While on his way to attend a meeting in his office, JSM, a 44-year-old executive slumped in the seat of his chauffer-driven car. His fists clenched and unclenched, body became stiff and eyes rolled up. His driver stopped the car and finding him unconscious, rushed him to a hospital. The doctors pronounced him dead. Told that he was absolutely normal when he left home, they remarked that it was a typical case of Sudden Cardiac Death.

Sudden Cardiac Death (SCD), also called cardiac arrest, is used to describe a situation in which the heart abruptly and without warning stops working, so no blood can be pumped to the rest of the body.

It is responsible for half of all heart disease deaths. It is a catastrophic presentation in a variety of cardiac diseases and on some occasions, happens without an obvious structural heart disease.

Heart attack is the result of a sudden blockage of an artery supplying blood to the heart muscle leading to muscle damage, pump failure and its consequences. Sudden cardiac death occurs due to electrical system malfunctioning of the heart — leading to complete cessation of heartbeat or a chaotic beating, which is not compatible with life.

If the heart is compared to a house, a heart attack can be put down to a plumbing problem. Sudden Cardiac Death can be due to an electrical problem.

The most common cause of cardiac arrest is a heart rhythm disorder or arrhythmia called ventricular fibrillation.

The heart has a built-in electrical system. In a healthy heart, a “pace-maker” triggers the heartbeat, then electrical impulses run along pathways in the heart, causing it to contract in a regular, rhythmic way. When a contraction happens, blood is pumped. But in ventricular fibrillation, the electrical signals that control the pumping of the heart suddenly become rapid and chaotic.

As a result, the lower chambers of the heart, the ventricles, begin to quiver (fibrillate) instead of contract and they can no longer pump blood from the heart to the rest of the body.

If blood cannot flow to the brain, it becomes starved of oxygen and the person loses consciousness in seconds. Unless an emergency shock is delivered to the heart to restore its regular rhythm, using a machine called a defibrillator, death can occur within minutes. It’s estimated that more than 70 per cent of ventricular fibrillation victims die before reaching the hospital.

Who is at risk?

Although this problem is occasionally seen in persons without an underlying heart disease and comes as a bolt from the blue, the truth is that sudden cardiac death is usually not a random event.

Most victims have underlying heart disease or related health problems. They or their families may not have been aware of it.

There are numerous contributors to cardiac arrest, but two of the most important ones are:

1. A previous heart attack: 75 per cent of people who die of SCD show signs of a previous heart attack.

2. Coronary Artery Disease: 80 per cent of victims have signs of coronary artery disease. This is a condition in which arteries that supply blood to the heart are narrowed or blocked.

There are a number of signs and symptoms that should warn the individual regarding the possibility of a risk of sudden cardiac arrest. These include:

• An abnormal heart rate or rhythm (arrhythmia) of unknown cause

• An unusually rapid heart rate (tachycardia) that comes and goes, even when the person is at rest

• Episodes of fainting (called syncope) of unknown cause

• A low ejection fraction (EF): The ejection fraction is a measurement of how much blood is pumped by the ventricles with each heartbeat. A healthy heart pumps 55 per cent or more of its blood with each beat. People at highest risk for SCD have ejection fractions of less than 40 per cent, combined with ventricular tachycardia (an abnormally fast heart rate in the lower chambers of the heart).

Tests to predict risk

A number of tests that can be performed to determine if someone is in a group that is at high risk for cardiac arrest. These include:

• Electrocardiogram: A painless test in which electrodes are attached to the patient’s chest to record the electrical activity of the heart in order to identify abnormal heart rhythms. Certain arrhythmias could point to an increased risk of SCD.

• Echocardiogram: A painless test in which sound waves are used to create a moving picture of the heart. The test can measure the pumping ability of the heart and identify other problems that may increase a person’s risk for SCD.

• Holter monitor: A Walkman-size recorder that patients attach to their chest for one to two days, recording a longer sampling of their heart rhythm. After the recorder is removed, the tape is analysed for signs of arrhythmia.

• Event recorder: A pager-sized device that also records the electrical activity of the heart over a longer period of time. Unlike a holter monitor, it does not operate continuously. Instead, patients turn on the device whenever they feel their heart beating too quickly or chaotically.

• Electrophysiology study: This test is performed at a hospital or clinic. A local anaesthetic is used to numb areas in the groin or neck and thin flexible wires called catheters are snaked up to the heart to record its electrical signals. During the study, the electrophysiologist studies the speed and flow of electrical signals through the heart, identifies rhythm problems and pinpoints areas in the heart that may be the sources of abnormal electrical signals that trigger arrhythmias. The physician can also determine if a patient has had a prior heart attack or evidence of prior heart damage without knowing it. All of this information can help determine if the patient is in a group at higher risk for SCD.