Singapore's Silent Killer


What is Sudden Cardiac Death?

Sudden Cardiac Death (SCD) is an abrupt loss of heart function triggered by any of a variety of heart conditions. The most common cause is a sudden onset of an abnormal heart rhythm. This is usually one that is fast and chaotic, called ventricular fibrillation (VF) or tachycardia (VT). Occasionally, SCD can be attributed to a very slow heartbeat due to abnormality of the heart pacemaker cells or during a heart attack.

The heart of a patient suffering from VF beats at a rate of 400 to 500 per minute, causing the normal rhythmic contractions of its lower chambers to stop. When this happens, the heart is unable to pump blood and oxygen to the rest of the body, starving the brain of oxygen within seconds and the victim loses consciousness. Without immediate treatment, the brain will cease to function and the person will die within minutes.

SCD is not the same as a heart attack. The former results from an abnormal heart rhythm caused by abnormal 'electrical circuitry' of the organ, whereas the latter is set off by blockage or occlusion of the arteries supplying blood to the heart. A heart attack damages a portion of the heart muscle which may lead to SCD.

SCD is a silent killer as it does not have the typical symptoms of chest pains and breathlessness. The only way to treat the condition and set the rapid heartbeat back to a normal pace is to deliver an electric shock to the heart using a defibrillator.

A growing problem in Singapore

A study carried out in 2003 by the National Heart Centre and Health Sciences Authority on the sudden unexpected 229 deaths in the 18 to 60 age group found that 91% of these SCD victims were males. Another important finding was that 81 % of all deaths from SCD were caused by coronary artery disease (artery occlusion) and almost half of these, irrespective of age, suffered triple-vessel disease prior to their death.

Prevention

Although SCD strikes unexpectedly, it can be prevented through some simple, effective steps.

1. Coronary Artery Disease

SCD can occur during a heart attack where the damaged heart muscle induces an abnormal heart rhythm or, if the damage is massive, a sudden loss of the heart-pumping function. Holding the development of coronary artery disease (CAD) in check can effectively keep heart attacks and SCD at bay.

Primary Prevention of CAD
The young or those who have not developed signs and symptoms of CAD should eat healthily, exercise regularly, quit smoking, control their weight, go for regular health checks and, most importantly, control cardiovascular risk factors.

Secondary Prevention of CAD
Those who already have documented CAD, such as heart attack, angioplasty or bypass surgery, should be more aggressive with the primary preventive measures, especially to cease smoking and control risk factors. In some cases, the critical narrowing of the heart artery should be treated not only to relieve the symptoms of angina but also prolong life. Some medications have also been proven to slow down the progression of CAD.

2. Poor Heart Function

SCD is one of the most frequent causes of death in patients with poor heart function (for example, heart failure), which usually stems from repeated injury to the heart muscle (heart attacks), leading to scarring and the subsequent loss of muscle-contraction function. Poor heart function can be due to cardiomyopathy, a heart-muscle disease that is inherited or the result of a viral infection.

It is proven that patients with severely impaired heart function, regardless of causes, will live longer with help from the ICD (implantable cardioverter defibrillator). With the early diagnosis of poor heart function and the appropriate medications or treatments instituted, SCD can be prevented in some heart-failure patients.

3. Strong History of SCD

Some heart diseases are inherited, passed on from parent to child or afflicting siblings. These include CAD, cardiomyopathy and certain heart-conduction disorders.

The commonest inherited-risk factor for CAD is high cholesterol. Extremely high cholesterol can lead to CAD and heart attacks at a rather young age. A person with a family history of CAD or high cholesterol in one or both parents or a very young sibling, should have his/her cholesterol level tested.

Hypertrophic cardiomyopathy (HCM), which can be hereditary, is due to the abnormal thickening and arrangement of cells in the heart muscle. This can cause VF or VT, which can lead to SCD. Diagnosis is made via ECG and/or echocardiogram. Certain types of HCM are prone to SCD. A person with HCM who has lost a sibling to SCD should have an ICD implanted.

Arrhythmogenic right ventricular dysplasia (ARVD), another inherited disorder, is presented with a structurally abnormal right ventricle. It can be detected by ECG, echocardiogram and, sometimes, cardiac magnetic resonance imaging (MRI) scan. An ICD is often required in those afflicted.

Dilated cardiomyopathy features a dilated heart with poor heart function. Although this, too, is inheritable, it can be caused by a viral infection and is linked to pregnancy in females, albeit rarely. Viral myocarditis (heart inflammation) is usually presented with typical flu symptoms followed by developed signs of heart failure. Diagnosis can be made via ECG and echocardiography.

4. Electrical Disorders of the Heart

Some electrical disorders of the heart can lead to SCD and can occasionally be picked up during routine ECG. Many of these are also hereditary.

One such disorder is caused by an extra nerve connecting the heart chambers. Known as the Wolff-Parkinson-White Syndrome, it can set off an 'electrical short-circuit' in the heart, causing rapid heartbeat. The good news is that the condition is now easily treated with catheter ablation, a procedure where a thin tube (catheter) is advanced into the heart via a vein (usually in the leg or groin) to deliver a burst of radio-frequency energy to burn off this abnormal nerve or pathway.

Another type of irregularity that can trigger SCD is abnormalities in the membrane of heart-muscle cells. The Brugada and Long QT Syndromes, as these abnormalities are called, frequently strike young, apparently healthy, individuals with no known heart problems but who show up some abnormalities on careful examination by ECG. In many cases, the first presentation is usually an attack of SCD, accompanied by frequent fainting episodes, or even a diagnosis of epilepsy. For such patients, the ICD is the only method of prevention.

What to do if you witness SCD

In the event a person collapses from SCD, the key to survival is prompt defibrillation. It has been found that each minute of defibrillation delay reduces survival by about 10%.

To help a victim, call for an ambulance and perform chest compression and cardiac pulmonary resuscitation (CPR), a proven measure where time is critical.

Heart-health screening is a crucial first step towards avoiding cardiovascular disease. Early treatment improves the chances of preventing or delaying complications. If you have one or many of the risk factors for cardiovascular disease, you should see your family doctor for advice and go for regular health screening. If you are above 40 years old, it is advisable for you to go for regular heart-health screening. Please call 6436-7840 if you wish to have a heart-health screening or e-mail nhc@nhc.com.sg.