Is an ECG showing low-amplitude baseline undulations without identifiable QRS complexes, in a post-CPR (Cardiopulmonary Resuscitation) patient with no vital signs, compatible with terminal electrical activity or death, and can a pacemaker (artificial cardiac pacemaker) cause such a tracing without capture?

Terminal Electrical Activity and Death Confirmation in Post-CPR Patients

An ECG showing low-amplitude baseline undulations without identifiable QRS complexes in a post-CPR patient with absent vital signs is compatible with terminal electrical activity and represents a non-VF/VT rhythm (likely agonal rhythm or fine ventricular fibrillation degenerating toward asystole), which carries an extremely poor prognosis with survival rates approximately 10-15% of VF/VT rhythms. 1

Understanding the Clinical Scenario

The clinical presentation described—absent carotid pulse, no heart sounds, no spontaneous respiration, and fixed dilated pupils—combined with low-amplitude baseline undulations without QRS complexes represents a terminal rhythm pattern. 1

ECG Pattern Classification

• Low-amplitude undulations without identifiable QRS complexes represent either fine ventricular fibrillation, agonal ventricular activity, or the terminal phase before asystole 1
• With the passage of time, all electrical rhythms associated with cardiac arrest deteriorate with the eventual production of asystole, and the abysmal prognosis of this degenerated rhythm is well justified 1
• This pattern falls into the non-VF/VT rhythm category, where defibrillation is not indicated as a primary intervention unless clear VF/VT can be identified 1

The Pacemaker Consideration

A pacemaker can produce visible pacing stimuli on ECG monitoring without mechanical cardiac capture, but this does not change death confirmation when all clinical signs of death are present.

Why Pacemaker Activity Doesn't Negate Death Determination

• Pacemaker stimuli can be interpreted by ECG monitors as electrical activity even when there is no myocardial capture or mechanical cardiac output 2
• Two documented cases demonstrated cardiorespiratory arrest not detected by ECG monitoring because pacemaker stimuli were misinterpreted as QRS complexes, highlighting that electrical pacing activity does not equal viable cardiac function 2
• Modern pacemakers produce stimulus outputs that are very small in amplitude and short in duration, which can significantly distort normal ECG morphology 3

Critical Distinction: Electrical Activity vs. Mechanical Function

• The presence of pacemaker spikes without capture represents a form of electromechanical dissociation (EMD), where coordinated electrical waveforms exist without mechanical cardiac activity 1
• Electromechanical dissociation implies absence of mechanical activity or undetectable activity in the presence of a continuing coordinated waveform 1
• Death confirmation relies on clinical assessment (absent pulse, heart sounds, respirations, fixed pupils) rather than ECG patterns alone 1

Clinical Management Implications

When This Pattern Appears During Resuscitation

• If VF/VT cannot be positively excluded, the right-sided path of advanced life support algorithms should be followed (non-VF/VT pathway) 1
• Continue CPR with advanced airway management, oxygenation, ventilation, and venous access 1
• Administer epinephrine 1 mg every 3 minutes 1
• Search for and correct reversible causes (the "H's and T's"), which become relatively more important in non-VF/VT rhythms 1

Prognostic Considerations

• The overall survival rate with non-VF/VT rhythms is about 10-15% of the survival rate with VF/VT rhythms 1
• Resuscitation should generally continue for at least 20-30 minutes from the time of collapse unless there are overwhelming reasons to believe that resuscitation is likely to be futile 1
• The development of persistent asystole or low-amplitude agonal rhythms after prolonged resuscitation efforts indicates extremely poor prognosis 1

Key Clinical Pitfalls

Don't Be Misled by Pacemaker Artifacts

• ECG monitors may inappropriately sense pacemaker stimuli as QRS complexes, creating a false impression of cardiac electrical activity 2
• There is a direct relationship between pacemaker stimulus amplitude seen by the monitor and inappropriate sensing 2
• Non-ECG monitoring modalities (pulse oximetry, end-tidal CO2, arterial line if present) are essential in pacemaker patients to confirm actual perfusion 2

Confirm True Asystole

• Low-amplitude baseline undulations may represent fine VF that could respond to defibrillation if amplitude can be increased 1
• Check lead connections and increase ECG gain to ensure you're not missing fine VF 1
• However, in the clinical context described (prolonged arrest, absent all vital signs, fixed pupils), this represents terminal activity regardless 1

Death Determination

When a patient demonstrates absent carotid pulse, absent heart sounds, absent spontaneous respirations, and fixed dilated pupils, death can be confirmed regardless of residual electrical activity on the monitor, including pacemaker stimuli. 1, 2 The ECG pattern of low-amplitude undulations without QRS complexes in this clinical context represents terminal electrical activity and is compatible with death determination.