Asystole Workup

Updated: Mar 31, 2020
  • Author: Sandy N Shah, DO, MBA, FACC, FACP, FACOI; Chief Editor: Barry E Brenner, MD, PhD, FACEP  more...
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Approach Considerations

Asystole is generally a diagnosis made via ongoing cardiac monitoring or electrocardiogram (ECG) and physical examination with pulselessness. Pulse oximetry may be used during resuscitation to monitor the effectiveness of forward flow or cardiopulmonary resuscitation (CPR); however, usually flow is too inadequate for the sensor to register results.

The "H's and T's of advanced cardiac life support" (ACLS) is a pneumonic that is used to help clinicians recall the major contributing factors of asystole and are as follows:

  • Hypovolemia
  • Hypoxemia
  • Hydrogen ion (acidosis)
  • Hyperkalemia, hypokalemia
  • Hypothermia
  • Toxins
  • Tamponde (cardiac)
  • Tension pneumothorax
  • Thrombosis (coronary and pulmonary)

Potassium level and ABG

A potassium level may be useful if deemed appropriate and results are immediately available.

Arterial blood gas (ABG) analysis may be used to obtain rapid reporting of potassium level in many institution's laboratories. In addition, ABG results may also help to evaluate the ventilatory and acid-base status of the patient as well as the hemoglobin level. Note that if the patient is in full arrest, a blood gas level does not accurately reflect the overall pH status of the tissues.



For documentation purposes, in addition to including rhythm strips from two separate leads identifying asystole, bedside ultrasonography may be useful to confirm cardiac standstill. The heart may be viewed via either a subxiphoid view or an intercostal view wall motion, or lack thereof is observed. An image of 2-dimensional echocardiography taken over time in M-mode may be taken, saved, and included in the medical record. This will further document the lack of heart wall motion.


Continuous Cardiac Monitoring

Isoelectric flat line is interpreted as asystole. Immediately rule out the following as causes of isoelectric flat line not due to asystole:

  • Loose or disconnected leads
  • Loss of power to the electrocardiographic (ECG) monitor
  • Low signals gain on the ECG monitor

Asystole is best determined in two separate cardiac leads. This helps protect against reading a flat line due to lead malfunction incorrectly as asystole, as well as helps in differentiating fine ventricular fibrillation (VF), particularly in an isoelectric lead, from asystole (see the following images).

Rhythm strip showing asystole. Rhythm strip showing asystole.
Rhythm strip showing ventricular fibrillation. Rhythm strip showing ventricular fibrillation.

Eliminate a possible diagnosis of VF, which may masquerade as asystole, by checking two leads perpendicular to each other. In spite of this caveat, Cummins et al found that using a flat-line protocol based on a 3-lead check, occult VF was documented in only 3 (2.5%) of 118 asystolic patients, indicating that VF masquerading as asystole is uncommon. [15] Technical problems were much more common, observed in 10 patients (8%). [15]

Exclude the possibility of lead misplacement by always checking for the presence of a pulse.

Spurious asystole can be seen when using manual defibrillator paddles to monitor the rhythm. [16] This is usually very brief, but nevertheless, can be avoided by switching to monitoring leads, especially after several successive shocks.