Transarterial chemoembolization using drug-eluting bead compared with radiofrequency ablation for treatment of single small hepatocellular carcinoma: a pilot non-randomized trial

Background/Aims@#Surgical resection, transplantation, and radiofrequency ablation (RFA) are generally accepted as amenable treatments for small hepatocellular carcinoma (HCC). Recently drug-eluting beads (DEB) which had several treatment advantages were introduced for transarterial chemoembolization (TACE). The aim of this study was to evaluate feasibility and safety of DEB-TACE compared with RFA for the treatment of single small HCC. @*Methods@#In this pilot non-randomized trial, we assessed retrospective data of 40 patients who underwent DEB-TACE (n=21) or RFA (n=19) for single small (≤3 centimeter in greatest dimension) HCC. The primary outcomes were tumor response and time to recurrence. The secondary outcome was treatment-related complications. @*Results@#Complete response rate to DEB-TACE and RFA after first follow-up assessment was 90.5% and 94.7%, respectively (P=1.000). During mean follow-up of 87.6 months (95% confidence interval: 74.4-102), 7 patients experienced local recurrence. The 6- and 12-month cumulative local recurrence rate was 5.0% and 21.8% in DEB-TACE vs. 11.1% and 17.0% in RFA group (P=0.877). A total 14 distant intrahepatic recurrences were developed and 12- and 24-month cumulative distant intrahepatic recurrence rate was 20.6% and 42.7% in DEBTACE vs. 17.2% and 36.3% in RFA group (P=0.844). Two patients experienced gangrenous cholecystitis after DEB-TACE requiring cholecystectomy as treatment-related adverse event. @*Conclusions@#Tumor response and recurrence rate after single session of DEB-TACE or RFA were similar. DEB-TACE could be applied selectively in patients with a single small HCC if the other therapeutic modality is unfeasible.

Transarterial chemoembolization using drug-eluting bead compared with radiofrequency ablation for treatment of single small hepatocellular carcinoma: a pilot non-randomized trial

Background/Aims@#Surgical resection, transplantation, and radiofrequency ablation (RFA) are generally accepted as amenable treatments for small hepatocellular carcinoma (HCC). Recently drug-eluting beads (DEB) which had several treatment advantages were introduced for transarterial chemoembolization (TACE). The aim of this study was to evaluate feasibility and safety of DEB-TACE compared with RFA for the treatment of single small HCC. @*Methods@#In this pilot non-randomized trial, we assessed retrospective data of 40 patients who underwent DEB-TACE (n=21) or RFA (n=19) for single small (≤3 centimeter in greatest dimension) HCC. The primary outcomes were tumor response and time to recurrence. The secondary outcome was treatment-related complications. @*Results@#Complete response rate to DEB-TACE and RFA after first follow-up assessment was 90.5% and 94.7%, respectively (P=1.000). During mean follow-up of 87.6 months (95% confidence interval: 74.4-102), 7 patients experienced local recurrence. The 6- and 12-month cumulative local recurrence rate was 5.0% and 21.8% in DEB-TACE vs. 11.1% and 17.0% in RFA group (P=0.877). A total 14 distant intrahepatic recurrences were developed and 12- and 24-month cumulative distant intrahepatic recurrence rate was 20.6% and 42.7% in DEBTACE vs. 17.2% and 36.3% in RFA group (P=0.844). Two patients experienced gangrenous cholecystitis after DEB-TACE requiring cholecystectomy as treatment-related adverse event. @*Conclusions@#Tumor response and recurrence rate after single session of DEB-TACE or RFA were similar. DEB-TACE could be applied selectively in patients with a single small HCC if the other therapeutic modality is unfeasible.

Percutaneous Cholecystostomy Is Appropriate as Definitive Treatment for Acute Cholecystitis in Critically Ill Patients: A Single Center, Cross-sectional Study / 대한소화기학회지

BACKGROUND/AIMS: Percutaneous cholecystostomy (PC) is an effective treatment for cholecystitis in high-risk surgical patients. However, there is no definitive agreement on the need for additional cholecystectomy in these patients. METHODS: All patients who were admitted to Cheju Halla General Hospital (Jeju, Korea) for acute cholecystitis and who underwent ultrasonography-guided PC between 2007 and 2012 were consecutively enrolled in this study. Among 82 total patients enrolled, 35 underwent laparoscopic cholecystectomy after recovery and 47 received the best supportive care (BSC) without additional surgery. RESULTS: The technical and clinical success rates for PC were 100% and 97.5%, respectively. The overall mean survival was 12.8 months. In the BSC group, mean survival was 5.4 months, and in the cholecystectomy group, mean survival was 22.4 months (p<0.01). However, there was no significant difference between these groups in multivariate analysis (relative risk [RR]=1.92; 95% CI, 0.77-4.77; p=0.16). However, advanced age (RR=1.05; 95% CI, 1.02-1.08; p=0.001) and higher class in the American Society of Anesthesiologists' physical status (RR=3.06; 95% CI, 1.37-6.83, p=0.006) were significantly associated with survival in the multivariate analysis. Among the 47 patients in the BSC group, the cholecystostomy tube was removed in 31 patients per protocol. Recurrent cholecystitis was not observed in either group of patients during the follow-up period. CONCLUSIONS: In high-risk surgical patients, PC without additional cholecystectomy might be the best definitive management. Furthermore, the cholecystostomy drainage catheter can be safely removed in certain patients.

A case of hepatocellular carcinoma in the caudate lobe successfully treated by transcatheter arterial chemoembolization using drug-eluting beads / 대한간학회지

Hepatocellular carcinoma (HCC) in the caudate lobe remains one of the most intricate locations where various treatments tend to pose problems with regard to the optimal approach. Surgical resection has been regarded as the most effective treatment; however, isolated resection of the caudate lobe is strenuous and associated with a high rate of early recurrence. Percutaneous ablation might be technically difficult or impossible to perform due to the deep location of tumors and adjacent large vessels. Treatment with drug-eluting beads (DEB) can potentially enhance the therapeutic efficacy for patients with unresectable HCC by drawing on the slower, more consistent drug delivery process. We described a case of a 62-year-old man with HCC in the caudate lobe who was successfully treated by DEB.

Multiple Pyogenic Spondylodiscitis with Bilateral Psoas Abscesses Accompanying Osteomyelitis of Lateral Malleolus: A Case Report

A psoas abscess is a potentially life-threatening infection. Multiple pyogenic spondylodiscitis with bilateral psoas abscesses accompanying an osteomyelitis of the lateral malleolus is an extremely rare event. We present our experience with needle aspiration for the treatment of osteomyelitis of the lateral malleolus and CT-guided percutaneous catheter drainage for a psoas abscess in an elderly patient. Both infections were completely resolved without recurrence. A psoas abscess should be included in the differential diagnosis of a patient with low back pain during musculoskeletal infection. Percutaneous needle aspiration or CT-guided percutaneous catheter drainage is an effective method for treating certain musculoskeletal infections.

The Endovascular Management of Saccular Posterior Inferior Cerebellar Artery Aneurysms

OBJECTIVE: The purpose of this retrospective study was to report the outcome of the endovascular treatment of eight patients with eight saccular posterior inferior cerebellar artery (PICA) aneurysms. MATERIALS AND METHODS: Over the last seven years (1999-2006), eight consecutive patients with saccular PICA aneurysms were treated by endovascular methods. Five of the aneurysms were presented with subarachnoid hemorrhaging, whereas three were discovered incidentally. Four of the aneurysms (3 ruptured and 1 incidental) were treated by intrasaccular coiling, whereas the remaining four (1 ruptured and 3 incidental) were treated by vertebral artery (VA) occlusion. RESULTS: Of the four aneurysms treated by intrasaccular coiling, three were completely packed with coils and one was partially packed. In three of four patients who underwent vertebral artery occlusions, follow-up digital subtraction angiographies demonstrated thrombosed aneurysms and PICA. No procedure-related morbidity occurred and no re-bleed was encountered during a follow-up examination (mean; 31 months). CONCLUSION: As a result of this study, we found that the endovascular management of saccular PICA aneurysms should be considered as safe and effective.

Giant Vertebrobasilar Junction Aneurysm Treated with Proximal Occlusion of Parent Artery Followed by Coil Embolization of Partially Thrombosed Aneurysm: A Case Report / 신경중재치료의학

In the case of giant vertebrobasilar junction aneurysm with an outflow directly draining into the basilar artery, trapping of ipsilateral vertebral artery is technically challenging. Endosaccular coil embolization may be an option, but it may aggravate symptoms due to mass effect or aneurysmal regrowth after coil compaction. Occlusion of the ipsilateral vertebral artery proximal to the aneurysm may be another option. However, complete thrombosis should be eventually achieved to prevent symptom progression from the retrograde flow or mass effect by the partial thrombosis within the aneurysm. The authors describe a case of giant vertebrobasilar aneurysm initially treated with proximal occlusion. As the aneurysm getting partial thrombosis, the bulbar compression symptom was slowly aggravated. We performed endosaccular coiling of small remaining sac 2 months later, which resulted in complete resolution of compression symptom.

Clinical Characteristics and Risk Factors of Contrast Dye Nephrotoxicity in Patients Performing Arteriography / 대한신장학회잡지

BACKGROUND: Because of increasing incidence of astherosclerosis, the incidence of contrast nephrotoxicity is increasing in Korea. This study was designed to investigate the clinical characteristics and risk factors of contrast dye nephrotoxcity in patients performing arteriography. METHODS: This study included 511 adult patients who performed arteriography. We retrospectively evaluated the incidence, clinical course, and risk factors of contrast dye-induced acute renal failure via medical records. Acute renal failure was defined as a rise of serum creatinine more than 50% of baseline levels 2-3 days after exposure of contrast dye. RESULTS: Of the total 511 patients, 23 patients (4.5%) had acute renal failure. The mean age of these patients was 57+/-0 years and the number of male was 14. The mean duration between the exposure and development of acute renal failure was 2.0+/-.7 days. The serum creatinine level maximally increased to 3.2+/-.9 mg/dL at 6.3+/-.1 days after the exposure. Oliguria and pulmonary edema developed in 8 and 7 patients, respectively. Four patients needed hemodialysis treatment. Of the total 23 patients with acute renal failure, 19 patients recovered with conservative treatment and 3 patients died without recovery of renal function and 1 patients progressed end stage renal failure. Renal insufficiency and dosage of contrast dye were independent risk factors of development of acute renal failure. CONCIUSION: Contrast dye-induced acute renal failure occurred in 4.5% of patients performing arteriography. Most cases of acute renal failures completely recovered but 4 case needed hemodialysis and 1 case progressed to end stage renal failure. Renal insufficiency and dosage of contrast dye were independent risk factors of development of acute renal failure.

Usefulness of CT Perfusion Imaging in Adult Moyamoya Disease

PURPOSE: The purpose of this study was to evaluate the role of perfusion CT in adult moyamoya disease. MATERIALS AND METHODS: The study population consisted of 13 adult moyamoya patients (10 women and 3 men, mean age: 40.4 years) and 11 age-matched normal controls (5 men and 6 women, mean age: 43 years). We retrospectively assessed the perfusion CT scan both visually and by a quantitative regional analysis, and we assessed the relationship between the perfusion CT scan findings and the angiographic findings. RESULTS: The mean relative cerebral blood volume (rCBV) values in moyamoya patients were 8.0% for the MCA area, 6.4% for the PCA area, and 7.7% for the basal ganglia. The rCBV values in the patients were higher than those in the control group with statistical significance (p<0.0001). The time to peak enhancement (TTP) values of the MCA area and the basal ganglia were delayed more than those in the controls; this was statistically significant (p<0.05). Moderate correlation was found between the rCBV in the basal ganglia area and angiographic stage of the basal moyamoya vessels. CONCLUSION:Perfusion CT demonstrates a statistically significant increase in rCBV in the MCA, PCA and basal ganglia areas and the TTP in the MCA and basal ganglia areas in patients with moyamoya disease. The visual brain perfusion patterns correlate with the extent and severity of the basal moyamoya vessels.

Traumatic Carotid-cavernous Fistula with Contralateral Proptosis: Case Report

Traumatic carotid-cavernous fistula frequently results in proptosis on the side of the fistula by retrograde drainage from the cavernous sinus to the superior ophthalmic vein. The involvement of the opposite orbit is due to the presence of connections between the cavernous sinuses on both sides, but exclusive contralateral orbit involvement is rare. We report a case in which the CCF with a contralateral proptosis developed in a 63 year-old man after a motor vehicle accident. MR angiography depicted the markedly dilated left cavernous sinus and left superior ophthalmic vein, sparing the right side. However, angiography showed a direct fistula between the right internal carotid artery and cavernous sinus with exclusive contralateral venous drainage via the intercavernous sinus. A detachable balloon was used to occlude the fistula, and the contralateral orbital symptom regressed.

Successful Treatment of Resistant Arteriovenous Fistula Stenosis by Cutting Balloon Angioplasty / 대한신장학회잡지

Percutaneous transluminal angioplasty (PTA) is an effective method in treating arteriovenous fistula (AVF) stenosis in hemodialysis patients. But, some stenoses are resistant to these procedures. Recently, cutting balloon angiopasty has been introduced as an alternative method for resistant AVF stenosis. We here report two cases of resistant AVF stenosis successfully treated by cutting balloon angioplasty in hemodialysis patients.

Arterial Embolism after Percutaneous Thrombolysis for the Treatment of Thrombosed Hemodialysis Graft / 대한신장학회잡지

Percutaneous thrombolysis with angioplasty is commonly used to treat thrombosed hemodialysis grafts. Arterial embolism is a rare but yet potentially serious complication. Here we report a case of symptomatic embolism of radial artery after percutaneous thrombolysis for the treatment of thrombosed graft in a hemodialysis patient. A 77-year old man was admitted because of numbness and coldness on the right hand and color change on the 4th of the right finger. He had been treated with percutaneous thrombolysis with angioplasty for the treatment of thrombosed graft 2 days before. Arteriograhy showed total occlusion of proximal radial artery. After intraarterial injection of urokinase and a subsequent angioplasty, the radial artery was recanalized and his symptom and sign had also been completely recovered.

Efficacy of Percutaneous Transluminal Angioplasty for Treating Non-Maturing Brescia-Cimino Fistulas

PURPOSE: We wished to report our experiences for the treatment of non-maturing Brescia-Cimino fistulas by using percutaneous transluminal angioplasty (PTA). MATERIALS AND METHODS: From January 1997 and December 2003, we treated 22 patients with non-maturing Brescia-Cimino fistulas by using percutaneous transluminal angioplasty (PTA). A retrospective analysis was performed on the findings of the fistulograms, techniques and success rate of the PTA, and the patency rate. RESULTS: Seventeen segmental stenoses and 5 segmental occlusions of the cephalic veins were identified. Sixteen stenoses and 2 occlusions were located at the cephalic vein adjacent to the anastomosis site, and 3 occlusions and 1 stenosis are seen at the proximal vein near the elbow joint. In addition to venous stenosis, a focal arterial stenosis at the anastomosis site and two accompanying accessory veins that might hamper the maturation of main cephalic vein was seen in each of two patients, respectively, and the simultaneous occlusion of the left innominate vein as well as occlusion of the cephalic vein was noted in one patient. The initial success rate of the PTA procedures was 95.5% (21/22). The overall success rate including the 11 additional PTAs that were performed during follow-up was 96.9% (32/33). No major complication were noted to have occurred. The primary and secondary patency rates were 72% (16/22) and 95% (21/22) at 3 months, and 50% (11/22) and 77% (17/22) at 6 months, respectively. CONCLUSION: PTA is an effective and safe method for treating non-maturing Brescia-Cimino fistulas.

Central Venous Stenosis in Chronic Hemodialysis Patients: The Effect of Percutaneous Angioplasty and Stenting / 대한신장학회잡지

BACKGROUND: Central venous stenosis in chronic hemodialysis patients occurs in about 17% of all venous stenosis and it is associated with central vein catheterization. We evaluated the effect of percutaneous angioplasty and stenting in the treatment of central venous stenosis in hemodialysis patients. METHODS: We retrospectively investigated medical records of total 31 dialysis patients who had central venous stenosis. We reviewed the causes of central venous stenosis, clinical manifestations, venographic findings, and patency rate of radiological intervention. RESULTS: Of the total 31 patients, 28 patients had past history of central vein catheterization ipsilateral to vascular access. Mean duration of the catheterization was 32+-14 days. Venography showed complete obstruction of central vein (n=14) and stenosis (n=17). The site of venous lesion was right subclavian vein (n=11), innominate vein (n=9), left subclavian vein (n=7), and superior vena cava (n=14). total 30 procedures of angioplasty with or without stenting were performed in 26 of 31 patients. Initial success rate was 96.1% and there was no severe complication such as rupture or bleeding. The primary patency rate at 6, 12, 24, and 48 month after the procedure was 87.3%, 75.6%, 67.9%, 65.4%, respectively. The cumulative patency rate at the same time point was 96.0%, 90.6%, 74.0%, 72.8%, respectively. CONCLUSION: Our data suggest that angioplasty with or without stenting is safe and effective in the treatment of central venous stenosis in hemodialysis patients.

Early Dysfunction of Radiocephalic Arteriovenous Fistula: Primary and Secondary Patency Rate of Percutaneous Angioplasty / 대한신장학회잡지

BACKGROUND: The radiocephalic arteriovenous fistula (AVF), which provides the best vascular access for hemodialysis, continues to have a high incidence of early failure. This was studied to determine primary and secondary patency rate of percutaneous transluminal angioplasty (PTA) in hemodialysis patients who had early dysfunction of this AVF within 1 year after the operation. METHODS: This retrospective study enrolled 39 hemodialysis patients with early dysfunction of radiocephalic AVF who received PTA between January, 1997 and December, 2002 at Uijongbu St. Mary's Hospital. The lesions occurred at proximal vein of upper arm and central vein were excluded. The primary and secondary patency rate of PTA was evaluated using Kaplan-Meier method. According to diabetes, age, sex, onset of AVF dysfunction after the operation, thrombosis, patency rate was compared with log-rank test. RESULTS: The mean age of the patients was 54+/-13 years and the number of male was 16 (41.2%). Twenty-four patients (61.5%) had diabetes and Among 39 lesions observed at venography, there were 33 cases of stenosis and 6 cases of complete occlusion due to thrombosis. The onset of AVF dysfunction after the operation was 5.3+/-3.6 months and 11 cases developed before the first needling. Total PTAs were performed and initial success rate was 94.2% (n=49). Primary patency rate at 6, 12, 24, and 48 months was 74.8%, 55.8%, 55.8%, and 55.8%, respectively. Secondary patency rate at 6, 12, 24, 48 months was 89.7%, 86.1%, 81.8%, 81.8%. Diabetes, age, sex, onset of AVF dysfunction after the operation, thrombosis did not influenced primary patency rate of PTA. There was no PTA-related complication. CONCLUSION: Percutaneous transluminal angioplasty is considered to be effective and safe treatment for early dysfunction of radiocephalic arteriovenous fistula in hemodialysis patients.

Bilateral Renal Artery Stenosis with Renal Insufficiency: Successful Angioplasty Using Gadopentetate Dimeglumine as a Contrast Agent / 대한신장학회잡지

With the increasing number of interventional angiographic procedures, iodinated contrast induced nephropathy has become an important cause of iatrogenic acute renal failure. Gadopentetate dimeglumine, gadolinium chelated by DTPA, are widely used in magnetic resonance imaging without adverse effect on renal function in patients with renal insufficiency. It also has sufficient radiographic density to allow visualization and has been described as an alternative contrast agent for angiography. Here we report a case of successful angioplasty using gadopentetate dimeglumine as a contrast agent in a patient with both renal artery stenosis and renal insufficiency. The patient had a history of iodinated contrast induced acute renal failure. Using this contrast agent, angioplasty was successfully performed and contrast induced acute renal failure did not occur after this procedure.

Right Common Iliac Artery Thrombosis and Aortic Artery Thrombosis Associated with Renal Infarction in Adult Minimal Change Nephrotic Syndrome / 대한신장학회잡지

The nephrotic syndrome frequently causes a hypercoagulable state, leading to thromboembolic complications in veins, but arterial thrombosis is relatively rare, and is usually associated with a poor prognosis. We report 50-year-old female patient who presented with minimal change disease complicated with aortic and right iliac arterial thrombosis. She was admitted to our hospital with severe pain in her right leg and left flank. No pulse was palpable in her right femoral artery. Aortography demonstrated a focal eccentric thrombus attached to the left wall of aorta, in which the left renal artery was occluded, and another thrombus obstructing the right common iliac artery. An emergency thrombectomy was performed. Although the patient had satisfactory reperfusion of right common iliac artery, her left renal function was not recovered. A renal biopsy revealed histologic evidence of minimal change of glomerulonephritis. After 8 weeks of steroid therapy, cytoxan was started. After 3 weeks, she developed pneumonitis and died with sepsis.

Radiologic Placement of Subcutaneous Infusion Ports in Cancer Patients: Analysis of 45 Cases / 대한암학회지

PURPOSE: We undertook this study to evaluate the usefullness of radiologic placement of subcutaneous infusion ports (SIP). MATERIALS AND METHODS: Between August 1999 and May 2000 we performed 45 implantations of SIP in radiologic suite. Both sonography and fluoroscopy were used for venipuncture and to guide port insertion. We prospectively evaluated 45 systems in 45 patients with solid tumors. RESULTS: Median follow-up time was 189 days (61~352 days). Technical success rate is 100% without any venipuncture-related complications. Early complication rate within 30 days of procedure was 4.4%, including wound dehiscence (n=1) and pocket hematoma and local infection (n=1). Catheter-related infection rate was 6.7% and catheter-related venous thrombosis rate was 4.4%. Mean duration of catheter use was 208 96 days (total, 9,381 days). Overall port survival rate was 38.5%, and four systems (8.9%) were prematurely removed because of catheter tunnel infection (n=1), pocket infection (n=1), and central venous thrombosis (n=2). CONCLUSION: Radiologic placement of SIP had higher success rate and equal or lower complication rate compared with reported conventional surgical technique using anatomical landmarks. Moreover, clinical convenience, resulting from ease of scheduling could make it replace surgical method.

Proximal Vein Obstruction or Stenosis Failed to Angioplasty in Hemodialysis Patients: Treatment with Endovascular Stent / 대한신장학회잡지

Although percutaneous angioplasty is effectively used in the treatment of vascular access stenosis in hemodialysis patients, it has low initial success rate and high recurrence rate for proximal vein obstruction or stenosis. We evaluated the effect of endovascular stent placement on the treatment of proximal vein obstruction or stenosis irresponsive to angioplasty in hemodialysis patients. Wallstent was placed in 8 hemodialysis patients with vascular access obstruction or stenosis. All lesions were proximal to a functioning access which had been created one month to 4 years prior to onset of symptoms. Of the total patients, 4 patients had central vein stenosis(2 subclavian, 2 innominate vein stenosis) and they all had a history of subclavian vein catheterization for hemodialysis. Seven patients presented with arm edema, one suffered from needling difficulty. Venography showed complete obstruction in 4 patients and severe stenosis in 4 patients. Angioplasty was attempted before stent placement but failed in all patients. The stent placement initially succeeded in all patients. There were no acute complications such as stent displacement, sepsis, and bleeding. After this intervention, clinical symptoms disappeared and all patients could be immediately treated with hemodialysis via corrected access. The patients were followed for 8.0+/-4.6 months (3-16 months). During this period, restenosis occurred in 2 patients. Of the 2 patients, one patient was successfully treated with angioplasty. In conclusion, endovascular stent placement seems to be effective on the treatment of proximal vein obstruction or stenosis irresponsive to angioplasty in hemodialysis patients.

The effect of percutaneous angioplasty on the treatment of poor maturation of the native arteriovenous fistula / 대한내과학회지

BACKGROUND: Although percutaneous transluminal angioplasty (PTA) is effective on the treatment of chronic venous stenosis during hemodialysis, its effect on poor maturation of native arteriovenous fistula (AVF) before cannulation is not well known. We evaluated the effect of PTA on the treatment of poor maturation of native AVF before cannulation in hemodialysis patients. METHODS: Venography was performed in 17 patients with poor maturation of native AVF before cannulation. If the stenosis was a 70% or greater decrease in lumen diameter, PTA was performed. RERULTS: The incidence of diabetes mellitus was 70.6% (n=12). Of those patients studied, total occlusion was observed in 3 cases, discrete stenosis in 12 cases, no stenosis with multiple accessory veins in 2 cases. Of the 15 patients with stenosis or total occlusion, 9 had such lesions in the proximal vein and 4 at the AV anastomosis and 2 in the artery. Of thirteen of 15 patients with these lesions who underwent PTA, 12 patients initially had successful dilatation and the follow up patency rate at 6.0+/-5.8 months was 61.5%. Two of the patients with restenosis underwent re-PTA with successful dilatation. CONCLUSION: PTA seems to be effective on the treatment of poor maturation of native AVF before cannulation.