What is cardiac standstill?

Cardiac Standstill: Definition and Clinical Significance

Cardiac standstill is the absence of electrical and mechanical activity in the heart, characterized by no visible cardiac movement on ultrasound imaging, and is associated with 100% mortality when observed during cardiac arrest resuscitation in the emergency department setting. 1

Definition and Characteristics

Cardiac standstill can be identified through bedside cardiac ultrasonography (BCU) during resuscitation efforts. It represents a state where:

• No cardiac wall motion is visible on ultrasound
• No contractile activity is present in any cardiac chamber
• The heart appears completely motionless during real-time imaging

This condition differs from other cardiac arrest rhythms such as ventricular fibrillation (VF), pulseless ventricular tachycardia (VT), or pulseless electrical activity (PEA) where electrical activity may still be present despite ineffective mechanical function.

Clinical Significance and Prognostic Value

Cardiac standstill has profound implications for resuscitation outcomes:

• When identified on emergency department echocardiogram during cardiac arrest, it has a 100% positive predictive value for death regardless of the electrical rhythm displayed on the monitor 1
• No patient with sonographically identified cardiac standstill has been documented to survive to leave the emergency department 1

The American College of Emergency Physicians guidelines specifically note that "sonographic evidence of cardiac standstill should be interpreted in the context of the entire clinical picture" 2, suggesting its importance as a prognostic indicator.

Mechanisms and Causes

Cardiac standstill results from:

1. Failure of impulse formation or transmission in the ventricles 3
2. May occur in previously healthy hearts or diseased hearts through different mechanisms:
   • In healthy hearts: Occurs when sinus node activity is suppressed or AV conduction is blocked
   • In diseased hearts: May result from direct damage to ventricular pacemakers, anoxia, ionic imbalances, or altered sympathetic innervation 3

Types of Cardiac Standstill

Cardiac standstill can be categorized as:

• Atrial standstill: Absence of electrical and mechanical activity specifically in the atria, which can be transient or persistent, complete or partial 4
• Ventricular standstill: Complete absence of ventricular contraction
• Complete cardiac standstill: No movement in any cardiac chamber

Clinical Applications and Limitations

Use in Resuscitation Decision-Making

• Bedside cardiac ultrasound can identify cardiac standstill during CPR when pulses are checked 1
• This finding may help inform decisions about continuation or termination of resuscitative efforts

Limitations in Pediatric Patients

Critical care guidelines specifically note that "pediatric BCU alone is insufficient to diagnose irreversible pulseless cardiac activity in cardiac arrest in critically ill children" 2. This is because:

• Children may recover from apparent cardiac standstill, particularly after severe cardiac insult
• Pediatric hearts may experience severe myocardial stun but still be ultimately recoverable
• Pediatric cardiac arrest is often respiratory in origin, with different recovery patterns than adult cardiac arrest 2

Practical Considerations

When cardiac standstill is identified during resuscitation:

• The finding should be integrated with other clinical factors
• In adults, it strongly suggests futility of continued resuscitation efforts
• In pediatric patients, it should not be used as the sole criterion for terminating resuscitation
• Proper technique requires visualization of the heart through multiple tissue planes in two orthogonal directions 2

Cardiac standstill represents one of the most ominous findings during resuscitation efforts and serves as a valuable prognostic indicator when properly identified in the appropriate clinical context.