Pharmacological prevention of atherothrombotic events in patients with peripheral arterial disease

Do we have a unified consensus on antithrombotic management of PAD?

Peripheral artery disease (PAD) is one of the most frequent manifestations of atherosclerosis with high rates of morbidity and mortality. Platelets and coagulation are involved in the progression of atherosclerosis and thromboembolic complications. PAD patients have increased prothrombotic potential, which includes platelet hyperaggregability and increased pro-coagulant state. Therefore, antithrombotic treatment is of utmost importance for the prevention of cardiovascular events in this group of patients. Aspirin is the basic antiplatelet drug, but with limited efficacy in PAD. In contrast to coronary artery disease, its effect on the prevention of cardiovascular events in PAD has been limited proven. Particularly in asymptomatic PAD, there is no evidence for risk reduction with aspirin. Clopidogrel and ticagrelor are more effective than aspirin. Clopidogrel is thus an effective alternative to aspirin for prevention of cardiovascular events in symptomatic PAD. In patients who are non-responders to clopidogrel, ticagrelor is indicated. Dual antiplatelet treatment (DAPT) with aspirin and ticagrelor in patients with coronary artery disease and concomitant PAD significantly decreased the rate of major adverse cardiovascular events, including adverse limb events. However, in the CHARISMA Trial, aspirin and clopidogrel were not more effective than aspirin alone and increased bleeding complications. Therefore, DAPT seems effective only in PAD accompanied by coronary artery disease. Anticoagulant treatment for symptomatic PAD with vitamin K antagonists alone or in combination with aspirin is not more effective than single antiplatelet treatment but increases the rate of major bleeding. Low dose rivaroxaban combined with aspirin in PAD patients significantly reduces cardiovascular events, including limb-threatening ischemia and limb amputations. Anticoagulation and antiplatelet treatment after percutaneous or surgical revascularization of PAD improve the patency of treated vessels. Aspirin with or without dipyridamole improved patency of infra-inguinal by-pass grafts at one year. The combination of clopidogrel with aspirin was more effective than aspirin alone in the prevention of prosthetic graft occlusions in patients undergoing below-knee by-pass-grafting. Oral vitamin K antagonists were not more effective than aspirin in the prevention of infra-inguinal by-pass occlusion. The combination of low dose rivaroxaban and aspirin was effective in preventing major adverse cardiovascular events and adverse limb events after infrainguinal endovascular or surgical revascularization in patients with intermittent claudication. However, the data on antithrombotic treatment after revascularization for limb-threatening ischemia is scanty and inconclusive. In conclusion: Antithrombotic treatment of PAD is a cornerstone for the management of these patients. Antiplatelet drugs prevent the initiation and progression of atherosclerosis and are effective also in the prevention of thromboembolic events. Simultaneous use of antiplatelet and anticoagulation drugs is accompanied by an increased risk of bleeding. However, combined treatment with aspirin and low-dose rivaroxaban is more effective than single antithrombotic treatment and safer than full-dose combined treatment.

Effect of exercise training on clot strength in patients with peripheral artery disease and intermittent claudication: An ancillary study

Objectives:

Patients with peripheral artery disease have walking impairment, greater thrombotic risk, and are often treated with exercise training. We sought to determine the effect of a 3-month-long exercise program on clot strength among patients with peripheral artery disease and intermittent claudication.

Methods:

Twenty-three symptomatic peripheral artery disease patients were randomly assigned to a walking exercise program or to an attention control group who performed light resistance exercise. We investigated the effect of exercise training on clot strength and time to clot formation was assessed by thromboelastography.

Results:

After 3 months of exercise, clot strength (maximal amplitude) and time to clot formation (R) did not change significantly from baseline, even after improvements in claudication onset time (p < 0.01) and peak walking time (p < 0.05). Furthermore, changes in clot formation parameters were not significantly different between groups. Among the 10 individuals demonstrating a reduction in clot strength (reduced maximal amplitude), one was a smoker (10%) compared to 9 of 13 non-responders (69%) whose maximal amplitude was unchanged or increased (p = 0.0097).

Conclusion:

In this ancillary study, a 12-week walking program improved ambulatory function in peripheral artery disease patients with claudication, but does not modify clot strength or time to clot formation. Larger studies are needed to confirm these hypothesis generating findings and to determine whether a different amount or type of exercise may induce a change in clotting in this patient population.

Ankle–Brachial Index Screening for Peripheral Artery Disease in Asymptomatic Patients between 50 and 70 Years of Age

Asymptomatic peripheral arterial disease (PAD) can be easily identified using the ankle–brachial index (ABI). This study was designed to investigate the benefits of performing ABI in patients aged 50-70 years. A random sample of 107 patients was chosen and data on gender, age, risk factors and laboratory tests were collected and the ABI measured. Twenty (19%) patients were found to have PAD. Smoking, high total cholesterol, high triglycerides and diabetes mellitus were shown to be associated with a low ABI and the presence of PAD. Age, diabetes and smoking were identified as the strongest predictors of PAD. Having more risk factors for PAD also predicted a lower ABI. These results suggest that measuring ABI is not necessary in patients aged 50-70 years if they only have one risk factor, with the exception of patients with diabetes and those who smoke. In contrast, measuring ABI seems to be useful for patients with multiple risk factors for PAD, although additional studies are required.

Simvastatin increases osteoblasts and osteogenic proteins in ovariectomized rats

BACKGROUND

Previous reports have indicated that statins could prevent bone loss in ovariectomized (OVX) rats and increase the expressions of osteogenic genes in cultured osteoblasts. In this study, we hypothesized that simvastatin might increase osteoblast number and protein expressions of osteogenic markers localized in bones in concomitance with the prevention of bone loss in OVX rats.

MATERIALS AND METHODS

Fifty-four 3-month-old OVX and sham-operated (SHAM) female Sprague-Dawley rats were used. Simvastatin (10-20 mg kg(-1) day(-1)) was administrated orally for 6 weeks. Trabecular volume, osteoblast number and osteogenic proteins including BMP2, collagen type I and osteocalcin on bone sections obtained from lumbar vertebral body, distal femur and proximal tibia were measured.

RESULTS

The results showed that SHAM rats had significantly less trabecular bone volume and osteoblast number than that of OVX rats 6 weeks after operation. Oral simvastatin treatment (10-20 mg kg(-1) day(-1)) increased bone volume and osteoblast number in the distal femurs, proximal tibiae and vertebrae of OVX rats. Furthermore, the osteoblastic cells with immuno-stained BMP2, collagen type I and osteocalcin in vertebral bones were significantly increased by simvastatin treatment (20 mg kg(-1) day(-1)) in OVX rats.

CONCLUSIONS

This study demonstrates that simvastatin enhances the production of osteogenic proteins in bone and this effect may contribute to the prevention of bone loss in OVX rats.

The association of acute exercise-induced ischaemia with systemic vasodilator function in patients with peripheral arterial disease

Abstract

Patients with peripheral arterial disease (PAD) frequently experience ischaemic attacks of the affected tissues during exercise. The present study assesses the association of transient exercise-induced leg ischaemia with vasodilator function of the clinically unaffected brachial artery over the course of 4 hours. Thirty male patients with symptomatic PAD and 14 age- and sex-matched healthy controls were included in the study. They performed a treadmill exercise until intolerable exercise-induced ischaemic pain occurred in the affected lower extremity, or for at most 10 min. Flow-mediated dilation (FMD) of the brachial artery was measured at baseline, 30 minutes, 2 hours and 4 hours after exercise. Baseline FMD values were significantly diminished in patients (7.03 ± 1.99% vs 8.22 ± 1.60% in controls, p = 0.009). A significant decrease in FMD was observed in patients after exercise (at 30 minutes: 3.92 ± 1.78% vs 7.03 ± 1.99% at baseline, p < 0.001; at 2 hours: 6.36 ± 2.12% vs 7.03 ± 1.99% at baseline, p = 0.005), followed by a gradual return to its baseline value, whereas FMD in controls non-significantly increased after exercise. The difference in the pattern of FMD change over time between patients and controls was significant ( p < 0.001). This study shows that in PAD patients ischaemia during intermittent claudication is related to a transitory functional deterioration of the distant arteries. This indicates the harmful systemic effects of repeated ischaemic attacks during exercise and might explain the generalized and advanced nature of atherosclerotic disease in PAD patients.

A new rat model for thrombus-induced ischemic pain (TIIP); development of bilateral mechanical allodynia

Patients with peripheral arterial disease (PAD) commonly suffer from ischemic pain associated with severe thrombosis. However, the pathophysiology of peripheral ischemic pain is not fully understood due to the lack of an adequate animal model. In this study, we developed a new rodent model of thrombus-induced ischemic pain (TIIP) to investigate the neuronal mechanisms underlying ischemic pain. Ischemia was induced by application of 20% FeCl(2) onto the surface of the femoral artery for 20min. Induction of peripheral ischemia was confirmed by measurement of the concentration of Evans blue and by increases in the ischemia-specific markers, hypoxia-inducible factor-1 alpha and vascular endothelial growth factor in the ipsilateral plantar muscles. Ischemic pain, as indicated by the presence of mechanical allodynia, developed bilaterally and peaked at days 3-9 post-FeCl(2) application and gradually decreased through day 31. Systemic heparin pretreatment dose dependently suppressed ischemic pain, suggesting that thrombosis-induced ischemia might be a key factor in TIIP. Intraplantar injection of BMS-182874, an ET(A) (endothelin-A) receptor antagonist, at day 3 selectively blocked ipsilateral pain, indicating that ET(A) receptor activity mediated TIIP. Spinal GFAP expression was significantly increased by FeCl(2) and intrathecal injection of carbenoxolone (an astrocyte gap junction decoupler) at day 3 significantly reduced TIIP, suggesting that spinal astrocyte activation plays an important role. However, the anti-inflammatory agent, ibuprofen, did not affect TIIP. In conclusion, we have developed a novel animal model of TIIP that should be useful in investigating the pathophysiological mechanisms that underlie human peripheral ischemic pain.