Over the last seven decades, heart attacks among Indians have gone up in both cities and rural areas, significantly so in cities. Now air pollution has emerged as a risk factor along with stress, food and hectic lifestyle. Ahmedabad-based Dr Sameer Dani, Director, Cardiology Services, Apollo CVHF Heart Institute, has done many comparative surveys and cautions about increased incidence of heart attacks in the cold season.
What is the percentage increase in heart attack during winter?
Hospital admissions because of heart-related ailments are up by almost 20-30 per cent during winters. A lot has been researched but we don’t have a final definitive answer. It is believed that cold weather affects your heart in many ways. One is the heart needs to pump more blood compared to routine warm weather, which our body is used to. For every mile you walk, your heart has to do more work, compared to that in summers or more ambient temperatures. So, in extreme heat and extreme cold, the heart is stressed.
Second, cold weather affects the blood vessels, causing them to contract and keep the body warm. Blood vessels have an increased sympathetic tone. The sympathetic nervous system is the body’s control mechanism which maintains heart rate and blood pressure. The surge in blood pressure may cause plaques to rupture, resulting in winter morning heart attacks. Third, there are allergic contributors that stress the cardiopulmonary system, that is the heart and lungs. Cold weather is a time of respiratory infections, say viral pneumonia, bacterial pneumonia, flu, all of which stress out the heart. Flu has a direct relationship with heart attack. All respiratory infections decompensate people who have heart disease and are otherwise well-compensated.
Then there are diurnal variations of our hormones, which are associated with our sleep cycle and one can compare this to booting a computer. A computer is more likely to conk off during the booting and rebooting process. That’s why we see the highest number of heart attacks in the early morning hours, when you wake up or are about to wake up and this is more pronounced and prominent in cold weather.
Air pollution is emerging as a significant factor. Among those with no comorbidities, family history can be a risk factor despite being a healthy individual. Apart from that, lung conditions, diabetes, smoking or tobacco, hypertension and stress or lack of physical activity are known triggers.
Does the degree of cold affect incidence?
Very surprisingly, there is no linear relationship with the degree of cold. Other conditions such as comorbidities and environmental factors are at play. For example, what kind of air pollution you have, what kind of food habits or lifestyle change you have in the winters are important factors.
Does the extent of air pollution play a role in exacerbating incidence of heart attacks in winter?
Air pollution, which is otherwise neglected and under emphasised, definitely plays a role. Because of the cold weather, the pollutants are suspended closer to the earth’s surface, which trigger inflammation and in turn heart attacks. We have had surveys in both cities and rural areas and found that compared to cities, heart attacks are lesser in rural areas. But if you look at the last 70 years, heart attacks in rural areas have also increased almost ten-fold. Still there is a rural-urban gap in incidence. In cities, we now blame the higher incidence on mainly four factors — weather, stress, food and lifestyle — weather now emerging as one of the most important triggers.
We have epidemiological data that clearly shows how polluted cities have higher rates of heart attacks, especially in winters, but there’s no prospective study that measures pollution level vis-a-vis temperature on incidence of heart attacks.
What precautions can we take specific to winter?
The usual set of precautions remains the same. Only the level of activity would vary. You should not exert yourself physically, especially if you have comorbidities. For example, do not try out a heavy exercise schedule that you have never done before, or resume something you have done before but you are not used to anymore. Similarly, one must also be careful about binge-eating and binge-drinking because cold weather makes you feel hungry and there are more festivals and events this time of the year. One measure that we can take, and as we often suggest to our patients, is to take the flu vaccine in August-September. Usually, the strains change and WHO puts out information on the circulating strains so that the new vaccines are available accordingly. It is always preferable to get yourself vaccinated and prepare yourself for winter.
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Why Dr Sameer Dani? He is Director, Cardiology Services, Apollo CVHF Heart Institute, Ahmedabad. He has been the former Professor and Chief, Department of Cardiology, U.N.Mehta Institute of Cardiology & Research centre, Civil Hospital campus, Ahmedabad. He has been founder course director of the National Endovascular workshop and was honoured with the Dr B. C. Roy Award for 2018.
