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Dr. Agbetoyin is a board certified, invasive cardiologist who practices at The Cardiovascular Clinic of West Tennessee, P.C.

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The heat and your heart

Dr. Adey Agbetoyin, at left, talks to Billy Macon of Gadsden about his heart.

You watch your spouse working outdoors in the summer heat. He comes in complaining that he's dizzy and not feeling well. You panic. Is it heat exhaustion? A heat stroke? Or even a mild heart attack? Should you go to the emergency room?

The combination of warm temperatures and high relative humidity can be potentially dangerous for patients with heart conditions. Dr. Adey Agbetoyin, a board-certified cardiologist with the Cardiovascular Clinic of West Tennessee, discusses how the body copes with heat, how heat particularly affects people with heart disease and the difference between a heat stroke, mild heart attack and heat exhaustion.

How does the body cope with heat?
In warm weather, the blood pressure usually drops and the heart rate increases. The body usually copes with heat by trying to lower the temperature through a combination of sweating and dissipating heat into the surrounding environment by directing blood flow to the blood vessels in the skin.

The heart sometimes has to pump as much as four times the usual amount of blood in an attempt to keep the core temperature constant. However, these mechanisms are not as effective when the temperature is hotter than 98 degrees. With high humidity, sweat is unable to evaporate from the skin.

Effects on patients with heart disease
The combination of increased cardiac work, faster heart rate and lower blood pressure places the heart under physiological stress.

Patients with heart artery blockages may experience an increase in frequency of chest pains (angina). In fact, clinical studies have shown an increase in the frequency of heart attacks during periods of prolonged heat and high relative humidity.

Overweight patients with heart disease are more likely to suffer from heat exhaustion or heat stroke.

Exercising or prolonged exertion in hot weather can lead to increased frequency of certain heart rhythm irregularities.

In patients with heart failure, the heart is unable to pump blood any harder to keep the body sufficiently cooled or to keep the blood pressure high enough. As a result, the body can become overheated. This means that heart failure patients are more likely to develop symptoms of heat exhaustion or heat stroke.

The lower blood pressure can also cause patients to become dizzy or lightheaded or even lose consciousness. The common advice to increase fluid intake and consume sports drinks high in sodium and other electrolytes in the summer can be potentially harmful to heart failure patients. If patients with weak or damaged hearts drink excessive amounts of fluid, this could lead to worsening of congestive heart failure symptoms with swelling and shortness of breath.

Instead, in hot and humid weather, the most practical advice for the heart failure patient is to continue all prescribed medications and follow his or her physician's directions, including regular checkups. Patients also are advised to weigh themselves daily. A weight gain of more than a pound a day usually indicates worsening fluid retention. On the other hand, a weight loss of more than two pounds a day without any recent changes in medication dose may indicate dehydration.

Effect of heart medications
To compound the problem, medications that are prescribed to control heart failure symptoms, such as diuretics (water pills), could potentially worsen the low blood pressure and dehydration. Diuretics can cause muscle cramps due to low potassium, which can be difficult to differentiate from heat cramps. Other kinds of heart failure and heart rhythm medications, such as beta blockers and calcium channel blockers, can interfere with the body's cooling mechanisms. Heart rhythm medications prevent the heart from beating faster in hot weather, limiting the body's ability to cool itself.

Heat stroke
A person may be having a life-threatening heat stroke if his or her cooling system, which is controlled by the brain, stops working and the internal body temperature rises to the point where brain damage or damage to other internal organs may result. The body's temperature may reach 105 degrees or greater.

Heat stroke symptoms include:
-Unconsciousness or a markedly altered mental status, such as dizziness, confusion, hallucinations, or coma.
-Flushed, hot, and dry skin (although it may be moist initially from previous sweating or from attempts to cool the person with water).
-Slightly elevated blood pressure at first that falls later.
-Hyperventilation (excessive breathing)

Heat stroke may develop rapidly, and some medical conditions or medications that impair the body's ability to sweat may predispose people to this problem. Taking antihistamines and certain types of high blood pressure and depression medications can also increase the risk.

Heat exhaustion
On the other hand, heat exhaustion occurs when people, who are not adjusted to working or playing in a hot humid environment, start losing body fluids through sweat, causing the body to overheat. The person's temperature may be elevated, but not above 104 degrees.

At high temperatures and humidity, the body's mechanism to cool itself largely through evaporation of sweat does not work properly and the body loses fluids and salts (electrolytes). When fluids are not adequately replaced, disturbances in the circulation may result, which can be similar to a mild form of shock.

Heart Attack
A mild heart attack also can be triggered by physical exertion in the heat. But unlike heat exhaustion and heat stroke, a strong sign of heart attack is pain or tightening in the chest. Pain may radiate to the neck, jaw or upper back, or over the left side.

Other symptoms include left hand discomfort, difficulty breathing, a burning sensation in the middle part of the chest, sweating, nausea, choking sensation in the throat, heaviness in the upper abdomen and weakness.

"Angina or heart attack symptoms should not be ignored," says Dr. Agbetoyin.