What Are The Different Cardiac Rhythms?

Learn about different cardiac rhythms, from normal sinus rhythm to dangerous arrhythmias, and how defibrillators save lives.

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The human heart beats in a steady pattern that keeps blood and oxygen moving around the body. This pattern, known as a cardiac rhythm, is controlled by the heart’s electrical system. When the rhythm is normal, it helps the heart work efficiently. However, if the rhythm becomes irregular, too fast, or too slow, it can put a person’s life at risk.

Knowing the difference between common cardiac rhythms can help bystanders and first aiders act quickly in an emergency. With the right training and access to a defibrillator, lives can be saved.

Normal Sinus Cardiac Rhythm

A normal sinus rhythm is the healthy rhythm of the heart. It originates in the sinoatrial node, often called the natural pacemaker. In adults, a normal resting heart rate usually falls between 60 and 100 beats per minute.

This rhythm shows that the heart is working effectively to pump blood. No treatment is required when the heart is in sinus rhythm.

Bradycardia

Bradycardia is when the heart beats slower than normal, typically below 60 beats per minute. Some people, such as athletes, may have a naturally slow heart rate with no issues. However, in others, bradycardia can cause fatigue, dizziness, and fainting.

Severe bradycardia may require medical intervention, such as a pacemaker, to regulate the heart’s rhythm.

Learn more about heart rhythm problems on the NHS website.

Tachycardia

Tachycardia is when the heart beats faster than normal, usually above 100 beats per minute at rest. There are different types of tachycardia:

  • Atrial fibrillation (AF) – the most common type of abnormal rhythm, where the upper chambers of the heart beat irregularly.

  • Supraventricular tachycardia (SVT) – a sudden burst of rapid heartbeats that start in the upper chambers.

  • Ventricular tachycardia (VT) – a dangerous rhythm originating in the lower chambers. If untreated, VT can lead to sudden cardiac arrest.

Ventricular Fibrillation

Ventricular fibrillation (VF) is one of the most serious cardiac rhythms. In VF, the heart quivers instead of pumping, meaning blood is not circulated effectively. This rhythm will quickly lead to death if not treated immediately.

The only effective treatment for VF is defibrillation. This is why public access to Automated External Defibrillators (AEDs) is so important.

Asystole

Asystole is known as a flatline, where there is no detectable electrical activity in the heart. Unfortunately, a defibrillator cannot shock asystole. In these cases, immediate CPR should be performed until advanced medical help arrives.

Find out more about CPR guidance from the NHS.

Why Understanding Cardiac Rhythms Matters

Recognising the difference between rhythms such as ventricular fibrillation and asystole can guide the correct use of a defibrillator. In a cardiac arrest, every minute without CPR and defibrillation reduces the chance of survival by 10 percent.

This is why having an AED in the workplace or community setting is vital. Quick access to the right equipment gives bystanders the confidence to act and increases survival rates.

Different cardiac rhythms can range from harmless variations to life-threatening emergencies. With the right knowledge and the presence of a defibrillator nearby, anyone can play a part in saving a life.

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