no velocity rate before or on postoperative day 14.

  3. c

    Late occlusion was defined as the absence of a velocity rate after 2 weeks.

Early occlusion (n = 6)b47.5 ± 29.7 (13.5-92.6)46.5 ± 41.1 (13.5-92.6)49 ± 12 (40.6-57.6)0.56
Late occlusion (n = 27)c46.0 ± 32.5 (11.5-166.6)43.5 ± 23.3 (11.5-87.3)48.6 ± 41.2 (14.7-166.6)0.03
No occlusion (n = 47)51 ± 36.3 (1.6-168)49.6 ± 40.8 (11.5-168)53 ± 29.6 (1.6-107.9)0.83

DISCUSSION

The surgical technique for adult-to-adult RLG LDLT has been progressively refined during the last decade; particular attention has been given to the outflow reconstruction of the graft in order to prevent graft congestion in the immediate postoperative period.[20, 21] Congestion of the right anterior sector of an RLG increases the risk of hepatic artery thrombosis and sinusoidal injury, which can lead to impaired regeneration, atrophy, and, finally, graft failure.[3, 22, 23]

Kilic et al.[8] and Hwang et al.[11] reported that a CVG is a suitable choice for reconstructing MHV tributaries and thereby preventing congestion of V5 and V8. Sellers et al.[13] reported the use of CVGs preserved for <1 month to reconstruct the hepatic artery in the treatment of aneurysms after LT.

The use of RPMI-1640 and DMSO solutions for the cryopreservation of VGs with a computer-controlled freezing program has been important for minimizing the consequences of freezing injury, which is caused by lesions from ice crystals and the increased concentration of solutes as more ice is formed.[24] Faggioli et al.[15] and Pascual et al.[14] reported the effects of long-term cryopreservation and structural graft damage on rats and rabbits. Their findings were related to vascular degeneration in vessels preserved for <30 days. Mirabet et l.[25] reported the impact of 9 years of cryopreservation of cardiac and pulmonary valves; the structure of leaflets and vascular walls could be well preserved without a significant loss of cell viability. Martínez et al.[26] showed in a human LT setting the following thrombosis rates: 0 of 21 stored arteries, 7 of 68 fresh arteries (10%), 3 of 21 stored veins (14%), and 3 of 32 fresh veins (9%; all P values not significant). In our series, the existence of intimal thickening or degeneration and different degrees of atherosclerotic change in arterial CVGs did not affect the patency of the interposition VGs in the outflow reconstruction of RLGs. During the posttransplant process of liver regeneration, the overall velocity of CVGs decreased from 30 to 10.3 cm/second over a period of 2 years. This velocity further decreased throughout the follow-up period (P = 0.57). Initially good patency, however, prevented allograft congestion. According to a literature review, a rat experiment in which arterial CVGs were used as vessel substitutes showed that general thinning of the arterial wall with delayed formation of the neointima and degeneration of the tunica media in arterial CVGs did not give rise to aneurysm formation 90 days after implantation (short term).[14] Another animal experiment involving arterial CVGs showed a complete loss of the muscle component of the tunica media along with the formation of a stable neointima in arterial CVGs in long-term implants (180 days).[27] In LDLT, the short-term patency of the outflow in V5 and V8 via interposition CVGs can prevent congestion of the anterior segment. Also, there is a low risk of aneurysm formation in arterial CVGs in the low-pressure system of the hepatic vein.

Eleven of 29 arterial CVGs (38%) had different degrees of intimal thickening and atherosclerosis (Table 1). The number in this study was too small for drawing any solid results from a statistical analysis of histological changes in arterial CVGs with respect to graft function.

Six CVGs were found to be occluded early (≦ 2 weeks after LDLT). No clinical impact on RLGs was detected. A possible explanation is the development of functional venous anastomoses between either V5 or V8 and right hepatic veins in RLGs.[20]

Many factors have been found to influence the regeneration of RLGs after LDLT.[28, 29] The patency of reconstructed hepatic venous tributaries is one of the major factors affecting liver graft regeneration with statistical significance (P = 0.02). In Chen et al.'s report,[30] an RLG with tributary reconstruction of the MHV had better graft regeneration and a less transient period of prolonged hyperbilirubinemia than an RLG without tributary reconstruction of the MHV.

In conclusion, the length of storage has no impact on structural changes in or the patency of CVGs or on the regeneration of RLGs in LDLT. CVGs stored for >1 year can, therefore, safely be used in LDLT. In the future, more detailed research focusing on the impact of the cryopreservation time on histological changes in arterial CVGs should be studied.

ACKNOWLEDGMENT

Professor Makuuchi and Professor Motomura of the Red Cross Hospital and the University of Tokyo are thanked for their help with the setup of the Kaohsiung Chang Gung Memorial Hospital CVG tissue bank.

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