The following are key points to remember from this editorial comment on late gadolinium enhancement (LGE) and better selection of patients with hypertrophic cardiomyopathy (HCM) for primary prevention implantable cardioverter-defibrillators (ICDs):

1. Some patients with HCM are at high risk of sudden cardiac death (SCD), and ICD devices can be useful for primary prevention of these events.
2. Clinical variables can identify patients with HCM at increased risk of SCD, and include HCM-related sudden death in relatives, unexplained syncope, massive left ventricular hypertrophy, prolonged nonsustained ventricular tachycardia, attenuated blood pressure with exercise, and high-risk subgroups such as those with left ventricular dysfunction, apical aneurysms, or regional scar.
3. Existing clinical risk scores may miss some patients. Some patients without risk factors experience SCD, and other patients may be difficult to classify. There is a need for improved risk assessment to more accurately identify HCM patients at risk of SCD who may benefit from ICD implantation.
4. Cardiac magnetic resonance (CMR) imaging can identify abnormal myocardium, and late-gadolinium enhancement (LGE) imaging can identify areas of fibrosis. Over one-half of patients with HCM exhibit LGE, with a variety of observed patterns and sites.
5. Recent prospective multicenter data have observed that the presence of extensive LGE (≥15% of myocardium) is independently associated with SCD. Among asymptomatic patients without typical risk factors, those with extensive LGE had twice the risk of SCD. Among patients with HCM and risk factors, extensive LGE identified individuals at greater risk. Finally, patients without LGE experience low rates of SCD.
6. A recent meta-analysis including almost 3,000 HCM patients has also demonstrated that extensive LGE was associated with about double the risk of SCD, even after accounting for traditional risk factors. It also noted a linear relationship between the extent of LGE and risk of SCD, suggesting that a single cutpoint such as 15% LGE may be inadequate, and that the actual proportion of LGE should also be weighed when considering the risks and benefits of ICD implantation.
7. Existing data support the standard use of CMR with LGE to evaluate patients with HCM to help identify the risk of SCD and the appropriate role of ICD implantation for primary prevention of SCD.

Keywords: Aneurysm, Arrhythmias, Cardiac, Blood Pressure, Cardiomyopathy, Hypertrophic, Death, Sudden, Cardiac, Defibrillators, Implantable, Heart Failure, Gadolinium, Hypertrophy, Left Ventricular, Magnetic Resonance Spectroscopy, Myocardium, Primary Prevention, Risk Assessment, Risk Factors, Syncope, Tachycardia, Ventricular, Ventricular Dysfunction, Left

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