Electronic Thesis and Dissertation Repository


Master of Science


Epidemiology and Biostatistics


Episodes of physical exertion are associated with an immediately higher risk of cardiovascular events while physical activity over the long-term is cardioprotective. To assess the transient and long-term risk of ventricular arrhythmia (VA), we conducted a nested case-crossover study within a prospective cohort of 97 patients with implantable cardioverter-defibrillators (ICD). Within an hour of episodes of exertion, the risk of VA was 5.3 (95% CI 2.7 – 10.6) times greater compared to periods of rest. The association was higher among patients with aerobic fitness below the median (RR[relative risk]=17.5, 95% 5.2 – 58.5) than for patients with aerobic fitness above the median (RR=1.2, 95% CI 0.4 – 4.2, p-homogeneity = 0.002) and higher among patients who were sedentary (RR=52.8, 95% 10.1 – 277) compared to individuals who were not (RR=3.2, 95% 1.3 – 7.6, p-homogeneity=0.0002). We found no statistically significant difference in time-to-VA by aerobic fitness or sedentary behaviour. In this clinical cohort, there is an elevated risk of VA within an hour of exertion, particularly in patients with low aerobic fitness and sedentary behaviour.