Sudden Cardiac Death

Sudden cardiac death is an unexpected death from a heart cause, usually within an hour of symptoms starting. Most cases follow a sudden cardiac arrest, when a dangerous heart rhythm stops the heart from pumping. In older adults the most common cause is coronary artery disease. In younger people, causes include inherited heart muscle diseases such as hypertrophic cardiomyopathy, inherited rhythm disorders such as long QT syndrome, inflammation of the heart muscle (myocarditis), and structural heart problems present from birth. Immediate CPR and use of a defibrillator (AED) can save lives.

Lab tests linked to sudden cardiac death:

• EPA+DPA+DHA: a combined omega-3 fatty acid measurement. The sample type and calculation depend on the lab, so check your report rather than assuming it is a red-cell omega-3 index. Observational studies link lower levels with higher cardiovascular risk, but trials of omega-3 supplements have had mixed results for preventing sudden death.
• Blood tests can't predict sudden cardiac death in an individual. Doctors assess risk with heart tests: an ECG, an echocardiogram, sometimes an exercise test or heart rhythm monitoring, and genetic testing when inherited conditions run in the family. Blood tests for coronary risk (lipids, HbA1c) and electrolytes such as potassium and magnesium are also used.

How results are read:

• A low omega-3 level is one minor risk factor. It doesn't mean a person is at high risk of sudden death, and a high level doesn't remove the risk.
• The strongest warning signs come from the history and heart tests: fainting during exercise, a family history of sudden death at a young age, or a known weak heart muscle.
• Very low or high potassium or magnesium can trigger dangerous rhythms and are corrected promptly.

When to see a doctor:

• If someone collapses and isn't breathing normally, call your emergency number, start CPR and use an AED if one is available.
• Get emergency care for ongoing palpitations with chest pain, dizziness or faintness. If the episode has stopped, or you fainted during exercise and recovered, get urgent medical assessment.
• See a doctor about heart screening if a close relative died suddenly before age 50 or has an inherited heart condition.

Clinical takeaway: sudden cardiac death risk is assessed mainly with heart tests and family history, and omega-3 levels are at most a minor risk indicator.