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Hs and Ts

As you are moving through your algorithms during ACLS and PALS, it is important to also consider reversible causes for the emergent condition. Pulseless electrical activity (PEA), asystole, ventricular fibrillation (VFib or VF), and ventricular tachycardia (VTach or VT) may have a reversible cause in your patient (though most often PEA). The reversible causes of PEA can be remembered with a mnemonic of sorts, the H’s and T’s.

The H’s and T’s are 12 reversible conditions, 7 that start with H and 5 that start with T.

  • Hypovolemia
  • Hypoxia
  • Hydrogen ion excess (acidosis)
  • Hypoglycemia
  • Hypokalemia
  • Hyperkalemia
  • Hypothermia
  • Tension pneumothorax
  • Tamponade – Cardiac
  • Toxins
  • Thrombosis (pulmonary embolus)
  • Thrombosis (myocardial infarction)

While it is important to continue to deliver compressions, ventilation, and medications according to the algorithm, it is always best to treat underlying causes of PEA and related conditions as soon as possible.

Potential Cause

How to Identify


Hypovolemia Rapid heart rate and narrow QRS on ECG; other symptoms of low volume Infusion of normal saline or Ringer’s lactate
Hypoxia Slow heart rate Airway management and effective oxygenation
Hydrogen ion excess (acidosis) Low amplitude QRS on the ECG Hyperventilation; consider sodium bicarbonate bolus
Hypoglycemia* Bedside glucose testing IV bolus of dextrose
Hypokalemia Flat T waves and appearance of a U wave on the ECG IV Magnesium infusion
Hyperkalemia Peaked T waves and wide QRS complex on the ECG Consider calcium chloride, sodium bicarbonate, and an insulin and glucose protocol
Hypothermia Typically preceded by exposure to a cold environment Gradual rewarming
Tension pneumothorax Slow heart rate and narrow QRS complexes on the ECG; difficulty breathing Thoracostomy or needle decompression
Tamponade – Cardiac Rapid heart rate and narrow QRS complexes on the ECG Pericardiocentesis
Toxins Typically will be seen as a prolonged QT interval on the ECG; may see neurological symptoms Based on the specific toxin
Thrombosis (pulmonary embolus) Rapid heart rate with narrow QRS complexes on the ECG Surgical embolectomy or administration of fibrinolytics
Thrombosis (myocardial infarction) ECG will be abnormal based on the location of the infarction Dependent on extent and age of MI

*Hypoglycemia is not officially one of the H’s and T’s for adults, but it still can be an important cause of PEA, especially in children. If another reversible cause has not been discovered or if the patient is known to be susceptible to hypoglycemia (e.g., brittle diabetes, past surreptitious use of insulin) then this potential cause of PEA should be considered.