What is Late Gadolinium Enhancement (LGE) on an HCM MRI?

Late Gadolinium Enhancement (LGE) is a technique used during a cardiac MRI (Magnetic Resonance Imaging of the heart) to detect and measure areas of scar tissue in the heart muscle. In people with Hypertrophic Cardiomyopathy (HCM), LGE appears as bright, highlighted spots on the MRI scan, indicating where the heart muscle has been replaced by fibrosis (permanent scar tissue) ^[1][2].

Why Does Scar Tissue Form in HCM?

Hearing that you have scar tissue in your heart can sound frightening, but it is a common and monitorable part of having HCM. The heart muscle in HCM becomes abnormally thick. Sometimes, this thickening outgrows its blood supply, leading to microvascular ischemia (a lack of adequate blood flow through the smallest blood vessels) ^[1]. Over time, this lack of blood flow damages the heart muscle cells, causing them to be replaced by fibrous scar tissue ^[2]. While existing scar tissue is permanent, doctors use medications and regular monitoring to manage the condition and protect your heart.

The Role of LGE in Assessing Risk

A key purpose of measuring LGE—once HCM is diagnosed—is to help evaluate your safety. The overall risk of sudden cardiac events in HCM is actually very low. Measuring the amount of scar tissue helps doctors identify the specific people who could benefit from extra protection ^[3][4].

Extensive scarring can disrupt the heart’s electrical system, making it easier for dangerous arrhythmias (irregular heartbeats) to start and spread ^[3][4].

The 15% Threshold

When doctors review an MRI report, they often calculate the percentage of the left ventricle’s mass that is made up of scar tissue. According to the American Heart Association (AHA) and American College of Cardiology (ACC) guidelines, having an LGE extent of 15% or greater is considered “extensive” ^[5][3].

Research shows that having 15% or more LGE is a major, independent risk factor for dangerous arrhythmias ^[6][7]. Even if a patient doesn’t have other traditional risk factors—like unexplained fainting or a family history of sudden cardiac events—an LGE of 15% or higher significantly changes how their risk is managed ^[6][4].

If your LGE is under 15%, it doesn’t mean you are at zero risk, but rather that your doctor will evaluate your LGE alongside other traditional risk factors to make the best care plan for you ^[5][8]. Also, keep in mind that not all radiology reports list a precise numerical percentage. If your report uses words like “focal,” “mild,” or “extensive,” you can ask your cardiologist to estimate how your scarring aligns with the 15% threshold.

Location Matters

Beyond the total percentage, the location of the scar tissue is also important. In HCM, it is common to have a small amount of LGE at the “junctional points” or “hinge points” (where the right and left ventricles meet). However, scarring that extends outside these standard areas, or involves the inner lining of the heart (subendocardial), can indicate a higher risk and requires closer attention ^[9][10].

What LGE Means for Your Treatment Plan

The ultimate goal of assessing LGE is prevention. If your LGE is 15% or higher, the AHA/ACC guidelines explicitly state that your doctor may recommend an ICD (Implantable Cardioverter-Defibrillator) ^[5][3][8]. An ICD is a small device placed in the chest that constantly monitors the heart’s rhythm and can deliver a life-saving shock if a dangerous arrhythmia occurs. By using LGE to identify who needs an ICD, doctors can successfully turn a scary risk into a highly manageable one ^[4][11].