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Emerging evidence suggests that handgrip strength (HGS), a typical measure of muscular strength, is prospectively and inversely associated with mortality and vascular outcomes such as cardiovascular disease (CVD), coronary heart disease (CHD), and heart failure.
Given the relationship between HGS and vascular outcomes, we hypothesized that HGS would be linked to the risk of SCD. Handgrip strength could be a novel risk predictor of SCD; however, the prospective association between HGS and SCD is uncertain. We read with interest the research letter published in this month’s issue.
reported moderate muscular strength to be protective against SCD risk; however, this study was limited by the low event rate (23 SCD cases). In this context, we aimed to assess the association between HGS and the risk of SCD in a population-based prospective cohort of 861 men and women with a relatively higher number of events.
The Kuopio Ischemic Heart Disease Risk Factor Study was set up to investigate the potential risk factors for CVD outcomes.
Handgrip strength (in kilopascals) was measured by a hand dynamometer (Martin-Balloon-Vigorimeter, Gebrüder Martin). Two measurements were taken for the dominant hand, and the mean of both values was used for analysis. To take into account the effect of body mass on muscular strength, the values of HGS were divided by weight in kilograms to yield relative HGS (in kilopascals per kilogram). The study protocol was approved by the Research Ethics Committee of the University of Eastern Finland, Kuopio, Finland, in line with the Helsinki Declaration, and each participant provided written informed consent. We included all SCDs that occurred from the study enrollment to 2017. Hazard ratios (HRs) with their 95% CIs for SCD were calculated using Cox proportional hazards models. All statistical analyses were conducted using Stata/MP version 16 (StataCorp).
The mean age of the study participants at baseline was 69±3 years, and 47.3% comprised men. The mean value of relative HGS at baseline was 1.03±0.34 kPa/kg. During a median (interquartile range) follow-up of 17.3 (12.6-18.4) years, 50 SCDs occurred. Cumulative hazard curves revealed a lower risk of SCDs in participants in the top median of HGS levels than in those in the bottom median (log-rank test, P=.001) (Figure A ). The age- and sex-adjusted HR per 1SD increase in relative HGS was 0.52 (95% CI, 0.34-0.79), which persisted on additional adjustment for systolic blood pressure, total and high-density lipoprotein cholesterol levels, and history of type 2 diabetes with a HR of 0.52 (95% CI, 0.33-0.81). Comparing the top and bottom medians of relative HGS levels, it was found that the corresponding adjusted HRs were 0.47 (95% CI, 0.25-0.59) and 0.51 (95% CI, 0.28-0.95), respectively (Figure B). The results were minimally attenuated in a third model that adjusted for age, sex, resting heart rate, smoking status, prevalent CHD, and physical activity (Figure B).
In this first prospective study of the association between relative HGS and the risk of SCD, relative HGS was inversely and independently associated with the future risk of SCDs. It has been speculated that the protective effect of higher muscle strength (assessed by relative HGS) on CVD mortality may be mediated by reduction in the incidence of weight gain, abdominal adiposity, insulin resistance, and inflammation.
Hence, given the close interrelationship between muscle strength, CHD, and SCD, we postulate that similar pathways may underlie the relationship between HGS and the risk of SCD. These findings are therefore not unexpected given that SCDs and vascular outcomes, particularly CHD, have shared risk factors. The present findings are relevant and add to the existing evidence that HGS, a measure of body muscle strength, promotes vascular benefits. The assessment of HGS is simple and not time-consuming compared with other physical fitness assessments.
Strengths of the present evaluation include its novelty, long-term and complete follow-up of participants, and the representative sample of middle-aged to elderly men and women. Some study limitations include the low event rate for SCDs, which precluded analyses such as the dose-response relationship and effect modification and the inability to adjust for other potential confounders such as socioeconomic status and cardiorespiratory fitness. However, we took into account the levels of resting heart rate and physical activity in our multivariable analyses. In conclusion, this study suggests that relative HGS is inversely associated with the future risk of SCDs. Further research is needed to evaluate whether the assessment of HGS levels can be used to identify individuals at high risk of SCD.
We thank the staff of the Kuopio Research Institute of Exercise Medicine and the Research Institute of Public Health and the University of Eastern Finland, Kuopio, Finland, for the data collection in the study.
The role of cardiorespiratory fitness on the risk of sudden cardiac death at the population level: a systematic review and meta-analysis of the available evidence.
Grant Support: The work was supported in part by grants from the Finnish Foundation for Cardiovascular Research , Helsinki, Finland. Dr Kunutsor was supported by the National Institute for Health Research ( NIHR ) Biomedical Research Centre at University Hospitals Bristol NHS Foundation Trust and the University of Bristol (BRC-1215-20011). The views expressed in this publication are those of the author and not necessarily those of the NHS, the NIHR, or the Department of Health and Social Care. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Potential Competing Interests: The authors report no competing interests.