The effects of cold and exercise on the cardiovascular system

### Learning objectives Acute coronary syndromes Decreased exercise tolerance and worsening of angina symptoms during the winter months is a well-documented phenomenon among patients with coronary artery disease (CAD).1 There is a significant increased risk of acute myocardial infarction (AMI) with cold temperatures,2 even when taking into account confounding factors such as altered glucose and cholesterol levels and higher incidence of respiratory infections.3 ,4 When comparing seasonal differences in the northern and southern hemispheres, a higher incidence of AMI correlates with periods of cold weather in both hemispheres (figure 1).5 ,6 The risk of AMI in cold temperatures is further increased if exercise is being performed. Notable examples are shovelling snow7 and downhill skiing,8 which involve significant isometric exercise and dynamic exercise components. While epidemiological studies suggest a strong link between exercising in the cold and AMI, a causal relationship is yet to be demonstrated. Figure 1 Seasonal differences in the incidence of myocardial infarction in the northern and southern hemispheres. This figure represents data from two observational studies investigating the incidence of myocardial infarction in the northern (the USA) and southern (Australia) hemispheres. The figure demonstrates the percentage change in the incidence of myocardial infarction compared with their respective winters. Of note the average temperatures in the summer months for the northern and southern hemispheres were 21°C and 22°C, whereas the winters were significantly colder in the northern hemispheres, 2°C vs 10°C. This might explain the greater seasonal variation in the northern hemisphere. Adapted from Loughnan et al 5 and Spencer et al 6. The exact mechanism by which cold increases the risk of AMI remains unclear. Proposed mechanisms include a myocardial oxygen supply and demand mismatch or an …