Reversible causes of Sudden Cardiac Arrest

Cardiac arrest results from inadequate or absent ventricular contractions which lead to circulatory failure. It is associated with respiratory arrest as one can lead to the other. In giving advanced life support to patients who suffer cardiac arrest, it is important to determine what was the cause of the arrest. A mnemonic of “6Hs and 6Ts” have been brought out to enumerate the reversible causes of cardiac arrest for healthcare givers to work with when providing advanced life support. These causes if not properly and quickly  tackled can eventually lead to sudden death of the patient.

Inadequate contractions of the heart muscle primarily occurs from electrical dysfunction of the heart (as in ventricular fibrillation, ventricular tachycardia and asystole) and mechanical dysfunction (as in myocardial infarction).





This occurs as a result of loss of body fluids or blood volume from bleeding, anaphylaxis, severe vomiting in pregnancy or severe diarrhoea.

It is treated by restoring blood volume with intravenous fluids or blood transfusion and stopping the source of the haemorrhage whether from internal or external bleeding.


This refers to inadequate oxygen supply reaching vital organs in the body like the brain, kidneys and heart.

Treating this would require assessing the airway and support ventilation for the individual through cardiopulmonary resuscitation (CPR), Oxygen supply.

Hydrogen ions (acidosis) 

This accounts for a reduction in the PH level as a result of lactic acidosis in hypoxia, severe infection, diabetic ketoacidosis, renal failure with uraemia, ingestion of toxic agents and overdose of pharmacological agents like aspirin, ethanol or other alcohols, isoniazid and iron sulphate.

Treatment is by providing proper ventilation and CPR, sodium bicarbonate buffers and emergency haemodialysis.


Hyperkalaemia or high potassium levels can result from acute renal failure and use of other medications. It can be treated with calcium gluconate, nebulized salbutamol, insulin in dextrose, loop diuretics and dialysis.

Hypokalaemia or low potassium levels on the other hand, can result from malnutrition or use of loop diuretics or diarrhoea. It can be treated with potassium infusion with care. Digitalis can be used to reduce the risk of arrhythmia.


This is defined as temperature < 35 degrees Celsius and can occur when an individual is exposed to extremely cold conditions.

This can be managed or treated by warming up the patient using cardiac bypass or irrigation of body cavities (thorax, peritoneum and bladder) with warm fluids. Administering warmed intravenous fluids and CPR can also be given although it is not effective at lower temperatures.


Although this has been removed from the list in recent times, it is still important to note it when assessing patients with cardiac arrest.

Hypoglycemia or low blood glucose levels can occur from taking an overdose of oral hypoglycemic medications or insulin and also in some rare endocrine disorders. Hypoglycemia can be treated by a rapid infusion of concentrated glucose (25mls of 50% dextrose in adults and half of that in children). 10% dextrose is used for neonates.

Hyperglycemia is not fatal in itself but it can cause diabetic ketoacidosis which can make PH to drop and also non ketotic hyperosmalar coma that can cause hypovolemic state.





This comes from using herbal medications, trycyclic antidepressants, phenothiazines, beta blockers, calcium channel blockers, cocaine, digoxin, aspirin or paracetamol inappropriately.

The treatment is by using the specific antidotes (e.g sodium bicarbonate for tricyclics, glucagon or calcium for calcium channel blockers, and benzodiazepines for cocaine)  and fluids for volume expansion.


Cardiac tamponade occurs when there is fluid accumulation in the pericardium of the heart which can be clinically diagnosed by thin pulse pressure, muffled heart sounds, distended neck veins and with ECG.

The treatment of cardiac tamponade is by the procedure of pericardiocentesis or subxiphoid window to cut the pericardium open and release the accumulated fluid.

Tension Pneumothorax

This refers to the build up of air in one side of the pleural cavity which causes kinking of great vessels, particularly the superior Vena cava, reducing blood return to the heart. It is clinically diagnosed by hypoxia, jugular vein distention, hyperrosonant percussion sounds in the affected side and mediastinal shift away from the affected side.

The treatment is by needle thoracotomy at the 2nd intercostal space, mid clavicular line, to release the pressure.


Thrombosis or blood clot in the coronary artery can lead to myocardial infarction which may result in cardiac arrest.

The treatment is by thrombolytic therapy or percutanous coronary intervention to correct myocardial infarction if the patient has been successfully rescucitated.


In some cases, a thrombus or blood clot which develop elsewhere can travel to another location in the body to cause problems. Thromboembolism to the pulmonary artery is the cause of pulmonary embolism which is very fatal.

Treatment is with thrombolytics and thrombolectomy can also be attempted.


This has also been scrapped off the list in recent times but it’s still worthy of note in assessing cardiac arrest.

Cardiac arrest can occur after a hard blow to the chest at a precise moment in the cardiac cycle known as “commotio cordis”. Traumatic events such as high speed car crashes can also cause sufficient damage to induce cardiac arrest.




Wikipedia : “Hs and Ts” : “Hs and Ts of ACLS”





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