A Sudden Cardiac Death (SCD) attack is when there is an abrupt loss of heart function and can be due to a variety of heart conditions. However, 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). Occasionally SCD can be due to a pause in heart rhythm due to abnormality of the heart pacemaker cells or during a heart attack. It is estimated that 1000 Singaporeans die from SCD every year, about half of whom are below 60 years old.

When a patient suffers from VF (a form of cardiac arrest), the heart beats 400 to 500 beats per minute, causing the normal rhythmic contractions of the lower chambers of the heart to stop. When the heart contraction stops, 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 will die within minutes.

A SCD attack is not the same as a heart attack. SCD is caused by an abnormal heart rhythm due to abnormal “electrical circuitry” of the heart. A heart attack is caused by blockage or occlusion of the arteries supplying blood to the heart, causing a portion of the heart muscle to be damaged. This may or may not lead to an SCD attack.

What makes sudden cardiac death a silent killer is that unlike a heart attack, which has the typical symptoms of chest pains and breathlessness, sudden cardiac death however, has no warning signs and symptoms. The only way to treat a SCD attack and to set the rapid heartbeat back to its normal pace is to deliver an electrical shock to the heart using a device called a defibrillator. For individuals who are identified as patients at a higher risk of suffering from a SCD attack, an implantable cardioverter defibrillator (ICD), a pocket-sized device which sends an electric current to the heart when the heart beat becomes abnormal, could be implanted in the body.

Collaborating with the Health Sciences Authority, the National Heart Centre Singapore conducted a study on 229 sudden unexpected deaths in people aged 18 - 60 years old for the year 2003. Despite the fact that the study was only based on the results from an isolated year, the findings were astounding.

The study found that about 0.6 Singaporeans below 60 years old fall victim to SCD every day and that 91% of the people who died from sudden cardiac death were males. In addition, the study found that although Chinese people made up more than half of the sudden cardiac deaths in 2003 (53.2%), a significant percentage of people who had died were Malay (16.4%) and Indian (14%) as well. The study also found that the mean age for males dying from SCD in 2003 was 46 ±9 years and 49 ±9 years for females. An important finding of the study was that 81% of all SCD deaths were caused by coronary artery disease (which is the occlusion of blood arteries), with almost half of all patients irrespective of age having triple vessel disease prior to dying of SCD.

Although SCD is becoming a growing problem in Singapore, it does not randomly occur in people. It has been found that 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 be leading to SCD.

A person who has family members who die of SCD at young age is also at risk as some heart conditions that predisposed to SCD can be inherited. As such, the following groups of people are more prone to developing SCD: 

Although SCD by definition occurs unexpectly, there are several ways to prevent it through some simple and effective steps.

1. Coronary Artery Disease (CAD)

A SCD attack can occur during a heart attack where the damaged heart muscle induces abnormal heart rhythm or there is a sudden loss of heart pumping function due to massive damage to the heart muscle. Strategies to prevent development of CAD and heart attack will therefore be effective in preventing SCD.

Primary Prevention of CAD

Those who are young or have not developed signs and symptoms of CAD should:

1. Eat a healthy diet 
2. Exercise regularly 
3. Stop smoking 
4. Watch your weight 
5. Take it easy
6. Regular health check-ups 
7. Control cardiovascular risk factors

Secondary Prevention of CAD

Those who already have documented CAD (e.g. had angina, heart attack, angioplasty or bypass surgery) should be more aggressive with the primary prevention steps, especially with smoking and controlling the risk factors. In some cases, critical narrowing of the artery of the heart should be treated either by ballooning or coronary artery graft bypass operation, as these treatments not only can relieve the symptoms of angina but also prolonging life in certain cases. Some medications have also been proven to reduce the progression of CAD and therefore the risk of heart attack and heart failure, which are the two most common causes of SCD.

2. Poor Heart Function or Heart Failure

SCD is one of the commonest modes of death in patient with poor heart function (e.g. 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. However, poor heart function can be due to disease of the heart muscle itself (termed cardiomyopathy) either due to inherited heart muscle disease or virus infection.

The symptoms for heart failure are mainly difficulty in breathing on exertion or swelling of the legs. The diagnosis can be made on clinical examination, chest X-ray and ultimately on echocardiography (ultrasound scan of the heart). Patients with poor heart function should be on long-term medications that are proven to improve symptoms and prolong life expectancy.

It is also proven that patients with severely impaired heart function, irrespective of causes, will live longer if they are implanted with the ICD. However, ICDs are expensive at the moment and not all patients can afford or will benefit from it. Studies are on-going to see who are the most appropriate patients to be implanted with this device.

Therefore, if the diagnosis of poor heart function is made early and appropriate medications or treatments instituted, some SCD attacks in heart failure patients can be prevented.

3. Strong Family History of SCD

Some heart diseases are inherited and the parents or siblings may have the same problem. These include CAD, cardiomyopathy and some heart conduction disorders.

The commonest inherited risk factor for CAD is high cholesterol. Extremely high cholesterol can lead to CAD and heart attack in very early age. A person who had parents or sibling who had CAD at very young age or high cholesterol should have his/her cholesterol check. Aggressive reduction of cholesterol can reduce the chance of developing CAD and therefore SCD.

Hypertrophic cardiomyopathy (HCM) can be inherited and is due to abnormal thickening and arrangement of the heart muscle cells. These changes in the heart muscle can cause VF or VT that can lead to SCD. Diagnosis can be made on ECG and/or echocardiogram. Certain types of HCM are prone to SCD and a person with HCM who has had siblings die of SCD should have an ICD implanted.

Arrhythmogenic right ventricular dysplasia (ARVD) is also an inherited disorder presenting with a structurally abnormal right ventricle. The diagnosis can be made using a variety of non-invasive methods, including a combination of ECG, echocardiogram, and sometimes a cardiac magnetic resonance imaging (MRI) scan. An ICD is often required in these patients.

Dilated cardiomyopathy features a dilated heart with poor heart function and, although can be inherited, it can be due to virus infection and, rarely, related to pregnancy in females. Viral myocarditis usually presents with typical flu symptoms and later developed symptoms of heart failure. The diagnosis can be made on ECG and echocardiography.

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 is caused by an extra nerve connecting the heart chambers (known as the Wolff-Parkinson-White Syndrome), which can cause an “electrical short-circuit” in the heart, causing a rapid heartbeat. The good news is that this condition is now easily treatable with a procedure called catheter ablation, 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 disorder that can cause SCD is due to abnormalities attributable to the membrane of the heart muscle cells (Brugada and Long QT Syndromes). They frequently occur in young, apparently healthy individuals with no known heart problems, although the ECG can often show some abnormalities on careful examination. In many, the first presentation is usually an attack of SCD. However, frequent fainting episodes or even a diagnosis of epilepsy may accompany such conditions. For such patients, the ICD is the only alternative to prevent SCD.

What to do if you witness a Sudden Cardiac Death

In the event a person collapses from sudden cardiac death, 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 sudden cardiac death, the following steps have proven to be vital especially since time is precious:

The Unit for Pre-Hospital Emergency Care (UPEC) at SGH established the DARE programme to facilitate easier learning of CPR. Click here for more details on the DARE programme.

Conclusion

In conclusion, 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 still remain very important. Implantation of an ICD is useful for SCD survivor or for patients who are at a high risk of SCD. However, not all patients who survive a SCD attack would require an ICD, especially after a heart attack.