The functional and morphological consequences of balloon catheter injury in veins

[Prospects and peculiarities of the procedure of ultrasound ablation of subcutaneous veins of the lower limbs]

The last decade has seen active development of minimally invasive (endovenous) methods of surgical removal of lower limb varicose veins (LLVV); however, the problem of increasing efficacy of these methods and improving long-term results still remains of current importance. The authors of this work propose a method of ultrasound ablation of subcutaneous veins of lower extremities. Our experimental study was aimed at determining the pattern of venous wall damage after ultrasound exposure. Samples of segments of the trunk of the great saphenous vein (GSV) were divided into 5 groups: group 1 - the control group, group 2 - treatment with a sclerosant in the amount of 0.3 ml for 30 s, group 3 - treatment with ultrasound at a frequency of 26 kHz and amplitude 40 μm and 0.3-ml sclerosant for 30 s, group 4 - exposure to ultrasound at a frequency of 26 kHz and amplitude 40 μm and 0.3-ml sclerosant for 60 s, group 5 samples were exposed to ultrasound at 26 kHz and amplitude of 40 μm for 60 s. The results of analysing the histological sections of the samples of the 2nd and 3rd groups demonstrated that the degree of alteration in the GSV wall on combined exposure to ultrasound and a sclerosant was 4.5-fold higher as compared with treatment with a sclerosant solution alone. During ultrasound exposure, the maximum temperature of the venous wall of group 5 samples was by 20 °C higher than in samples of group 4. Analysing the histological sections demonstrated a similar pattern of structural alterations of the samples of group 4 and 5, thus suggesting a possibility of controlling the temperature of the venous wall during ultrasound ablation without changing quality of structural lesions. The obtained findings showed a possibility of initiating irreversible dystrophic alterations in the venous wall on exposure to ultrasound by means of combining the mechanisms of chemical, mechanical, and thermal ablation.

Role of Platelet Activation in Catheter-Induced Vascular Wall Injury

PURPOSE

To investigate the role of smooth muscle cell (SMC) response and platelet activation in peripheral venous catheterization using a model of catheter injury associated with thrombocytopenic treatment.

METHODS

Silicon elastic catheters were inserted into New Zealand White rabbit external jugular veins from 24 hours to 60 days. Immunocytochemical procedures with antibodies to differentiation markers specific for SMCs, myofibroblasts, and endothelial cells were used to ascertain the phenotypic features of injured venous SMCs and the tissue sleeve formed around the catheter. Thrombocytopenia was induced in rabbits by busulfan treatment and the effect on catheter injury development examined after 15 days. The putative direct effect of this drug on the venous SMC proliferation, migration, and differentiation was assayed in vitro for 48 hours.

RESULTS

Catheter injury is characterized by the progressive formation of (1) a neointima, containing differentiating SMCs, which are derived from the media and adventitial layer, and (2) by the organizing thrombus formed around the catheter, which contains myofibroblasts. In busulfan-treated thrombocytopenic animals, there was no evidence for either neointimal development or thrombus formation. A direct role of this drug in the unresponsiveness of vascular wall can be excluded by the unchanged proliferation and migration pattern of cultured venous SMCs treated with busulfan compared to control cultures.

CONCLUSIONS

In our model, accumulation of differentiated SMCs in the neointima and myofibroblast appearance in the thrombus are linked, although distinct, events regulated by platelet activation, which is able to furnish the appropriate microenvironment for vascular SMC recruitment from the media/adventitial layer.

Vein adaptation to arterialization in an experimental model

PURPOSE

The events preceding myointimal thickening in vein grafts after vascular reconstructions are not well characterized. Indeed, the injury response associated with vein graft arterialization may be different than that observed in the balloon angioplasty model. Therefore, we used a rat model to study the early cellular response after arterialization of vein grafts.

METHODS

Epigastric veins were placed as femoral artery interposition grafts in 37 male Lewis rats (weight range, 350-400 g). Vein grafts and contralateral epigastric veins were harvested at different time points (6 hours, 1 day, 2 days, 3 days, 7 days, 14 days, 21 days, 30 days, and 70 days). Tissue specimens were processed for histology and immunohistochemistry with antibodies for the proliferating cell nuclear antigen (PCNA) and for different cell types. Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) assay was used as a means of determining the presence of apoptosis. Electron microscopy was used as means of assessing the integrity of the endothelial cell surface (SEM) and confirming the presence of apoptosis (TEM). Specimens were also snap frozen in liquid nitrogen for RNA isolation and molecular analysis.

RESULTS

At 1 day, endothelial denudation with platelet deposition on the surface was shown by means of SEM. Both apoptosis and necrosis of smooth muscle cells (SMCs) were present in the media, along with monocyte infiltration. Cellular proliferation and apoptosis were most intense within the first week of implantation. PCNA staining was first seen in the adventitial fibroblasts and microvessels, then in the medial SMCs at 3 days. With reverse transcriptase polymerase chain reaction, upregulation of vascular endothelial growth factor (VEGF) messenger RNA (mRNA) was noted at 1 day. Myointimal thickening progressively developed, with no apparent diminution of the luminal area as long as 70 days after implantation. By means of the analysis of the transforming growth factor beta1, mRNA showed expression during intimal thickening and accumulation of extracellular matrix. Reendothelialization was complete at 30 days.

CONCLUSIONS

These observations indicate that the cellular composition in our vein graft model is similar to human stenotic explants. Endothelial denudation is observed in rat vein grafts with complete regeneration by 30 days. VEGF mRNA is upregulated at 1 day, followed by proliferation of microvessel endothelial cells in the adventitia. Cellular proliferation and apoptosis are minimal after 21 days, with progressive intimal thickening likely to be the result of matrix accumulation.

Functional characterization of alpha1-adrenergic receptors in experimental vein grafts

BACKGROUND

Studies on the pharmacology of the smooth muscle cells in vein bypass grafts suggest that the function of G-proteins and adrenergic receptors is altered. This study examines the alpha-adrenergic responsiveness of smooth muscle cells in vein bypass grafts as compared with those in the common carotid arteries and external jugular veins.

METHODS

New Zealand White rabbits received jugular vein interposition bypass grafts of the common carotid. Vessel segments of the vein bypass grafts harvested after 28 days, common carotid arteries, and external jugular veins were sectioned into 5-mm rings (four per vessel) for studies of isometric tension in response to phenylephrine (10(-10) to 10(-4) M) alone and in the presence of prazosin, an alpha1-adrenergic antagonist; WB4101 and 5-methylurapidil (5-MU), alpha1A antagonists; chloroethylclonidine (CEC); an alpha1B antagonist; or the Gi/o G-protein inhibitor pertussis toxin (PTx).

RESULTS

All vessels had prazosin-sensitive responses. The jugular veins appear to have functional alpha1A receptors (WB4101 and 5-MU sensitive, CEC insensitive) which are associated with pertussis toxin-sensitive G-proteins. Carotid arteries appear to have atypical alpha1 receptors (WB4101 and 5-MU insensitive, CEC insensitive) associated with pertussis toxin-insensitive G-proteins. Vein grafts appear to have functional alpha1B receptors (WB4101 and 5-MU insensitive, CEC sensitive) which are associated with pertussis toxin-insensitive G-proteins.

CONCLUSIONS

These results show that placement of a vein into the arterial circulation induces a change in alpha1-adrenergic receptor subtypes (alpha1A to alpha1B) and in the G-protein coupling of the receptors (PTx sensitive to PTx insensitive), reflecting a signficant phenotypic change in smooth muscle cell signal transduction.

Adenosine responses in experimental vein bypass grafts

PURPOSE

Veins develop unique endothelial and smooth muscle cell physiologic phenotypes after implantation as vein grafts in the arterial circulation. Receptor-mediated relaxation is reduced or absent in these grafts. This study examines the responses of vein grafts to adenosine, a known potent endogenous vasodilator, and compares these responses with the native veins and arteries.

METHODS

The presence of adenosine receptors (A1 and A2) by radioligand binding and the in vitro responses to the adenosine analogue N-ethyl-carboxyamido-adenosine were assessed in precontracted common carotid jugular vein bypass grafts placed in New Zealand white rabbits for 28 days. Results were compared with those obtained in precontracted jugular veins and carotid arteries. Both endothelialized and de-endothelialized vessels were studied. The contribution of nitric oxide (NO) and prostanoid production to relaxation was also determined by preincubation with the specific inhibitors l-monomethylarginine and indomethacin, respectively. Finally, the in vitro relaxation in response to the respective A1 and A2 adenosine receptor agonists R-phenyl-isopropyl-adenosine and CGS-21680 was also examined.

RESULTS

The results show that the adenosine-induced responses of the vein grafts differ from those of the jugular vein and carotid artery. First, in contrast to the carotid artery, vein graft adenosine-mediated relaxation is NO and prostanoid dependent, similar to the response of the jugular vein. Second, A1 receptor activation in the vein graft produces an endothelium-dependent contractile response. Third, the A2 receptor-mediated responses in the vein grafts appear to be independent of the endothelium. Fourth, radioligand studies show the presence of both receptor subtypes (A1 and A2) on the vein grafts with a ratio (A1/A2 = 1.4) closer to that of the jugular vein (A1/A2 = 1.8) than to that seen in the carotid artery (A1/A2 = 0.5).

CONCLUSIONS

Vein graft adenosine responses appear to be unique in that they neither maintain a venous phenotype nor acquire an arterial phenotype. In particular, endothelial A1 receptor-mediated responses change from relaxation to contraction, and receptor activated NO-mediated relaxation is preserved within the vein grafts probably via A2 receptor signalling.

Central venous catheter failure is induced by injury and can be prevented by stabilizing the catheter tip

PURPOSE

Thrombosis associated with central venous catheters is a significant cause of device failure, morbidity, and loss of access sites. We hypothesized that central vein thrombosis is caused by catheter injury to the vein wall and that it can be reduced by stabilizing the catheter tip. To test these hypotheses, we studied central vein catheters in a porcine model. Test catheters had a silicone-encased stainless steel loop at the indwelling end that contacted the vein wall and stabilized the catheter tip in the center of the vessel.

METHODS

Sealed silicon elastic (Silastic) catheters (3.2 mm outer diameter) with and without a stabilizing loop were inserted via the external jugular vein into the superior vena cava just above the right atrium. Animals were killed at 1, 2, 4, and 8 weeks, and the vena cava was inspected for the presence of thrombus and entrapment of the catheter tip.

RESULTS

In control animals mural thrombus developed at the site of the catheter tip. This thrombus organized by invasion of macrophages and smooth muscle cells, eventually forming a lesion similar to intimal hyperplasia. Lesion cross-sectional area was significantly smaller in animals with loop catheters than in control animals at 2 weeks (1.2 +/- 1.3 vs 34.5 +/- 23.9 mm2; p = 0.05) and 4 weeks (2.8 +/- 0.3 vs 13.9 +/- 5.8 mm2; p < 0.05). By 8 weeks the vena cava was nearly occluded in most animals and the catheter tip was entrapped in this lesion in all cases. Test catheters eliminated the injury process for up to 8 weeks (p < 0.01, chi2 control vs loop catheter entrapment). Very little injury response was found where the loop contacted the vein wall, and the catheter tip was free of thrombus in all cases.

CONCLUSIONS

Mural thrombosis at the tip of indwelling central catheters is caused by chronic mechanical venous wall injury. Vessel injury and the resulting thrombosis can be prevented by a catheter modification that stabilizes the tip. Such a catheter may significantly reduce catheter malfunction and morbidity associated with these devices.

Balloon catheter injury and vein graft morphology and function

Endovascular interventions to salvage failing vein bypass grafts are often associated with suboptimal outcomes. This study examines the effect of experimental vein graft catheter injury on vein graft morphology and vasomotor function. Thirty New Zealand white rabbits underwent a right common carotid interposition vein bypass graft. Ten grafts were harvested at 14 days, 10 were harvested at 28 days, and 10 had a balloon catheter injury induced at 14 days (4 F Fogarty catheter, 0.6 to 0.75 ml water inflation, 3 passes) and these 10 grafts were harvested after an additional 14 days. Morphologic and morphometric determinations (n = 5) or in vitro contractile studies (n = 5) were performed on segments of the vein grafts. Intimal thickness, without any intervention, increased by 84% from 14 to 28 days (p < 0.01), whereas catheter injury at 14 days induced a twofold increase (p < 0.001) in the formation of intimal hyperplasia by 28 days. Scanning electron microscopy demonstrated near-complete endothelial denudation after balloon catheter injury. In the 14- and 28-day control vein grafts, and in the balloon-injured vein grafts, the vascular surfaces had confluent endothelial linings. However, the ultrastructural features of the endothelial cells were group specific. Transmission electron microscopy of the same specimens confirmed this. There were no significant differences in contractility between the 28-day control and the catheter-injured vein grafts. This study demonstrates that balloon catheter injury doubles the rate at which intimal hyperplasia develops in vein grafts without significantly altering the physiologic phenotype of the smooth muscle cells as defined by their vasomotor function.