Sudden Cardiac Death

Sudden cardiac death is a death that happens suddenly from a heart cause, usually within one hour of symptoms starting, or in a person found dead after being seen healthy within the previous 24 hours. The event that comes before it is called sudden cardiac arrest: the heart suddenly stops pumping blood, so the person collapses, becomes unconscious, and does not breathe normally. Cardiac arrest does not always end in death. If help is given within a few minutes, some people can be saved.

How the Heart Suddenly Stops

In the majority of cases, cardiac arrest is caused by a dangerous rhythm disorder starting in the heart's lower chambers, either a very fast ventricular tachycardia or ventricular fibrillation, in which the lower chambers only quiver without pumping. These rhythms and how to help are covered on the Ventricular Fibrillation page. Less often, the heart stops because of a very slow heartbeat or because electrical activity no longer produces a pumping action.

Causes Differ by Age

In adults over 35, a common cause is coronary artery disease, including a heart attack in progress or scar tissue from an old heart attack. Heart failure with a weak pump also increases the risk. In children, teenagers, and young adults, the cause is more often an inherited cardiomyopathy, inflammation of the heart muscle, a congenital electrical disorder such as long QT syndrome and Brugada syndrome, or a congenital abnormality of the coronary arteries.

Often Preceded by Warning Signs

Cardiac arrest often seems to come without warning. However, some people have symptoms in the days or weeks before, such as chest pain, shortness of breath, palpitations, or fainting during activity. Symptoms like these, as well as a family history of sudden death at a young age, need to be checked.

Preventing and Helping

Prevention follows two paths. The first is controlling coronary artery disease and assessing the risk of people who already have heart disease; some are advised to have an implantable cardioverter defibrillator (ICD). The second is preparing the community: the more people who can give chest compressions and use an AED, the greater the chance that a victim survives. If someone dies suddenly at a young age, investigating the cause and screening the family help protect their relatives.

Cardiac arrest is recognized from clinical signs: the person is unconscious, unresponsive, and not breathing normally. Rescuers do not need to wait for any tests. An AED will read the heart rhythm and give instructions.

In survivors, testing looks for the cause and the risk of recurrence, as explained on the Ventricular Fibrillation page: an ECG, blood tests including troponin and electrolytes, coronary angiography, echocardiography, and cardiac MRI. In people who have never had a cardiac arrest but are at risk, the doctor assesses the heart's pumping strength, arrhythmias recorded on a Holter monitor, any history of fainting, and family history. If someone dies suddenly at a young age, guidelines recommend an autopsy with a careful examination of the heart and, if needed, genetic testing of samples from the person who died. Close relatives are then advised to have an ECG, echocardiography, and other tests based on the suspected cause.

Sudden cardiac death is preceded by cardiac arrest, which is always an emergency. If you see someone suddenly collapse, not respond, and not breathe normally, call emergency services at 119 right away, start chest compressions, and ask someone else to get an AED.

Make an appointment with a cardiologist to assess your risk if:

• You have fainted during exercise, when startled, or without a clear cause
• A family member died suddenly before age 50
• You have coronary artery disease, heart failure, or cardiomyopathy and have never had your arrhythmia risk assessed
• You often have a very fast heartbeat with dizziness
• You have chest pain or shortness of breath during activity that has never been checked