Antithrombotic therapy in peripheral vascular disease

Perioperative use of eicosapentaenoic acid and patency of infrainguinal vein bypass: A retrospective chart review

Abstract.

BACKGROUND

A significant proportion of autogenous vein grafts fail in the long term. Currently, there is no treatment to improve graft patency.

OBJECTIVE

This study was designed to assess the effectiveness of eicosapentaenoic acid (EPA) to prevent late failure of an autogenous vein graft and other perioperative risk factors affecting long-term patency.

METHODS

A retrospective chart review was performed on grafts of patients who underwent infrainguinal bypass surgery using autogenous vein grafts for peripheral arterial disease in a lower limb. Patients were stratified by the perioperative use of EPA. The EPA group was those patients who administered EPA ≥1 time within 3 months of surgery. The non-EPA group was made up of those patients who did not administer EPA within 3 months of surgery. Primary, assisted primary, and secondary patency rates of the grafts in each group were calculated by the Kaplan-Meier method and compared by the log-rank test. To evaluate the effect of other perioperative risk factors, a Cox proportional hazards analysis was performed.

RESULTS

One hundred sixty-one grafts were analyzed from 159 patients who underwent surgery between July 1991 and July 2005. The primary patency rates of the EPA and non-EPA groups were 93% and 86%, 89% and 74%, and 83% and 68% at 1, 3, and 5 years, respectively. In terms of primary patency, the EPA group was significantly better than the non-EPA group (P=0.042). There was no significant difference between the groups in either assisted primary or secondary patency. A Cox proportional hazard analysis found that the minimum graft diameter and perioperative use of EPA were significant factors for primary patency (P=0.002 and P=0.004, respectively). Graft diameter was the only significant factor for assisted primary and secondary patency (P=0.021 and P=0.003, respectively).

CONCLUSION

Although graft diameter was the most important factor for long-term patency of infrainguinal vein bypass grafts, the perioperative use of EPA significantly improved primary patency among these subjects.

Mediators of restenosis

The multitude of actions and interacting components involved in inciting and sustaining myointimal hyperplasia and restenosis effectively precludes the use of a single type of intervention. No pharmacologic approach has been conclusively shown to prevent coronary restenosis after balloon angioplasty or graft restenosis after peripheral arterial bypass. Although no human studies have been performed to prevent restenosis with gene therapy, the animal data are compelling, and the local delivery of various inhibitory agents may represent a novel way of preventing restenosis in vascular beds subjected to endovascular or traditional open procedures. Until these modalities are proved effective, the treatment of vascular stenosis due to internal hyperplasia remains within the domain of the surgeon.

Claudication as an 'orphan disease': rationale and goals of drug therapy for peripheral arterial disease

Patients with peripheral arterial disease are often perceived to suffer from a disorder whose pathogenesis and symptoms are not amenable to drug therapies. This clinical misperception remains prevalent despite an abundance of data suggesting that diverse pharmacotherapies may modulate the natural history of this disease. Patients with chronic limb arterial occlusive disease suffer from a disease that is characterized by: (1) a prolonged asymptomatic state that can be identified by simple physical examination and confirmed by measurement of the ankle brachial index; (2) a multi-year period of symptomatic claudication; and (3) a variable rate of progression to critical limb ischemia or acute arterial occlusion. This stage-dependent disease progression is mediated via the dynamic, but as yet incompletely understood, interaction of factors that elicit endothelial dysfunction, atherogenesis, and thrombosis. Current data suggest that each of these contributory disease processes can be modulated by extant pharmacotherapies. Additionally, many novel pharmacotherapeutic agents that are currently under investigation may further improve the ability of clinicians to modulate these fundamental biologic processes. Pharmacologic therapies should be targeted to decrease the rate of limb arterial disease progression, to improve limiting symptoms, and to prolong life. Symptoms of claudication can be objectively assessed via both exercise testing and disease-specific questionnaires. The presence of lower extremity atherosclerotic disease is predictive of the presence of coronary heart disease and a foreshortened five-year survival. Current data suggest that clinical investigations should be able to effectively stratify this relative risk via use of both clinical variables (e.g., age, diabetes mellitus, tobacco use, etc.) or by measurement of the ankle brachial index (ABI). The role of the physician is to decrease suffering and to prolong life. Judicious administration of medical therapies can play a critical role in helping the vascular practitioner accomplish these goals.

Peripheral arterial disease

Peripheral arterial diseases are common problems because atherosclerosis, the most common cause of both occlusive peripheral arterial disease and aneurysmal disease, is a feature of an aging population. The less common types of occlusive peripheral arterial disease--the vasospastic disorders and the arteritides--although frequently not addressed to any extent in medical school curricula or in residency programs in family and internal medicine, offer the alert and informed clinician diagnostic and therapeutic opportunities that are too important to neglect. As a group, abnormalities of the peripheral arteries are easy to detect if careful observation and examination of the extremities is included in the physical examination and attention to functional disorders is included in the medical history. In this presentation, the clinical features, physical findings, complications, useful noninvasive diagnostic tests, imaging techniques, and therapeutic options for atherosclerotic occlusive peripheral arterial disease (both chronic and acute), uncommon types of occlusive arterial disease of both the lower and upper extremities, the vasospastic disorders, and the peripheral arterial presentations of the arteritides are reviewed. The application of natural history and comorbidity of a particular arterial disease, when available, is emphasized in the formulation of management for the individual patient.

Effect of ticlopidine on blood loss, platelet turnover and platelet deposition on prosthetic surfaces in patients undergoing aorto-femoral bypass grafting

Sixty patients in whom a prosthetic aorto-femoral bypass graft was inserted were pretreated with ticlopidine (250 mg b.i.d.) or placebo in a double-blind study. Blood loss and transfusion need were higher in ticlopidine treated patients. Platelet survival was partially corrected and platelet deposition on prosthetic surfaces was inhibited with ticlopidine. The study suggests that ticlopidine does not increase excessively the bleeding risk during peripheral vascular surgery and that the antiplatelet drug may have beneficial effects in the early phase after insertion of prosthetic vascular graft.

Warfarin and the international normalized ratio: reducing interlaboratory effects

In North America, the dose of warfarin has been unintentionally increased during the past two decades because of failure to recognize the effect on the anticoagulation test of less sensitive tissue thromboplastins. Although there still is some controversy, the suggested dose of warfarin has now been adjusted downward to reduce the risk of bleeding. These revised dosing recommendations incorporate the international normalized ratio (INR), which takes into account the source of thromboplastin. However, there is considerable variability in the sensitivities of thromboplastin from manufacturer to manufacturer and lot to lot. Therefore, prothrombin times (PTs) are not comparable from laboratory to laboratory without knowing the sensitivity of the thromboplastin. Unless laboratories adopt a standardized tissue thromboplastin, the PT should be reported as an INR.

Platelet inhibitor agents in cardiovascular disease: an update

Platelets interact with the coagulation and fibrinolytic systems in the maintenance of hemostasis. However, these physiologic mechanisms may become pathologic, requiring prevention and treatment. In this review, the following clinical developments are analyzed: 1) the role of platelets in thrombogenesis; 2) the pharmacology of platelet inhibitory agents; and, most important, 3) the results of recent randomized trials of platelet inhibitor agents in different cardiovascular disorders. Aspirin reduces mortality and infarction rates in unstable angina and significantly decreases vascular mortality in acute myocardial infarction. Platelet inhibitors decrease mortality and recurrent cardiovascular events in the chronic phase after myocardial infarction. They also decrease vein graft occlusion rates after coronary bypass surgery. Although platelet inhibitors are beneficial in preventing acute vessel occlusion during coronary angioplasty, they are ineffective in preventing chronic restenosis. Antiplatelet agents, combined with warfarin, reduce thromboembolic events in patients with a mechanical prosthesis. Platelet inhibitors are also effective in secondary prevention of vascular events in patients with cerebrovascular disease. Finally, the use of aspirin for primary prevention of cardiovascular disease is still evolving, particularly in individuals at high risk. In conclusion, platelet inhibitors are effective in patients with a variety of cardiovascular disorders. The best studied, most inexpensive and least toxic agent is aspirin at a daily dose of 160 to 325 mg. Studies using new platelet inhibitor agents with different mechanisms of action are currently underway.