Editorial

Frailty and cardiovascular disease: A two-way street?

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Despite a marked increase in awareness in recent years surrounding the prevalence and prognosis of frailty in our aging population and its association with cardiovascular disease, itself highly prevalent in elderly cohorts, the exact pathobiological links between the 2 conditions have not been fully elucidated. As a consequence, this has led to difficulty not only in accurately defining cardiovascular risk in vulnerable elderly patients, but also in adequately mitigating against it.

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It is well accepted that cardiovascular disease, whether clinical or subclinical, is associated with an increased risk of developing the frail phenotype.1,2 Frailty, in turn, has been consistently identified as a universal marker of adverse outcomes in patients at risk of, and in patients with already manifest, cardiovascular disease.2,3 However, whether or not frailty is its own unique risk factor for cardiovascular disease, independent of co-associated risk markers, or is merely a downstream byproduct indicating a more advanced disease state, has yet to be determined. Furthermore, the question of whether modification of frail status may impact the development and progression of cardiovascular disease has not yet been established.

The article by Orkaby et al4 in this issue delves deeper into this question by looking specifically at the interaction between frailty and standard risk factors as they relate to the prevention of cardiovascular disease.

NEEDED: A UNIVERSAL DEFINITION OF FRAILTY

It is important to acknowledge up front that before we can truly examine frailty as a novel risk entity in the assessment and management of cardiovascular risk in older-age patients, we need to agree on an accepted, validated definition of the phenotype as it relates to this population. As acknowledged by Orkaby et al,4 lack of such a standardized definition has resulted in highly variable estimates of the prevalence of frailty, ranging from 6.9% in a community-dwelling population in the original Cardiovascular Health Study to as high as 50% in older adults with manifest cardiovascular disease.1,2

The ideal frailty assessment tool should be a simple, quantitative, objective, and universally accepted method, capable of providing a consistent, valid, reproducible definition that can then be used in real time by the clinician to determine the absolute presence or absence of the phenotype, much like hypertension or diabetes. Whether this optimal tool will turn out to be the traditional or modified version of the Fried Scale,1 an alternative multicomponent measure such as the Deficit Index,5 or even the increasingly popular single-item measures such as gait speed or grip strength, remains to be determined.

Exact choice of tool is perhaps less important than the singular adoption of a universal method that can then be rigorously tried and tested in multicenter studies. Given the bulk of data to date for the original Fried phenotype and its development in an older-age community setting with a typical prevalence of cardiovascular risk factors, the Fried Scale appears a particularly suitable tool to use for this domain of disease prevention. Single-item spin-off measures from this phenotype, including gait speed, may also be useful for their increased feasibility and practicality in certain situations.

A TWO-WAY STREET

Given what we know about the pathophysiological, immunological, and inflammatory processes underlying advancing age that have also been implicated in both frailty and cardiovascular disease syndromes, how can we determine if frailty truly is an independent risk factor for cardiovascular disease or merely an epiphenomenon of the aging process?

We do know that older age is not a prerequisite for frailty, as is evident in studies of the phenotype in middle-aged (and younger) patients with advanced heart failure.6 We also know not only that frail populations have a higher age-adjusted prevalence of cardiovascular risk factors including diabetes and hypertension,1 but also that community-dwellers with prefrailty (as defined in studies using the Fried criteria as 1 or 2 vs 3 present criteria) at baseline have a significantly increased risk of developing incident cardiovascular disease compared with those defined as nonfrail, even after adjustment for traditional risk factors and other biomarkers.3 Exploring the differences between these subgroups at baseline revealed that prefrailty was significantly associated with several subclinical insults that may serve as adverse vascular mediators, including insulin resistance, elevated inflammatory markers, and central adiposity.3

A substudy of the Cardiovascular Health Study also found that in over 1,200 participants without a prior history of a cardiovascular event, the presence of frailty was associated with multiple noninvasive measures of subclinical cardiovascular disease, including electrocardiographic and echocardiographic markers of left ventricular hypertrophy, carotid stenosis, and silent cerebrovascular infarcts on magnetic resonance imaging.7

These findings support a mechanistic link between evolving stages of frailty and a gradient of progressive cardiovascular risk, with a multifaceted dysregulation of metabolic processes known to underpin the pathogenesis of the frailty phenotype likely also triggering risk pathways (altered insulin metabolism, inflammation) involved in incident cardiovascular disease. Although the exact pathobiological pathways underlying these complex interlinked relationships between aging, frailty, and cardiovascular disease have yet to be fully elucidated, awareness of the bidirectional relationship between both morbid conditions highlights the absolute importance of modifying risk factors and subclinical conditions that are common to both.

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