How To Repair Vein Valves
Abstract
Current techniques for treating chronic venous disease caused by venous valve incompetence all have deficiencies. A need exists for a unproblematic technique to restore competence to the diseased valves at multiple sites in the venous arrangement. The Venocuff is an implantable device adult to restore venous valve competence past reducing the vein circumference. Two fauna models are described that are useful in the report of venous valve incompetence; the device was tested in these two models in the jugular vein of sheep. The first model was of naturally incompetent valves. The device was implanted around 11 completely incompetent and seven partially incompetent valves in xviii veins of 11 sheep. Afterwards implantation competence was restored or improved in all valves. The 2d model made utilize of an arteriovenous fistula to produce incompetence in the jugular vein in four sheep. The implant increased the pressure divergence across the valve from sixteen to 68 mm Hg. The Venocuff implant was thus effective at restoring valvular competence in the two animal models studied. There is evidence that valvular incompetence in these models and the results observed may be applicative in some cases of chronic venous disease in humans. J VASC SouthURG 1988;8:569-75.)
The usual treatment for varicose veins associated with saphenofemoral incompetence is either high ligation (with or without stripping) or sclerotherapy. A disadvantage of these techniques is that the vein is no longer available for coronary and peripheral graft surgery. Ligation alone can exist used to preserve the vein simply sometimes causes phlebitis.
Occlusion of the saphenofemoral junction in patients with coexistent chronic deep venous insufficiency volition have hundred-to-one do good and may in some cases be detrimental by increasing venous pressures.
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Information technology would exist more than physiologic to restore competence to the valve at the saphenofemoral junction. This would foreclose retrograde menstruum while still allowing forward period.
Chronic deep venous insufficiency is a illness with a loftier socioeconomic price but no generally accepted surgical treatment for those in whom bourgeois therapy has failed. Multiple methods of preventing reflux take been tried, including ligation of perforators, ligation of the femoral or popliteal vein, valve transfer, valve transplant, and valvuloplasty. In that location have as well been attempts at producing artificial valve mechanisms.
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All these methods have issues; a unproblematic technique is needed that tin be used to repair valves at multiple sites and that prevents recurrence of incompetence.
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This written report was conducted to determine the rubber and efficacy of a new technique of restoring venous valve competence.
Material and methods
Surgical implant
The Venocuff is a Dacron reinforced silicone cuff manufactured by Vaso Products Pty Ltd (Artarmon, New Southward Wales, Australia). The cuff is i.five cm wide and was placed around the vein at the site of the valve to reduce the circumference and to bring the valve cusps into apposition. Competence was tested as described below. When optimal competence had been restored, the cuff was secured at that circumference with stainless steel surgical staples. The cuff was so sutured to the surrounding fascia. This was necessary to forestall the gage moving along the vein. No sutures were placed in the vein wall itself. A modification used for the terminal 10 implants apart from implant No. 13 was the addition of a tag on each side of the cuff to facilitate the suturing of the cuff to the surrounding fascia (Fig. one).
Fig. one The cuff was placed effectually vein to reduce its circumference at site of incompetent valve. A, Tags (arrows) were added to facilitate suturing of the device to surrounding fascia. Excess strap (A) allows adjustment of circumference and is trimmed once optimal circumference has been achieved (B).
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Surgical process
Mature cross-bred merino sheep were used in this study. All procedures were performed with the animals under pentobarbital anesthesia with an endotracheal tube and spontaneous ventilation. The external jugular vein was dissected bilaterally in fifteen sheep and unilaterally in 2 sheep to yield a full of 32 veins. The external jugular vein in sheep is a thin-walled vessel with a mean diameter of approximately 0.ix cm. It is formed by the wedlock of the external and internal maxillary veins near the ventral border of the parotid gland. The vein runs in the subcutaneous tissue forth the groove between the sternocephalic and brachiocephalic muscles. It is joined by the internal jugular vein (which is usually small and sometimes absent) at the base of the neck.
The valves were identified by the white semilunar lines that are formed by the attachment of the valve cusps to the vein wall. The vein usually contains one to three valves but in three instances no valves were constitute.
Two models of venous valve incompetence were used to test the Venocuff. The first model used was that of valves establish at the initial operation to be naturally incompetent, whether complete or partial. The Venocuff was applied to these valves at the same performance to restore competence (Fig. 2).
Fig. ii Left, Start sheep model was that of naturally incompetent valves in the external jugular vein (JV). Correct, The Venocuff is shown around vein. Valve cusps have been brought into apposition and competence restored.
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This procedure was performed on 18 veins in eleven sheep. The wound was closed and the vein was dissected once more at 12 to 41 weeks after implantation.
The second model used was that of valves establish to exist competent at the initial operation. Incompetence was produced by an arteriovenous fistula (Fig. iii).
Fig. 3 Left, Second sheep model of valve incompetence produced past proximal arteriovenous fistula between exernal jugular vein (JV) and the common carotid artery (CA). Correct, The Venocuff implanted to restore competence.
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A 1 cm side-to-side fistula with the mutual carotid artery was created proximal to the valve with vi-0 continuous polypropylene (Prolene) sutures. One to four weeks afterwards a Venocuff was placed around the valve to restore competence. This procedure was performed on four valves in four sheep. The veins were harvested at 5 to 9 weeks.
Animal care complied with the "Principles of Laboratory Animate being Care" and the "Guide for the Care and Use of Laboratory Animals" (National Institutes of Wellness Publication No. 80-23, revised 1978).
Qualitative assessment of competence
Valve competence was assessed immediately before and subsequently application of the Venocuff and at harvesting. Competence of the valve was assessed qualitatively by means of the following milking technique (Fig. 4).
Fig. 4 The external jugular vein was occluded with Vesseloops 3 cm proximal and distal to valve (a). Blood was milked from distal into proximal segment of vein (b). Pressure was applied digitally to proximal segment of vein. Incompetence resulted in filling of distal vein (c).
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The vein was occluded 3 cm distal and proximal to the middle of the valve. The distal segment was then emptied past milking the blood into the proximal segment. Whatever filling of the distal segment thus represents reflux of blood through the valve. The valve tin can be stressed further by manual compression of the proximal segment of vein. The filling of the distal segment was first observed with no proximal pressure practical. If the segment filled in less than ten seconds, the valve was regarded as incompetent. This was repeated with balmy, moderate, and firm proximal pressure applied. If the distal segment filled in less than x seconds with whatever of these pressures, the valve was regarded as severely, moderately, and minimally incompetent, respectively. If the distal segment did not fill up in 10 seconds even with business firm proximal pressure, the valve was regarded as completely competent. If more than one valve was present, but the most competent valve was used in the written report.
Quantitative assessment of competence
A quantitative cess was also used on 13 veins. Two methods were used. The outset method was used in vi veins. The milking maneuver was performed every bit above. The intraluminal pressure was measured 1 cm proximal and distal to the valve. A proximal pressure of 75 to 100 mm Hg was applied by manual compression of the proximal segment of vein and the time required to fill the distal segment was observed. The average pressure gradient maintained beyond the valve was measured. The degree of incompetence was estimated as follows. The volume of the distal vein was approximated as that of a cylinder 3 cm long. The circumference was measured and the approximate volume was calculated. This volume was multiplied past 60 and divided by the time in seconds information technology took to fill the distal segment. The result gave the approximate volume of retrograde flow per minute at an average pressure gradient. The average pressure gradient was divided by the retrograde flow to requite the retrograde resistance.
The second technique was used in 7 veins. This besides required measurement of pressures proximal and distal to the valve. The sheep was given 5000 units of sodium heparin intravenously, the vein was occluded 5 cm proximal to the valve, and the sheep's own claret was injected through a xix-gauge cannula into the proximal vein 3 cm from the valve. The blood was injected at a charge per unit sufficient to maintain a proximal force per unit area of 75 to 100 mm Hg. The average pressure gradient was then divided by the required charge per unit of injection to give the retrograde resistance of the valve.
The competence of the valves with a proximal arteriovenous fistula was assessed by measuring the pressure gradient beyond the valve.
Pressure measurement
Pressures were measured through two nineteen-gauge cannulas, which were placed so that the tips lay ane cm proximal and distal to the valve. Bentley 500 pressure transducers were used with a Grass 5P1 bridge preamplifier and 5D polygraph. The equipment was calibrated before each utilize.
Morphology
All specimens were inspected advisedly at harvest for testify of thrombosis, stricture, thickness of vein wall, and the appearance of the valve cusps. Lite microscopy was performed in x of the veins that had no fistula. One-half of these were curt-term implants (hateful xiv weeks) and the other half were long-term implants (mean 36 weeks). Light microscopy was also performed on the veins with an arteriovenous fistula. Sections were fabricated of the vein wall under the implant and iii cm proximal and distal to the implant.
Results
Initial findings
At the initial dissection, in that location were six competent valves, 12 partially incompetent valves, and xi completely incompetent valves. No valves were found in 3 veins. The mean circumference of the competent, partially incompetent, and completely incompetent veins was 2.four cm, 2.6 cm, and 2.8 cm, respectively.
Model 1
An effort was made to restore competence with the Venocuff used in 18 of the 23 incompetent and partially incompetent valves in 11 sheep. The results are given in Table I.
Table I Results of restoring competence to naturally incompetent valves
| Implant No. | Initial | Venocuff | Harvest | Weeks implanted |
|---|---|---|---|---|
| i | + + + | − | − | 41 |
| 2 | + + + + | + | + + | 41 |
| 3 | + + + +(0) | −(>25) | Died | |
| 4 | + + + +(0) | +(21) | Thrombosed | 14 |
| 5 | + + + +(0) | −(>25) | − (>25) | 14 |
| 6 | + + (4) | −(>25) | + (9) | xiv |
| seven | + + + +(0) | −(>25) | −(nineteen) | 13 |
| 8 | + + + +(0) | −(>25) | +(viii) | xiii |
| ix | + + + (0) | −(>25) | − (>25) | 12 |
| 10 | + + (0) | −(>12) | − (7) | 12 |
| 11 | + + + (0) | −(23) | Not harvested | |
| 12 | + + + +(0) | +(sixteen) | − (>25) | 17 |
| xiii | + + + +(0) | −(>25) | + (12) | 17 |
| xiv | + + + (ane) | −(>25) | − (>25) | 16 |
| fifteen | + + + (0) | −(>25) | + (12) | 16 |
| 16 | + + + + | + + | − | 32 |
| 17 | + + + + | − | − | 32 |
| eighteen | + + + + | − | − | 32 |
Numbers in parentheses refer to retrograde resistance expressed in millimeters of mercury per minute per milliliter. −, competent; +, mildly incompetent; + +, moderately incompetent; + + +, severely incompetent; + + + +, completely incompetent.
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On qualitative assessment, eleven of the 18 valves were completely incompetent with five severely incompetent and two moderately incompetent. Afterward application of the Venocuff, 14 valves were completely competent, three valves minimally incompetent, and ane valve moderately incompetent. At harvest at a hateful of 21 weeks (range 12 to 41 weeks), 10 valves were competent, iv were minimally incompetent, and one was moderately incompetent. One vein was thrombosed, one sheep died considering of a complexity of a fistula on the opposite side, and one vein was not harvested. The caste of competence at harvest was greater in all except 1 valve than the virtually competent valve found initially. The exception (implant No. two) was moderately incompetent at harvest. This appeared to be related to movement of the gage along the vein. Despite this, the valve was more than competent than it was before implantation. When the position was corrected, the valve was completely competent. This valve was the only one of the five long-term implants (32 to 41 weeks) that was non completely competent at harvest. The device with the tags that minimized movement along the vein wall immune deterioration of role on qualitative assessment in only one valve; the remaining seven valves were competent. The early epitome allowed three cases of deterioration in function with three valves maintaining competence and 1 vein thrombosed.
The mean reduction in circumference required for these results was 24% and the mean reduction in surface area was 41%. The mean circumference was reduced from 2.8 to two.1 cm.
The quantitative methods confirm the improvement of valve function with the Venocuff shown by the qualitative data. However, information technology revealed two instances of balmy deterioration in function of the valve non detected by the qualitative assessment. All other instances of deterioration or improvement were confirmed.
Macroscopically the silicone cuff produced a fine fibrous capsule, which was approximately 1 mm thick on the outside of the cuff. This was much thinner inside the gage. No stricture or ulceration occurred. Light microscopy showed a mild fibrosis of the vein wall. The endothelial cell lining was intact. There were no giant cells and there was hyalinization indicating maturation of the gristly tissue. Both the long- and short-term implants had a similar appearance and the control specimens had a similar response.
The one complication was a wound infection that resolved with antibiotics. However, this vein was found to be thrombosed at harvest. The thrombosis extended between the puncture sites for measuring pressure level.
Model 2
The second model of valve incompetence was used for implants in 4 sheep. In all four sheep the competent valves became incompetent inside 7 days of creation of the arteriovenous fistula as detected by palpation. The mean pressure gradient beyond the valve at the second operation was 16 mm Hg. Later on application of the Venocuff this gradient increased to 68 mm Hg. The circumference of the vein was measured in two sheep. A mean reduction in circumference of 22% in the fistularized vein was required to produce this result. However, this was 45% greater than the original circumference earlier the fistula was created. At harvest 9 weeks later, 1 sheep maintained the aforementioned force per unit area gradient. One sheep had an infected wound before insertion of the Venocuff. This resulted in hemorrhage from the fistula and the sheep died. The remaining two sheep maintained a loftier gradient but the vein had become occluded at the site of the valve. This occlusion was localized, extending for ii to 3 mm under the proximal part of the cuff. The vein lumen under the cuff distal to this occlusion was macroscopically normal. No thrombosis occurred. Histologic examination showed intimal hyperplasia of the proximal vein and the vein under the cuff; this was much less marked in the distal vein.
Discussion
Operative techniques of assessing competence that accept been reported include milking techniques that reveal incompetence by filling of the vein distal to the valve.
,
Transection of the vein has also been used to enable direct visualization of incompetent flow. The anesthetist may increment intrathoracic pressure to further test the valve.
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These techniques do not quantify incompetence. McLachlin et al.
used a xc cm column of normal saline solution to exam competence but did not quantify the caste of incompetence by measuring menstruation. The milking technique in this report was used in combination with two quantitative techniques. The start quantitative method was a milking technique that used measurement of the pressure divergence beyond the valve and an approximation of retrograde menstruation to judge retrograde resistance of the valve. The 2nd quantitative method has the advantage of measuring menstruum direct at a known force per unit area difference. Another advantage is that it does not rely on emptying the distal segment. This can cause an incompetent valve to appear more than competent as shown by Timmons.
The disadvantage of these quantitative techniques is that they cause trauma to the vein and may result in thrombosis, every bit occurred in one vein in this study.
The first sheep model in this study was of valves that were initially incompetent. The incompetence in these valves is analogous to the incompetence of venous valves in the lower extremity in humans. The external jugular vein in sheep is subjected to increased pressure while the fauna is grazing. This is a thin-walled vein that is easily distended. The incompetence may thus be secondary to dilatation of the vein wall. Another possible cause is abnormality of the valve cusp; this appears less likely because the valve cusps appeared macroscopically normal and competence was successfully restored by reducing the circumference of the vein. The second model was created by the employ of an arteriovenous fistula to produce high pressures, which act on what announced to be normal valve cusps and vein wall. This model mimics proximal valve deficiency or venous obstacle in humans, which subjects distal valves to greater pressures. van Bemmelen et al.
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used this model with proxima ligation to written report valve incompetence in rats. The early on changes they found were separation of the cusps, with later damage to the cusps themselves. This finding is supported past two studies on varicose veins.
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The arteriovenous fistula does not seem appropriate to long-term implants of the Venocuff. A valve that is made competent by the Venocuff will not allow retrograde flow and the high fistula pressure prevents forward period. The valve cusps are thus held permanently closed. The loftier pressure and turbulence lead to intimal proliferation as is well described.
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Intimal proliferation may upshot in apoplexy, as observed in the two cases reported here. The fistula in these two sheep was within 2 cm of the valve, which was thus field of study to loftier pressure and turbulence.
In both animal models information technology was possible to better or restore competence of incompetent valves by means of the Venocuff. The repair was maintained in long-term implants if motility along the vein was prevented. This is seen in the improved results with the modified implant and past the fact that the only valve that was not competent later on long-term implant was made competent by aligning of the position of the device at harvest.
The question this study raises is that of the applicability of these models to chronic venous affliction in humans. These models are not intended as models of venous insufficiency. However, they are useful models of valve incompetence. Furthermore, they are non models of phlebitic damage but of valve incompetence caused initially by dilatation of the vein wall and separation of the commissures rather than impairment to the valve cusps.
Potent testify exists of a wall defect with relative preservation of valve cusps in varicose veins. The vein wall is more than distensible in apparently normal veins in people with varicose veins.
Cotton
found macroscopically normal valves in 123 of 156 valves examined. Edwards and Edwards
found separation of the commissures to be the early on change in varicose veins. Every case of 106 varicose veins showed such a modify whereas there was no constant lesion of the cusp.
Further evidence that the model may be applicative is that valve incompetence in humans may be reversed. The saphenofemoral valve that has been shown to be incompetent preoperatively may become competent during performance because of spasm of the vein.
Incompetence of valves is often worse in situations where there is dilatation of the veins. This happens during pregnancy,
later in the twenty-four hour period,
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and after the application of local anesthetic.
The syndrome of chronic deep venous insufficiency can be caused by destruction of valves by thrombosis. However, chronic deep venous insufficiency can often occur with no bear witness of thrombosis. A recent phlebographic study of patients with chronic deep venous insufficiency showed no evidence of phlebitic damage in 63.viii% of cases.
Ferris and Kistner
and Raju
noted cusp stretching with prolapse and contend for a primary valve defect. However, their ascertainment may exist explained by the complanate vein giving an appearance of stretched cusps.
Every bit with varicose veins there is some evidence in favor of primary vein wall dilatation in many cases. The incompetent valve may become competent when the patient lies down during Doppler test. This restoration of competence has been noted during functioning; this may exist due to spasm of the vein and a subtract in the vein diameter in the prone position. In this situation Ferris and Kistner
performed a plication in i example and Hallberg
and Raju
placed a cuff around the vein to maintain competence.
The Venocuff was constructive in repairing incompetent venous valves in the two animal models used. At that place is evidence that these models may be applicative to some patients with varicose veins and chronic deep venous insufficiency. Clinical trials are required to investigate the role of this method of repairing incompetent venous valves.
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Footnotes
*Supported in part by a National Research Fellowship granted by the Section of Science.
**Asking reprints: George Jessup, 5 Gibbon Road, Baulkham Hills, Sydney, 2153, Australia.
Identification
DOI: https://doi.org/10.1016/0741-5214(88)90307-2
Copyright
© 1988 Society for Vascular Surgery and International Society for Cardiovascular Surgery, Due north American Chapter. Published by Elsevier Inc. All rights reserved.
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