Endothelial lesions associated with vascular clamping--surface micropathology by scanning electron microscopy

Mechanical Properties and Biological Interaction of Aortic Clamps: Are These All Minimally Invasive?

Objective

Although specifically designed aortic clamps are mainstay of minimally invasive cardiac surgery, so far, no comparative reports about their mechanical properties and interaction with the aortic wall have been reported. In this study, the generated force in the clamps’ jaws and the biological response of the aorta after clamping are evaluated.

Methods

The jaw force of five commercially available clamps [Geister, Cygnet, Cardiovision (CV) 195.10, CV 195.40, and CV 195.83] was assessed by clamping a 2.2-mm compression load cell with a dedicated computer universal serial bus interface at the proximal, the middle, and the distal site from the fulcrum. Biological response of the aortic wall was assessed in five minipigs (weight, 38–40 kg) that underwent thoracic aorta clamping and leakage point test. Immunohistochemistry and morphometric analysis were carried out for each aortic segment tested.

Results

Force generation pattern is peculiar of each clamp, being higher in the proximal and the middle portion and lower in the distal part. One clamp (Cygnet) exhibited homogeneous maximal force generation at all three sites. All clamps exhibited peculiar crushing artifacts. A variable degree of endothelial layer disruption occurred in all clamping tests; three clamps (CV 195.10, Cygnet, and Geister) had the lower amount of intact endothelium. The clamping force was not associated with the degree of endothelial disruption (P value was not significant).

Conclusions

The choice of a clamp that is not only minimally invasive in design but also least traumatic will help avoid complications of aortic manipulation.

The effect of increasing clamping forces on endothelial and arterial wall damage: an experimental study in the sheep

PURPOSE

This study aimed to relate the level of physical force applied to the arterial wall by atraumatic clamps to the degree of endothelial and wall damage.

METHODS

Sixteen sheep carotid and femoral arteries were each demarcated into four segments 1 cm apart (total 64 segments). Each segment was clamped for 15 min with a standard angled DeBakey vascular clamp. Four levels of force were generated by closing the clamp at three, four, five and six notches of closure. The extent of endothelial injury was assessed by using a dedicated computer assisted image acquisition program to measure the area stained by Evan's blue dye. The extent of damage to the layers of the arterial wall was analyzed and compared by scanning electron microscopy and light microscopy.

RESULTS

For femoral arteries, the area of endothelial injury was considerably less for three notch (3.76 +/- 0.28 newtons) and four notch (5.68 +/- 0.29 newtons) closure compared with that for five notch (6.19 +/- 0.31 newtons) and six notch (6.61 +/- 0.16 Newtons) closure (p = 0.01). For carotid arteries, three notch (5.68 +/- 0.28 newtons) closure caused less damage than did four notch (7.98 +/- 0.29 newtons), five notch (9.17 +/- 0.40 newtons) and six notch (9.57 +/- 0.64 newtons) closure (P = 0.02). Scanning electron microscopy confirmed the extent and depth of arterial injury corresponded directly to the forces generated by the vascular clamps.

CONCLUSIONS

The closing forces generated by arterial clamps correlated positively with the extent of artery wall injury. Vascular clamps should be applied at the minimum level of force that will arrest blood flow.

Artery wall damage and platelet uptake from so-called atraumatic arterial clamps: an experimental study

A 'traumatic' clamps are routinely used to control arteries during reconstruction, but little is known about the arterial damage caused and the effects on platelet uptake. This experiment used sheep carotid arteries to correlate the degree of histologic damage observed with the level of indium-111-labelled platelet uptake in clamped arterial segments. Scanning electron microscopy and light microscopy enabled three degrees of injury to be recognized. In mild injuries, endothelial cell orientation was changed but local platelet uptake was little different from controls. In moderate injuries, the endothelial cells directly squeezed by the clamp were morphologically altered, superficial fissures developed which extended into the media, and local platelet uptake was usually increased. Severe injuries caused extensive endothelial cell desquamation, formation of deep cavities in the media and increased platelet uptake (mean 5.51 times that of control). Platelet uptake at the site of clamp application was not significantly different from non-clamped carotids for mild injuries. However, the increased platelet uptakes for moderate (P = 0.007) and severe (P = 0.005) injuries were statistically significant when compared with non-clamped control arterial segments.

Reduced intimal injury to canine arteries with controlled application of vessel loops

Arterial intimal damage caused by elastic vessel loops was quantitated to determine (1) if they produce intimal injury, (2) if the injury is proportional to the force applied, and (3) if the injury is less than that produced by vascular clamps. Vessel loops were wrapped around 30 canine artery segments (5 mm in diameter) and a gram scale was connected to each to measure the force applied. The minimal occlusive force (MOF) and 150, 200, and 250 g force were applied for 30 min. For comparison, a Fogarty vascular clamp was applied at MOF for 30 min. Arteries were then reperfused for 30 min. Half was immediately harvested (group I); the remaining half was harvested at 2 weeks (group II). Scanning electron micrographs were made of each artery's intimal surface and graded from 0 (no injury) to 5 (severe intimal fracture). Mean injury grades were calculated. The MOF for vessel loops was 99 g. In group I, arteries subjected to less than 200 g force had a mean injury grade of 1.0 +/- 0.4; while those exposed to 200-250 g force had an injury grade of 3.5 +/- 0.7. The severity of injury was linearly correlated with the force applied (r = 0.72, P less than 0.009). In group II, the injury grade of 0.4 +/- 0.5 in arteries at MOF was significantly less than the injury grade of 2.8 +/- 0.5 in those at 200-250 g force, (P less than 0.0005). Injury grades of 3.7 and 3 were seen in groups I and II, respectively, when Fogarty clamps were applied. We conclude that vessel loops applied at MOF produce minimal injury. At greater occlusive forces, the injury is proportional to the force applied approaching that of a Fogarty clamp. Intimal injuries may be minimized when vessel loops are applied at MOF.

The initial blood retention properties of arterial prostheses

The initial contact between blood and vascular grafts may be a determinant of the fate of the implants. They behave in different ways depending upon their nature: the processed human umbilical vein and the bovine heterograft just lead to minimal thrombotic retention; the expanded PTFE is even more antithrombogenic; the porous polyesters which are porous textiles, should be totally impregnated with a thrombotic matrix to make the wall impervious. These observations were clearly determined by exposing the grafts to blood, incorporating either labeled platelets or labeled fibrinogen, and they were correlated by SEM examination.