Extreme Heat Strains Heart, Increases Stroke Risk

Extreme heat waves are placing dangerous stress on the cardiovascular system, increasing the risk of severe cardiac events such as heart attacks and strokes. As temperatures climb, the human body activates automatic mechanisms to regulate internal temperature, with the heart playing a central role in this response. In hot weather, the heart must work significantly harder, blood pressure tends to drop, and in some individuals, these adjustments can spiral out of control, leading to fainting, arrhythmias, and life-threatening emergencies.

The physiological response begins with the dilation of blood vessels, particularly those in the skin, to facilitate heat dissipation. This reduces vascular resistance and lowers arterial pressure. To compensate for this drop, the heart rate accelerates to maintain adequate blood flow. However, this process is often compounded by fluid loss through sweating, which reduces circulating blood volume. The combination of vasodilation and dehydration forces the heart to pump faster and harder, often resulting in symptoms like dizziness, weakness, and blurred vision. These risks are amplified by the loss of electrolytes such as sodium and potassium, which can disrupt the heart's electrical system and trigger arrhythmias.

While heart attacks and strokes are traditionally associated with cold weather, recent studies indicate that prolonged heat waves also elevate these risks, especially in vulnerable groups. The added stress on the cardiovascular system, combined with dehydration, can precipitate acute events. Experts emphasize that specific populations must exercise heightened caution during the summer months to avoid these potentially fatal complications.

The body's primary response to rising temperatures is the dilation of blood vessels located near the skin's surface. This mechanism reduces vascular resistance and typically causes a drop in blood pressure. According to Fernando Ribas, a cardiologist at BP – A Beneficência Portuguesa de São Paulo, the organism attempts to compensate for this decrease by accelerating heart rate to ensure adequate blood flow. While this adjustment usually functions properly in healthy individuals, it can fail in others.

The combination of vasodilation and fluid loss through sweat significantly reduces the volume of circulating blood. With less blood returning to the heart, the body forces an increase in heart rate, which can provoke typical symptoms of intense heat such as dizziness, weakness, darkened vision, and fainting sensations. Individuals with a predisposition to hypotension or vasovagal syncope are likely to experience these effects more intensely.

Dehydration is a critical point of imbalance. Sweat is essential for cooling the body, but it removes vital water and minerals, including sodium and potassium. Bruno Sthefan, a cardiologist and sports medicine specialist, explains that dehydration reduces blood volume, accelerates the heart to compensate, and impairs organ perfusion. The loss of these electrolytes interferes with the heart's electrical system, increasing the risk of arrhythmias, particularly in those with pre-existing cardiovascular diseases.

Although extreme heat affects everyone, certain groups are at a much higher risk of cardiovascular complications. Specialists have identified the following vulnerable demographics:

• Elderly individuals, who often feel less thirsty and become dehydrated easily.
• People with hypertension, diabetes, or heart failure.
• Those who have previously suffered a heart attack or stroke.
• Athletes and workers exposed to intense sunlight.

For these groups, the danger lies in the imbalance between heat, hydration, and physical exertion. Patients taking diuretics and anti-hypertensive medications may feel the effects of the heat more acutely. Fernando Ribas warns that these medications promote fluid loss and can potentiate drops in blood pressure. He advises that patients should never suspend or adjust their doses on their own without medical guidance.

Recognizing the signs of heat-induced cardiovascular distress is vital for preventing severe outcomes. Certain symptoms require immediate medical attention, especially during periods of extreme heat. Orlando Maia, a neurosurgeon at Hospital Quali Ipanema, notes that even if symptoms pass, sudden drops in blood pressure and changes in heart rhythm must be evaluated by a professional.

Critical symptoms to watch for include:

• Fainting or syncope
• Chest pain
• Persistent palpitations
• Shortness of breath beyond the usual
• Mental confusion, particularly in the elderly

Orlando Maia explains that heat imposes additional stress on the cardiovascular system. "With dehydration, the heart works harder to compensate for the drop in pressure, and the loss of electrolytes favors arrhythmias. This combination can precipitate heart attacks and strokes," he states.

Physical activity in hot weather presents specific challenges. During exercise, the heart must simultaneously irrigate muscles and skin, elevating heart rate and perceived exertion. Orlando Maia warns that in intense heat, this increases the risk of heat exhaustion and arrhythmias. Consequently, medical professionals recommend avoiding the hottest hours of the day, seeking shade, and reinforcing hydration.

Hydration should not be limited to water alone; when sweating is intense, the replenishment of electrolytes is necessary. General safety recommendations for heat waves include:

• Drinking water consistently throughout the day.
• Avoiding alcohol and excessive caffeine.
• Wearing light, breathable clothing.
• Taking frequent breaks and resting.
• Seeking ventilated or air-conditioned environments.
• Avoiding strong sun during peak hours.

These simple yet fundamental precautions can significantly reduce the impact of heat on the heart and prevent the escalation of symptoms into medical emergencies.