It is estimated that 1000 Singaporeans die from Sudden Cardiac Death (SCD) every year, about half of whom are below 60 years old. What is SCD and is it the same as a heart attack?
"A SCD is not a heart attack", said Dr Aaron Wong, Senior Consultant at National Heart Centre Singapore (NHCS).
"A SCD can be due to many causes but is usually caused by an abnormal heart rhythm due to abnormal 'electrical circuit' of the heart. A heart attack is caused by blockages in the heart arteries supplying blood to the heart, causing a portion of the heart muscle to be damaged. Heart attack may lead to abnormal heart rhythm, and therefore SCD, but not always."
Unlike a heart attack, which has symptoms such as chest pains and breathlessness, SCD usually has no warning signs. The only way to treat a SCD is to set the rapid heartbeat back to its normal pace by delivering an electrical shock to the heart using a device called a defibrillator.
Patients at high risk of SCD may be advised by their doctors to have an Implantable Cardiac Defibrillator (ICD) implanted. The ICD is a pocket-sized device which detects abnormal heart beats or rhythm and sends an electric current to the heart. This electric current shocks the heart and helps to reset the heart rhythm like a mini defibrillator.
Common cause of SCD
The most common cause of SCD is a sudden onset of abnormal heart rhythm. This is usually due to a fast but chaotic heart rhythm called ventricular fibrillation (VF) or tachycardia (VT). Extremely slow heart rate may cause SCD as well but usually present with prior symptoms of giddiness or fainting episodes.
In a patient with VF (a form of cardiac arrest), the heart beats 400 to 500 beats per minute and the normal rhythmic contractions of the lower chambers of the heart stops. When this happens, blood and oxygen are not pumped to the rest of the body and within seconds, the brain becomes starved of oxygen and the person loses consciousness. Without immediate treatment, the brain will cease to function and the person can die within minutes.
Who are likely to suffer from Sudden Cardiac Death?
SCD do not randomly occur in people. Almost 75% of all SCD patients show signs of a previous heart attack and 80% 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 SCD.
According to Dr Ching Chi Keong, Consultant, Department of Cardiology at NHCS, 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.
For those who are younger than 35 years old, risk factors include family history of sudden deaths or unexplained drownings, recurrent chest pain and/or fainting episodes during physical exertion and known to have heart disease especially hypertrophic cardiomyopathy.
Risk factors of SCD
1. Coronary Artery Disease (CAD)
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 present initially with symptoms of difficulty in breathing.
Dr Wong advises, "Patients who have CAD (e.g. had 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 medications dosage without consulting their doctors."
In some cases, critical narrowing of the artery of the heart can be treated either by ballooning and stenting or a coronary artery graft bypass (CABG) operation, to relieve the symptoms of angina and prolong life in some cases.
2. Poor Heart Function or Heart Failure
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) due to an inherited heart muscle disease or virus infection.
SCD is one of the most common mode 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.
Risk factors, continued
3. Strong Family History
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 sibling 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, related to pregnancy in females.
4. Electrical Disorders of the Heart
Some electrical disorders of the heart can lead to SCD and occasionally can be picked up during 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 radiofrequency energy to burn off this abnormal nerve or pathway.
Another type of electrical disorders that can cause SCD is due 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, 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 levels) and stop smoking, especially for those with family history of CAD. For those who are less than 35 years old, learn to recognise the above symptoms and go for a medical check up for assessment", says Dr Ching.
What to do
What to do if you witness a Sudden Cardiac Death
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%.
To help a person who has collapsed from SCD, the following steps have proven to be vital.
1. Call the ambulance
2. Perform Cardiopulmonary Resuscitation (CPR)
3. Perform the Automated External Defibrillator (AED), if available
Sudden cardiac death is a major cause of mortality in Singapore and the rest of the world but this silent killer may be preventable to a certain extent. Primary prevention and early identification and treatment of CAD and heart failure remain very important. Patients with high risk of SCD can be identified by history of fainting, family history of SCD and abnormal features on ECG. Implantation of an ICD is useful for SCD survivor and patients who are at a high risk of SCD.
This article was contributed by National Heart Centre Singapore (NHCS) and is part of a series on heart health.