India started to sizzle early in the first week of April, with Delhi recording its highest temperature of the season at 40.2°C. The Indian Meteorological Department (IMD) on Monday (Apr 7) issued a heatwave alert across northwest and central India and also predicted that the temperatures will be high and the air quality will be poor in the coming days. 

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The rising temperatures have an adverse impact on health, as the World Health Organization (WHO) said in a report that heat is an important environmental and occupational health hazard. It also added that heat stress is the leading cause of weather-related deaths. 

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Heatwaves can also worsen underlying illnesses, including cardiovascular disease, diabetes, mental health and asthma. It can also increase the risk of accidents and the transmission of some infectious diseases. 

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Delhi is experiencing its first heatwave of the year. To tackle this, the Government of India recommends staying indoors at the peak heat hours of the day, having lots of water and refraining from working outdoors. "This is particularly important for individuals with pre-existing heart conditions as excessive heat can put the heart under undue strain," Dr Virbhan Balai, Consultant - Interventional Cardiology, Manipal Hospital Dwarka, New Delhi, told WION. 

"Individuals with comorbidities such as high blood pressure, heart disease, diabetes or elderly people, outdoor workers, and children should be particularly careful," Dr Balai added. 

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How does the heart get impacted during heatwaves?  

"The hot weather makes the blood vessels dilate, which reduces blood pressure. This implies that the heart has to beat faster for the blood to circulate properly, and this poses a threat of developing abnormal heartbeats. Sweating also results in loss of body fluids and vital salts, which result in muscle cramps, weakness, and dehydration, contributing to straining the heart even further," Dr Balai further said. 

A new study revealed that more people die from heart problems during heatwaves when high temperatures stretch through both the day and night. Heatwaves that offer no relief at night - known as compound heatwaves - are much more deadly than soaring daytime temperatures alone, researchers reported on April 1 in the Journal of the American College of Cardiology. 

Dr Joy Shome, Cardiologist and Head of TAVR/TAVI at BM Birla Heart Hospital explained to WION, "In the aftermath of heatwaves, the body exhibits various physiological responses to accommodate itself in extreme environmental conditions. The rise in ambient temperature, therefore, stimulates several mechanisms in the human body to regulate its core temperature." 

"Sweating is perhaps the most classic of the mechanisms, which encourages the evaporation of moisture and cooling down of the body. As sweating causes fluid loss, the heart has to work harder to maintain blood flow and pump oxygen to the vital organs. As a result, the heart rate and cardiac output could increase—at times, two to three times more than normal," Dr Shome added. 

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The increased heart rate and strain upon the heart can be extremely dangerous for those who have some pre-existing heart conditions. The increased work on the heart must meet with oxygen demand to maintain blood circulation; to compromise this overwhelmed state due to severe exertion is detrimental to heart disease patients. 

"Furthermore, common dehydration during heatwaves from excessive sweating tends to worsen the situation. Dehydration renders blood thick and may promote clots as well; this increases the likelihood of heart attacks or strokes," he said. 

Heatwaves can create further instabilities in electrolytes for people on certain medications, like diuretics, which are medications that help remove excess fluid from the body by increasing urine production. They are commonly used to treat conditions such as hypertension, heart failure and edema. The impact of diuretics on the heart can be significant. Along with water loss through sweating, the body loses trace amounts of sodium and potassium that are essential for maintaining homeostasis. 

"Disturbance of this process can lead to disturbances in heart rhythm or arrhythmias that can aggravate heart dysfunction and increase the likelihood of major cardiovascular events," Dr Shome noted. 

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What are the preventive measures? 

Dr Balai said that to protect oneself, one needs to remain indoors during the golden hour, stay in relatively cold and ventilated spaces, drink plenty of liquids and dress lightly. "If anybody experiences chest pain, extreme fatigue, or has trouble breathing, it is advised to seek medical assistance," Dr Balai said. 

During heatwaves, always remember these five points: 

1) Staying hydrated: Drink plenty of water and electrolyte-rich fluids to stay hydrated.

2) Avoid strenuous activities: Avoid strenuous activities during the hottest part of the day.

3) Seek shade and cool spaces: Seek shade and cool spaces to escape the heat.

4) Monitor weather forecasts: Stay informed about weather forecasts and heatwave warnings.

5) Consult healthcare professionals: Consult healthcare professionals if you have concerns about your heart health during a heatwave. 

But staying hydrated can also be challenging, especially for those with heart failure or kidney problems as they may need to alter their fluid intake based on medical advice. 

Dr Shome said, "In some cases, doctors may suggest slightly easing fluid restrictions in hot weather, particularly for those on diuretics, to help prevent excessive dehydration. It is also advisable to avoid exposure to heat during the hottest part of the day, which is generally from late morning to early afternoon, and to remain indoors in air-conditioned environments whenever possible."