Is gout a risk factor for incident heart disease?

One of the key metabolic abnormalities in gout, hyperuricaemia, is known to be associated with increased risk of cardiovascular disease, although causality has not been proved.6–9 On the other hand, while there are some data suggesting that gout is a risk factor for incident heart disease, the overall literature in the area is somewhat mixed and debateable (table 1). The authors also cite it as the main reason for conducting the current study. The risk imparted by hyperuricaemia is of a small magnitude compared to other traditional cardiovascular risk factors, but it is significant. In addition, hyperuricaemia has also been shown to be a risk factor for peripheral vascular disease, another manifestation of atherosclerosis.10 ,11 Some studies indicate that gout is an independent risk factor for incident cardiac disease (table 1).

Why do gout patients have higher risk of cardiovascular disease? The contributions of endothelial dysfunction and systemic inflammation

Gout, a metabolic disease associated with hyperuricaemia, leads to acute joint inflammation as part of a response to precipitation of urate crystals in the joint that commonly manifests as acute gout. Also, there is chronic inflammation around microtophi. Hyperuricaemia, a cardinal feature of gout, is associated with endothelial dysfunction, which may contribute to the risk of heart disease in patients with gout.12 However, depending on the chemical microenvironment, uric acid may have antioxidant or pro-oxidant function.13 In addition, uric acid likely contributes to the oxidation of lipoproteins within atherosclerotic plaque, thus contributing to the progression of lesions in coronary arteries.14 Gout is associated with systemic inflammation. Markers of systemic inflammation, such as erythrocyte sedimentation rate and C reactive protein, are often elevated during acute gouty arthritis15 and may even be raised in chronic active gouty arthritis.16 Studies have linked systemic inflammation to the risk of heart disease in other similar chronic systemic inflammatory conditions, such as rheumatoid arthritis and lupus.3 ,4 ,17 ,18

A model for increased cardiovascular disease in gout is proposed, based on the current literature (figure 1). In the model, we allude to the mechanisms of cardiovascular disease, but due to lack of further evidence cannot propose what (hyperuricaemia vs acute inflammation vs chronic inflammation vs other yet unknown mechanism) exactly leads to that pathogenic step in cardiovascular risk (endothelial dysfunction, oxidation of low density lipoprotein (LDL), etc). Potential pathogenic mechanisms shown in patients with gout are either known (solid line) or suspected (dotted line). Similarly, the association of these mechanisms to the risk of heart disease is either known (solid line) or suspected (dotted line) in gout patients, or in general. For example, the association of hyperuricaemia (a cardinal feature of gout) with endothelial injury and acute and chronic inflammation is known, while its contribution to oxidation of LDL and elevation of other pro-atherogenic factors/mechanisms/pathways is suspected.

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Figure 1

Potential pathogenic pathways for higher risk of cardiovascular disease in patients with gout. Solid lines indicate current evidence supporting the mechanism/pathway and dotted lines indicate potential mechanism/pathway, for which more evidence is needed. Several links from gout to the intermediate event (endothelial dysfunction, etc) may be through (mediated by) hyperuricaemia or non-hyperuricaemic pathways (eg, systemic inflammation).

Why does the cardiovascular risk with gout differ by sex?

Heart disease risk differs by sex in the general population. Women have a lower risk of heart disease compared to age-matched men in the pre-menopausal years—a protective effect of oestrogen. This benefit is lost in post-menopausal years and therefore the risk of heart disease in post-menopausal women catches up with men's risk of heart disease. Despite the differences in prevalence rates, the same risk factors for heart disease are key in both men and women—that is, smoking, diabetes, hypertension, hyperlipidaemia, and family history of heart disease. The early evidence from the current study and some others (table 1) indicates that the increase of heart disease risk might differ slightly by sex, the association being stronger in women compared to men. The absolute risk of any cardiovascular disease was 24.0/1000 person-years in men and 23.1/1000 person-years in women with gout, compared with 19.2 and 14.8/1000 person-years in men and women without gout, respectively. This shows that there is a difference in the risk of cardiovascular disease by sex in patients without gout and that this sex difference in cardiovascular disease risk is abolished in men and women with gout. It is possible that systemic inflammation induced by gout in women, who otherwise have a lower prevalence of cardiac risk factors than age-matched men, is more atherogenic than that in men. Studies are needed to test whether there are sex-based differences in the pathogenesis of gout-associated heart disease.

Does this mean gout patients should be carefully screened for cardiovascular disease risk factors?

Considering the ease of screening for risk factors, the suggestion is to screen gout patients older than 35 years (arbitrary—one may pick 40 years, for instance) with fasting lipid profile and glycated haemoglobin (HbA1c) monitoring, blood pressure measurement and current smoking status, and counsel/discuss with the patient if any risk factors are present. Patients should also be screened at regular intervals if their baseline is not normal and managed aggressively. Regardless of causality, the fact remains that patients with gout have a higher prevalence of numerous comorbidities, each of which can contribute to cardiovascular risk, and therefore require appropriate screening and management, as suggested by previous gout guidelines.19 ,20 Since most gout patients receive care from primary care physicians, rather than rheumatologists, this is relatively easy. The only difference from the general population is an earlier age for screening, given the increased prevalence of cardiovascular disease risk factors in patients with gout and an increased associated risk. The goals are to prevent the onset of heart disease in patients with gout, and in those with early evidence of heart disease based on the workup with traditional markers and surrogates (such as serological and imaging biomarkers), institute treatments to improve outcomes.

What should change in primary care and rheumatology practice based on these data?

The end-organ damage from gout may not be limited only to the musculoskeletal system. Evidence is accumulating that the presence of gout matters for cardiac and vascular health, just as it does for joint health. It is to our advantage that a significant proportion of gout patients are managed by internists and cardiologists. A small, but significant, proportion of patients with gout may see cardiologists in addition to internists due to refractory pre-existing/concomitant cardiac conditions (coronary heart disease, congestive heart failure) and/or risk factors (hyperlipidaemia, hypertension, etc). However, in some of these cases, the cardiac or vascular disease has already manifested, meaning the window of opportunity may have been missed, and only secondary prevention (avoiding future myocardial infarction, etc) is possible. Real progress in the care of gout patients can be measured by our ability to improve overall outcomes in gout patients including proactive recognition, early diagnosis, and optimisation of the treatment of heart disease—that is, primary prevention.

Primary prevention is always the goal of an epidemiologist, since the public health and individual level impact is much more substantial than secondary or tertiary prevention. It is very desirable to intervene early in high risk patients to modify traditional and non-traditional cardiac and vascular disease risk factors, before cardiac disease actually manifests. Mitigation of traditional cardiovascular disease risk factors such as hypertension is key to reducing this risk. Another approach might be to target and reduce systemic inflammation due to chronic gouty arthritis as well as acute gouty arthritis, by providing optimal urate-lowering (and anti-inflammatory) therapy, in order to additionally (potentially) prevent or delay the onset of cardiac disease in patients with gout. An effectiveness trial where the intervention targets systemic inflammation, with a sample size large enough to study cardiovascular disease or a surrogate outcome, is needed to test the following hypothesis: Does reduction in systemic inflammation in gout decrease the risk of cardiac disease and improve outcomes? Such a study will generate data that can lead to a change in the clinical practice for the treatment of gout. I anticipate that in the next decade aggressive management of gout will be key to implementing a ‘healthier heart programme in gout’.

In summary, considerable data show an increased risk of cardiac disease in patients with gout, above and beyond that contributed by the traditional risk factors for heart disease. It is not known whether gout is an equivalent risk factor for cardiovascular disease to conditions such as diabetes or not. Future studies need to address this important question. At least two studies, including the current study, suggest that there may be an interaction with sex, meaning that the relative risk is different for men versus women. An implication of this new knowledge is that gout patients should be monitored and screened regularly for cardiovascular disease. Those with existing risk factors, such as hypertension, smoking, diabetes, hyperlipidaemia and others, are likely to be at high risk for cardiovascular disease. A comprehensive approach to treating uric acid appropriately to a target level, and to diagnosing and treating cardiac disease early, may lead to improved outcomes in patients with gout.