Effect of vascular clamp on endothelial integrity of the internal mammary artery

Pilot study of minimum occlusive force of vascular clamps on arterial vessels in rats

Our aims were to determine the accuracy of an improved formula for determining the minimum occlusive force (MOF) of a vascular clamp on rats' abdominal aortas, compare our findings with the calculated theoretical MOF, and provide reference data for clinical research and development of medical instruments that cause minimal damage. We created a vessel closure model and developed a formula for calculating the theoretical MOF of arterial vessels when they are occluded. This formula utilises the blood pressure in the blood vessel, its diameter, and the width of the vascular clamp. We then measured the actual MOF in 24 rat abdominal aortic segments with different diameters and different blood pressures and compared the theoretical and actual MOFs. Analysis of the experimental data showed a probability of 0.315, which means that, under the condition of normal distribution, the difference between the theoretical and actual MOF is not significant at the α = 0.05 level. Thus, the actual measured MOF tended to be consistent with the theoretical MOF calculated by the formula we developed. The improved formula will provide a reference for clinical research and development of medical instruments that cause minimal injury, thus contributing to the development of microsurgery.

Arterial clamping leads to stenosis at clamp sites after femoropopliteal bypass surgery

BACKGROUND

To date, the incidence and clinical relevance of arterial stenosis at clamp sites after femoropopliteal bypass surgery is unknown.

METHODS

Ninety-four patients underwent a femoropopliteal bypass in which the arterial inflow and outflow clamp sites were controlled by the Fogarty-Soft-Inlay clamp and marked with an hemoclip. The number of pre-existing atherosclerotic segments, clamp force, and clamp time were recorded and the occurrence of a stenosis at the clamp site was determined.

RESULTS

After a mean follow-up of 83 months, a significant stenosis was confirmed at 23 of the 178 clamp sites (12.9%; 95% confidence interval 8.4 to 18.8). The mean number of pre-existing atherosclerotic segments (P = .28) and the mean clamp force (P = .55) was similar between the groups with and without a stenosis. There was a significant difference regarding clamp time between the group with and without a stenosis (38 minutes and 26 minutes, P = .001).

CONCLUSION

Arterial clamping, even with the Fogarty-Soft-Inlay clamp, can lead to clamp stenosis and seems to be related to the duration of clamping, but not to pre-existent atherosclerotic burden.

The impact of vessel clamps on endothelial integrity and function of saphenous vein grafts

BACKGROUND

Saphenous vein graft (SVG) failure can be associated with endothelial damage during coronary artery bypass grafting (CABG). Endothelial damage may develop after application of occlusive vessel clamps on SVGs. This study was designed to investigate the effect of plastic and metal clamps on the endothelial integrity and function of SVGs.

METHODS

Saphenous vein samples were obtained from 10 consecutive patients, who underwent an elective CABG using SVG. Plastic (group 1) and metal (group 2) clamps were sequentially applied on the vein. Each set of clamps (1 plastic and 1 metal) was removed and sampled at 5, 15, and 30 min, respectively. A short SVG segment was removed as control. The samples were fixed for histopathologic study using hematoxylin-eosin staining and immunostaining for endothelial nitric oxide synthase (eNOS) expression. In each group, endothelial, elastic tissue, muscular layer, and adventitial changes were investigated under light microscope and compared using a histologic scoring system. The intensity of eNOS expression was assessed using histochemical scoring system.

RESULTS

In both groups, histopathologic examinations showed progressive endothelial damage in the zones of clamp application, compared with the control group (P<0.001). Histopathologic changes were more favorable with the metal clamps, compared with the plastic clamps, at 5 and 15 min. No significant increase in endothelial damage occurred after 15 min. The eNOS immunoreactivity of SVGs significantly decreased in the damaged areas of the endothelium (P<0.05). In metal clamps, the intensity of eNOS immunostaining was significantly high at 5 min, compared with plastic clamps (P<0.05). However, the intensity of eNOS expression in metal clamps was significantly lower than plastic clamps at 15 min (P<0.05). No significant difference was observed between the groups at 30 min.

CONCLUSIONS

The endothelial cells can be better preserved with short-term application of SVGs with metal clamps rather than plastic clamps. These findings suggest that temporary use of metal clamps can be preferred without major effects on vascular integrity and function.

Myocardial rewarming mirrors intraoperative mammary artery graft function

BACKGROUND

The internal mammary artery (IMA) bypass graft provides a satisfactorily long-lasting blood supply to the myocardium. However, its initial flow capacity can be insufficient with subsequent regional myocardial ischemia. We evaluated a method to assess the IMA graft function intraoperatively.

METHODS

Twenty-five patients with three-vessel coronary artery disease underwent coronary artery bypass grafting on cardiopulmonary bypass. The in situ IMA was grafted to the left anterior descending coronary artery (LAD) in combination with two saphenous vein grafts to the left circumflex and right coronary artery. Distal anastomoses were performed during cold intermittent blood cardioplegia. After unclamping of the aorta and of the grafted IMA, the temperature at the cardiac anterior and posterior side was measured during the first 5 minutes of warm reperfusion.

RESULTS

A sufficient IMA graft function was expressed by a typical rise in temperature: the cardiac anterior and posterior sides showed a parabolic and exponential course, respectively. The rewarming velocity expressed as the first derivative of temperature over time led to a sharp and early peak for the anterior side, and a smaller and delayed peak for the posterior side. Insufficient IMA graft function could be recognized by an atypical temperature course.

CONCLUSIONS

Temperature measurement of the heart during warm reperfusion after hypothermic cardioplegia can help to assess the effectiveness of the IMA-LAD graft function.

Comparison of laparoscopic aortic clamps in a pulsatile circulation model

PURPOSE

This study was designed to evaluate the fatigue characteristics and the safety and effectiveness of laparoscopic aortic clamps in a pulsatile circulation model.

METHODS

A heart-lung machine was used to create a pulsatile circulation model with bovine aortas resembling the vessels being cross-clamped. Four different models (A-D) of laparoscopic aortic clamps were investigated, and three identical probes of each model underwent testing. Preliminary examinations were conducted to define the size and thickness of the bovine aortas that would allow effective cross-clamping and to detect gross material or functional deficits of the clamps. Then, the instruments were placed in the circulation model, which was set at a frequency of 82/min and a pressure of 200/120 mm Hg. Each clamp was subjected to these conditions for 120 hours and was opened and closed 40 times to stimulate real-life conditions. Clamping failures and mechanical defects were recorded, and the clamp parts were afterward examined with an electron microscope.

RESULTS

Two clamp models had to be eliminated from the study after the preliminary examinations. All three probes of model B displayed mechanical defects after a few applications. All probes of model D were excluded because none effectively occluded the aortas. All probes of model A and one probe of model C provided effective cross-clamping during the 120-hour test phase and showed no signs of mechanical failure. Two probes of model C broke after 51 and 57 hours of testing, respectively. Both times, the defect occurred during application of the clamps. The detailed analysis of all instruments after the testing, including electron microscope imaging, revealed that several construction deficits and weak points were responsible for the mechanical failures.

CONCLUSION

A surprisingly high incidence of clamping failures and mechanical deficits were encountered during the testing. Of the four clamps tested, only one (model A) seemed to be safe and effective enough for routine clinical use. These disappointing results demonstrate the need for further cooperation between vascular surgeons and instrument manufacturers to develop safe and effective laparoscopic vascular clamps.

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.

The effect of arterial clamp duration on endothelial injury: an experimental study

BACKGROUND

Arterial clamp-related endothelial damage was investigated in an animal model to quantify the surface area of endothelial disruption. The influence of the duration of clamp application on this damage was evaluated.

METHODS

Four identical angled DeBakey vascular clamps were applied on each of eight carotid arteries in four heparinized adult sheep for durations of 15, 30, 45 and 60 min. The applied clamping forces were measured and kept constant. After the last clamp was removed, the areas of endothelial loss were identified by in vivo staining with Evan's blue dye. The vessels were excised and the blue stained areas measured by computer-assisted analysis. The morphological appearance of the specimens was assessed by scanning electron microscopy.

RESULTS

Endothelial damage following clamping for 15 min (10.6 +/- 4.3 mm2) was significantly less than for 30 min (19.0 +/- 4.7 mm2), 45 min (19.8 +/- 4.6 mm2) and 60 min (20.4 +/- 4.9 mm2, P = 0.005), but there were no significant differences between the areas of endothelial loss observed for 30, 45, and 60 min. These results corresponded to the damage seen using scanning electron microscopy, which showed partial disruption of endothelium at 15 min compared to more complete destruction at longer durations.

CONCLUSIONS

Evan's blue staining combined with computer-assisted surface area measurement is an accurate method for quantifying endothelial damage. The extent of damage caused by vascular clamps is partly time-dependent, being less for 15 min than for 30 min of clamping, but not significantly increasing for durations greater than 30 min.

Direct measurement of clamping forces in cardiovascular surgery

Equipment for measuring the direct tip force of a clamp arm on the vessel wall is designed as an adjustable surgical clamp with strain gauges applied and connected via an amplifier to a computer-based data acquisition system. A mechanical model that incorporates the resistance of tissue against momentary deformations is developed to analyse and justify measured results. In in vivo experiments on rat thoracic aorta, the minimum occlusion force, stationary clamping force and the momentary peak clamping force are measured and observed as an important cause of damages in the endothelial layer of vascular walls.

Endothelial effects of hemostatic devices for continuous cardioplegia or minimally invasive operations

BACKGROUND

Improvements in myocardial protection may include the continuous delivery of normothermic blood cardioplegia. Technical aids are required for optimal visualization of the operative field during the performance of coronary anastomoses if cardioplegia is to be given continuously or during minimally invasive operations. However, the effects of the different hemostatic devices on coronary endothelial function are unknown.

METHODS

We compared the effects on endothelial function of two commonly used hemostatic techniques, coronary clamping and gas jet insufflation, with those of a technique using extravascular balloon occlusion to mimic systolic luminal closure by the surrounding myocardium. The three techniques were applied for 15 minutes on porcine epicardial coronary arteries from explanted hearts. For coronary clamping, standard bulldog clamps were used. Gas jet insufflation was applied by blowing oxygen (12 L/min) tangentially at a 45-degree angle 1 cm away from a 3-mm arteriotomy. Extravascular balloon occlusion was achieved with a needle-tipped silicone loop, the midportion of which, once positioned beneath the coronary artery, was inflated to push a myocardial "cushion" against the back of the vessel until its occlusion. Control rings were taken from the same coronary artery. The endothelial function of control and instrumented arterial rings was then studied in organ chambers filled with modified Krebs-Ringer bicarbonate solution.

RESULTS

Contractions to potassium chloride and prostaglandin F2 alpha and endothelium-independent relaxation to sin-1, a nitric oxide donor, were unaffected in all groups. Endothelium-dependent relaxation to serotonin was impaired after clamping and preserved after gas jet insufflation and extravascular balloon occlusion. Maximal endothelium-dependent relaxation to serotonin was as follows: for coronary clamping, 63% +/- 6% versus 87% +/- 3% in controls; for gas jet insufflation, 67% +/- 12% versus 88% +/- 7%; and for extraluminal balloon occlusion, 79% +/- 6% versus 85% +/- 5%.

CONCLUSIONS

Whereas commonly used hemostatic devices may impair endothelial function, extravascular balloon occlusion appears to achieve effective hemostasis while preserving endothelial integrity.

The comparison of vascular reactivities of arterial and venous grafts to vasodilators: management of graft spasm

Graft spasm in the perioperative or postoperative period increases the risk of morbidity and mortality after coronary revascularization and hence necessitates urgent treatment. We have studied the effects of various vasodilators against noradrenaline- and endothelin-1-induced spasms in saphenous vein, internal mammary artery and gastroepiploic artery. In internal mammary and gastroepiploic arteries, the nitrovasodilators, sodium nitroprusside and glyceryl trinitrate, effectively reversed the spasms induced either with noradrenaline (for sodium nitroprusside; internal mammary artery: 101.07% +/- 1.63%; gastroepiploic artery: 94.10% +/- 2.07%) or endothelin-1 (for sodium nitroprusside; internal mammary artery: 97.67% +/- 4.94%; gastroepiploic artery: 90.69% +/- 2.61%). However, in saphenous vein contracted with endothelin-1, the responsiveness to nitrovasodilators was significantly blunted (for sodium nitroprusside: 52.33% +/- 5.19%) than that of rings contracted with noradrenaline (for sodium nitroprusside: 95.04% +/- 1.94%). Both arterial and venous grafts exhibited moderate beta-receptor function in response to isoproterenol. Isoproterenol was less effective in inhibiting the contractions of endothelin-1 in saphenous vein and gastroepiploic artery but not in internal mammary artery. On the other hand, nifedipine and papaverine were fully effective in reversing all the spasms in three of the graft materials. From these results, it can be deduced that saphenous vein is refractory against cyclic guanidine monophosphate (cGMP)-dependent and beta-receptor mediated relaxations when endothelin-1 was used as the spasmogenic agent. Internal mammary artery is the most responsive graft material to the vasodilators regardless of the nature of spasmogenic stimulus. Gastroepiploic artery exhibits functional similarity with internal mammary artery, with the exception of beta-receptor responsiveness.

Human mammary artery endothelial sparing with fibrous jaw clamping

BACKGROUND

Temporary clamping of the internal mammary artery pedicle is required for visualization during coronary artery bypass grafting. A nylon fibril jaw surface has been developed for these clamps that exerts pressure only at discrete sites on the pedicle surface. The effect of this new jaw surface on endothelial cell function and integrity after compression is investigated in this study.

METHODS

Internal mammary artery specimens from 10 patients each were divided into three separate rings, and two of these rings were clamped for 30 minutes with either a smooth or fibrous jaw clamp. Isometric tensions were measured in organ chambers after contraction by relaxing the rings with the endothelium-dependent agent acetylcholine followed by the endothelium-independent agent sodium nitroprusside. The intimal surfaces of similar rings were silver stained to assess the percentage of intact endothelium.

RESULTS

Endothelium-dependent relaxation was spared after fibrous jaw clamping (75% versus 89%) but significantly impaired after smooth jaw clamping (25% versus 89%; p < 0.001). Endothelium-independent relaxation was unaffected by either intervention. The percentage of remaining intact endothelium upon silver staining was significantly less after smooth than after fibrous jaw clamping (24% versus 48%; p < 0.01).

CONCLUSIONS

Foam silicone with nylon fibrils on the jaw surface of internal mammary artery clamps preserves endothelial cell function and integrity. The remaining undamaged cells also may facilitate the subsequent regeneration of a confluent endothelial cell layer.

Thermal coronary angiography for intraoperative patency control of arterial and saphenous vein coronary artery bypass grafts: results in 370 patients

BACKGROUND AND AIM OF THE STUDY

Early graft failure is often associated with technical failures and is therefore potentially avoidable. We used thermal coronary angiography (TCA) for intraoperative graft patency control in 370 patients undergoing routine coronary artery bypass graft surgery to determine whether consequent intraoperative bypass graft control may result in improved patency rates.

METHODS

The temperature differences generated in between the myocardium and the grafts by injecting cold cardioplegic solution into the proximal end of a vein graft or by warmer blood running through an internal thoracic artery (ITA) graft were detected using three different infrared camera systems. The resulting "heat pictures" were evaluated for anastomotic patency and to outline graft anatomy.

RESULTS

A total of 693 vein grafts were visualized. In 9.4% TCA failed to produce usable images. In the remaining 628 grafts, TCA revealed intraoperative patency in 98.8%. Out of 370 ITA grafts, only 14 could not be sufficiently visualized by TCA. Nineteen ITA occlusions (5.3%) were found: 5 intimal flaps; 11 suture imposed strictures; and 3 proximal ITA occlusions. All occluded grafts were subsequently revised or replaced. All sequential ITA as well as 15 right ITA grafts proved to have patent anastomoses.

CONCLUSION

Using TCA an early graft dysfunction rate of 1% for vein grafts and 5.3% for ITA grafts could be demonstrated. Most occlusions were due to technical mistakes at the distal anastomosis. TCA outlines grafts and the attached coronaries by temperature differences without the need for a contrast agent. There is no interference with the surgical procedure. It is an ideal, noninvasive method to immediately document the success or failure of myocardial revascularization.