Interactions of platelets and vessel wall in the development of restenosis after coronary angioplasty

Peripheral arterial balloon angioplasty: effect of short versus long balloon inflation times on the morphologic results

PURPOSE

To evaluate the effect of different balloon inflation times on angiographic results in peripheral angioplasty.

MATERIALS AND METHODS

Seventy-four infrainguinal arteriosclerotic lesions were randomized prospectively to undergo balloon dilation for 30 seconds (group I) or 180 seconds (group II). Each group consisted of 37 patients. Postinterventional angiograms were evaluated by two blinded readers. Dissections were graded as follows: 1 = no dissection; 2 = minor flap; 3 = extensive dissection membrane, not flow limiting; or 4 = flow-limiting flap. The rate of major-grade dissections (grades 3 and 4), residual stenosis (>30%), and further interventions were compared with the two-tailed chi(2) test.

RESULTS

In group I, major dissections were noted in 16 patients (43%) compared with five patients (14%) in group II (P =.009). Residual stenoses were found in 12 patients (32%) in group I compared with five patients (14%) in group II (P =.096). The rate of additional interventions was significantly higher in group I than in group II (20 of 37 vs nine of 37; P =.017).

CONCLUSION

A prolonged inflation time of 180 seconds improves the immediate angioplasty result of infrainguinal lesions compared to a short dilation strategy. Significantly fewer major dissections and a modest reduction of residual stenoses are observed. The requirement of costly and time-consuming further interventions is significantly reduced.

Both increased and decreased platelet adhesion to thermally injured subendothelium is caused by denaturation of von Willebrand factor

BACKGROUND

Thermal angioplasty methods heat the arterial wall. We related platelet adhesion to the temperature to which subendothelium and purified adhesive proteins had been exposed.

METHODS AND RESULTS

Cultured subendothelium, purified von Willebrand factor, collagen types I and III, or fibronectin was applied to glass coverslips. Coverslips were mounted on a heating device that applied a temperature gradient from 30 to 100 degrees C. De-endothelialized umbilical arteries were heated by immersion in phosphate-buffered saline. After cooling to room temperature, the surfaces were perfused with blood at 37 degrees C (shear rate, 1600 sec-1). Compared with 37 degrees C, platelet adhesion to endothelial cell matrix was significantly reduced by 25%, 50% or 75% after heating to 69 +/- 1 degree C (mean +/- SEM, P < .05), 72 +/- 1 degree C, or 75 +/- 1 degree C, respectively. Platelet coverage to umbilical artery subendothelium was in the same way significantly reduced after heating to 71 +/- 1 degree C, or 77 +/- 1 degree C, respectively. In contrast to endothelial cell matrix, however, heating to about 55 degrees C increased platelet coverage from 30 +/- 5% to 54 +/- 6% (P < .05). Both platelet adhesion to von Willebrand factor and monoclonal antibody binding against the GpIb binding site of von Willebrand factor showed a comparable temperature dependence as platelet adhesion to subendothelium, provided the proper von Willebrand factor concentration was used. Platelet adhesion to heated collagen types I and III was increased and maximal at 57 +/- 2 degrees C and 62 +/- 2 degrees C, respectively. Preincubation of collagen III with proteins resulted in decreased platelet adhesion with increasing temperatures. Heating did not affect the reactivity of fibronectin.

CONCLUSIONS

In vitro platelet adhesion to human subendothelium is reduced by more than 50% after heating it briefly to more than 74 degrees C. Temperatures in excess of 80 degrees C reduce platelet adhesion by at least 85%. Thermal denaturation of von Willebrand factor is responsible not only for the decreased thrombogenicity above 71 degrees C but also for the increased thrombogenicity near 55 degrees C, provided that the von Willebrand factor concentration is low.

Effects of thrombocytopenia and shear rate on neutrophil and platelet deposition on endothelial and medial arterial surfaces

Both platelets and neutrophils interact with the injured vessel wall and may contribute to thrombosis and vasospasm. The effect of platelets on neutrophil interactions with the vessel wall was studied in normal and thrombocytopenic pigs. 51Cr-labeled platelet deposition (x10(6)) and 111In-labeled neutrophil deposition (x10(3)) on undamaged aortic strips with intact endothelium or damaged aortic strips with exposed media were quantified in superfusion flow chambers before and after platelet depletion by specific rabbit antisera. Arterial blood was drawn at a constant flow rate through the superfusion chambers at 37 degrees C. Under basal conditions, platelets did not adhere to the uninjured vessel wall with intact endothelium, whereas neutrophil interaction with the endothelium was low and constant at shear rates of 427, 853, and 1280 s-1 and did not change significantly after thrombocytopenia. On exposed aortic media simulating deep arterial injury, platelet deposition increased over these shear rates from 14.0 +/- 3.4 to 37.5 +/- 12.0 (P < .05) to 68.0 +/- 9.0, respectively (P < .05). Similarly, neutrophil deposition on the media increased from 48.7 +/- 8.7 to 73.7 +/- 14.3 (P < .05) to 118.3 +/- 22.9, respectively (P < .05). Platelet deposition on the media did not occur after thrombocytopenia (80% reduction in platelet count); however, neutrophil deposition persisted, but was less intense and was now independent of shear rates (23.3 +/- 5.2 at 427 s-1, 18.7 +/- 3.2 at 853 s-1, and 24.1 +/- 3.9 at 1280 s-1; not significant).(ABSTRACT TRUNCATED AT 250 WORDS)

Restenosis following coronary angioplasty

Restenosis is the most important problem limiting the success of coronary angioplasty. Clinically, restenosis is seen in approximately one-third of patients undergoing percutaneous transluminal coronary angioplasty. Several clinical and angiographic risk factors have been identified which may contribute to the development of restenosis. Histopathologic studies indicate that restenosis is characterized by intimal proliferation of smooth muscle cells in a loose connective tissue matrix. These intimal lesions are associated predominantly with the nonatheromatous portion of the vessel wall. Thinning of the media of the plaque-free wall and marked fragmentation of the internal elastic lamina are also seen. Traumatic injury of the vessel wall during angioplasty probably triggers a series of cellular and subcellular events which may ultimately lead to myointimal proliferation and restenosis. Although the exact mechanism by which this occurs is unknown, several factors may enhance smooth muscle cell growth and therefore may play a role in the development of restenosis. These include platelet deposition, mechanical stretching of the media, inflammation of the vessel wall, the activity of growth factors, and alterations in vessel geometry. These possible mechanisms of restenosis suggest several potential ways to limit the proliferative response to vascular injury. Anticoagulants and platelet antagonists, direct inhibitors of smooth muscle proliferation, anti-inflammatory agents, growth factor inhibitors, and new devices which improve final vessel geometry are currently being tested as methods to curb restenosis. Unfortunately, no treatment has yet been shown to reduce significantly the rate of restenosis following angioplasty. The problem of restenosis will most likely be solved by better understanding of the basic molecular and biologic phenomena involved in vascular injury and repair.

Prospects for the use of antagonists to the platelet glycoprotein IIb/IIIa receptor to prevent post-angioplasty restenosis and thrombosis

Despite many advances since its inception in humans in 1977, coronary angioplasty continues to be limited by the problems of abrupt arterial closure and late restenosis. Excessive platelet deposition at the site of angioplasty undoubtedly plays an important role in the pathophysiology of both of these problems. Monoclonal antibodies and snake venom-derived or synthetic peptides directed against a common protein recognition sequence on the platelet glycoprotein IIb/IIIa receptor are currently in the early stages of preclinical and clinical testing and hold promise of preventing abrupt closure and restenosis by inhibiting platelet function. Whether any of these agents will eventually be commonly used in clinical practice will depend on their effects on the complex pathophysiology of these problems and on their safety profile when administered to patients who are likely to receive other antithrombotic medications and who are instrumented for coronary angioplasty.