What are the Reversible Causes of Cardiac Arrest?

A cardiac arrest occurs when the heart suddenly stops pumping blood around the body. Early CPR and use of a defibrillator (AED) is critical in order to improve survival from cardiac arrest.

However, there may be a reversible cause underlying the cardiac arrest. In these situations, every effort should be made to treat the underlying cause of the cardiac arrest as well as providing high-quality CPR and early defibrillation.

The reversible causes of cardiac arrest are commonly taught on Advanced Cardiac Life Support (ACLS) and Advanced Life Support (ALS) classes. However, it’s important for all rescuers to have an understanding of the common reversible causes of cardiac arrest.

The most common reversible causes of cardiac arrest can be remembered by thinking about the ‘four Hs and four Ts’. Let’s take a look at these reversible causes in more detail.

The Four Hs

• Hypoxia: low oxygen levels
• Hypovolemia: low circulatory volume, eg: due to blood loss
• Hypothermia: low body temperature:
• Hypo/hyperkalemia: low or high potassium levels

The Four Ts

• Toxins: administered intentionally or unintentionally, e.g: recreational drugs
• Thrombosis: a blood clot in the lung or the heart
• Tamponade (cardiac): a large collection of blood compressing the heart, occurs following trauma to the chest
• Tension Pneumothorax: a build-up of air inside the chest cavity putting pressure on the heart and blood vessels

Not all cardiac arrests will have a clear reversible cause. However, if a reversible cause is found it should be aggressively treated and resuscitation continued until the treatment of the reversible cause is complete.