The Powerlink system for endovascular abdominal aortic aneurysm repair: Six-year results

Article Outline

• Abstract
• Methods
  • Trial design
  • Device
  • Patient selection
  • Device sizing/selection/deployment
  • Follow-up evaluation
  • Statistical analysis
• Results
  • Patients and procedures
  • Perioperative morbidity/mortality
  • Late morbidity and mortality
  • Sac dynamics after Powerlink
    • Aneurysm diameter and volume before and after EVAR
  • Sac straightening after Powerlink
  • Explants
• Discussion
• Conclusions
• Author Contributions
• Acknowledgment
• Tables (online only). 
• References
• Copyright

Objective

We compared the results of endovascular repair using the Powerlink endovascular graft with conventional open abdominal aortic aneurysm repair through a 6-year follow-up period.

Methods

Two hundred fifty-eight patients with abdominal aortic aneurysms were prospectively enrolled in a multicenter trial and underwent endovascular repair (N = 192) or conventional open surgery (N = 66). All endovascular repairs were approached through a surgically exposed femoral artery and a percutaneously accessed femoral artery. Study endpoints included all-cause mortality and morbidity. Follow-up imaging consisted of contrast-enhanced CT scans and plain abdominal x-rays at 1, 6, 12 months, and annually postoperatively.

Results

Technical success was achieved in 97.9% of test patients, with four failed insertions (three early conversions because of deployment issues, one access failure). Mean follow-up was 4.1 ± 1.7 years (test group) and 3.1 ± 1.9 years (control group). Perioperative morbidity and mortality were significantly reduced in the test group compared with the control group (P < .05). At 6 years, all-cause mortality and morbidity was no different in the Powerlink group compared with the open repair group. There were no reported stent fractures, graft disruptions, or aneurysm ruptures. Core laboratory-reported endoleaks included proximal or distal type I (n = 1) and type I/II (n = 3), with no type III or type IV endoleaks. One explant (0.5%) was undertaken to resolve a refractory type I endoleak. A total of 37 secondary procedures were performed in 26 patients to treat site-reported endoleak (n = 26; 7 for type I and 19 for type II), graft limb occlusion (n = 7), native artery occlusion (n = 3), or endograft migration (n = 1). A reduction in mean aneurysm sac diameters and volumes has been noted at every follow-up interval.

Conclusion

Consistent with other reports, perioperative morbidity and mortality were significantly reduced in the endovascular group compared with the open repair group. Six-year follow-up of patients treated with the Powerlink system demonstrates the continued safety and efficacy of its treatment of abdominal aortic aneurysm.

The Powerlink device is a unibody bifurcated endovascular graft utilized for repair of abdominal aortic aneurysms. Delivery is achieved through one surgically exposed femoral artery. The safety and efficacy of this device at early and intermediate time points have previously been reported.¹, ² We now report our experience with this device over a long-term follow-up interval.

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Methods 

Trial design 

A prospective nonrandomized concurrently controlled trial of the safety and efficacy of the Endologix Powerlink bifurcated system was conducted at 15 centers according to US Food and Drug Administration guidelines. The Powerlink trial enrolled patients between July 18, 2000 and March 31, 2003 and followed them over a 72-month period. Mean follow-up was 4.1 ± 1.7 years (test group) and 3.1 ± 1.9 years (control group). Comparisons were made between the endovascular and open AAA repair groups regarding perioperative and delayed mortality as well as morbidity defined as a major adverse event.

Device 

The Powerlink system is a unibody bifurcated self-expanding fully stented endovascular graft. The endoskeleton is a continuous cobalt-chromium wire woven into a double spine without sutures or welds. The endoskeleton is covered with graft material made of expanded polytetrafluoroethylene (ePTFE). During the trial, the device was supplied in two neck diameters (25 mm, 28 mm) and two lengths (135 mm, 155 mm), although other sizes are currently commercially available. The limbs of the bifurcated stent graft are 16 mm in diameter. The delivery sheath has a 21F outer diameter and a tapered tip. Both proximal and distal extension cuffs were available with diameters of 16, 20, 25, and 28 mm.

Patient selection 

Patients with nonruptured infrarenal aortoiliac aneurysms were eligible for enrollment. There were 471 patients screened, out of which 258 were enrolled in the study (192 test, 66 controls). All patients underwent CT angiography with three-dimensional reconstruction to determine anatomic suitability for enrollment. Scans were analyzed by the core laboratory (M2S, West Lebanon, NH). Control and test patients met the same inclusion and exclusion criteria with additional vascular anatomic criteria required for Powerlink test patients. Eligibility for endovascular repair was dependent on specific anatomic criteria felt to be met by the operating surgeon (Table I, online only). An infrarenal aortic clamp site was required in the open repair group.

Device sizing/selection/deployment 

Preoperative measurements of aneurysm neck diameter and distance from lowest renal artery to aortic bifurcation and hypogastric arteries were performed to determine the appropriate diameter and length of the endograft. The graft diameter was determined by oversizing the graft 10% to 20% with respect to measured neck diameter. Graft length was chosen so as to preserve at least one hypogastric artery. Aneurysm volume was calculated according to M2S protocol. Using axial slices, the first slice below the lowest renal artery, and the last slice above the origin of the right internal iliac artery were marked as the proximal and distal extent of volume calculation. The Powerlink may be deployed at the level of the renal arteries or seated on the aortic bifurcation (anatomic fixation). The latter method most often requires the placement of a proximal aortic cuff in order to achieve a proximal infrarenal seal. Investigators were allowed to deploy the graft in either manner.

Follow-up evaluation 

Abdominal four-view x-ray studies (anteroposterior, lateral, left and right anterior oblique) were performed at device implantation as well as prior to hospital discharge. Physical examination, x-ray and computed tomography (CT) angiography were performed at 1, 6, 12 months and annually thereafter. Graft integrity, migration, wire fracture, presence of endoleak, and aneurysm size were evaluated. These studies were evaluated by each local site and independently by the central core laboratory.

Statistical analysis 

Baseline continuous variables were compared with the Wilcoxon rank sum test and categorical variables were compared with the Fisher exact test. Kaplan-Meier survival estimates were used to analyze rates of mortality and major adverse events through the 6-year follow-up period. Groups were compared using the log rank statistic. Endoleak and aneurysm size data are presented descriptively. Changes in aneurysm diameter or volume over time were analyzed with a paired t test. Early and late major adverse events are presented descriptively. Proportions of patients with events are compared between groups using Fisher exact test. Statistical significance is considered for P values less than .05. All statistical analyses were performed using SAS software version 8.2 (SAS Institute, Cary, NC).

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Results 

Patients and procedures 

The Powerlink trial enrolled 258 patients (192 test, 66 control). Patient and aneurysm characteristics are shown in Table II. Test patients were significantly older than patients in the control group, but did not differ significantly with respect to gender distribution or medical comorbidities. The aneurysms in the test group were significantly smaller than those in the control group (51.0 ± 6.6 vs 58.0 ± 11.6 mm, P < .0001). Renal to bifurcation length was shorter in the test group compared with the control group (113.3 ± 17.1 vs 122.8 ± 24.8 mm, P < .0009). Proximal neck diameter was smaller (22.4 ± 2.3 vs 26.0 ± 4.7 mm, P < .0001) and neck length was longer 29.3 ± 11.3 vs 18.4 ± 19.7, P < .0001) in the test group compared with the control group.

Table II. Patient and aneurysm characteristics in Powerlink and control groups

Characteristic	Powerlink (N = 192)	Control (N = 66)	P->value
Male	170(88%)	57(86%)	.6627
Female	22(11%)	9(14%)	.6627
Average age	73(52–88)	69(56–83)	.0008
Coronary artery disease	88(46%)	39(59%)	.0657
Congestive heart failure	13(7%)	2(3.0%)	.3675
Arrhythmia	31(16%)	5(7.6%)	.1002
Valvular heart disease	7(3.7%)	5(7.6%)	.1911
Recent (<6 mo.) MI	4(2.1%)	3(4.6%)	.3767
Prior (>6 mo.) MI	47(24%)	19(28.8%)	.5149
Angina	25(13%)	8(12%)	1.0000
Prior CABG	54(28%)	20(30%)	.3675
Prior PTCA	25(13%)	12(18%)	.3127
Valve replacement	5(2.6%)	1(1.5%)	1.0000
Pulmonary disease	61(31.8%)	16(24.2%)	.2779
Diabetes mellitus	25(13.1%)	12(18.2%)	.3142
Hypertension	122(64%)	46(70%)	.4541
Smoking history	159(82.8%)	57(86%)	.5667
Peripheral vascular disease	32(17%)	10(15%)	.8488
Cerebrovascular disease	38(19.8%)	10(15%)	.4668
Liver disease	8(4.2%)	1(1.5%)	.4549
Prior abdominal surgery	91(47.4%)	25(37.8%)	.1987

Characteristic	Powerlink mean (SD) N Median (Min, Max)	Control mean (SD) N Median (Min, Max)	P-value
Distal neck diameter (mm)	22.0(6.3)173a	29.5(20.4)46a	.0008
	22.0(0.0,48.0)	25.2(0.0,146.0)
Distal non-aneurysmal Right iliac diameter (mm)	12.3(2.3)186b	19.1(25.7)50b	.0012
	12.0(8.0,25.0)	13.1(1.4,169.4)
Distal non-aneurysmal Left Iliac diameter (mm)	12.1(1.8)184c	16.2(14.3)49c	.0001
	12.0(8.0,18.0)	13.8(1.7,105.0)
Distal non-aneurysmal Proximal neck diameter (mm)	23.5(2.8)184d	27.4(4.7)51d	<.0001
	24.0(17.0,42.0)	27.0(18.0,40.0)
Left distal seal zone (mm)	45.5(19.0)182e	38.8(23.7)44e	.0866
	45.0(0.0,100.0)	39.6(0.0,75.0)
Renal to bifurcation length (mm)	113.3(17.1)185f	122.8(24.8)47f	.0009
	110.0(55.0,198.0)	122.0(35.0,180.0)
Maximum aneurysm Diameter (mm)	51.0(6.6)188g	58.0(11.6)58g	<.0001
	50.0(40.0,74.0)	55.0(37.0,98.0)
Proximal seal zone length (mm)	29.3(11.3)184h	18.4(19.7)49h	<.0001
	27.0(7.9,70.0)	13.9(0.0,127.0)
Proximal non-aneurysmal Left iliac diameter(mm)	12.4(1.9)183i	15.7(7.5)50i	.0002
	12.0(8.5,18.0)	14.0(5.5,52.0)
Proximal non-aneurysmal Right iliac diameter (mm)	12.7(2.4)182j	15.9(5.8)51j	.0002
	12.1(8.0,25.0)	14.0(5.5,37.0)
Non-aneurysmal proximal Neck diameter (mm)	22.4(2.3)188k	26.0(4.7)55k	<.0001
	22.0(18.0,26.0)	25.5(17.1,40.0)
Right distal seal zone Length (mm)	49.1(36.5)181l	38.6(34.7)42l	.0011
	45.4(0.0,425.0)	30.0(0.0,190.0)

Technical success was achieved in 188 patients in the test group (97.9%). Endovascular repairs were performed with the patient under general anesthesia (n = 129, 67.2%), regional anesthesia (22, 11.5%), or local anesthesia (41, 21.4%).

The devices used are listed in Table III, online only. Proximal cuffs (n = 89, all 28 mm) were required in 79 patients (42%). Distal extensions (n = 29) were used in 25 patients (13.3%). Cuffs were placed intraoperatively to obtain proximal seal in 55 patients (62 cuffs). An additional 24 patients received 27 cuffs to accommodate a wide range of patient anatomic features in an attempt to reduce the incidence of endoleaks.

Mean blood loss and operative time were significantly less in the Powerlink group compared with the control group (341 mL vs 1583 mL, P < .0001; 136 minutes vs 222 minutes, P < .0001). Mean hospital length of stay as well as days in intensive care unit (ICU) were significantly shorter in the test group compared with the control group (3.3 days vs 9.5 days, P < .0001), and (0.78 days vs 4.1 days, P < .0001).

There were three intraoperative conversions to open repair, all resulting from failed device deployment. In one patient, early in the study, a delivery catheter limb sheath problem prevented device deployment and necessitated open conversion. This catheter problem was rectified with a minor change to the delivery catheter design and was not subsequently observed. Another conversion was done in a patient who demonstrated bleeding from the left external iliac artery after deployment of the device. Upon opening, a tear in the external iliac artery remote from the device was noted, which was attributed to injury from a catheter or wire. The remaining conversion was performed because of premature deployment of the ipsilateral limb before positioning within the iliac artery, attributable to user inexperience. There was also one access failure secondary to iliac disease on the cutdown side that prevented advancement of the device into the aorta. This patient later underwent placement of a commercially available device. There was one explant at 13 months with conversion to open repair to attempt to resolve a refractory type I endoleak.

Perioperative morbidity/mortality 

The overall incidence of serious adverse events was significantly reduced in the Powerlink group compared with the control group (25% vs 42%, P < .0075). There were significantly less cardiac (P < .0375), gastrointestinal (P < .0199), infectious (P < .0042), pulmonary (P < .0002), and renal (P < .0042) complications in the Powerlink group compared with the control group at 30 days. Results summarized in Table IV.

Table IV. Comparison of perioperative (within 30 days) complications in test and control groups. (P < .05 between Powerlink and control groups marked in bold.)

Serious adverse event/complication	Powerlinka n/N (%)	Controla n/N (%)	P value
Patients experiencing at least one serious AE	47/192(24.48)	28/66(42.42)	.0075
Access failure	1/192(0.52)	—	—
Anemia	1/192(0.52)	2/66(3.03)	.1618
Bleeding	4/192(2.08)	4/66(6.06)	.2091
Cardiac disorders	16/192(8.33)	12/66(18.18)	.0375
Coagulation	1/192(0.52)	0/66(0.00)	1.0000
Conversion	3/192(1.56)	—	—
Death	2/192(1.04)	4/66(6.06)	.0389
Delivery failure	1/192(0.52)	0/66(0.00)	1.0000
Device kink	0/192(0.52)	—	—
Endoleak	4/192(2.08)	—	—
Gastrointestinal or bowel disorders	4/192(2.08)	6/66(9.09)	.0199
Graft occlusion	1/192(0.52)	1/66(1.52)	.4469
Graft thrombosis	0/192(0.00)	1/66(1.52)	.2558
Hepatobiliary disorders	1/192(0.52)	2/66(3.03)	.1618
Infections and infestations	2/192(1.04)	6/66(9.09)	.0042
Metabolic/nutritional	1/192(0.52)	1/66(1.52)	.4469
Multi-organ failure	0/192(0.00)	1/66(1.52)	.2558
Musculo/skeletal	1/192(0.52)	0/66(0.00)	1.0000
Neoplasms	5/192(2.60)	2/66(3.03)	1.0000
Neurological disorders	2/192(1.04)	1/66(1.52)	1.0000
Otherb	6/192(3.13)	6/66(9.09)	.0821
Pain	4/192(2.08)	0/66(0.00)	.5750
Pulmonary	5/192(2.60)	11/66(16.67)	.0002
Renal disorders	2/192(1.04)	6/66(7.58)	.0042
Respiratory	0/192(0.00)	1/66(1.52)	.2558
Sepsis	0/192(0.00)	2/66(3.03)	.0647
Supplemental procedure	5/192(2.08)	0/66(0.00)	.3328
Thrombocytopenia	0/192(0.00)	1/66(1.52)	.2558
Vascular disorders	19/192(9.90)	8/66(12.12)	.6428
Wound	1/192(0.52)	2/66(3.03)	.1618

All-cause mortality was decreased in the Powerlink group (1.0% vs 6.1%, P < .0389). There were two deaths in the test group. One patient developed internal bleeding and suffered a myocardial infarction and cardiac arrest on postoperative day one. An autopsy was declined by the family and the etiology of the bleeding was thus not confirmed. The other patient died of a myocardial infarction during an emergency thoracic stent graft procedure nine days after the index procedure. There were four deaths in the control group. One died of hemorrhagic shock, one died of massive pulmonary embolism, and two patients developed multisystem organ failure 2 to 3 weeks postoperatively.

Late morbidity and mortality 

Patients were followed for a mean of 49 months (median, 53 months; range, 0.03-81 months). Follow-up data are summarized in Table V, online only. There was no statistically significant difference in all-cause mortality between the test and control groups (21.9% vs 19.7%, P =.8618), see Fig 1; data in Table IX, online only. There were no aneurysm ruptures and only one late conversion to open repair in the test group. This patient initially underwent placement of a bifurcated device and a proximal cuff. A type I endoleak was detected at 1 month, which was initially managed conservatively, then intervened upon at 13 months. The surgeon placed two infrarenal cuffs as well as a suprarenal cuff to treat what appeared to be caudal cuff migration. Ballooning in the region of the four overlapped cuffs resulted in aortic rupture and immediate surgical conversion, although the patient expired from hemorrhage. There was no difference in freedom from abdominal aortic aneurysm (AAA) mortality between the two groups (P = .1001), see Fig 2; data in Table X, online only. There were no aneurysm-related deaths in the control group beyond 6 months and none in the test group beyond 13 months. Freedom from AAA-related mortality in the test group was 97.9%. Freedom from device-related re-hospitalization at 60 months was 83.1%, see Fig 3; data in Table XI, online only. There was no difference in freedom from major adverse events between the test and control groups (P = .5251), see Fig 4; data in Table XII, online only.

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• Fig 1. 

  The Kaplan-Meier survival curves for the Powerlink and control groups are presented in the figure below. The log-rank test was not statistically significant with P = .5065. The observed survival rates and 95% confidence limits of the rates are presented in Table IX.

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• Fig 2. 

  Kaplan-Meier AAA-related survival curves for Powerlink and control groups through 72 months.

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• Fig 3. 

  Kaplan-Meier curve of freedom from device-related hospitalization in Powerlink group.

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• Fig 4. 

  Kaplan-Meier curve of freedom from major adverse events through 72 months in Powerlink and control groups. The log-rank test of the difference in freedom from major adverse event curves between the two treatment groups was not statistically significant (P =.5251).

At the 72-month follow-up period, there was a 14.3% endoleak rate (see Fig 5; data in Table XIII, online only, and Table VI). There were no type III or IV endoleaks and the majority of endoleaks were type II. Within 30 days, the rate of secondary procedures was 3.1% (6 of 192 test patients), whereas after 30 days, the need for secondary procedures was 10.9% (21 of 192 test patients). Thirty-seven secondary procedures were required in 26 patients; one patient had a secondary procedure peri-operatively followed by another secondary procedure after 30 days. The majority of procedures were performed to treat endoleak (70.3%). There were seven secondary procedures performed in six patients to treat type I endoleak and 19 procedures performed in 13 patients to treat type II endoleak. All type I endoleaks were addressed with additional cuff placement or balloon angioplasty while the majority of type II endoleaks were treated with embolization (89.5%). The range of time to intervention for treatment of endoleaks was broad (2-2081 days), but a greater proportion of patients were treated more than 2 years postoperatively (63.2%).

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• Fig 5. 

  Kaplan Meier analysis of freedom from endoleak through 72 months. The curve terminates at 72 months with detection of last endoleak.

Table VI. Detected endoleaks, subdivided by type, over time (Core Lab)

Endoleak	1 mo N = 123	6 mo N =119	12 mo N =147	24 mo N = 142	36 mo N = 130	48 mo N =119	60 mo N = 90	72 mo N = 35
None	86(77.48)	88(87.13)	112(86.15)	103(89.56)	95(92.23)	85(89.47)	64(86.49)	24(85.71)
All flow	25(22.32)	13(12.87)	18(13.85)	12(10.43)	8(7.78)	10(10.75)	10(13.51)	4(14.29)
Type I	1(0.89)	0(0.00)	0(0.00)	0(0.00)	0(0.00)	0(0.00)	0(0.00)	0(0.00)
Type I and II	2(1.79)	0(0.00)	1(0.77)	0(0.00)	0(0.00)	0(0.00)	0(0.00)	0(0.00)
Type II	20(17.85)	13(12.87)	15(11.54)	10(8.70)	7(6.80)	8(8.60)	8(10.81)	2(7.14)
Type III	0(0.00)	0(0.00)	0(0.00)	0(0.00)	0(0.00)	0(0.00)	0(0.00)	0(0.00)
Type IV	0(0.00)	0(0.00)	0(0.00)	0(0.00)	0(0.00)	0(0.00)	0(0.00)	0(0.00)
Indeterminate	2(1.79)	0(0.00)	2(1.54)	2(1.74)	1(0.97)	2(2.15)	2(2.70)	2(7.14)
Total evaluated	111	101	130	115	103	95	74	28

Graft limb stenosis/occlusion was an infrequent complication, occurring in six patients (6/384 limbs, 1.6%). The range of presentation was 26 to 480 days with the majority presenting within two months postoperatively. Four of the patients exhibited narrowing without occlusion and were successfully treated with angioplasty and stenting. Two of the six patients presented with graft limb occlusion which required a combination of thrombolysis or thrombectomy in addition to angioplasty and stenting to restore luminal flow. In defining anatomical predictors for graft stenosis or occlusion, there was no detectable correlation between tortuosity of iliacs and graft limb occlusion, but 2/6 patients demonstrated severe atherosclerotic narrowing of their iliacs, and 3/6 patients exhibited iliac diameters of <11.0 mm.

There was only one incidence of left femoral pseudoaneurysm from percutaneous access, which was detected 1 month postoperatively and was treated with thrombin injection with resolution documented 2 days later.

The overall major adverse event rate was 41.2% for test patients and 36.4% for controls (P = .5609). The overall serious adverse event rate was 61.5% for test patients and 68.2% for controls (P = .3761). While the percentages of adverse events seem high, the various causes of morbidity were included for completeness sake, and are a reflection of the sick vasculopath population. The more relevant device-related adverse event rate was 13.8%. Results are summarized in Table VII, Table VIII. There were no significant differences between test and control groups with regard to the late incidence of myocardial infarction, renal failure, and respiratory failure, and pulmonary, gastrointestinal, vascular, or bleeding complications. There was no statistically significant difference in all-cause mortality between the test and control groups (21.9% vs 19.7%, P = .8618). Pulmonary complications were most commonly cited as the cause of death in the test group (28.6%) as well as the control group (46.2%) followed by cardiac events (21.4% and 23.1%, respectively). Graft migration was observed in 4.3% of patients over the 72-month period, but only one had clinical sequelae with a secondary procedure (an additional cuff) required. Review of the operative notes revealed that all cases of migration occurred in patients for whom the Powerlink device was implanted at the level of the renal arteries rather than seated on the aortic bifurcation. There have been no stent fractures or ePTFE fabric defects through 6 years.

Table VII. Serious adverse events (SAE) following Powerlink implant through 72 months (n [%])^a

SAE	31 d - 6 mo (N = 190)	6-12 mo (N = 180)	12-24 mo (N = 172)	24-36 mo (N = 158)	36-48 mo (N = 145)	48-60 mo (N = 130)	60-72 mo (N = 118)
Patients experiencing at least one serious AE	37(19)	24(13)	49(28)	32(20)	40(28)	31(24)	12(10)
Anemia	0(0.0)	0(0.0)	0(0.0)	1(0.6)	0(0.0)	1(0.8)	1(0.8)
Bleeding	4(2.1)	0(0.0)	1(0.6)	1(0.6)	0(0.0)	2(1.5)	1(0.8)
Cardiac disorders	8(4.2)	6(3.3)	14(8.1)	8(5.1)	15(10)	6(4.6)	0(0.0)
Coagulation	0(0.0)	0(0.0)	0(0.0)	0(0.0)	0(0.0)	0(0.0)	1(0.8)
Conversion	0(0.0)	1(0.6)	0(0.0)	0(0.0)	0(0.0)	0(0.0)	0(0.0)
Death	6(3.2)	5(2.8)	8(4.6)	5(3.2)	7(4.8)	6(4.6)	3(2.5)
Device migration	1(0.5)	0(0.0)	0(0.0)	0(0.0)	2(1.4)	0(0.0)	0(0.0)
Endoleak	3(1.6)	2(1.1)	3(1.7)	2(1.3)	2(1.4)	0(0.0)	0(0.0)
Eye disorder	0(0.0)	0(0.0)	0(0.0)	0(0.00)	1(0.7)	0(0.0)	0(0.0)
GI or bowel disorders	3(1.6)	0(0.0)	3(1.7)	5(3.2)	4(2.8)	3(2.3)	2(1.7)
Graft occlusion	1(0.5)	1(0.6)	0(0.0)	0(0.0)	0(0.0)	0(0.0)	0(0.0)
Hepatobiliary	0(0.0)	0(0.0)	1(0.6)	1(0.6)	1(0.7)	1(0.8)	0(0.0)
Infections and infestations	4(2.1)	5(2.8)	5(2.9)	4(2.5)	3(2.1)	5(1.5)	2(1.7)
Metabolic/nutritional	0(0.0)	0(0.0)	0(0.0)	0(0.0)	0(0.0)	0(0.0)	1(0.8)
Multi-organ failure	0(0.0)	0(0.0)	2(1.2)	0(0.0)	0(0.0)	0(0.0)	0(0.0)
Musculoskeletal	1(0.5)	1(0.6)	5(2.9)	1(0.6)	1(0.7)	4(3.1)	2(1.7)
Neoplasms	6(3.2)	5(2.8)	6(3.5)	4(2.5)	6(4.1)	2(1.5)	0(0.0)
Neurological disorders	4(2.1)	2(1.1)	3(1.7)	1(0.6)	4(2.8)	4(3.1)	0(0.0)
Other	6(3.2)	4(2.2)	8(4.7)	8(5.1)	4(2.8)	4(3.1)	1(0.8)
Pain	1(0.5)	0(0.0)	5(2.9)	4(2.5)	1(0.7)	2(1.5)	0(0.0)
Pulmonary	3(1.6)	2(1.1)	2(1.2)	8(5.1)	5(3.5)	5(3.9)	1(0.8)
Renal disorders	2(1.1)	1(0.6)	1(0.6)	1(0.6)	1(0.7)	0(0.0)	1(0.8)
Respiratory	0(0.0)	0(0.0)	0(0.0)	0(0.0)	0(0.0)	0(0.0)	1(0.8)
Sepsis	1(0.5)	2(1.1)	0(0.0)	1(0.6)	0(0.0)	1(0.8)	0(0.0)
Supplemental procedure	6(3.2)	4(2.2)	4(2.3)	3(1.9)	1(0.7)	3(2.3)	1(0.8)
Urinary	1(0.5)	0(0.0)	1(0.6)	1(0.6)	0(0.0)	2(1.5)	0(0.0)
Vascular disorders	5(2.6)	6(3.3)	5(2.9)	4(2.5)	8(5.5)	4(3.1)	2(1.7)
Wound	0(0.0)	0(0.0)	1(0.6)	0(0.0)	0(0.0)	0(0.0)	0(0.0)

SAEs are defined as events that result in death, are life-threatening, permanently or severely disabling, require or prolong hospitalization, congenital anomaly, cancer or overdose.

Table VIII. Major adverse events following Powerlink implant through 6 years (n [%])

Major adverse event/complication	≤30 d N = 192	<30 d 12 mo N = 190	<1 to ≤2 y N = 172	<2 to ≤3 y N = 158	<3 to ≤ 4 y N = 145	<4 to ≤ 5 y N = 130	<5 to ≤ 6 y N = 118
Patients experiencing at least one major adverse event	12(6.3)	35(18)	23(13)	14(8.9)	20(14)	12(9.2)	5(4.2)
AAA rupture	0(0.0)	0(0.0)	0(0.0)	0(0.0)	0(0.0)	0(0.0)	0(0.0)
Coronary intervention	0(0.0)	3(1.6)	5(2.9)	3(1.9)	11(7.6)	4(3.1)	0(0.0)
Deathf	2(1.0)	11(5.8)	9(5.2)	7(4.4)	5(3.4)	7(5.4)	3(2.5)
Myocardial infarction	2(1.0)	3(1.6)	5(2.9)	2(1.3)	5(3.4)	0(0.0)	0(0.0)
Renal failure	2(1.0)	4(2.1)	0(0.0)	0(0.0)	0(0.0)	0(0.0)	1(0.8)
Respiratory failure	2(1.0)	2(1.1)a	0(0.0)	0(0.0)	0(0.0)	1(0.8)	0(0.0)
Secondary procedure	6(3.1)	14(7.4) b	5(2.9)c	4(2.5)d	2(1.4)	2(1.5)e	1(0.8)
Stroke	0(0.0)	3(1.6)	2(1.2)	0(0.0)	2(1.4)	2(1.5)	0(0.0)
Transient ischemic attack	0(0.0)	2(1.1)	2(1.2)	0(0.0)	1(0.7)	0(0.0)	0(0.0)
Conversion to open repair	3(1.6)	1(0.5)	0(0.0)	0(0.0)	0(0.0)	0(0.0)	0(0.0)

Sac dynamics after Powerlink 

Preoperative mean AAA diameter in the Powerlink group was 51 mm (range 40-74 mm; P < .0001. Significant mean diameter reduction was observed at each follow-up interval starting at 6 months. At 6 months, the mean AAA diameter was 48.2 mm and at 72 months, the mean AAA diameter was 39.4 mm (Fig 6, A). By 72 months, 82.7% of patients exhibited a decrease in aneurysm diameter ≥5 mm. In contrast, 10.3% (3/29) patients exhibited an increase in sac diameter of >5mm. All sac expansion patients had type II endoleaks documented on CT scan, the majority of which were successfully embolized (67%), and one of which is being managed conservatively.

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• Fig 6. 

  A, Aneurysm sac diameter reduction over time in Powerlink group. Error bars represent standard deviation. B, Aneurysm sac volume reduction over time in Powerlink group. Error bars represent standard deviation.

Preoperative mean AAA volume was 135.4 mL (range 71-271 mL). Significant reduction in AAA volume was noted at each follow-up interval starting at 6 months (131 mL; P < .0023), which persisted through a mean of 72 months (118 mL; P < .006). By 72 months, 78.6% of patients exhibited a 5% or greater decrease in aneurysm volume (Fig 6, B). Conversely, aneurysm volume increase by >5% was noted in 17.2% (5/29) patients.

There was one reported instance of endotension in a patient with enlargement of the aneurysm sac in the absence of identifiable endoleak. This patient was successfully treated with sac aspiration of serous fluid and filling of the sac with glue with subsequent regression of aneurysm.

Sac straightening after Powerlink 

Straightening of the aortic sac was noted in 82.8% (n = 53/64) of patients. Straightening of more than 10 degrees was exhibited in 39.0% (n = 25/64) of patients. Only 17.2% (n = 11/64) of patients exhibited no change or had a slight decrease in sac angle (aorta becoming more angulated). The mean distance between the distal renal and bifurcation increased over time by 3.6% (Fig 7).

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• Fig 7. 

  Aneurysm sac straightening over time. The MMS reconstructions demonstrate a 22.6° sac angle reduction between 1 month and 3 years.

Explants 

A total of three Powerlink devices (1.6%) have been explanted to date; however, only one explant was device-related. This patient was converted to open repair 13 months postoperatively due to a refractory type I endoleak. Two other explants were retrieved at autopsy following patient deaths from cancer and multiple organ failure at 18 and 24 months postprocedure, respectively. In each explant, there was no evidence of stent fracture or corrosion or fabric erosions. Moreover, the degree of device wear was consistent with that observed in preclinical in vitro durability testing.

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Discussion 

A controlled clinical trial was conducted to evaluate the safety and efficacy of using the Powerlink device to treat abdominal aortic aneurysms. The Powerlink group exhibited significantly less perioperative adverse events compared with the control cohort. Long-term follow-up of the test group did not reveal an increase in mortality rate compared with the control group, thus establishing the noninferiority of using the Powerlink device in repairing AAA over a 6-year follow-up period.

The Powerlink system is unique among endovascular aneurysm repair (EVAR) devices in that it only requires one surgically exposed femoral artery for deployment. The contralateral 9F sheath is placed percutaneously. This enables it to be used in patients with one small or diseased iliac system. Anatomic guidelines grading severity of iliac disease have been provided by the Society for Vascular Surgery (SVS)/American Association for Vascular Surgery (AAVS).³ Severe iliac disease has been defined by: >50% calcification of vessel, diameter <7 mm, stenotic diameter <7 mm for >3 cm in length, more than one focal stenosis <7 mm in diameter, tortuosity index >1.6, and iliac angle <90 degrees. These criteria have been proposed to help stratify patients at risk for access failure or endograft limb obstruction. The Powerlink device thus helps to broaden the population of patients that can be treated endovascularly.

Many of the Powerlink procedures were performed under local or regional anesthesia; limiting open surgical exposure of the femoral artery to one side likely facilitated this. The avoidance of having to cannulate the contralateral limb separately also simplifies deployment compared with modular bifurcated systems.

Deployment of the device on top of the aortic bifurcation allows for fixation of the device separate from the infrarenal and iliac seal zones. While attention chiefly has been directed towards proximal endograft fixation using a variety of fixation mechanisms, including suprarenal fixation, radial force, penetrating hooks and barbs, device migration continues to be an issue. The combination of radial forces at the proximal and distal fixation sites in combination with seating the device at the aortic bifurcation allow for positional stability secondary to frictional forces.⁴ Graft migration was observed in 4.2% of patients over the 72-month period, but only one secondary procedure (an additional cuff) was required. The long graft body design enables placement of the graft on the aortic bifurcation, making migration unlikely. Review of the operative notes from the cases of migration revealed that these were all cases in which the Powerlink was placed at the renal arteries rather than on the aortic bifurcation. It is clear that use of anatomic fixation by seating the graft on the aortic bifurcation is the preferred embodiment of the device to prevent migration.

The rate of secondary procedures consisting of additional cuff placement and balloon angioplasty to treat type I endoleak, embolization of type II endoleaks, and reintervention for graft limb stenosis/occlusion was 13.8%. These results are comparable to those in other series employing other commercially available devices.⁵, ⁶, ⁷ The use of adjunctive cuffs was common with the Powerlink device. Forty-one percent (79 out of 192 subjects) had a total of 89 cuffs placed. Placement of the main body on the aortic bifurcation leads to planned placement of a proximal cuff to achieve a proximal seal. The long body of the device (80 or 100 mm) and 75 mm cuffs permit long lengths of overlap, which allow accommodation for a wide range of patient anatomy. Use of a cuff converts the Powerlink from a unibody graft to a modular-type graft. Despite this, no type III endoleaks were observed.

Perioperative comparison of adverse events between Powerlink and control groups mirrored that of other controlled trials of EVAR vs open AAA repair with a significant reduction in ICU use, hospital length of stay, blood loss, and operative time. While the absolute percentages of overall serious adverse events (61.5%) and major adverse events (41.2%) seem high, readers should note the inclusion of various events, which were not included in prior studies,⁸, ⁹ including discovery of neoplasms, metabolic/nutritional disorders, musculoskeletal symptoms, anemia, and pain. The relatively longer-term follow-up also accounts for the greater inclusion of adverse events, ie, myocardial infarction, vascular events, neurologic events, and renal disorders occurring in the vasculopath population. The overall adverse event rate is similarly high in the control group, lending further support to this theory. The overall major adverse event rate was 41.2% for test patients and 36.4% for controls (P = .5609). The overall serious adverse event rate was 61.5% for test patients and 68.2% for controls (P = .3761). The device-related adverse event rate was 13.8%. All-cause and aneurysm-related mortality was not different between the test and control groups.

Endoleaks were the most common adverse event requiring secondary intervention in the Powerlink group. The vast majority of the endoleaks were of type II and only 3.1% of patients required secondary intervention for treatment of type I endoleak. It is important to note that no type III endoleaks developed, despite the use of cuffs in 42% of patients to achieve a proximal seal. There were no type IV endoleaks noted. There have been no reports of late fabric erosion or defects, as have been reported with other devices. At explantation, no evidence of material fatigue was appreciated at 24 months.

There was a very low endotension rate noted with this device, despite its utilization of polytetrafluoroethylene (PTFE) in its design. The Powerlink does not seem to be subject to the same transudative phenomenon that was witnessed with the original Gore Excluder graft, which prompted a change to a lower-permeability fabric.¹⁰

Mean aneurysm diameter and volume were significantly reduced at every examination interval from the first postoperative month up to 60 months. At the 72-month follow-up interval, the mean aneurysm diameter (39.4 mm) and mean aneurysm volume (118 mL) had stabilized and plateaued. A percentage of patients (82.7%) exhibited a decrease in aneurysm diameter of ≥5 mm at 72 months, while 78.6% of patients exhibited a decrease in volume of ≥5% at 72 months. These data demonstrate the successful exclusion of aneurysm sac flow.

There were specific anatomic differences noted between the test and control groups. The aneurysms in the test group were significantly smaller than those treated in the control group. Renal to aortic bifurcation length was shorter, proximal neck diameter was smaller, and proximal neck length was longer in the test group. These very favorable characteristics are a reflection of surgeon compliance to eligibility criteria for the Powerlink graft. In order to be anatomically suitable for the Powerlink endograft, the proximal infrarenal neck diameter had to be smaller than 26 mm and the neck length had to be greater than 15 mm. The test group also included patients with “small” aneurysms in the 4.0 to 5.5 cm range. The excellent long-term results from this study imply that adherence to anatomic criteria leads to successful and durable repair. In addition, there have been numerous reports over the past 5 years positing a relationship between aneurysm diameter and EVAR suitability and long-term outcome. Ouriel et al published a study comparing the outcomes in patients undergoing EVAR who had small (<5.5 cm) vs large (5.5 cm) aneurysms.¹¹ While there was no difference in perioperative mortality between groups, at 24 months, the large aneurysm group had more type I endoleaks, device migration and late conversion to open surgical repair. These results were similar to those published by Zarins et al, who cited a higher risk of rupture, AAA-related death, and surgical conversion in the large aneurysm subset.¹² The EUROpean collaborators on Stent-graft Techniques for abdominal aortic Aneurysm Repair (EUROSTAR) registry, likewise, demonstrated a higher aneurysm-related mortality, type I endoleak rate and rate of surgical conversion in the large aneurysm group.¹³ Taken together, these data imply that patients undergoing EVAR for large AAA may fare worse than those patients with small AAA. Patients with larger aneurysms may also have anatomy that is less amenable to endovascular repair. Rockman et al demonstrated a higher type I endoleak rate, shorter neck length, and greater neck tortuosity in the large aneurysm group.¹⁴ Welborn et al performed an anatomic study, which showed that small AAAs had significantly longer necks, less neck angulation, longer common iliac landing zones, and less aortic tortuosity.¹⁵ The smaller aneurysm diameter in the test group in this study thus may have contributed to the excellent success of endovascular repair.

In contrast to most other endograft devices, the Powerlink cohort demonstrated a straightening rather than an angulation of the aortic aneurysm sac over time. This geometric configuration may prove to be ideal in the avoidance of delayed complications. Harris et al described longitudinal sac foreshortening and subsequent endograft kinking and buckling as a risk factor for graft limb occlusion, endoleak and disruption of modular graft components.¹⁶ Umscheid et al described a mechanism whereby aortic pulsations exert differential axial stresses on the anterior and posterior walls of the graft causing anterior angulation of stent grafts over time and increased risk of endoleak.¹⁷ Perhaps the long-body design and seating of the Powerlink device on the aortic bifurcation prevents foreshortening of the sac and the potential for endograft buckling or endoleak formation. It is clear that the relationship between aneurysm sac and endograft is a dynamic one, and that changes in aneurysm sac configuration are inseparable from translated changes in the endograft device. It would make intuitive sense that an endograft with enough longitudinal flexibility and “recoil” to withstand the repetitive forces of aortic pulsation would maintain a straight-geometrical configuration over time. This in turn would prevent sac shortening and the attendant complications of buckling and kinking. The single-wire woven stent design of the Powerlink serves as a rigid scaffold around which the excluded aneurysm sac can remodel.

Adverse events that have been observed with other EVAR devices have not been observed with the Powerlink. Wire fractures, common in nitinol stent grafts, have not been observed. The Powerlink employs a cobalt chromium alloy stent skeleton woven from a single wire. Also, there has been no fabric erosions related to porosity.

Graft occlusion, which has been reported with other devices, has been uncommon, affecting 3.7% of patients. This is less than the 7.2% rate cited in a recent article assessing predictors for graft limb occlusion.¹⁸ Graft limb occlusions with the Powerlink device have been attributed to extrinsic compression from underlying iliac disease, ie, presence of thrombus or plaque, which is why preliminary angioplasty of the iliac arteries is recommended in this particular subset of patients. Graft limb occlusions also seemed to occur in patients with smaller iliac arteries (<11.0 mm), mirroring the results reported by Carrocio et al.¹⁹ Taken together, these data indicate that patient selection and anatomic evaluation are paramount in considering utilization of any endograft device. The majority of graft limb occlusions were able to be treated endovascularly or locally via thrombectomy rather than with femoral-femoral crossover or extra-anatomic bypass procedures. When graft limb thrombosis occurs, thrombolytic therapy is preferred to catheter thromboembolectomy, as balloon catheter manipulation can be associated with device displacement.

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Conclusions 

The Powerlink device appears to be durable and effective in excluding aneurysm flow and prevention of sac enlargement over a period of long-term follow-up. The graft and stent materials have been free from failure and fatigue. The requirement for only one surgically exposed femoral artery facilitates graft placement in patients with limited access routes and reduces the morbidity of an additional groin wound. The perioperative morbidity and mortality rate is significantly reduced with Powerlink repair compared with open repair of AAA. The overall survival at 72 months was no different between the two groups, indicating that the Powerlink system is just as durable in protecting patients from aneurysm-related death as open repair.

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Author Contributions 

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The authors thank Richard Chiacchierini, PhD, for statistical support.

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Tables (online only) 

Table I, online only. Inclusion and exclusion criteria

Proximal infrarenal neck

≥15 mm length

<60-degree angle

26 mm maximum diameter, 18 mm minimum diameter

AAA ≥4.0 cm diameter or rapidly growing AAA

Iliac diameter ≥7 mm on at least one side

Dispensable inferior mesenteric artery

Preservation of at least one hypogastric artery

Iliac seal zone of ≥1.5 cm

Aortic bifurcation diameter ≥18 mm

No pregnancy

Candidate for open AAA repair

Serum creatinine level ≤1.7 mg/dL

Willingness to comply with follow-up schedule

No bleeding disorders

Life expectancy >2 years

No connective tissue disorders

Table III. online only. Devices implanted and percentage of proximal cuff and distal limb extension usage

Table V, online only. Patient follow-up from 1 to 72 months^a

	Powerlink N = 192
	1 mo	6 mo	12 mo	24 mo	36 mo	48 mo	60 mo	72 mo
No deviceb	1	1	0	0	0	0	0	0
Conversion to open repairc	3	2	3	2	2	1	0	0
Expired	2	8	13	22	29	34	41	42
Withdrawn/lost to follow-up	0	4	7	16	24	29	36	39
Available	190	180	175	158	148	132	102	43
Clinical examination n (%)	135(71.1)	127(70.6)	152(86.9)	151(95.6)	143(96.6)	125(94.7)	82(80.4)	33(76.7)
Site CT imaging n (%)	186(97.9)	171(95.0)	157(89.7)	144(91.1)	133(89.9)	111(84.1)	72(70.6)	28(65.1)
Core Lab CT imaging n (%)	123(64.7)	119(66.1)	147(84.0)	142(89.9)	130(87.8)	119(90.2)	90(88.2)	35(81.4)
Site KUB imaging n (%)	114(60.0)	107(59.4)	136(77.7)	132(83.5)	115(77.7)	101(76.5)	68(66.7)	23(53.5)
Core Lab KUB imaging n (%)	114(60.0)	107(59.4)	136(77.7)	132(83.5)	115(77.7)	101(76.5)	68(66.7)	23(53.5)
Site evaluated for endoleak	186(97.9)	171(95.0)	157(89.7)	144(91.1)	133(89.9)	111(84.1)	72(70.6)	28(65.1)
Core Lab evaluated for endoleak	111(58.4)	101(56.1)	129(73.7)	115(72.9)	103(69.6)	95(72.0)	74(72.5)	28(65.1)
Site evaluated for aneurysm enlargement	n/a	82(45.6)	100(57.1)	102(64.6)	96(64.9)	88(66.7)	59(57.8)	27(62.8)
Core Lab evaluated for aneurysm enlargement	n/a	85(47.2)	102(58.3)	101(63.9)	95(64.1)	89(67.4)	64(62.7)	29(67.4)

Table IX, online only. Survival estimates and 95% confidence limits through 72 months for Powerlink and control groups

Table X, online only. AAA related survival estimates and 95% confidence limits through 72 months for Powerlink and controls

Table XI, online only. Estimated rates of freedoms from device related secondary procedures through 72 months

Table XII, online only. Estimated rates of freedoms from major adverse event through 72 months

^bMajor adverse events include myocardial infarction within 30 days; coronary intervention within 30 days; respiratory failure between 24 hours and 30 days; aneurysm rupture; kidney failure; additional procedures; conversion to open surgical repair; stroke; or death.

Table XIII, online only. Estimated rates of freedom from endoleak through 72 months

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References 

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