Ventricular fibrillation

Articolo redatto e revisionato del Dott. Luca Moretti

Ventricular fibrillation is an arrhythmia in which ventricular electrical activation becomes disorganized and fails to produce a contraction capable of maintaining effective circulation. In humans it causes cardiac arrest and requires immediate resuscitation and defibrillation. The tracing shows irregular oscillations without reproducible QRS complexes, but its appearance varies according to the duration of the event, myocardial conditions, the lead, and recording characteristics. The electrical diagnosis must be linked to the clinical assessment of cardiac arrest.

Ventricular fibrillation may be the first recognized event in a person or may complicate previously known heart disease. Coronary ischemia, scar, cardiomyopathies, inherited electrical diseases, drugs, and metabolic abnormalities represent different settings. How often it is observed also depends on the time to arrival of rescuers: an arrest that was initially shockable may later be recorded as asystole. Epidemiologic data on initial rhythms therefore reflect both the disease and the organization of the emergency response.

The clinical problem comprises two inseparable phases: rapidly restoring circulation and identifying what made the arrhythmia possible. An effective shock terminates fibrillation but does not necessarily eliminate the substrate or prevent recurrence. Subsequent prevention requires distinguishing reversible causes, persistent disease, and forms in which the initial workup does not clarify the etiology. Prognosis includes survival, neurologic recovery, and the risk of new events.

Electrical dynamics and loss of pump function

Fibrillation is sustained by spatially and temporally heterogeneous propagation. Multiple wavefronts, rotors, and fragmentation of activation may contribute in different proportions depending on the substrate and phase of the episode. These models are not necessarily mutually exclusive, and the surface tracing does not allow them to be fully distinguished. The common result is the absence of coordinated ventricular depolarization capable of producing effective systole.

A trigger may be a premature ventricular contraction, ventricular tachycardia, or a disturbance of repolarization. Its ability to initiate fibrillation depends on its timing and on the tissue it encounters. A premature beat in homogeneous myocardium does not have the same effect as the same stimulus in the presence of ischemia, scar, or dispersion of refractoriness. The distinction between trigger and substrate explains why eliminating a focus may reduce episodes without necessarily abolishing all vulnerability.

The Purkinje system may play a role in initiation, especially when PVCs with reproducible morphology precede episodes. Surviving fibers in infarcted regions or Purkinje activity in hearts without macroscopic abnormalities may generate early impulses. Subsequent maintenance of fibrillation may nevertheless depend on more diffuse properties. Trigger mapping is therefore a selected therapeutic option, not proof that every episode of fibrillation originates from a single eliminable point.

During cardiac arrest, lack of perfusion causes energy depletion, ionic disturbances, and progressive changes in excitability. Fibrillation may evolve from relatively coarse waves to a finer signal, but amplitude is not a reliable clock for event duration. Anatomy, electrodes, and pre-existing conditions influence the tracing. Treatment should not be delayed until fibrillation becomes more obvious or coarser once it has already been recognized.

Defibrillation applies an electrical field that interrupts fibrillatory activity and allows an organization compatible with function to resume. It does not necessarily initiate sinus rhythm and may be followed by pulseless electrical activity or bradycardia. Electrical success and circulatory success are therefore different. Resuscitation supports perfusion while an adequate rhythm and function are being restored and remains necessary when shock alone does not re-establish circulation.

Refractory fibrillation persists despite defibrillation attempts, whereas recurrent fibrillation terminates and then returns. Distinguishing the two situations helps interpret failure: the electrical field may need optimization, or a mechanism that continuously reinitiates the arrhythmia may need to be controlled. A sequence of shocks without reassessment of compressions, pad position, and underlying causes may leave the main problem unresolved. Response is assessed from the entire tracing, not only from the rhythm present at the subsequent rhythm check.

Etiologies and clinical phenotypes

Acute myocardial ischemia can produce sufficient heterogeneity of conduction and refractoriness to initiate fibrillation. The setting may include coronary occlusion, intermittent ischemia, or vasospasm. Fibrillation during the acute phase does not necessarily carry the same meaning as a late event arising on scar. Timing, ischemic signs, and residual substrate must be reconstructed because they influence coronary treatment and assessment of long-term protection.

In structural heart disease, fibrillation may result from degeneration of ventricular tachycardia or emerge through other mechanisms. Fibrosis, dysfunction, inflammation, and regional heterogeneity create different forms of vulnerability. Dilated, hypertrophic, and arrhythmogenic cardiomyopathies, sequelae of myocarditis, and infiltrative diseases require specific pathways. Ejection fraction is important but does not summarize all risk information, particularly when scar or electrical disease is present despite relatively preserved function.

Channelopathies may cause cardiac arrest without evident structural abnormalities. Brugada syndrome, long-QT syndrome, and catecholaminergic polymorphic ventricular tachycardia have different circumstances, baseline findings, and therapeutic responses. The ECG between events may be nondiagnostic and the family history may initially appear negative. Investigation should be phenotype-guided, including the context of exercise, rest, fever, emotion, and medications, without assigning definitive value to a single normal test.

Drugs and substances may increase risk through QT prolongation, sodium-channel blockade, adrenergic effects, or myocardial toxicity. Electrolyte abnormalities and organ failure may amplify these effects. Identifying a correctable factor is clinically useful but does not prove that it is sufficient to explain the entire event. Concomitant heart disease may maintain residual risk even after drug withdrawal or normalization of laboratory values.

Acute noncoronary causes include hypoxia, hypothermia, electrocution, and conditions that directly alter excitability. Commotio cordis is a specific example in which a chest impact during a vulnerable phase may initiate fibrillation without a structural injury necessarily being responsible. These scenarios require causal interventions in addition to standard resuscitation. The history of the event, when available, may immediately point toward a cause that the tracing alone does not reveal.

The term idiopathic ventricular fibrillation is used when an adequate investigation does not identify a structural, ischemic, metabolic, or toxic cause or a recognizable electrical syndrome. It is not proof of a heart without any vulnerability. Some cases are reclassified as the phenotype evolves or new family information emerges. The workup should therefore document what has been excluded and maintain surveillance capable of recognizing later findings.

Recognition of cardiac arrest and rhythm diagnosis

Ventricular fibrillation should be suspected in the setting of cardiac arrest, with loss of consciousness and absent or abnormal breathing. Gasping may occur in the early phase and does not demonstrate effective ventilation. Activation of emergency services, chest compressions, and retrieval of a defibrillator should not await an etiologic diagnosis. For healthcare professionals, pulse assessment should be rapid and must not delay the start of resuscitation when circulation cannot be confidently identified.

On the monitor, fibrillation appears as irregular oscillations without reproducible complexes or an organized relationship between depolarization and repolarization. Waves may be coarse or fine and may have different appearances in different leads. Absence of recognizable atrial activity is compatible with VF but is not the principal criterion. When the signal is uncertain, technical problems should be excluded while attention remains focused on the patient's clinical state.

Fine ventricular fibrillation may be mistaken for asystole. Connections, gain, and an alternative lead should be checked when this can be done rapidly. If fibrillation is recognized, it remains a shockable rhythm regardless of amplitude; if genuine uncertainty persists between asystole and extremely fine fibrillation, compressions should continue while the signal is clarified. Confirmed asystole is not treated with shock because the electrical mechanism that defibrillation is intended to interrupt is absent.

Compression artifacts may obscure the underlying rhythm and simulate fibrillation. The brief rhythm analyses specified by the algorithm are intended to clarify the rhythm without prolonging interruptions. Conversely, apparently chaotic activity in a conscious patient with an effective pulse requires immediate checking of contacts, motion, and interference. Automated interpretation by a device must be integrated with the clinical picture, particularly when signal quality is inadequate.

Polymorphic ventricular tachycardia may retain distinguishable ventricular complexes despite marked variability; ventricular flutter appears relatively more organized. During degeneration, the boundaries may change within moments. In a pulseless patient, these distinctions must not delay treatment of a shockable rhythm. Their reconstruction becomes useful after recovery to identify long QT, ischemia, or an initiating circuit.

A twelve-lead ECG is not required before the first shock. The priority is reliable rhythm recognition and rapid treatment. Once circulation returns, the full tracing and stored data are obtained for etiologic investigation. The external defibrillator and any implanted devices may preserve information about onset, number of shocks, and transitions that cannot subsequently be reproduced.

Resuscitation, defibrillation, and refractory fibrillation

In adults, high-quality cardiopulmonary resuscitation includes compressions at 100-120 per minute, to a depth of approximately 5-6 cm, complete chest recoil, and minimal interruptions. Before an advanced airway is placed, a ratio of 30 compressions to 2 ventilations is generally used; subsequent management is adapted to the device and operator expertise. Hyperventilation may impair perfusion and should be avoided. Adult parameters are not directly transferred to children.

Early defibrillation is the fundamental specific intervention. Pads should have adequate contact and correct positioning, generally anterolateral initially, with the lateral pad sufficiently lateral on the midaxillary line. Initial energy and any escalation depend on waveform and device instructions. Safety procedures should be rapid and coordinated, minimizing pauses before and after shock delivery. After the shock, compressions are resumed immediately for the planned cycle, without a prolonged pulse check in the absence of convincing signs of recovery.

Intravenous access is initially preferred for drug administration in the adult algorithm; if it cannot be obtained rapidly, intraosseous access is an appropriate alternative. In the ERC 2025 pathway for shockable rhythms, epinephrine is administered at a dose of 1 mg after the third shock and repeated every 3-5 minutes during resuscitation. The drug must not delay shocks or compressions. The sequence differs from that used for nonshockable rhythms, in which epinephrine is given early.

Amiodarone is used in adults with ventricular fibrillation or pulseless ventricular tachycardia after three shocks, at an initial dose of 300 mg, with an additional dose of 150 mg after five shocks. Lidocaine is an alternative according to availability and protocol, with an initial dose of 100 mg and a further 50 mg bolus after five defibrillation attempts. Shock counts refer to all shocks delivered even when the arrhythmia terminates and subsequently recurs. Amiodarone and lidocaine are not automatically combined as a mandatory sequence.

The search for reversible causes proceeds during resuscitation: hypoxia, hypovolemia, metabolic and electrolyte abnormalities, temperature disturbances, coronary or pulmonary thrombosis, tamponade, tension pneumothorax, and toxins should be considered according to the clinical picture. Calcium, bicarbonate, and magnesium are not universal drugs for every episode of fibrillation; they are used when a specific indication makes them appropriate. In particular, magnesium has a role in torsades de pointes and in correction of relevant deficiencies, not as a substitute for defibrillation.

In persistent fibrillation after three consecutive shocks, the quality of compressions, energy, pad contact, and pad position should be checked. The 2025 recommendations consider changing the shock vector, for example to an anteroposterior configuration, after optimizing the initial position. Double sequential defibrillation using two devices is not a routine intervention in the RCUK pathway because of limitations in the evidence and operational difficulties. Any change in strategy should be organized without unnecessarily increasing no-flow time.

An advanced airway is managed by operators with appropriate expertise while avoiding prolonged interruptions; capnography helps confirm tube position and monitor ventilation. Exhaled carbon dioxide may provide information about perfusion during resuscitation but is not an isolated criterion for terminating efforts. Ultrasound and other assessments should be used without compromising fundamental resuscitation measures. The quality of team organization influences effectiveness as much as the availability of individual tools.

Extracorporeal cardiopulmonary resuscitation may be considered in selected patients when the emergency system and receiving center allow timely activation and there is a reasonable possibility of treating a reversible cause. It is not a solution that can be applied indiscriminately to every refractory arrest. If fibrillation terminates but recurs, the problem may be a trigger that remains active and may require causal, antiarrhythmic, or ablative strategies. Assessment should distinguish failure to convert from repeated reinitiation of the arrhythmia.

Care after return of circulation and secondary prevention

Return of spontaneous circulation opens a critical phase in which perfusion and oxygenation must be supported while avoiding both deficits and unnecessary excesses. Ventilation, blood pressure, myocardial function, and temperature are managed according to the post-cardiac arrest picture. A stable organized rhythm does not exclude brain injury or transient myocardial dysfunction. Active prevention of fever and a temperature-control strategy are part of care in appropriate patients, together with investigation of the cause.

The post-resuscitation ECG guides coronary assessment but must be interpreted in light of drugs, electrolytes, and the phase of recovery. Persistent ST-segment elevation or instability with suspected ischemia requires urgent evaluation for revascularization. In stable patients without these features, immediate coronary angiography is not a universal rule independent of context. Elevated troponin may reflect different mechanisms and does not by itself prove an acute coronary occlusion.

Cardiac imaging defines function, wall motion, and a possible substrate. Cardiac magnetic resonance may identify scar, inflammation, or cardiomyopathy not evident on echocardiography. Initially depressed function may improve after post-arrest myocardial stunning, so a single examination does not complete the assessment. Family history and an ECG obtained before the event help distinguish new findings from pre-existing characteristics. Tests for inherited disease are selected according to the phenotype and accompanied by specialist interpretation.

Secondary prevention with an implantable cardioverter-defibrillator is a central decision when fibrillation is not due to a completely reversible cause and the expected benefit is consistent with overall prognosis and goals of care. The presence of a precipitating factor does not always mean complete reversibility. Scar, a channelopathy, or a persistent predisposition may maintain risk after treatment of the acute episode. This decision should be distinguished from ejection-fraction thresholds used in some primary-prevention pathways.

Ablation of ventricular triggers may reduce recurrence in selected patients, particularly when the same PVC precedes repeated episodes. Documentation of the initial morphology and the presence of the trigger during mapping are important. A favorable result does not necessarily demonstrate elimination of every substrate and does not automatically justify foregoing a defibrillator when one is indicated. Drugs, ablation, and the device pursue complementary goals: reducing the occurrence of events and treating those that nevertheless occur.

Treatment of specific electrical diseases differs: beta-blockade and flecainide may be relevant in catecholaminergic forms, whereas other syndromes require different strategies. Control of ischemia, treatment of heart failure, and review of proarrhythmic drugs may also modify risk. Simply choosing a generic antiarrhythmic drug after any episode of fibrillation is insufficient. The plan should state the probable mechanism, the evidence supporting it, and the elements that remain to be clarified.

Neurologic prognosis, recurrence, and continuity of care

Prognosis depends substantially on the duration of absent circulation and on the quality of the resuscitation response, but also on the cause and pre-existing conditions. Fibrillation amplitude or the number of shocks is not sufficient, by itself, to predict the individual outcome. After recovery, neurologic prognostication should be multimodal and performed at appropriate times, taking sedation, temperature, and other confounders into account. Premature conclusions based on a single finding may be misleading.

Follow-up assesses recurrence, function, and etiologic diagnosis. In initially unexplained cases, new ECGs, imaging, or family information may lead to reclassification. The term idiopathic should remain linked to the quality and timing of the investigation performed. Development of symptoms or events in relatives may change the pathway even when initial genetic testing was negative. Preservation of cardiac-arrest data remains useful for comparing hypotheses over time.

In patients with a defibrillator, programming and remote monitoring help ensure protection and identify episodes, lead problems, and inappropriate therapies. Every shock should be interpreted using the recorded rhythm because not every device intervention corresponds to a new episode of fibrillation. A cluster of events over a short period requires prompt assessment for possible electrical storm. Reducing unnecessary shocks does not mean delaying treatment of genuinely life-threatening arrhythmias.

Rehabilitation after cardiac arrest includes cardiologic, neurologic, cognitive, and psychological aspects. Fatigue, memory difficulties, anxiety, and fear of new events may persist even when cardiac function improves. Support for relatives and a clear plan for return to activities promote continuity of care. Sports, work, and driving are addressed according to the diagnosis, recovery, and applicable regulations, without deriving universal recommendations solely from the presence of a device.

When an inherited disease is identified, counseling and family screening should distinguish pathogenic variants from uncertain findings. Targeted testing may identify relatives at risk, whereas an inconclusive result does not replace clinical assessment when the family history is significant. Prevention and emergency-response education may also be relevant for the family. Management remains proportionate to risk and should not turn every genetic finding into an automatic diagnosis.

Ventricular fibrillation is a common final electrical event of very different conditions. The best clinical outcome requires timely defibrillation, post-cardiac arrest care, and cause-specific prevention. Survival of the episode does not conclude the pathway, just as the absence of recurrence during a brief observation period does not prove that vulnerability has disappeared. An updated diagnosis, an appropriate protection plan, and recovery followed over time connect the emergency response with the patient's ongoing care.