Understanding Cardiac Arrest: Causes, Rhythms, and Initial Response

Non-Shockable Rhythms in Cardiac Arrest

In some cardiac arrest cases, the heart enters a non-shockable rhythm. During the initial stages, the primary treatment involves high-quality chest compressions and ventilations. It's crucial to note that the chances of reverting asystole (flatline) back into a life-supporting rhythm are less than 6%. In contrast, for ventricular fibrillation, the success rate is approximately 40%.

Understanding the Causes

Cardiac arrest can be attributed to various factors, and a helpful mnemonic to remember these causes is the four H's and four T's. Recognizing these reversible causes is essential during a cardiac arrest scenario:

The Four H's

• Hypoxia: Inadequate oxygen supply
• Hypothermia: Dangerously low body temperature
• Hypovolemia: Low blood volume
• Metabolic Imbalances: Includes hypo/hypercalcemia, hyponatremia, hyperkalemia, and metabolic acidosis

The Four T's

• Cardiac Tamponade: Compression of the heart due to fluid accumulation
• Tension Pneumothorax: Build-up of air in the chest, causing pressure on the heart
• Toxins: Poisoning or exposure to harmful substances
• Thromboembolic: Blood clots or embolisms, often following a heart attack or stroke

In the pre-hospital setting, thromboembolic events, such as those occurring after a myocardial infarction (heart attack) or a significant cerebrovascular accident (CVA or stroke), are among the more frequently encountered causes of cardiac arrest.