How the heart works, and how it can cause sudden death
In order to understand why sudden death can happen, it helps to understand how the heart works.
The heart is a specialised muscle that contracts regularly and continuously, pumping blood to the body and the lungs. The pumping action is caused by a flow of electricity through the heart that repeats itself in a cycle. If this electrical activity is disrupted - for example by a disturbance in the heart's rhythm known as an 'arrhythmia' - it can affect the heart's ability to pump properly.
In order to understand why sudden death can happen, it helps to understand how the heart works.
The heart is a specialised muscle that contracts regularly and continuously, pumping blood to the body and the lungs. The pumping action is caused by a flow of electricity through the heart that repeats itself in a cycle. If this electrical activity is disrupted - for example by a disturbance in the heart's rhythm known as an 'arrhythmia' - it can affect the heart's ability to pump properly.
Figure 1: How the heart functions electrically The heart's natural pacemaker - the SA node - sends out regular electrical impulses from the top chamber (the atrium) causing it to contract and pump blood into the bottom chamber (the ventricle). The electrical impulse is then conducted to the ventricles through a form of 'junction box' called the AV node. The impulse spreads into the ventricles, causing the muscle to contract and to pump out the blood. The blood from the right ventricle goes to the lungs, and the blood from the left ventricle goes to the body. |
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The electrical activity of the heart can be detected by doing an 'electrocardiogram' (also called an ECG). An ECG recording looks something like the one shown below.
A death is described as sudden when it occurs unexpectedly, spontaneously and/or even dramatically. Some will be unwitnessed; some may occur during sleep or during or just after exercise. Most sudden deaths are due to a heart condition and are then called sudden cardiac death (SCD). Up to 95 in every 100 sudden cardiac deaths are due to disease that causes abnormality of the structure of the heart. The actual mechanism of death is most commonly a serious disturbance of the heart's rhythm known as a 'ventricular arrhythmia' (a disturbance in the heart rhythm in the ventricles) or 'ventricular tachycardia' (a rapid heart rate in the ventricles). This can disrupt the ability of the ventricles to pump blood effectively to the body and can cause a loss of all blood pressure. This is known as a cardiac arrest. If this problem is not resolved in about two minutes, and if no-one is available to begin resuscitation, the brain and heart become significantly damaged and death follows quickly.
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