What triggers a heart attack?

Heart attacks, strokes, and cardiac arrests seem like they come out of the blue, but most don’t. They usually appear after cholesterol-rich plaque has festered for decades in arteries nourishing the heart and brain. So what makes one happen at a particular time? A trigger.

Researchers have identified about two dozens of these. They’re a diverse crew, ranging from anger and earthquakes to simply waking up in the morning. The ongoing search for triggers is generating ways to prevent potentially deadly cardiovascular events.

Some triggers cause a sudden surge in blood pressure. Some make the heart beat faster and harder. Others encourage the formation of blood clots, constrict blood vessels, or cause bursts of inflammation. Any of these changes can set into motion processes that culminate in the sudden formation of a blood clot (leading to a heart attack or ischemic stroke), a tear in a blood vessel (leading to a hemorrhagic stroke), or a wild heart rhythm (leading to sudden cardiac arrest).

One pathway common to many triggers is the activation of the sympathetic nervous system, which is responsible for the body’s fight-or-flight response. The stress hormone it sends into the bloodstream can be hard on the heart and on the vulnerable atherosclerotic plaque. The most important triggers include:

• Waking from sleep. Long before you wake up, your body prepares for a new day by trickling stress hormones into the bloodstream. They signal small blood vessels to constrict, make your heart beat faster, and begin boosting your blood pressure from its sleep-time low. This activity ensures adequate blood flow through your blood vessels by the time you are ready to get out of bed. It’s no coincidence that cardiovascular problems peak between 6 a.m. and noon. The slight dehydration that occurs during sleep may also contribute to this early morning peak, as may the overnight fade in protection from blood pressure drugs and other heart medicines.

• Heavy physical exertion. Lifting heavy objects, running, or shoveling snow (for those living in temperate countries), as well as other types of strenuous physical activity, can trigger heart attacks, strokes, and cardiac arrests. Don’t take this as a reason to stop exercising. In fact, the opposite is true — exertion is much less likely to cause trouble in people who exercise regularly than in those who don’t.

• Anger. A furious argument or gut-churning anger can provoke a heart attack, stroke, or cardiac arrest. In two large studies, a bout of anger increased the chances of having a heart attack between nine-fold and 14-fold over a two-hour period following the anger-provoking event. A study presented at the 2006 American Heart Association meeting showed that anger often preceded shocks from implanted cardioverter-defrillators, pacemaker-like devices used to halt potentially deadly, fast or chaotic heart rhythms.

• Natural disasters and war. Heart attacks and cardiac arrests spiked abruptly in the day of the early-morning earthquake in Northridge, California in 1994. Israeli researchers saw spikes in heart attacks during the first week of Iraqi missile attacks in 1991, while New Jersey researchers found a 49-percent increase in heart attacks within a 50-mile radius of the World Trade Center immediately after the attacks on September 11, 2001. 

• Weather. Severe heat waves, such as the ones that struck Europe in 2003 or the US Midwest in 1995, increased heart-related deaths. Cold weather triggers cardiovascular problems, too — in the United States, deaths from heart disease peak in December and January.

• Air pollution. Breathing air full of tiny particles from car, bus, and truck tail pipes, and fuel-burning factories or electricity generators is a trigger for heart attack and stroke.

• Infections. Pneumonia, the flu, and upper respiratory tract infections are potent triggers for stroke and heart attack. Urinary tract infections have also been linked to strokes.

• Sexual activity. Sexual activity briefly raises heart attack risk. Sex with a new partner in an unfamiliar setting increases the risk more than sex with a familiar partner in a familiar setting. In one Japanese study, cardiac deaths were found to be more common in extramarital than in intramarital sexual activity.

• Overeating. A heavy meal, especially one that is chock-full of saturated fat or carbohydrates, can raise the risk of having a heart attack by temporarily making blood more likely to clot, interfering with the blood vessel’s ability to relax and contract, or increasing the heart rate and release of stress hormones.

• Other triggers. These include grief, lack of sleep, mental and work-related stress, the use of cocaine and other “recreational” drugs, holidays, and sporting events (if your team loses).

Silencing Triggers

With triggers lurking everywhere, waiting to assail you even before you wake up, what’s a person to do? Relax, for one thing. The vast majority of people, including those with cardiovascular disease, get out of bed in the morning, do heavy physical exertion, make love, get angry, and suffer through the flu just fine.

Still it’s scary to hear that something like a sexual activity doubles your risk. But keep in mind that the chance of having a heart attack, stroke, or cardiac arrest in any particular hour or during a particular activity is very low, in the order of one in a million. So sex increases the absolute risk from one in a million to two in a million. In other words, not that much. What’s more, the risks are averages, and so are lower for people without cardiovascular disease and higher for those with it. That said, there are ways to inactivate those triggers.

• Lower your absolute risk. The more flexible your arteries and the less plaque they contain, the lower your chances of having a heart attack, stroke, or cardiac arrest. Exercise, not smoking, eating a heart-healthy diet, and controlling your blood pressure, cholesterol, blood sugar, and weight go a long way to warding off all cardiovascular problems.

• Blunt specific triggers. The more you exercise, the less likely you are to have a heart attack while exercising or doing strenuous activity. If you are prone to stress, anger, or anxiety, learning to manage these emotions can nip these triggers in the bud. Get vaccinated against pneumonia and get a yearly flu shot. In the morning, give yourself a few extra minutes to wake up and get out of bed.

• Avoid some triggers. If you’ve already had a heart attack or stroke, or are at high risk for one, avoiding some triggers may minimize your risk. Hire someone younger and stronger to do the strenuous work. Wash your hands often, especially if you’ve been around someone with a cold or other respiratory infection. Walk away from confrontations. Try not to indulge in rich, high-calorie meals. Stay indoors where it’s cool during a heat wave or on days when air pollution is high.

• Stick with your medications. Many of the standard medications taken for cardiovascular disease prevent or interrupt triggered pathways. Aspirin makes it more difficult for blood clot to form. Beta blockers calm the activity of the sympathetic nervous system. Statins stabilize plaque, making it less likely to rupture. If you take one or more medications to control your blood pressure, make sure they last long enough to do their job through the night and into the early morning.

This description of triggers is meant to empower you, not frighten you. Knowing the things that can set off a heart attack, stroke, or cardiac arrest, can help you avoid them or blunt their power. Being aware of possible triggers can also help you respond faster if they do, indeed, set off a heart attack or stroke. The faster you act, the better off you’ll be.

But knowing your triggers doesn’t alter the conventional wisdom about preventing heart attacks and strokes, which is, that nothing truly works without changes in risk factors such as diabetes, eliminating smoking, relieving high blood pressure and lipid disorders. This is where medicine should focus its attention. Today, doctors are learning more about what triggers heart attacks — but prevention, not prediction, remains the prime strategy for helping patients.