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Handgrip Strength Is Inversely Associated With Sudden Cardiac Death

      To the Editor:
      The protective effect of cardiorespiratory fitness on vascular outcomes including sudden cardiac death (SCD) is well established.
      • Jiménez-Pavón D.
      • Lavie C.J.
      • Blair S.N.
      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.
      • Laukkanen J.A.
      • Lavie C.J.
      • Khan H.
      • Kurl S.
      • Kunutsor S.K.
      Cardiorespiratory fitness and the risk of serious ventricular arrhythmias: a prospective cohort study.
      • Laukkanen J.
      • Laukkanen T.
      • Khan H.
      • Babar M.
      • Kunutsor S.K.
      Combined effect of sauna bathing and cardiorespiratory fitness on the risk of sudden cardiac deaths in Caucasian men: a long-term prospective cohort study.
      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.
      • Celis-Morales C.A.
      • Lyall D.M.
      • Anderson J.
      • et al.
      The association between physical activity and risk of mortality is modulated by grip strength and cardiorespiratory fitness: evidence from 498 135 UK-Biobank participants.
      • Cooper R.
      • Kuh D.
      • Hardy R.
      Mortality Review GroupFALCon and HALCyon Study Teams
      Objectively measured physical capability levels and mortality: systematic review and meta-analysis.
      • Sillars A.
      • Celis-Morales C.A.
      • Ho F.K.
      • et al.
      Association of fitness and grip strength with heart failure: findings from the UK Biobank population-based study.
      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.
      • Jiménez-Pavón D.
      • Brellenthin A.G.
      • Lee D.C.
      • Sui X.
      • Blair S.N.
      • Lavie C.J.
      Role of muscular strength on the risk of sudden cardiac death in men.
      In this recent analysis of the Aerobics Center Longitudinal Study, Jiménez-Pavón et al
      • Jiménez-Pavón D.
      • Brellenthin A.G.
      • Lee D.C.
      • Sui X.
      • Blair S.N.
      • Lavie C.J.
      Role of muscular strength on the risk of sudden cardiac death in men.
      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.
      • Laukkanen J.A.
      • Mäkikallio T.H.
      • Rauramaa R.
      • Kiviniemi V.
      • Ronkainen K.
      • Kurl S.
      Cardiorespiratory fitness is related to the risk of sudden cardiac death: a population-based follow-up study.
      Study recruitment, baseline examinations (from March 1, 1998 through December 31, 2001), and the diagnostic classification of SCDs have been described previously.
      • Kunutsor S.K.
      • Blom A.W.
      • Whitehouse M.R.
      • Kehoe P.G.
      • Laukkanen J.A.
      Renin-angiotensin system inhibitors and risk of fractures: a prospective cohort study and meta-analysis of published observational cohort studies.
      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).
      Figure thumbnail gr1
      FigureAssociations of relative handgrip strength with sudden cardiac death. A, Cumulative hazard curves for sudden cardiac death by medians of relative handgrip strength. B, Hazard ratios (HRs) of relative handgrip strength for sudden cardiac death. Model 1: adjusted for age and sex. Model 2: model 1 plus systolic blood pressure, total cholesterol level, high-density lipoprotein cholesterol level, and history of type 2 diabetes. Model 3: model 1 plus resting heart rate, smoking status, prevalent coronary heart disease, and physical activity.
      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.
      • Artero E.G.
      • Lee D.C.
      • Lavie C.J.
      • et al.
      Effects of muscular strength on cardiovascular risk factors and prognosis.
      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.

      Acknowledgments

      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.

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