New Hypertrophic Cardiomyopathy Study Reveals Who's at Highest Risk

A major new study led by UVA Health gives heart doctors more tools to identify which patients with hypertrophic cardiomyopathy (HCM) may face the highest risk of sudden cardiac death. HCM, a very common genetic heart disease, is also the most frequent cause of sudden cardiac death in young people in the United States. It can affect people of any age, and many people don't even know they have it.

“This is an important next step to do a better job of identifying HCM patients at high risk,” says Christopher M Kramer, MD, a heart disease researcher and chief of Cardiovascular Medicine at UVA Health who led the study for UVA Health in partnership with researchers from the University of Oxford.

What Is Hypertrophic Cardiomyopathy?

Every so often, a story makes the news: a young athlete collapses and dies with no warning at all. Often, the cause is to be related to hypertrophic cardiomyopathy.

If you have HCM, your heart muscle grows to be much thicker than it should be. That thickening can make it harder for the heart to pump blood. In some people, it can also block blood from flowing out of the heart properly.

Over time, the thickened muscle can develop scar tissue. That scarring can interfere with the heart's electrical signals. This raises the risk of dangerous, fast heart rhythms.

HCM affects at least 1 in 500 people. Some people with HCM never have any symptoms. Others develop shortness of breath, chest pain, or heart failure (a condition in which your heart gradually loses its ability to pump enough blood for the body).

Hypertrophic Cardiomyopathy Study Uncovers New Way to Predict Risk

The study followed almost 2,700 people with HCM. Researchers tracked patients at 44 medical centers in the United States and Europe. In total, the study included six countries.

The researchers followed these patients after each patient got a detailed heart MRI, (cardiac magnetic resonance imaging, or CMR). They also got a blood test, a genetic test, and a health history questionnaire. Over time, they noted who developed dangerous heart rhythms, who needed a heart transplant, and who died from causes related to their HCM.

The findings, published in the Journal of the American Medical Association, or JAMA, found that the CMR scans turned out to be especially useful. It let researchers measure things like the heart's size, how well it's pumping, and how much scar tissue has built up in the muscle.

The researchers found that these factors raised a patient's risk of sudden cardiac death the most:

• More scar tissue. Every 10% increase in scar tissue nearly doubled a patient's risk. Once scarring reached about 9% of the heart muscle or more, risk rose sharply.
• A bigger, heavier heart muscle. This mattered more than simply measuring how thick the heart wall was in one spot.
• Weaker pumping strength. This was especially important for predicting sudden cardiac death.
• A history of heart failure. Patients who'd already had heart failure were about three times more likely to have a serious event.
• Higher levels seen on a blood test of a blood marker called NT-proBNP. This substance rises when the heart is under stress or strain.

Kramer and the team combined all of this information into one model. It correctly predicted a patient's risk about 77% of the time. "That's very high for this kind of model," Kramer said.

Interestingly, some factors doctors have leaned on for years turned out to be less useful in this study. These included a family history of sudden death, fainting spells, the heart wall's thickness in a single spot, and genetic test results by themselves. Measuring the heart's overall size, shape, and pumping strength mattered more.

What This Means for You or a Loved One

If you or someone you love has HCM, this research could change how doctors evaluate their risk.

"This study identifies MRI markers and a blood test that identifies patients with this disease who are at higher risk of death from heart failure, stroke or sudden death from fast heart rhythms," Kramer says.

Catching high-risk patients early matters, because it opens the door to treatment. "The patients with HCM who are identified early can then receive therapies that can save lives," Kramer notes. "It points out that every patient who is newly diagnosed with HCM should have a cardiac MRI study and blood drawn for NT-proBNP to assess their risk."

This kind of testing can help in another way, too. It can spare lower-risk patients from getting treatment they don't need. Many high-risk HCM patients are treated with a device called an implantable cardioverter defibrillator, or ICD. It's placed in the chest and can shock the heart back into a normal rhythm if something goes wrong. ICDs save lives, but they carry real risks, too. Better risk prediction means doctors can save ICDs for the patients who truly need them.

Cardiac MRI is widely available at large medical centers, but it can be harder to find in rural areas, Kramer points out. That's worth asking about if you or a loved one is being evaluated for HCM.

What's Next?

Kramer and his team are now building a risk calculator based on these findings. They plan to test it using another large group of patient records. If it holds up, it could eventually help shape official treatment guidelines for HCM patients everywhere.

Better Tools Can Help HCM Patients Live Longer

This large, long-term study is helping heart doctors with new tool to tell who's truly at risk for a serious heart emergency as a result of hypertrophic cardiomyopathy, and who isn't. If you or a family member has HCM, or a family history of sudden cardiac death, talk to a UVA Health heart specialist. Ask whether a cardiac MRI and an NT-proBNP blood test make sense for you.