Asystole

Asystole
A rhythm strip showing two beats of normal sinus rhythm followed by an atrial beat and asystole.
Pronunciation	/əˈsɪstəliː/
Classification and external resources
Specialty	cardiology
ICD-10	I46.0
ICD-9-CM	427.5

Asystole (1860, from Modern Latin, from Greek α "not, without" + systole "contraction") is the absence of ventricular contractions lasting longer than the minimum possible to sustain life (about 2 seconds for a human). A flatline is the state of total cessation of electrical activity from the heart, which means no tissue contraction from the heart muscle and therefore no blood flow to the rest of the body. Asystole is the most serious and irreversible form of cardiac arrest. Asystolic patients (as opposed to those with a "shockable rhythm" such as ventricular fibrillation or ventricular tachycardia, which can be potentially treated with defibrillation) usually present with a very poor prognosis: asystole is found initially in only about 28% of cardiac arrest cases,^[1] but only 15% of these patients ever leave the hospital alive, even with the benefit of an intensive care unit, with the rate being lower (only 6%) for those already prescribed drugs for high blood pressure.^[2]

Asystole is treated by cardiopulmonary resuscitation (CPR) combined with an intravenous vasopressor such as epinephrine (a.k.a. adrenaline). Sometimes an underlying reversible cause can be detected and treated (the so-called 'Hs and Ts', an example of which is hypokalaemia). Several interventions previously recommended—such as defibrillation (known to be ineffective on asystole, but previously performed in case the rhythm was actually very fine ventricular fibrillation) and intravenous atropine—are no longer part of the routine protocols recommended by most major international bodies.^[3] Asystole may be treated with 1 mg epinephrine by IV every 3–5 minutes as needed. Vasopressin 40 units by IV every 3–5 minutes may be used in place of the first and/or second doses of epinephrine, but doing so does not enhance outcomes.

Survival rates in a cardiac arrest patient with asystole are much lower than a patient with a rhythm amenable to defibrillation; asystole is itself not a "shockable" rhythm. Out-of-hospital survival rates (even with emergency intervention) are less than 2 percent.^[4]

Cause

Possible underlying causes include the Hs and Ts.^[5][6][7]

• Hypovolemia
• Hypoxia
• Hydrogen ions (acidosis)
• Hypothermia
• Hyperkalemia or Hypokalemia
• Hypoglycemia
• Tablets or Toxins (drug overdose)
• Electric shock
• Tachycardia
• Cardiac Tamponade
• Tension pneumothorax
• Thrombosis (myocardial infarction or pulmonary embolism)
• Trauma (hypovolemia from blood loss)

While the heart is asystolic, there is no blood flow to the brain unless CPR or internal cardiac massage (when the chest is opened and the heart is manually compressed) is performed, and even then it is a small amount. After many emergency treatments have been applied but the heart is still unresponsive, it is time to consider pronouncing the patient dead. Even in the rare case that a rhythm reappears, if asystole has persisted for fifteen minutes or more, the brain will have been deprived of oxygen long enough to cause brain death.

• 
  ECG lead showing asystole (flatline)
• 
  Asystole
• 
  Asystole coarse

See also

• Agonal heart rhythm
• Cardiac arrest
• Ictal asystole
• Myocardial infarction
• Ventricular fibrillation

References