Dr Laukkanen said: "Sudden cardiac death (SCD) accounts for approximately 50% of deaths from coronary heart disease. SCD typically occurs shortly after the onset of symptoms, leaving little time for effective medical interventions, and most cases occur outside hospital with few or no early warning signs. Finding ways to identify individuals at elevated risk of SCD would allow early interventions on risk factors to be implemented."
The current study investigated the impact of high leisure-time physical activity (LTPA) combined with cardiorespiratory fitness (CRF) on risk of SCD. It included 2,656 randomly selected men aged 42 to 60 years from the Kuopio Ischemic Heart Disease Risk Factor Study, a Finnish study of risk predictors for cardiovascular outcomes and SCD in the general population. Baseline cycle exercise test and risk factor assessment were performed in 1984-89. SCD was defined as death with cardiac origin within 24 hours after onset of symptoms.
LTPA was assessed using a 12-month physical activity questionnaire. One third of subjects had low LTPA (energy consumption <191 kcal>
For the analyses the study population was divided into 4 groups: 1) high CRF and high LTPA, 2) high CRF and low LTPA, 3) low CRF and high LTPA and 4) low CRF and low LTPA. Group 1 was used as a reference. The risk of SCD was adjusted for previously established cardiovascular risk factors (age, smoking, alcohol consumption, body mass index, systolic blood pressure, low density lipoprotein cholesterol, C-reactive protein, prevalent type 2 diabetes and previously diagnosed coronary heart disease).
During the mean 19 years of follow-up 193 SCDs occurred. There was a 2-fold increased risk of SCD in men with low CRF and LTPA (group 4, see figure) compared to men with high CRF and high LTPA (hazard ratio [HR] 2.0, 95% confidence interval [CI] 1.3-2.9). Men with low CRF and high LTPA (group 3) did not have a statistically significant increased SCD risk compared to men with high CRF and high LTPA (HR 1.3, 95% CI 0.9-1.8). Dr Laukkanen said: "This indicates that a higher amount of leisure-time physical activity might reduce the risk of SCD among men with low cardiorespiratory fitness."
The amount of LTPA did not affect the risk of SCD among the men with high CRF (groups 1 and 2). Dr Laukkanen said: "Our study shows that CRF is a risk factor for SCD. High leisure-time physical activity exerts a protective effect on the risk of SCD among men with low cardiorespiratory fitness but does not affect risk in men with high baseline CRF."
He added: "It is widely believed that the level of CRF is determined by physical exercise, genetics and other lifestyle factors. Our study shows that exercise training and LTPA may be especially important in individuals with low CRF. One possible explanation is that CRF can be improved with regular exercise training."
Dr Laukkanen concluded: "The importance of CRF has often been neglected in the equation of SCD risk, despite appearing to be one of the most important correlates of overall health status. Our study emphasises the importance of regular physical exercise, especially among men with low CRF. An exercise test could be used to identify individuals with low CRF and high risk of SCD, who should then be urged to exercise more."