Sizing of Crimped Dacron Crafts John
D.S. Reid, MD, FRCSC,FACS, Joseph G. Sladen, MD,
Tbe aim of this study was to correlate the stated size of Dacron grafts (Microvel) with their actual internal diameter and to compare this with measurements by ultrasound in the early postoperative period. Grafts of stated diameters of 7,8,9, and 10 mm were studied. Crafts were measmed by graded the width of the longituprobes and by measur@ dinally opened graft and calculating the diameter. Eachgraftacceptedaprobe1mmlargertha.nits stated sizevery easilyand 2 mm greater when stretched. By open measutemen Z the grafts were 1.3 to 1.8 mm greater than their stated diameter without stretching. Twenty grafts were studied by duplex ultrasound for diameter and peak systolic velocity witbin 3 months of implantation. The grafts were 1% larger than their stated graft size. Some of the larger grafts showed low velocity and wall tbrombus. We conclude that Microvel grafts are larger than their stated diameter. Tbe same sire discrepancy was seen in in uitro measure ments of Vascutek (Dacron) grafts but not in polytetrafluoroethylene (Cortex) grafts. Since flow velocity is related to tbe diameter of the graf& tbis information should be useful when choosing the diameter of a prosthetic vascular graft.
FRCSC,
Vancouver, British Columbia, Canada
acron grafts are known to dilate after implantation D [1,2] and may become frankly aneurysmal. However, we suspected that early “dilation” could be, in part, related to discrepancies between the size stated by the manufacturer and the actual diameter. The purpose of this study was to quantify these differences in graft diameters to aid in the choice of graft size. MATERIALS AND METHODS Knitted, double-velour, collagen-impregnated Dacron grafts (Microvel, Meadox Inc., Oakland, NJ) of stated sixes 7,8,9, and 10 mm diameter were measured in vitro and in vim Two samples of each graft were opened, and their circumferences were measured directly. Measurements were made using a metal ruler under 2.5 times loupe magnification to the nearest mm (‘t 0.5 mm). In no case was there a discrepancy in size measurement between the two samples. During measurement, the grafts were flattened and not stretched. A theoretical graft diameter could then be computed to the nearest 0.1 mm, eliminating the effect of graft crimping that is a feature of the manufacturing process. Grafts of stated size 7,8,9, and 10 mm were measured with graded probes to establish the actual size of the crimped graft when exposed to gentle pressure. The probes were measured by micrometer to confirm their Sizes.
Twenty grafts, chosen at random, were measured by ultrasound using a color flow duplex (model 128, Acuson, Mountainview, CA) within 3 months of implantation. The manufacturer reports an error of 0.5 mm in measurement. Initial measurement was confiied by two inde pendent reviewers, and the results were compared with the stated graft size using a oneway Student’s r-test for matched pairs. Circumferential and probe measurements of Vascutek (Inchinnan, Renfewshire, Scotland) 8-mm Dacron grafts and of 8-mm polytetrafluoroethylene (FTFE) (Gortex, Gore Inc., Flagstaff, AZ) grafts were also made.
From the Divkian of Vascular Surgery, Univmity d British Columbia, and St. Paul’s Hospital, Vancouver, British Cdumbia, Canada. RcqmtsfornqxinbhouldbcaddrcadtoJohnD.S.Reid,MD. 606-1160 Bumud Sbwt, Vanamu, Britiih Cahmth, V6Z 2E8, Canada. PrcamtaJ at the 78th Annual Mating of the North Pacific Sqical Aswciation, hdand, Orc~on, Novanbcr 8-9.199 I.
RESULTS Measurement of the graft circumference produced calculated diameters larger than the stated graft size for Microvel and Vascutek grafts. The FTFE (Gortex) graft calculated diameter equaled the stated size (Table I). Microvel and Vascutek grafts accepted a surgical probe 1 mm larger than their stated size easily with only flattening of the crimping. Probes 2 mm larger were introduced with minimal graft stretching, and, in the 9mm Microvel grafts, a probe 3 mm larger could be intro duced (Ffgpes 1,2, and 3). This phenomenon was not seen with 8-mm FTFE (Gortex) grafts, which did not accept probes larger than theii stated size.
THE AMERICAN JOURNAL OF SURGERY
VOLUME 163 MAY 1992
541
TABLE I Calculated Diameter of Gmfts Circumference Graft
(mm) (*OS mm)
Dacron Microvel 7mm 9mm 9mm 1Omm Vascutek 0mm PTFE Gortex 9mm
Calculated Diameter (mm)
Calculated Error
29 29 33 37
9.3 9.2 10.5 11.8
(8.1-9.4) (9.1-9.4) (10.3-10.7) (11.6-11.9)
29
9.2
(9.1-9.4)
25
9.0
(7.a9.1)
Pl?=E-~wXoethylens.
542
THE AMERICAN
JOURNAL
OF SURGERY
VOLUME
Ultrasound measurements of grafts within 3 months of implantation showed grafts that were on average 12% larger than their stated size (p >O.OOS)(TabIe II). Wall thrombi and low peak systolic velocities (below 45 cm/set) were seen in some grafts. COMMENTS There is ample evidence that knitted Dacron grafts can enlarge over time [I -6j. Failme of the Dacron fiber is suggested as the cause of local dilations and graft holes [7-91, whereas loosening of the knit is thought to be responsible for generalized graft dilations [IO]. We had noted a combination of wall thrombi in some Dacron grafts associated with low peak systolic velocities on duplex scanning follow-up. In other grafts, the low velocity was associated with a large graft diameter on early follow-up. Wall thrombi were probably the result of extremely slow laminar flow at the graft-blood interface.
163
MAY 1992
When we examined Dacron grafts prior to implantation, it was obvious that the graft could easily accept a larger probe than the stated graft size. The aim of this study was to correlate the stated size of Dacron grafts with the actual internal diameter and to compare this with measurements by ultrasound during the early postoperative period. The finding that Dacron grafts will easily accommodate probes of a larger size than their stated diameter was confiled by the finding that 7- to lo-mm grafts have calculated diameters that are 1.3 to 1.8 mm larger when they are opened and measured circumferentially. This overcomes the effect of graft crimping on size. Whereas these findings were similar in Vascutek Dacron grafts, there did not appear to be a size discrepancy in PTFE (Gortex) grafts. Ultrasound measurements demonstrate that newly implanted grafts are 12% or about 1 mm larger, than stated. Knitted Dacron grafts can be expected to dilate 15% to 20% [2,9]. However, we suggest that at least 12% of this “dilation” can be attributed to differences between the stated and actual size of the graft. On some grafts, the ominous finding of low peak systolic velocity on duplex ultrasound measurement may suggest a graft at risk for early failure. This association has been demonstrated for vein grafts whose peak systolic velocities fall below 45 cm/set [21,I 21. In Dacron grafts, with a marginal distal vascular bed for outflow, precise sizing of grafts may be of importance. In choosing the diameter of a Dacron graft, it may be useful to select a graft size that will maintain an adequate velocity. Knowledge of the size discrepancy in crimped Dacron grafts should be useful in making this choice. REFERENCES 1. Cook PA, Nobis PA, Stoney RJ. Dacron aortic graft failure. Arch Surg 1974; 108: 101-3. 2. Nunn DB, Freeman MH, Hudgins PC. Postoperative alterations in size of Dacron aortic grafts. Ann Surg 1979; 189: 741-4. 3. Ottinger LW, Darling RC, Wirthlin LS, Linton RR. Failure of ultralightweight knitted Dacron grafts in arterial reconstruction. Arch Surg 1976; 111: 146-9. 4. Nucho RC, Gryboski WA. Aneurysms of a double velour aortic graft. Arch Surg 1984; 119: 1182-4. 5. Tutassaura H, Gerein AN, Sladen JG. True aneurysms in prosthetic femoropopliteal grafts. Am Surg 1978; 44: 262-6. 6. Kim GE, Imparato AM, Nathan I, Riles TS. Dilation of synthetic grafts and junctional aneurysms. Arch Surg 1979; 114:
TABLE II Ultrasound Measurement of Crimped Dacron Grafts*
Grafls
Stated Size (mm)
Ultrasound Size (mm)
7.0 7.0 7.0 8.0 7.0 7.0 8.0 7.0 7.0 7.0 8.0 9.0 7.0 8.0
8.0 7.6 8.0 9.0 7.7 7.0 8.0 7.0 7.0 7.0 9.9 10.8 8.0 8.0 10.7 6.5 9.0 8.0 8.0 10.0
FP FP FP FP FP FP FP FP FP FP AF AF AF AF FxF FxF FxF FxF FxF FxF
10.0
8.0 10.0 8.0 8.0 10.0
FP = femoral-popliieal; ‘Mean ultrasound
stated
graft
Low velocity
Low velocity
Low velocity, wall thrombus Low velocity Low velocity Wall thrombus
AF = aolto-femoral; size:
7.9
mm.
Comments
Mean
FxF = femoral-femoral difference
crossover.
in measurement:
by
0.9 mm t (df = 19) = 9.105 (p > O.M)5).
1296-303. 7. Berger K, Sauvage LR. Late fiber deterioration in Dacron arterial grafts. Ann Surg 1981; 193: 477-91. 8. Watanabe T, Kusaba A, Kuma H, Kina M, Gradome K, Inokuchi K. Failure of Dacron arterial prostheses caused by structural defects. J Cardiovasc Surg 1983; 24: 95-100. 9. Sladen JG, Gerein AN, Miyagishima RT. Late rupture of prosthetic aortic grafts-presentation and management. Am J Surg 1987; 153: 453-8. 10. Clagett GP, Salander JM, Eddleman WL, et al. Dilation of knitted Dacron aortic pros&es and anastomotic false aneurysms: etiologic considerations. Surgery 1983; 93: 9-16. 11. Bandyk DF, Cato RF, Towne JB. A low flow velocity predicts failure of femoropopliteal and femorotibial bypass grafts. Surgery 1985; 98: 799-809. 12. Sladen JG, Reid JDS, Cooperberg PL, et al. Color flow duplex screening of infiainguinaf grafts combining low- and high-velocity criteria. Am J Surg 1989; 158: 107-12.
THE AMERICAN JOURNAL OF SURGERY
VOLUME 163 MAY 1992 543
D.S. Reid, MD, FRCSC,FACS, Joseph G. Sladen, MD,
Tbe aim of this study was to correlate the stated size of Dacron grafts (Microvel) with their actual internal diameter and to compare this with measurements by ultrasound in the early postoperative period. Grafts of stated diameters of 7,8,9, and 10 mm were studied. Crafts were measmed by graded the width of the longituprobes and by measur@ dinally opened graft and calculating the diameter. Eachgraftacceptedaprobe1mmlargertha.nits stated sizevery easilyand 2 mm greater when stretched. By open measutemen Z the grafts were 1.3 to 1.8 mm greater than their stated diameter without stretching. Twenty grafts were studied by duplex ultrasound for diameter and peak systolic velocity witbin 3 months of implantation. The grafts were 1% larger than their stated graft size. Some of the larger grafts showed low velocity and wall tbrombus. We conclude that Microvel grafts are larger than their stated diameter. Tbe same sire discrepancy was seen in in uitro measure ments of Vascutek (Dacron) grafts but not in polytetrafluoroethylene (Cortex) grafts. Since flow velocity is related to tbe diameter of the graf& tbis information should be useful when choosing the diameter of a prosthetic vascular graft.
FRCSC,
Vancouver, British Columbia, Canada
acron grafts are known to dilate after implantation D [1,2] and may become frankly aneurysmal. However, we suspected that early “dilation” could be, in part, related to discrepancies between the size stated by the manufacturer and the actual diameter. The purpose of this study was to quantify these differences in graft diameters to aid in the choice of graft size. MATERIALS AND METHODS Knitted, double-velour, collagen-impregnated Dacron grafts (Microvel, Meadox Inc., Oakland, NJ) of stated sixes 7,8,9, and 10 mm diameter were measured in vitro and in vim Two samples of each graft were opened, and their circumferences were measured directly. Measurements were made using a metal ruler under 2.5 times loupe magnification to the nearest mm (‘t 0.5 mm). In no case was there a discrepancy in size measurement between the two samples. During measurement, the grafts were flattened and not stretched. A theoretical graft diameter could then be computed to the nearest 0.1 mm, eliminating the effect of graft crimping that is a feature of the manufacturing process. Grafts of stated size 7,8,9, and 10 mm were measured with graded probes to establish the actual size of the crimped graft when exposed to gentle pressure. The probes were measured by micrometer to confirm their Sizes.
Twenty grafts, chosen at random, were measured by ultrasound using a color flow duplex (model 128, Acuson, Mountainview, CA) within 3 months of implantation. The manufacturer reports an error of 0.5 mm in measurement. Initial measurement was confiied by two inde pendent reviewers, and the results were compared with the stated graft size using a oneway Student’s r-test for matched pairs. Circumferential and probe measurements of Vascutek (Inchinnan, Renfewshire, Scotland) 8-mm Dacron grafts and of 8-mm polytetrafluoroethylene (FTFE) (Gortex, Gore Inc., Flagstaff, AZ) grafts were also made.
From the Divkian of Vascular Surgery, Univmity d British Columbia, and St. Paul’s Hospital, Vancouver, British Cdumbia, Canada. RcqmtsfornqxinbhouldbcaddrcadtoJohnD.S.Reid,MD. 606-1160 Bumud Sbwt, Vanamu, Britiih Cahmth, V6Z 2E8, Canada. PrcamtaJ at the 78th Annual Mating of the North Pacific Sqical Aswciation, hdand, Orc~on, Novanbcr 8-9.199 I.
RESULTS Measurement of the graft circumference produced calculated diameters larger than the stated graft size for Microvel and Vascutek grafts. The FTFE (Gortex) graft calculated diameter equaled the stated size (Table I). Microvel and Vascutek grafts accepted a surgical probe 1 mm larger than their stated size easily with only flattening of the crimping. Probes 2 mm larger were introduced with minimal graft stretching, and, in the 9mm Microvel grafts, a probe 3 mm larger could be intro duced (Ffgpes 1,2, and 3). This phenomenon was not seen with 8-mm FTFE (Gortex) grafts, which did not accept probes larger than theii stated size.
THE AMERICAN JOURNAL OF SURGERY
VOLUME 163 MAY 1992
541
TABLE I Calculated Diameter of Gmfts Circumference Graft
(mm) (*OS mm)
Dacron Microvel 7mm 9mm 9mm 1Omm Vascutek 0mm PTFE Gortex 9mm
Calculated Diameter (mm)
Calculated Error
29 29 33 37
9.3 9.2 10.5 11.8
(8.1-9.4) (9.1-9.4) (10.3-10.7) (11.6-11.9)
29
9.2
(9.1-9.4)
25
9.0
(7.a9.1)
Pl?=E-~wXoethylens.
542
THE AMERICAN
JOURNAL
OF SURGERY
VOLUME
Ultrasound measurements of grafts within 3 months of implantation showed grafts that were on average 12% larger than their stated size (p >O.OOS)(TabIe II). Wall thrombi and low peak systolic velocities (below 45 cm/set) were seen in some grafts. COMMENTS There is ample evidence that knitted Dacron grafts can enlarge over time [I -6j. Failme of the Dacron fiber is suggested as the cause of local dilations and graft holes [7-91, whereas loosening of the knit is thought to be responsible for generalized graft dilations [IO]. We had noted a combination of wall thrombi in some Dacron grafts associated with low peak systolic velocities on duplex scanning follow-up. In other grafts, the low velocity was associated with a large graft diameter on early follow-up. Wall thrombi were probably the result of extremely slow laminar flow at the graft-blood interface.
163
MAY 1992
When we examined Dacron grafts prior to implantation, it was obvious that the graft could easily accept a larger probe than the stated graft size. The aim of this study was to correlate the stated size of Dacron grafts with the actual internal diameter and to compare this with measurements by ultrasound during the early postoperative period. The finding that Dacron grafts will easily accommodate probes of a larger size than their stated diameter was confiled by the finding that 7- to lo-mm grafts have calculated diameters that are 1.3 to 1.8 mm larger when they are opened and measured circumferentially. This overcomes the effect of graft crimping on size. Whereas these findings were similar in Vascutek Dacron grafts, there did not appear to be a size discrepancy in PTFE (Gortex) grafts. Ultrasound measurements demonstrate that newly implanted grafts are 12% or about 1 mm larger, than stated. Knitted Dacron grafts can be expected to dilate 15% to 20% [2,9]. However, we suggest that at least 12% of this “dilation” can be attributed to differences between the stated and actual size of the graft. On some grafts, the ominous finding of low peak systolic velocity on duplex ultrasound measurement may suggest a graft at risk for early failure. This association has been demonstrated for vein grafts whose peak systolic velocities fall below 45 cm/set [21,I 21. In Dacron grafts, with a marginal distal vascular bed for outflow, precise sizing of grafts may be of importance. In choosing the diameter of a Dacron graft, it may be useful to select a graft size that will maintain an adequate velocity. Knowledge of the size discrepancy in crimped Dacron grafts should be useful in making this choice. REFERENCES 1. Cook PA, Nobis PA, Stoney RJ. Dacron aortic graft failure. Arch Surg 1974; 108: 101-3. 2. Nunn DB, Freeman MH, Hudgins PC. Postoperative alterations in size of Dacron aortic grafts. Ann Surg 1979; 189: 741-4. 3. Ottinger LW, Darling RC, Wirthlin LS, Linton RR. Failure of ultralightweight knitted Dacron grafts in arterial reconstruction. Arch Surg 1976; 111: 146-9. 4. Nucho RC, Gryboski WA. Aneurysms of a double velour aortic graft. Arch Surg 1984; 119: 1182-4. 5. Tutassaura H, Gerein AN, Sladen JG. True aneurysms in prosthetic femoropopliteal grafts. Am Surg 1978; 44: 262-6. 6. Kim GE, Imparato AM, Nathan I, Riles TS. Dilation of synthetic grafts and junctional aneurysms. Arch Surg 1979; 114:
TABLE II Ultrasound Measurement of Crimped Dacron Grafts*
Grafls
Stated Size (mm)
Ultrasound Size (mm)
7.0 7.0 7.0 8.0 7.0 7.0 8.0 7.0 7.0 7.0 8.0 9.0 7.0 8.0
8.0 7.6 8.0 9.0 7.7 7.0 8.0 7.0 7.0 7.0 9.9 10.8 8.0 8.0 10.7 6.5 9.0 8.0 8.0 10.0
FP FP FP FP FP FP FP FP FP FP AF AF AF AF FxF FxF FxF FxF FxF FxF
10.0
8.0 10.0 8.0 8.0 10.0
FP = femoral-popliieal; ‘Mean ultrasound
stated
graft
Low velocity
Low velocity
Low velocity, wall thrombus Low velocity Low velocity Wall thrombus
AF = aolto-femoral; size:
7.9
mm.
Comments
Mean
FxF = femoral-femoral difference
crossover.
in measurement:
by
0.9 mm t (df = 19) = 9.105 (p > O.M)5).
1296-303. 7. Berger K, Sauvage LR. Late fiber deterioration in Dacron arterial grafts. Ann Surg 1981; 193: 477-91. 8. Watanabe T, Kusaba A, Kuma H, Kina M, Gradome K, Inokuchi K. Failure of Dacron arterial prostheses caused by structural defects. J Cardiovasc Surg 1983; 24: 95-100. 9. Sladen JG, Gerein AN, Miyagishima RT. Late rupture of prosthetic aortic grafts-presentation and management. Am J Surg 1987; 153: 453-8. 10. Clagett GP, Salander JM, Eddleman WL, et al. Dilation of knitted Dacron aortic pros&es and anastomotic false aneurysms: etiologic considerations. Surgery 1983; 93: 9-16. 11. Bandyk DF, Cato RF, Towne JB. A low flow velocity predicts failure of femoropopliteal and femorotibial bypass grafts. Surgery 1985; 98: 799-809. 12. Sladen JG, Reid JDS, Cooperberg PL, et al. Color flow duplex screening of infiainguinaf grafts combining low- and high-velocity criteria. Am J Surg 1989; 158: 107-12.
THE AMERICAN JOURNAL OF SURGERY
VOLUME 163 MAY 1992 543
