Fibrinogen and carboxyhaemoglobin in peripheral arterial disease

Fibrinogen and cardiovascular risk

The hypothesis that fibrinogen is closely related to cardiovascular risk has been strengthened through the results of various lines of research, which this review will aim to unravel. Several prospective epidemiological studies convincingly show elevated fibrinogen to represent a major, independent cardiovascular risk factor. Cross-sectional studies strongly associate fibrinogen and conventional cardiovascular risk factors. Clinical cohort studies demonstrate that increased fibrinogen is also a risk factor for the sequelae of cardiovascular disease. Our knowledge about the determinants of the variable plasma level of fibrinogen in health and disease is incomplete. Understanding of the mechanisms that might be involved in the atherothrombogenic action of fibrinogen is also fragmentary. Fibrinogen strongly affects blood coagulation, blood rheology and platelet aggregation. In addition, it has direct effects on the vascular wall and is a prominent acute phase reactant. All of these phenomena might constitute pathophysiological mechanisms involved in the association between fibrinogen and cardiovascular events. Their relative importance is unclear at present. Even though many crucial questions await conclusive answers, little doubt exists that fibrinogen represents a major, independent risk factor.

Fibrinogen: an important risk factor for atherothrombotic diseases

Epidemiological follow-up studies have suggested that fibrinogen is a major, primary cardiovascular risk factor. Cross-sectional results also show associations between fibrinogen and cardiovascular risk factors or diseases. Clinical cohort studies demonstrate that fibrinogen might also be a secondary risk factor. The determinants of the plasma level of fibrinogen in health and disease are known only incompletely. Our understanding of the mechanisms involved in the atherogenic actions of fibrinogen is similarly fragmentary. These might include blood coagulation, blood rheology, platelet aggregation, direct effects on the vascular wall, and the acute phase response. Thus, many questions are yet to be answered. Nevertheless, the data available at present strongly suggest that fibrinogen represents a major, independent cardiovascular risk factor. Fibrinogen should be considered for screening programmes aimed at identifying individuals at risk.

The role of fibrinogen as a cardiovascular risk factor

Several epidemiological studies have produced longitudinal data identifying fibrinogen as a major cardiovascular risk factor. Cross-sectional results show strong associations between fibrinogen and a variety of demographic variables, cardiovascular risk factors, or diseases. Clinical cohort studies demonstrate that fibrinogen might also be a risk factor for the sequelae of cardiovascular disease. Knowledge about the determinants of the plasma level of fibrinogen in health and disease is as yet incomplete. Understanding of the mechanisms leading to the atherothrombogenic action of fibrinogen is also fragmentary. Fibrinogen strongly affects blood coagulation, blood rheology and platelet aggregation; in addition fibrinogen and its metabolites have direct effects on the vascular wall. Finally, fibrinogen is a prominent acute phase protein. All of these phenomena might provide some insight into the pathophysiological mechanisms involved. It is concluded that fibrinogen represents a major, independent risk factor that should now be included into the cardiovascular risk profile.

Plasma fibrinogen--an independent cardiovascular risk factor

Apart from being an acute phase reactant, fibrinogen appears to play an important although not widely recognized role in athero-/thrombogenesis. Arteriosclerotic diseases are associated with elevated levels of plasma fibrinogen. Strategies that lower the cardiovascular risk also lower fibrinogen levels. Virtually all accepted risk factors are associated with hyperfibrinogenaemia, while low risk populations usually have low fibrinogen levels. Epidemiological studies show that fibrinogen is a predictor of arteriosclerotic diseases. Its predictive power seems to be as high as or higher than accepted risk factors. These findings and other circumstantial, as well as experimental, evidence suggest that fibrinogen is a powerful, independent cardiovascular risk factor.

Current therapy of peripheral obstructive arterial disease. The non-surgical approach

In recent years double-blind trials have proved the effectiveness of nonsurgical therapy in the treatment of peripheral obstructive arterial disease (POAD). Among the non-pharmacologic measures taken, walking distance was increased by 40% in subjects who stopped smoking and by more than 100% in those who undertook physical exercise. Drug treatment reduces the atherosclerotic process and brings about an improvement in the symptoms of the disease. In subjects given hypolipidemic treatment the progression of the disease was reduced by two thirds. Two separate studies suggest that antiplatelet drugs, taken over a period of two to four years, significantly slow the progression of atherosclerosis in lower extremity arteries. In the treatment of claudication, two vasodilating drugs, naftidrofuryl and buflomedil, have shown a significant improvement in painfree walking distance and/or total walking distance, compared with treatment with placebo. Another effective approach is in the treatment of blood rheology through drugs such as pentoxifylline or by hemodilution. Double-blind trials with pentoxifylline demonstrated an average increase of 66% in maximum walking distance as compared with 22% with placebo. The effectiveness of hemodilution was demonstrated by two controlled trials, during which the reduction of the hematocrit to values of 40-42 for periods of four to six weeks increased both walking distance and resting blood flow. When introduced intraarterially in low doses in the vicinity of the occluding thrombus, thrombolytic agents have been found to be helpful in the treatment of acute and chronic POAD. This therapy should, however, be regarded as a substitute for surgical treatment only in high-risk patients. Further, after having produced the lysis of thrombi, the treatment permits the underlying parietal lesions to be accurately identified; at this point the appropriate therapy can be decided upon, either an operative procedure or a balloon dilation. In conclusion the many controlled clinical trials carried out over the past few years have clearly demonstrated that conservative treatment can alleviate clinical signs and symptoms in patients with claudication and pain at rest.

Influence of smoking and plasma factors on patency of femoropopliteal vein grafts

OBJECTIVE

To determine the effects of smoking, plasma lipids, lipoproteins, apolipoproteins, and fibrinogen on the patency of saphenous vein femoropopliteal bypass grafts at one year.

DESIGN

Prospective study of patients with saphenous vein femoropopliteal bypass grafts entered into a multicentre trial.

SETTING

Surgical wards, outpatient clinics, and home visits coordinated by two tertiary referral centres in London and Birmingham.

PATIENTS

157 Patients (mean age 66.6 (SD 8.2) years), 113 with patent grafts and 44 with occluded grafts one year after bypass.

MAIN OUTCOME MEASURE

Cumulative percentage patency at one year.

RESULTS

Markers for smoking (blood carboxyhaemoglobin concentration (p less than 0.05) and plasma thiocyanate concentration (p less than 0.01) and plasma concentrations of fibrinogen (p less than 0.001) and apolipoproteins AI (p less than 0.04) and (a) (p less than 0.05) were significantly higher in patients with occluded grafts. Serum cholesterol concentrations were significantly higher in patients with grafts that remained patent one year after bypass (p less than 0.005). Analysis of the smoking markers indicated that a quarter of patients (40) were untruthful in their claims to have stopped smoking. Based on smoking markers, patency of grafts in smokers was significantly lower at one year by life table analysis than in non-smokers (63% v 84%, p less than 0.02). Patency was significantly higher by life table analysis in patients with a plasma fibrinogen concentration below the median than in those with a concentration above (90% v 57%, p less than 0.0002). Surprisingly, increased plasma low density lipoprotein cholesterol concentration was significantly associated with improved patency at one year (85%) at values above the median compared with patency (only 68%) at values in the lower half of the range (p less than 0.02).

CONCLUSIONS

Plasma fibrinogen concentration was the most important variable predicting graft occlusion, followed by smoking markers. A more forceful approach is needed to stop patients smoking; therapeutic measures to improve patency of vein grafts should focus on decreasing plasma fibrinogen concentration rather than serum cholesterol concentration.