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Heart stopping: Cardiologists battle the causes of sudden cardiac death

02/29/2016

It accounts for half of all heart disease fatalities, and it is the single largest cause of natural death in the country, yet many of us know little about sudden cardiac death. Commonly referred to as SCD, sudden cardiac death occurs when the electrical system in a person’s heart goes haywire. Seemingly out of the blue, the heart begins to beat rapidly and irregularly, making it unable to pump blood to the rest of the body: cardiac arrest. Within moments the person collapses. 

“The person dies because not enough oxygen is getting to the brain and other organs,” explains Martin Maron, MD, Director of the Hypertrophic Cardiomyopathy Center at Tufts Medical Center. It’s estimated that SCD results in more than 326,000 deaths per year, or nearly 900 each day in the U.S.

Learn about cardiac death and how to prevent it.Part of the reason for those high numbers is that less than 8 percent of people survive when they experience cardiac arrest outside the hospital. But it doesn’t have to be that way. “A bystander who knows how to quickly deliver simple and effective CPR can make it two to three times more likely that someone survives,” says cardiologist Mark Link, MD, Professor of Medicine at Tufts Medical Center. Dr. Link has helped lead an American Heart Association initiative to get more people trained in CPR, a drive that also resulted in updated CPR guidelines (see page 6). “One of the most important changes is a recommendation of ‘handsonly’ CPR,” Dr. Link says. “Not that mouth-to-mouth is bad, but it’s easier and less complex to do hands-only.”

What causes the cardiac arrest that can lead to sudden cardiac death? There are a number of heart diseases and conditions that can make someone susceptible to cardiac arrest. “Coronary disease related to bad diet, lack of exercise, smoking, and so on remains the number one cause of death,” Dr. Maron says. So healthy eating and exercise habits can go a long way toward reducing the chances of cardiac arrest, but some risk factors are congenital.

Long QT syndrome and Brugada syndrome, for instance, are disorders of the heart’s electrical system that can cause abnormal heart rhythms. And Marfan syndrome predisposes some people to cardiac arrest by causing parts of the heart to stretch and become weak. And then there’s Dr. Maron’s specialty, hypertrophic cardiomyopathy. HCM is a genetic disease in which the heart muscle is thicker than it should be, which can make it difficult to pump blood, especially during exercise.

“HCM tends to develop in puberty,” Dr. Maron says. “It affects approximately one out of every 500 people in the general population, and it’s the most common cause of sudden death in young people in the U.S.” HCM is also the leading cause of death among athletes. Still, many people live their whole lives with the disorder and never know it. For some, though, the condition results in symptoms such as chest pain, shortness of breath, heart palpitations, and passing out or collapsing. Dr. Maron says that only a small number of patients with HCM will ever experience actual symptoms. “Which patients?” he asks. “That’s what we try to do every day—determine which patients with HCM are actually at risk of sudden death and heart failure.”

To help figure that out, Tufts Medical Center provides referring cardiologists with a number of important tools. Tufts MC specialists can perform a cardiac MRI to provide better heart imaging than is often possible with echocardiograms available to many general cardiologists, and they can conduct genetic testing that is not available everywhere. Finally, Tufts MC is a leader in providing patients with implantable cardioverter defibrillators, or ICDs.

An ICD is a small device that is implanted under the skin and then monitors a patient’s heart. When the ICD detects that the heart is beating abnormally, it sends an electric shock to get things back on track and keep the blood flowing. “The ICD is one of the most impactful developments in medicine over the past 50 years,” Dr. Maron says.

Tufts MC is also a national resource for another cause of sudden cardiac death which is unrelated to genetics or lifestyle issues. Commotio cordis is the term for cardiac arrest that results from a young athlete being struck in a precise area of the chest, with a precise amount of force, at a precise moment of the cardiac cycle. It often involves a baseball player getting hit with a baseball, but lacrosse, hockey, softball and karate are other sports in which children have died after sustaining a blow to the chest. As many as 20 incidents are reported each year in the country, but it is widely believed that many occurrences go unreported.

Dr. Link, whose research has contributed much of what is known about commotio cordis, says that CPR can be effective when a child becomes unresponsive after sustaining a blow to the chest. “But a significant problem, historically, has been that coaches, parents and bystanders have not understood the severity of the problem,” he says. “Blows that can turn out to be life-threatening don’t always look serious when they occur.” That has begun to change, however. Dr. Link says that officials involved in youth athletics are much more aware of the problem today. “We’re now seeing a commotio cordis survival rate of up to 60 percent,” he says. “That’s because of improved recognition and improved resuscitation.”

Still, Dr. Link says more can be done. His research has found that the hardness of a ball has a significant effect on how likely it is to trigger cardiac arrest. In laboratory testing, Dr. Link has found that the softest balls can trigger cardiac arrest 11 percent of the time, compared with about 20 percent of the time for balls of intermediate hardness, and 69 percent of the time for standard baseballs. Given these results, Dr. Link says, a switch to softer “safety” baseballs in youth leagues could reduce the risk of sudden death on the playing field. And there’s another equipment change he advocates. “The available chest protectors don’t actually do that much,” he says, pointing out that nearly 20 percent of commotio cordis victims—from baseball and hockey to lacrosse and football—were wearing chest-protection equipment at the time. “The problems with the chest protectors available now are related to materials and hardness,” Dr. Link says. “We’re doing work here at Tufts using some novel materials to try and make a better chest protector.”

Whatever the underlying causes of sudden cardiac death—problems with diet and exercise; genetics; accidents on the playing field—Tufts Medical Center is a global leader in diagnosing, treating and researching them. “We are fortunate here at Tufts MC to have some of the world’s experts at treating and preventing SCD,” Dr. Maron says.

To contact The CardioVascular Center, call 866-430-1660.