Chapter 04. Cardiac causes of cardiac arrest

Cardiac Causes of Cardiac Arrest (ALS Guidelines UK)

 Overview

Cardiac arrest occurs when the heart stops pumping blood effectively, leading to the cessation of circulation and oxygen delivery to vital organs. The most common cardiac causes of arrest include coronary artery disease, arrhythmias, and structural heart diseases.

According to ALS guidelines, cardiac causes of arrest must be rapidly identified and treated to improve survival outcomes.

 Cardiac Causes of Cardiac Arrest (4 Hs & 4 Ts)

The ALS guidelines highlight the 4 Hs & 4 Ts as reversible causes of cardiac arrest. Several of these are cardiac-related:

1. Cardiac Causes in the 4 H’s

 Hypoxia

• Inadequate oxygen delivery to the heart leads to myocardial dysfunction and cardiac arrest.
• Common in pulmonary embolism, myocardial infarction (MI), or severe heart failure.
• Treatment: Ensure high-flow oxygen, ventilation, and oxygenation support.

 Hypovolaemia

• Severe fluid or blood loss reduces cardiac output, leading to shock and cardiac arrest.
• Common in massive myocardial infarction (cardiogenic shock) or ruptured aortic aneurysm.
• Treatment: IV fluid resuscitation, blood transfusion if needed.

 Hypo-/Hyperkalaemia & Electrolyte Disturbances

• Potassium imbalances (hyperkalaemia or hypokalaemia) can cause life-threatening arrhythmias such as VF or asystole.
• Other electrolyte abnormalities (e.g., hypocalcaemia, hypomagnesaemia) can also trigger cardiac arrest.
• Treatment:
  • Hyperkalaemia: IV calcium gluconate, insulin-dextrose infusion, sodium bicarbonate.
  • Hypokalaemia: IV potassium replacement (administer carefully).

 Hypothermia

• Severe cold exposure (<30°C) can cause bradycardia, VF, and asystole.
• Treatment: Active warming, cardiac monitoring, delayed drug administration.

2. Cardiac Causes in the 4 T’s

 Thrombosis (Cardiac – Myocardial Infarction)

• Most common cause of sudden cardiac arrest.
• Acute myocardial infarction (MI) leads to VF/pulseless VT (shockable rhythms).
• Treatment:
  • Immediate CPR & defibrillation for shockable rhythms (VF/pVT).
  • Coronary reperfusion (PCI or fibrinolysis) after ROSC.
  • Aspirin, clopidogrel, heparin for clot prevention.

 Thrombosis (Pulmonary Embolism)

• Large clots in the pulmonary arteries can cause right heart failure and cardiac arrest.
• Often presents as PEA (non-shockable rhythm).
• Treatment:
  • Immediate CPR, oxygen therapy, thrombolysis (alteplase), and heparin.

 Tamponade (Cardiac)

• Fluid accumulation in the pericardium compresses the heart, reducing output.
• Commonly seen in post-MI rupture, aortic dissection, trauma, or pericarditis.
• Treatment: Emergency pericardiocentesis.

 Tension Pneumothorax

• Trapped air in the pleural space compresses the heart, reducing venous return.
• Can cause PEA or bradycardia leading to arrest.
• Treatment: Immediate needle decompression and chest drain insertion.

 Cardiac Arrhythmias Leading to Cardiac Arrest

The two major categories of arrhythmias that cause cardiac arrest are shockable and non-shockable rhythms.

1. Shockable Rhythms (VF & pVT)

• Ventricular Fibrillation (VF):
  • Disorganised electrical activity causing no cardiac output.
  • Commonly caused by MI, cardiomyopathy, or electrolyte imbalances.
  • Treated with immediate defibrillation and CPR.
• Pulseless Ventricular Tachycardia (pVT):
  • Fast, abnormal rhythm with no cardiac output.
  • Treated with defibrillation, CPR, and antiarrhythmics (amiodarone).

2. Non-Shockable Rhythms (Asystole & PEA)

• Asystole (Flatline):
  • No electrical activity, often from severe MI or prolonged hypoxia.
  • Managed with CPR, adrenaline, and treating reversible causes.
• Pulseless Electrical Activity (PEA):
  • Electrical activity without mechanical contraction.
  • Common in massive MI, cardiac tamponade, or PE.
  • Managed by identifying and treating reversible causes.

 Post-Resuscitation Care for Cardiac Causes

• Targeted Temperature Management (TTM)
  • Maintain 32-36°C for neurological protection.
• Coronary Angiography
  • PCI (Percutaneous Coronary Intervention) should be considered post-ROSC if MI is suspected.
• Haemodynamic Support
  • Fluids, vasopressors (e.g., noradrenaline), and inotropes may be needed to maintain perfusion.
• ECG Monitoring
  • Identify persistent ischaemia, arrhythmias, or electrolyte imbalances.
• Echocardiography
  • Helps detect cardiac tamponade, thrombus, or myocardial dysfunction.

 Key ALS Takeaways on Cardiac Causes of Arrest

✔ Myocardial infarction (MI) is the leading cardiac cause of arrest.
✔ VF and pulseless VT are shockable rhythms requiring immediate defibrillation.
✔ PEA and asystole require CPR and treatment of reversible causes.
✔ Post-resuscitation care should focus on reperfusion, haemodynamic support, and neuroprotection.
✔ Always assess for 4 Hs & 4 Ts when managing cardiac arrest.