Mnemonic Monday: The 5 Hs and 5 Ts of Cardiac Arrest

By Michael Spinner

Cardiac arrest, defined by the loss of functional circulation, is a true medical emergency that may rapidly progress to death if not addressed immediately.

Emergent stabilizing measures include defibrillation for patients with a “shockable rhythm” (i.e. ventricular fibrillation or pulseless ventricular tachycardia) and immediate CPR and epinephrine for patients with a “non-shockable rhythm” (i.e. asystole or pulseless electrical activity).

After calling a code and initiating these emergent stabilizing measures, the American Heart Association Advanced Cardiovascular Life Support (ACLS) program states that healthcare providers should assess for any potentially reversible causes of the arrest and treat the patient accordingly. Remember the 5Hs and 5Ts listed below to rapidly recall the causes of cardiac arrest:

Hypoxia                                            Tension pneumothorax

Hypovolemia                                     Tamponade

Hypo- or Hyperkalemia                     Thrombosis (MI)

Hypo- or Hyperthermia                     Thromboembolism (PE)

Hydrogen ions (acidosis)                   Toxins or Tablets (drug overdose)

Of note, this mnemonic is particularly helpful during a PEA arrest or when patients are not responding to interventions contained in the ACLS protocols.

When possible, the patient’s history should guide a rapid investigation of possible Hs and Ts that may have precipitated the arrest. For example, hypovolemia is a likely trigger in trauma patients with significant hemorrhage; hyperkalemia should be considered in renal patients who require dialysis; and MI should be considered in cardiac patients with a history of coronary artery disease or prior MIs.

Most of the Hs and Ts can be rapidly assessed with a few simple diagnostic tests: a pulse oximeter allows for a rapid assessment for hypoxia; a 12-lead EKG may uncover changes consistent with hypo- of hyperkalemia or an ST-elevation MI; and a bedside ultrasound can rapidly diagnose cardiac tamponade, tension pneumothorax, or hypovolemia (from visualizing the heart, lungs, and inferior vena cava, respectively).

Fortunately, many of the Hs and Ts can be rapidly reversed with the appropriate treatment (e.g. needle thoracotomy for tension pneumothorax, pericardiocentesis for cardiac tamponade, or potassium for hypokalemia).

The 5Hs and 5Ts are a great resource to rapidly recall the causes of cardiac arrest. Considering these causes, especially in light of the patient’s history, may help you to hone in on the underlying cause of the arrest and reverse it if possible. Finally, the Hs and Ts should always be considered in the aftermath of a code in attempt to ascertain why the patient coded in the first place. I hope this mnemonic will serve you well on the wards and help you to ace your ACLS training!