Ann Thorac Surg 1996;62:1045-1049
© 1996 The Society of Thoracic Surgeons
Original Articles: Cardiovascular
Improved Growth With Bioabsorbable Sutures in Both High- and Low-Pressure Zones
Ludwig K. von Segesser, MD,
Mario Lachat, MD,
Stefan Duewell, MD,
Duri Gianom, MD,
Marko I. Turina, MD
Clinic for Cardiovascular Surgery and Institute for Radiology, University Hospital, Zürich, Switzerland
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Abstract
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Background. Compromised growth after operation remains a significant problem in the cardiovascular field. Some benefit of absorbable suture materials has been demonstrated for arterial anastomoses. However, for the low-pressure zone, few data are available.
Methods. To assess growth in high- versus low-pressure zones we transected the abdominal aorta (high- pressure zone) as well as the inferior vena cava (low-pressure zone) in 10 young mongrel dogs using for reanastomosis 7-0 nonabsorbable versus absorbable running sutures in random order.
Results. All animals survived and were evaluated over 12 months including body weight (gain, 212% ± 45% for nonabsorbable versus 218% ± 8% for absorbable; not significant), angiography, and, after elective sacrifice, detailed studies of aorta and vena cava. Systematic compilation of angiographic data at 12 months showed at the suture level an area of 13.8 mm2 for nonabsorbable versus 24.3 ± 14.4 mm2 for absorbable sutures in the high-pressure zone as compared with 12.9 ± 4.9 mm2 for nonabsorbable versus 25.3 ± 15.4 mm2 for absorbable sutures in the low-pressure zone. Residual lumen, calculated as a function of the area above and below the suture, accounted for 35% ± 10% for nonabsorbable versus 92% ± 12% for absorbable sutures (p < 0.001) in the high-pressure zone as compared with 37% ± 13% for nonabsorbable versus 75% ± 15% for absorbable sutures (p < 0.003) in the low-pressure zone (high versus low, not significant). Poststenotic dilatation accounted for 199% ± 22% for nonabsorbable versus 126% ± 43% for absorbable sutures (p < 0.01) in the high-pressure zone. In the low-pressure zone, poststenotic dilatation remained below the inflow area, and the residual poststenotic lumen accounted for 52% ± 14% for nonabsorbable versus 77% ± 16% for absorbable sutures (p < 0.004). Macroscopic, light, and scanning electron microscopic studies confirmed different growth patterns in high- versus low-pressure zones.
Conclusions. Aortic narrowing resulted in poststenotic dilatation and unrestricted outflow path (hourglass-type stenosis). Caval narrowing was followed by restriction of poststenotic outflow path (funnel-type stenosis). Absorbable suture material allows for superior growth in both high- and low-pressure zones.
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Introduction
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See also page 1049.
Sutures in the cardiovascular field are nowadays supposed to be of a nonrestricting character provided that adequate surgical techniques are used. In the past, a number of approaches have been evaluated to achieve this goal, at least for the static environment. For vascular surgery, oblique anastomoses, cobra-head–type graft preparation, Royle's artifact [1], and other techniques have been propagated for enlargement of the suture site. Interrupted sutures, fewer sutures, and running sutures providing some excess length of the suture material have been advocated in the era of nonabsorbable suture material. With the advent of bioabsorbable suture material [2–6], one might therefore think that nowadays stenoses in the suture area should no longer exist at all. A closer look at suture sites reveals, however, that some degree of stenosis can be identified in a significant proportion of the procedures checked. In some cases, modification of the vascular wall compliance due to the healing process (scarring) might be responsible for this. However, considering the fact that most cardiovascular structures have dynamic character, ie, for vasoactive reactions [7], it becomes clear that an anastomosis that looks perfect at a given vascular tone may be rather poor at somewhat different vascular tone. An additional dimension has to be added for pediatric cardiovascular surgery. Growth from 3 kg to 90 kg can also be expressed as 3,000% of weight at birth and demonstrates impressively the challenge for sutures in this smaller subset of patients despite the progress made. Although a number of studies have shown benefits for absorbable suture material for cardiovascular repairs in the high-pressure zone [2–4], at this time not much is known about the low-pressure zone. For the latter problem mainly retrospective clinical data [8–10] are available. The present study was designed to characterize growth after transection and reanastomosis with either nonabsorbable or absorbable suture materials for the low-pressure zone in comparison with the high-pressure zone.
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Material and Methods
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Animals, Surgical Technique, and Follow-up
Ten young mongrel dogs (mean age, 3.9 ± 0.7 months) were included in this study. They received humane care in compliance with the "Guide for the Care and Use of Laboratory Animals" published by the National Institutes of Health (NIH publication 85-23, revised 1985). The animals were randomly assigned to two groups of atraumatic suture materials: (1) nonabsorbable polypropylene (Surgilene; Davis + Geck, American Cyanamid, Danbury, CT) and (2) absorbable polyglyconate (Maxon; Davis + Geck).
After standard premedication, general anesthesia was started with intravenous thiopental sodium and followed by endotracheal intubation. Volume-controlled ventilation with a positive end-expiratory pressure of 5 cm H2O was maintained with volatile anesthetics. Both the infrarenal aorta and the inferior vena cava were exposed through a median laparotomy. In sequential fashion, the infrarenal aorta and the inferior vena cava were clamped, transected, and reanastomosed with a single running circular suture using the respective 7-0 nonabsorbable monofilamentous polypropylene or 7-0 absorbable monofilamentous polyglyconate atraumatic suture material in accordance with the randomization. After accurate hemostasis, the abdomen was closed in standard fashion, and the animals were weaned from the respirator and extubated.
The patency of the aortic anastomoses initially was checked daily, and later was checked once a month by palpation. At the same time, weight gain was recorded. After 12 months, all animals were scheduled for biplane digitized angiographic evaluation of the infrarenal aorta and the inferior vena cava under general anesthesia as described above. Finally, the animals were electively sacrificed for autopsy after systemic heparinization (5,000 IU; Liquemin; Roche, Basel, Switzerland).
Data Analyses
The angiographic documentation of both vessels, infrarenal aorta and inferior vena cava, was digitized in two planes and analyzed morphometrically using imaging technology from Media Cybernetics (Image-Pro Plus; Media Cybernetics, Silver Spring, MD). Vessel diameters were determined in two planes at six precisely defined levels for both vessels as described in Table 1
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The cross-sectional area of the vessels studied was calculated by the following formula: a/2 x b/2 x 
, a being the vessel diameter in the frontal angiographic plane (values corrected for magnification) and b being the vessel diameter in the lateral angiographic plane (values corrected for magnification). The degree of stenosis at the suture level was expressed as the percentage of the mean area calculated at one vessel diameter proximal and one vessel diameter distal to the suture level for aortas and cavas. For aortic anastomoses, the degree of poststenotic dilatation was expressed as the percentage of the mean area calculated at the inflow and the outflow of the vessel. For caval anastomoses, the residual poststenotic lumen was expressed as the percentage of the inflow area.
Mean and standard deviation were derived for each parameter analyzed. Student's t test was used for comparison of parametric and Fisher's exact test for comparison of nonparametric data where applicable. A p value less than 0.05 was considered significant.
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Results
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All animals survived the procedure and the 12-month follow-up period. At that time, body weight had increased from 9.5 ± 2.9 kg to 20.2 ± 4.9 kg (212% ± 51%) for the group anastomosed with nonabsorbable sutures versus from 10.0 ± 4.1 kg to 21.8 ± 0.8 kg (218% ± 8%) for the group anastomosed with absorbable sutures (not significant). Systematic compilations of angiographic data at 12 months are given in Table 2 (aortic data: high-pressure zone) and Table 3 (caval data: low-pressure zone). At the suture level an area of 13.8 ± 10.6 mm2 for nonabsorbable versus 24.3 ± 14.4 mm2 for absorbable sutures was calculated for the high-pressure zone as compared with 12.9 ± 4.9 mm2 for nonabsorbable versus 25.3 ± 15.4 mm2 for absorbable sutures in the low-pressure zone. The residual lumen calculated as a function of the mean value taken from the areas at one vessel diameter above and one vessel diameter below the suture accounted for 35% ± 10% for nonabsorbable versus 92% ± 12% for absorbable sutures (p < 0.001) in the high-pressure zone (Fig 1) as compared with 37% ± 13% for nonabsorbable versus 75% ± 15% for absorbable sutures (p < 0.003) in the low-pressure zone (high versus low; not significant) (Fig 2). Poststenotic dilatation accounted for 199% ± 22% for nonabsorbable versus 126% ± 43% for absorbable sutures (p < 0.01) in the high-pressure zone (Fig 3). In the low-pressure zone, poststenotic dilatation remained below the inflow area, and the residual poststenotic lumen (Fig 4) accounted for 52% ± 14% for nonabsorbable versus 77% ± 16% for absorbable sutures (p < 0.004).
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Fig 1. . Residual lumen at the aortic suture level as a function of the mean cross-sectional areas one vessel diameter cranial and caudal to the suture level. A highly significant stenosis is found for nonabsorbable sutures versus only minor restriction for absorbable sutures.
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Fig 2. . Residual lumen at the caval suture level as a function of the mean cross-sectional areas one vessel diameter caudal and cranial to the suture level. A highly significant stenosis is found for nonabsorbable sutures versus only minor restriction for absorbable sutures.
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Fig 3. . Poststenotic dilatation defined as function of the mean cross-sectional areas at the inflow and at the outflow of the vessel. A much more important dilatation is found for nonabsorbable sutures.
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Fig 4. . Poststenotic residual lumen is given as a function of the cross-sectional area of the inflow. A much more important restriction of the poststenotic segment is documented for nonabsorbable sutures.
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The compiled aortic vessel profiles for nonabsorbable and absorbable suture materials given in Table 2
shows a clear difference between the two types of sutures. Nonabsorbable suture material results in significant stenosis as well as significant poststenotic dilatation. There is less variation of the sectional areas calculated for absorbable suture material. These findings are even more impressive after three-dimensional reconstruction as shown in Figure 5. Likewise, the compiled caval vessel profiles for nonabsorbable and absorbable suture materials given in Table 3 demonstrate the differences in cross-sectional areas observed. In the low-pressure zone, nonabsorbable suture material results in significant stenosis. The poststenotic cross-sectional area remains below the inflow area. The outflow area is similar to the suture level area. For absorbable suture material there is less stenosis, less poststenotic dilatation, and less restriction of the outflow path. The findings are again enhanced by three-dimensional reconstruction (Fig 6).
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Fig 5. . Three-dimensional reconstruction demonstrates the different aortic growth patterns achieved. The stenosis due to nonabsorbable suture material results in important poststenotic dilatation. Absorbable suture material allows for more harmonious growth.
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Fig 6. . Three-dimensional reconstruction demonstrates the different caval growth patterns achieved. The stenosis due to nonabsorbable suture material results in important poststenotic restriction of the outflow path. Absorbable suture material allows for more harmonious growth.
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Comment
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Different growth patterns are documented for the high- versus low-pressure zones in the given set-up: Aortic narrowing resulted in poststenotic dilatation and unrestricted outflow path (hourglass-type stenosis), whereas caval narrowing was followed by restriction of the poststenotic outflow path (funnel-type stenosis). Absorbable suture material allows for superior growth in both high- and low-pressure zones. Superior growth after aortic anastomoses with absorbable suture material is well documented in the literature. A number of studies evaluated growth after aortic sutures in the experimental set-up [2, 9, 11, 12] and provided findings similar to those demonstrated here. Looking at our aortic data, there seems to be an inverse relationship between the degrees of stenoses and poststenotic dilatations: significantly less stenosis for the absorbable sutures is accompanied by significantly less poststenotic dilatation as demonstrated in Figure 5. Likewise, reduced caval stenosis for absorbable sutures is associated with less poststenotic dilatation (see Fig 6). However, in the group with nonabsorbable sutures, there is a significant reduction of the poststenotic outflow tract. Obviously, in this group, the outflow cross-sectional area is closer to the area of the stenosis at the suture level than at the inflow level. In contrast, the outflow cross-sectional area in the group sutured with absorbable material and less stenosis at the suture level is closer to the inflow area.
Considering the different driving pressures in the high- versus the low-pressure zone one may speculate that poststenotic growth or dilatation is dependent on wall tension. Wall tension in the critical zone would result from driving pressure on one hand and afterload on the other. High or compensatory higher driving pressure in the aortic environment would allow for transport of a normal amount of blood (at higher velocity) despite a stenosis and therefore result in "adequate" or even excessive stimulation for growth of the caudal aorta. In contrast, absence of a compensatory increase in driving pressure in the low-pressure zone due to development of collateral run-off would result in reduced anatomic caval blood flow and therefore a reduced stimulation for growth of the poststenotic vena cava. This would explain the funnel-type growth pattern found in the low-pressure zone as compared with the hourglass-type growth pattern in the high-pressure zone. Of course, other elements such as the different structure of arterial and venous walls, different local cell populations, and different character of flow (pulsatile, continuous, laminar, or turbulent) have to be considered too. One might argue that the significant aortic stenosis found for nonabsorbable suture might limit the blood flow to the distal part of the body, which might compromise growth of the latter and in turn be responsible for limited growth of the inferior vena cava in these animals. However, the fact that there is no significant difference between absorbable sutures and nonabsorbable sutures for weight gain and the cross-sectional areas of the vena cavas proximal as well as distal to the suture levels speaks against this hypothesis.
Some authors expressed concerns with regard to aneurysm formation after aortic anastomoses with absorbable suture material and refer to data originating from pig studies with relatively rapid growth. In our experience with canine experiments, some degree of aortic dilatation at the suture level can be found in isolated animals. Overall, these positive dimensional variations are partially compensated for by some degree of negative variations in other animals and therefore do not appear in mean values (see Table 2). Microscopic analyses of canine aortic vessel walls demonstrated significant thickening in the suture area for nonabsorbable sutures as compared with moderate thinning for absorbable sutures [13]. In contrast, the poststenotic dilatation after significant stenosis is a constant finding on the arterial side in this study and remains well apparent after pooling of data as demonstrated in Figure 5. We have previously reported our clinical experience with coarctation repair using nonabsorbable and absorbable suture material with different suture techniques for end-to-end anastomoses in a series of 17 patients [14]. After a mean follow-up of 4 years, the pressure gradient at the suture site was 5 ± 9 mm Hg for nonabsorbable (8/17) as compared with 6 ± 8 mm Hg in 9/17 for absorbable circular running sutures (not significant). No aneurysmal dilatation was observed in either group.
In conclusion, the present study confirms superior growth for vascular anastomoses using absorbable suture material in both high- and low-pressure zones. Like for the arterial side, absorbable suture material is well tolerated on the venous side, including the vena cava and the right atrium [15]. As growth of cardiovascular structures seems to be dependent on wall tension, the benefit of absorbable suture material resulting in less stenoses and therefore less restriction of the poststenotic outflow path is even more striking for the low-pressure zone.
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Footnotes
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Presented at the Thirty-second Annual Meeting of The Society of Thoracic Surgeons, Orlando, FL, Jan 29–31, 1996.
Address reprint requests to Dr von Segesser, Service de Chirurgie Cardio-vasculaire, Centre Hospitalier Universitaire Vaudois, CHUV, 46, rue du Bugnon, CH-1011 Lausanne, Switzerland.
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References
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Top
Abstract
Introduction
