ECG criteria
- The attack is preceded by documented bradyarrhythmia: complete AV block or high-degree AV block (dropping ≥2 consecutive P waves); symptomatic 2:1 AV block can also cause a MAS attack, but a 2:1 ratio alone does not allow determination of the level of block (AV nodal vs. infra-nodal) or classification of it as high-degree without considering the clinical context, QRS width, and other data
- The ECG during symptoms shows a prolonged pause/absence of effective ventricular complexes, often with ongoing atrial activity (preserved P waves); there is no rigid duration threshold, and the diagnosis is confirmed by the temporal association of the pause with symptoms rather than its duration alone
- Alternatively, an abrupt transition from a normal rhythm to a slow escape rhythm: junctional escape typically with narrow QRS and a rate around 40–60/min, ventricular escape typically with wide QRS and a rate around 20–40/min; a delayed onset of the escape rhythm is also possible
- An alternative mechanism is possible: transition of AV block to polymorphic VT or torsades de pointes or VF with loss of consciousness, not directly related to asystole
- Atrial activity during AV dissociation usually continues at its own rate independently of QRS, most often sinus, but atrial fibrillation/flutter or ectopic atrial rhythm are also possible; the ventricular pause is due to impaired conduction and delayed or absent escape rhythm, rather than cessation of atrial activity
- Following rhythm restoration, sinus P-QRS or escape junctional/ventricular complexes may appear; with persistent AV dissociation, single capture or fusion beats are sometimes observed, but this is an optional sign
- Holter monitoring reveals a temporal correlation of the pause/asystole or tachyarrhythmia with the clinical episode (loss of cardio-consciousness, seizures, pallor)
What it looks like on ECG
A MAS attack is a clinical syndrome (syncope) rather than an independent ECG pattern, so its "appearance" on the tracing depends on the mechanism that triggered it.
Most commonly — complete AV block (third-degree): atrial activity, usually sinus, continues independently of the ventricular escape rhythm, without a constant PQ relationship; in complete AV block, other types of atrial activity are also possible — atrial fibrillation/flutter or ectopic atrial rhythm. If the ventricular escape focus "remains silent" or triggers with a delay after the block transitions from incomplete to complete, a pause occurs without effective QRS complexes against the background of ongoing atrial activity — this is the bradyarrhythmic (asystolic) variant of a MAS attack.
Second variant — high-degree AV block (dropping two or more consecutive P waves, i.e., 3:1 conduction and rarer) with a sudden dropout of several consecutive ventricular complexes while atrial activity is preserved. Symptomatic 2:1 block can also lead to a MAS attack, but by itself does not prove a high-degree or infra-nodal level of block — evaluation of clinical symptoms, QRS width, and, if possible, the level of block is required.
Third variant — bradycardia-dependent transformation of the block into polymorphic VT of the torsades de pointes type or ventricular fibrillation (chaotic oscillations without discernible QRS complexes are visible); in this case, the mechanism of syncope is tachyarrhythmic rather than asystolic.
The ECG outside of an attack typically reveals signs of second- to third-degree AV block or conduction abnormalities (wide QRS in bifascicular block) that indicate risk. The moment of the attack itself is documented only during synchronous recording — on a monitor, Holter, or pacemaker memory: during AV block, ongoing P waves without ventricular complexes or rare escape complexes are visible. An isoelectric line without visible P and QRS in a verified recording may correspond to asystole, but first it is necessary to immediately rule out technical malfunction (disconnected electrode, artifact) and check multiple leads; if P waves are preserved, this indicates ventricular asystole with preserved atrial activity, rather than complete cessation of the heart's electrical activity.
Mechanism
Normally, when sinus or AV conduction fails, a backup pacemaker takes over — the AV junction or His-Purkinje fibers, which assume the pacemaker function with a delay of several seconds (overdrive suppression). A MAS attack develops when this backup mechanism is delayed or absent: a ventricular pause/asystole occurs, and a sudden cessation of effective cardiac output rapidly reduces cerebral perfusion, which can lead to syncope — the specific time to loss of consciousness is individual and depends on baseline hemodynamics, body position, and the state of cerebral blood flow. If the escape rhythm triggers, consciousness is restored; if not, the pause may progress to irreversible circulatory arrest. The second mechanism is bradycardia-dependent prolongation of refractoriness and dispersion of repolarization, which provoke polymorphic VT or VF against the background of a slow rhythm; in this case, syncope is caused by tachyarrhythmia rather than cessation of ventricular rhythm.
Causes
- Complete AV block (congenital or acquired)
- High-grade second-degree AV block, including Mobitz II, progressing to complete block
- Sick sinus syndrome with prolonged sinus pauses
- Bifascicular/trifascicular block with intermittent complete block
- Failure or malfunction of an implanted pacemaker (failure to capture, battery depletion)
- Toxic effects of drugs that depress AV conduction (beta-blockers, calcium channel blockers, digoxin, antiarrhythmics)
- Acute myocardial infarction (especially inferior — AV nodal ischemia) and myocarditis involving the conduction system
- Infiltrative and degenerative diseases of the conduction system (Lenègre-Lev disease, sarcoidosis, amyloidosis)
Differential diagnosis
- Vasovagal syncope — a prodrome (nausea, diaphoresis) and gradual hemodynamic response are usually present, but the cardioinhibitory reflex can be accompanied by a pronounced sinus pause, asystole, or transient AV block; the decisive criterion is the clinical context and documented association of the rhythm with symptoms, rather than the mere presence of a pause.
- Epileptic seizure — compare the prodrome, duration and characteristics of the episode, recovery, postictal confusion, injuries, and tongue biting, rather than the sequence of "seizures before/after loss of consciousness": in generalized tonic-clonic seizures, loss of consciousness usually occurs at the onset of the episode, and convulsive twitching can also occur during a MAS attack itself in the setting of cerebral hypoperfusion.
- Orthostatic hypotension — associated with changes in body position, gradual development, no documented pause on the ECG.
- Sinus pause/sinoatrial block — a pause is present, but without signs of AV block: P waves are absent along with QRS, rather than continuing separately from the dropped QRS complexes.
- Asystole as an outcome of cardiac arrest of another etiology — it is important to check whether there is a documented bradyarrhythmia immediately preceding the pause.
Clinical significance and management
A MAS attack is an emergency situation with a risk of sudden cardiac death. In a witnessed episode with a pause/asystole or severe symptomatic bradycardia, the physician acts according to the unstable bradyarrhythmia algorithm: assessment of airway, breathing, and circulation; in the absence of a pulse — resuscitation measures according to the asystole/pulseless electrical activity (PEA) algorithm.
In unstable bradycardia with preserved circulation, transcutaneous (external) cardiac pacing must be prepared immediately; if high-grade or infra-nodal block is suspected, pacing should not be delayed for an atropine trial, as atropine is often ineffective in this setting and theoretically can worsen conduction below the AV node. Atropine is acceptable primarily when a nodal level of block is likely—it is administered concurrently with pacing preparation without delaying the latter. If atropine is ineffective or instability persists, proceed to pacing without delay for vasoactive infusion (epinephrine/dopamine may be used as temporary support, but must not delay pacing); if external pacing is ineffective or not tolerated, transition early to temporary transvenous pacing. Concurrently, identify and treat the underlying cause (discontinuation/correction of AV-block-suppressing drugs, treatment of ischemia, electrolyte correction).
The primary diagnostic objective is to capture the rhythm at the moment of symptoms (monitoring, Holter, implantable loop recorder) and confirm the association between syncope and bradyarrhythmia or tachyarrhythmia. Permanent pacing is indicated for persistent acquired complete or high-grade AV block after reversible causes have been excluded or eliminated; in acute myocardial infarction, drug toxicity, or electrolyte disturbances, temporary support and correction of the cause are performed first, while the decision regarding permanent pacing is based on the dynamics and persistence of the block.
Common interpretation errors
- Assuming that diagnosing Adams-Stokes syndrome is fundamentally impossible without rhythm registration: the absence of a recorded event does not exclude an arrhythmic origin of syncope—when suspected, evaluate the baseline ECG, medical history, monitoring results, and arrhythmia risk based on background conduction system abnormalities.
- Confusing Adams-Stokes syndrome with common vasovagal syncope due to a similar presentation of loss of consciousness, failing to account for the fact that a vasovagal reflex can also be accompanied by profound bradycardia and asystole.
- Disregarding short asymptomatic pauses on a Holter monitor as an incidental finding unrelated to the actual syncopal episode, without correlating them temporally with symptoms.
- Ignoring the baseline ECG between attacks—bifascicular block or second-degree AV block Mobitz II is an important marker of risk even in the absence of an attack during the recording.
- Forgetting that an attack can be triggered not only by asystole, but also by tachyarrhythmia (polymorphic VT/VF) on the background of bradycardia.
1. Which ECG phenomenon is typical for an Adams-Stokes attack?
The classical mechanism of an Adams-Stokes attack is ventricular pause/asystole due to a failure of the escape rhythm to kick in during complete or high-grade AV block.
2. What is the primary step required to confirm the association between syncope and an Adams-Stokes attack?
The diagnosis is most convincingly confirmed by a documented temporal relationship between the symptom and the rhythm disturbance on an ECG recording.
3. What is the indicated management for confirmed acquired complete AV block presenting with Adams-Stokes attacks after reversible causes have been excluded?
Persistent acquired complete AV block with symptomatic pauses, unrelated to a reversible cause, is a classic indication for permanent cardiac pacing.
Frequently asked questions
What causes an Adams-Stokes attack?
Most commonly—complete AV block or high-grade AV block with a pause or ventricular asystole when the escape rhythm fails to activate. Less commonly—pacemaker failure or transition of bradyarrhythmia into polymorphic VT/ventricular fibrillation.
How to confirm an Adams-Stokes attack on an ECG?
A rhythm recording at the exact moment of the episode is required—Holter monitoring, continuous in-hospital monitoring, or an implantable loop recorder. The diagnosis is most convincingly confirmed by recording a pause, asystole, or tachyarrhythmia coinciding temporally with the symptom; in the absence of such a recording, probability is assessed based on clinical presentation, baseline ECG, and prolonged monitoring results.
Is an Adams-Stokes attack dangerous?
Yes, this is a life-threatening condition carrying a risk of sudden cardiac death unless the pause/asystole resolves spontaneously or emergency pacing is performed.
How to distinguish an Adams-Stokes attack from vasovagal syncope?
During an Adams-Stokes attack, the ECG at the time of the episode typically shows documented bradyarrhythmia—AV block with a pause or asystole, and syncope often develops abruptly without prodrome. Vasovagal syncope usually has a prodrome (nausea, sweating) and a gradual hemodynamic reaction, although the cardioinhibitory variant can also present with marked bradycardia and asystole—the clinical context and temporal correlation between rhythm and symptoms remain decisive.
What is the physician's management strategy during an Adams-Stokes attack?
In the absence of a pulse, initiate resuscitation according to the asystole/PEA algorithm. If circulation is preserved, immediately prepare external cardiac pacing, without delaying it for atropine if infra-nodal block is suspected; if ineffective, proceed to transvenous pacing and treatment of the underlying cause, followed by a decision on permanent pacemaker implantation if persistent bradyarrhythmia is confirmed.
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Related terms
More in the «AV Blocks» section
Sources
- Orlov, V.N. «Electrocardiography Guide»
- Hampton J.R. «The ECG in Practice»
- Surawicz B., Knilans T. «Chou's Electrocardiography in Clinical Practice»
- Russian Ministry of Health clinical guidelines on bradyarrhythmias and conduction disorders
Educational material for medical students and physicians. Does not replace clinical guidelines and physical examination; the ECG must always be interpreted in conjunction with the clinical picture.