Almost 75 per cent of all sudden cardiac death patients show signs of a previous heart attack and 80 per cent of them have signs of coronary artery disease (CAD).

It has also been found that people who have high blood pressure, high cholesterol, diabetes mellitus, or a family history of CAD are at risk of developing CAD, which in turn could lead to sudden cardiac death.

According to Clinical Associate Professor Ching Chi Keong, Senior Consultant, Department of Cardiology and Director, Electrophysiology and Pacing, at National Heart Centre Singapore (NHCS), a member of the SingHealth group, a typical SCD patient is likely to be male, more than 35 years old and has a family history of early heart attack. There is also a higher incidence amongst South Asians.

• A family history of sudden deaths or unexplained drownings
• Recurrent chest pain and/or fainting episodes during physical exertion and
• Known heart disease, especially hypertrophic cardiomyopathy

• Sudden Cardiac Death (SCD) can occur during a heart attack where the damaged heart muscle induces an abnormal heart rhythm or there is a sudden loss of heart pumping function due to massive damage to the heart muscle. The latter is usually not sudden but presents initially with symptoms of difficulty in breathing.
• Clinical Associate Professor Aaron Wong, Head and Senior Consultant at NHCS advises, "Patients who have CAD (e.g. previous angina, heart attack, angioplasty or bypass surgery) should control their risk factors for CAD and stop smoking. Some medications have also been proven to reduce the progression of CAD, the risk of heart attack and heart failure but may have to be taken on a long term basis. Patients should not stop or reduce their medication dosage without consulting their doctors."

• Poor heart function is usually caused by repeated injury to the heart muscle (heart attacks) that leads to scarring and subsequent loss of muscle contraction function.
• Poor heart function can also be due to disease of the heart muscle (known as cardiomyopathy) because of an inherited condition, or a virus infection.
• SCD is one of the most common causes of death in patients with heart failure. Patients with heart failure should be on long-term medications that have been shown to improve symptoms and prolong life expectancy. Patients with severely impaired heart function may benefit from implanting an ICD to reduce the chance of dying from SCD.

Some heart diseases, including CAD, cardiomyopathy and some heart electrical disorders are hereditary.

• The most common inherited risk factor is high cholesterol.
• • Extremely high cholesterol can lead to CAD and heart attack at an early age. A person whose parents or siblings had CAD at a young age or high cholesterol should have his/her cholesterol checked regularly. Aggressive control of cholesterol levels can reduce the chance of developing CAD and therefore SCD.
• Hypertrophic cardiomyopathy (HCM)
• • An abnormal thickening and arrangement of the heart muscle cells can cause VF or VT leading to SCD, especially during exertion. Certain types of HCM are prone to SCD and a person with HCM who has close family members who passed away due to SCD should have an ICD implanted.
  • • Arrhythmogenic right ventricular dysplasia (ARVD)
    • • A structurally abnormal right ventricle is also an inherited disorder. An ICD is often required in these patients.
    • Dilated cardiomyopathy
    • • Features a dilated heart with poor heart function. The condition can also be caused by a virus infection or in some cases, is related to pregnancy.

• Some electrical disorders of the heart can lead to SCD and occasionally can be picked up during a routine ECG. Many of these disorders are also inherited, and a strong family history of SCD is important.
• One of these disorders (known as the Wolff-Parkinson-White Syndrome) is caused by an extra nerve connecting the heart chambers, which can cause an 'electrical short-circuit' in the heart, resulting in a rapid heartbeat. This condition is now easily treatable with catheter ablation, a procedure where a thin tube (catheter) is advanced into the heart via a vein (usually from the leg/groin), to deliver a burst of radio frequency energy to burn off this abnormal nerve or pathway.
• Another type of electrical disorder that can cause SCD is related to abnormalities in the heart muscle cell membrane (e.g. Brugada's and Long QT Syndromes).
• • They frequently present in young, apparently healthy individuals with no known heart problems, although some abnormalities can often be seen in the ECG on careful examination. In many patients, the first presentation is usually SCD.Frequent fainting episodes or even a diagnosis of epilepsy may accompany such conditions. For these patients, the ICD is the only alternative to prevent SCD.

Awareness of your risk factors is important. "If you are more than 35 years old, do adopt a healthy lifestyle. Screen yourself for risk factors of CAD (e.g. diabetes, high cholesterol) and stop smoking, especially if you have a family history of CAD. For those who are less than 35, learn to recognise the above symptoms and go for a medical check-up for assessment," says Dr Ching.

In the event a person collapses from SCD, the key to survival is early defibrillation. It has been found that each minute of delay before defibrillation reduces survival by about 10 per cent. To help a person who has collapsed from SCD, the following steps have proven to be vital.

1. Call an ambulance.
2. Perform cardiopulmonary resuscitation (CPR).
3. Use an automated external defibrillator (AED), if available.

Ref: N18

Check out other articles on the heart:

Why You Shouldn't Ignore Chest Pains

When are Fast Heart Beats a Concern?

How to Survive a Heart Attack When Alone

How Often Should You Eat Fast Food?

Tips for a Healthy Heart