Ventricular tachycardia

Articolo redatto e revisionato del Dott. Luca Moretti

Ventricular tachycardia is a rapid sequence of impulses originating in the ventricles or in the conduction system below the bifurcation of the bundle of His, rather than being driven by the normal supraventricular rhythm. The conventional clinical definition includes at least three consecutive ventricular beats at a rate above 100 beats per minute, with some operational differences among classifications. The term identifies a family of arrhythmias with very different mechanisms, substrates and prognoses.

Ventricular tachycardia may be brief and asymptomatic, sustained but initially tolerated, or associated with syncope, shock and cardiac arrest. Stability during a single episode neither demonstrates benignity nor excludes a ventricular origin. The overall assessment must integrate duration, morphology, circulation and underlying heart disease, without replacing this evaluation with a single descriptor. The pages dedicated to sustained, non-sustained, monomorphic and polymorphic forms and to specific mechanisms discuss their respective pathways in greater depth.

Definition, duration and classification of the forms

Non-sustained ventricular tachycardia terminates spontaneously before 30 seconds. The sustained form lasts at least 30 seconds or requires earlier termination because of clinical compromise. A brief episode is not automatically harmless: in some cardiomyopathies or inherited syndromes it may contribute to risk stratification. Likewise, the recorded duration may depend on intervention by a device or rescuers and must be interpreted together with the context.

The monomorphic form shows a relatively stable appearance of the QRS complexes during the episode, suggesting a repetitive ventricular activation sequence. The polymorphic form shows beat-to-beat variations in morphology and requires particular attention to ischemia, repolarization and electrical diseases. Morphology describes activation but does not by itself demonstrate the mechanism: monomorphic tachycardia may be reentrant or focal, whereas polymorphism may arise from different conditions.

Torsades de pointes is a form of polymorphic ventricular tachycardia associated with prolonged repolarization. Not every polymorphic arrhythmia deserves this designation: if the QT is not prolonged, ischemia and other mechanisms carry a different weight. The bidirectional form shows an organized alternation of axis or morphology and points toward particular settings, such as digitalis toxicity or catecholaminergic tachycardia, without in itself constituting a definitive etiologic diagnosis.

Accelerated idioventricular rhythm occupies a conventional overlap zone of rate and must be distinguished by considering rate, onset, context and behavior. A relatively slow ventricular sequence may compete with sinus rhythm and be transient, whereas a similar rhythm in an unstable patient requires a different interpretation. Merely crossing a threshold does not replace analysis of the phenomenon. Paced rhythms must also be recognized before every wide-complex sequence is attributed to spontaneous tachycardia.

Classification also includes the presence of a pulse, hemodynamic stability and the pattern of recurrence. Several closely spaced episodes may constitute an electrical storm according to the applicable criteria. A pulseless arrhythmia requires the cardiac-arrest pathway; a form with a pulse requires urgent assessment proportionate to the clinical picture. Rate, duration and morphology must be reported precisely, but the decisive datum for immediate intervention remains the patient's ability to maintain effective circulation.

Substrates and electrophysiological mechanisms

Scar-related reentry is common in structural heart disease. Viable tissue interspersed with fibrosis and areas of block can create slow-conduction channels that allow the impulse to circulate. A scar may support several circuits or exits and produce different morphologies in different episodes. The ECG provides clues to the activation sequence, whereas imaging and mapping define the substrate more accurately. Correction of ischemia does not necessarily eliminate a circuit established in a remote scar.

In non-ischemic cardiomyopathies, arrhythmogenic tissue may be intramural, subepicardial or distributed in less accessible locations. Inflammation and genetic disease may contribute to formation and progression of the substrate. Ventricular function may be only mildly impaired despite significant electrical risk in some phenotypes. Ejection fraction alone therefore does not describe all arrhythmogenic possibilities or the degree of difficulty of a potential ablation.

The His-Purkinje system may participate directly in circuits, as in bundle-branch reentry, or support other focal or fascicular mechanisms. Fascicular tachycardia has its own characteristics and is not equivalent to every relatively narrow tachycardia. Anatomical localization and drug response require a specialist diagnosis: the fact that some forms respond to a drug does not justify its empirical use in any wide-complex tachycardia.

Idiopathic forms may originate from the outflow tracts, papillary muscles, annuli or the conduction system, without heart disease identifiable by appropriate investigations. Automaticity and triggered activity play a role in several phenotypes. A normal echocardiogram, however, is not always sufficient to conclude that the condition is idiopathic. History, morphology, magnetic resonance when indicated and the course over time help exclude an initially occult disease.

Channelopathies and acquired repolarization disorders may cause tachycardias even without evident structural abnormalities. Acute ischemia, electrolyte disturbances and proarrhythmic drugs may act on a normal or already vulnerable substrate. Response to exercise, emotion, fever and rate changes may guide suspicion. Treatment changes according to the mechanism: the same description of ventricular arrhythmia does not justify uniform drug therapy.

Clinical presentation and diagnosis of wide-QRS tachycardia

Palpitations, dyspnea, chest pain, presyncope and syncope may accompany the episode, but ventricular tachycardia may also be discovered on incidental monitoring. Tolerance depends on rate, ventricular function and atrioventricular synchrony. The presence of preserved blood pressure does not exclude a ventricular origin and may be transient. Examination should assess perfusion, level of consciousness, ischemia and congestion while useful electrical information is being acquired.

A regular wide-QRS tachycardia requires first considering ventricular tachycardia, supraventricular tachycardia with aberrancy or bundle-branch block, and pre-excited tachycardia. In the presence of myocardial infarction or heart disease, the probability of a ventricular origin is high. If the diagnosis remains uncertain, management should avoid drugs potentially dangerous in ventricular tachycardia. Reassurance based solely on age or good tolerance may lead to a clinically relevant error.

Documented atrioventricular dissociation during a wide-complex tachycardia is an important feature, but P waves may be difficult to see. Failure to demonstrate it does not exclude ventricular tachycardia, because 1:1 retrograde conduction may be present. Capture and fusion beats, when truly present, support independent ventricular activation. Morphological mimics and artifacts require expert interpretation, especially when the judgment is based on only a few complexes or a single lead.

Axis, precordial concordance, morphology in selected leads and comparison with the baseline QRS contribute to the differential diagnosis. Published algorithms help organize interpretation, but their accuracy varies with population and experience and none eliminates every exception. The presence of an accessory pathway or complex heart disease may alter the usual criteria. A complete ECG during the episode should be preserved when available, even if the rhythm is rapidly terminated.

In irregular wide-complex rhythms, polymorphic ventricular arrhythmias and atrial fibrillation with aberrant or pre-excited conduction must be distinguished. The preceding QT, ischemia and variability of activation are key elements. Response to adenosine is not a universal diagnostic test and its use does not extend indiscriminately to every wide-complex tachycardia. If the patient is unstable, detailed analysis must not delay appropriate electrical treatment.

Assessment of heart disease and risk evaluation

After stabilization, previous events, syncope, exposures, ischemia, procedures and family history are reconstructed. Documentation from the defibrillator or emergency services may clarify duration, initiation and termination. The baseline ECG looks for abnormal conduction, signs of scar and repolarization abnormalities. Measurements performed immediately after a cardiac arrest or therapy may be transiently altered and require confirmation once the acute phase subsides.

Echocardiography assesses function and structure, whereas magnetic resonance may identify fibrosis, inflammation and distributions suggestive of cardiomyopathy. The finding of late gadolinium enhancement may modify assessment of the substrate, but it does not have the same meaning in every disease. Coronary assessment is guided by the clinical picture and probability of ischemia. An elevated troponin after a prolonged episode does not automatically demonstrate an acute coronary occlusion, although it requires appropriate interpretation.

Ambulatory monitoring documents recurrences, short runs and their relationship with symptoms. Morphology and behavior during activity may guide further investigations. An exercise test is useful when the question concerns adrenergic arrhythmias or ischemia, with supervision appropriate to the risk. Absence of arrhythmia during a single test does not exclude every phenotype, particularly if the usual circumstances have not been reproduced or if therapy modifies its expression.

An electrophysiological study can demonstrate circuits, localize the target and contribute to risk stratification in selected settings. It is not a universal test for all channelopathies, and non-inducibility does not guarantee absence of future recurrence. Genetic testing is proposed when history, imaging or the electrical phenotype suggests an inherited disease. Concordant pathogenic variants may guide family management; a variant of uncertain significance should not become an independent criterion for invasive protection.

Prognostic assessment integrates documented events and the specific disease. A sustained episode without a completely reversible cause may have different implications from a short run during a correctable acute condition. However, identifying a modifiable factor does not prove that the entire substrate is reversible. Function, scar, timing relative to myocardial infarction, recurrences and comorbidities must be considered together, avoiding application of the same criterion to all ventricular tachycardias.

Treatment of the episode and management of acute recurrences

Pulseless ventricular tachycardia requires resuscitation and defibrillation according to the cardiac-arrest algorithm, together with a search for reversible causes. Monomorphic ventricular tachycardia with a pulse causing shock, ischemia, syncope or acute heart failure requires synchronized cardioversion. Sedation is considered when compatible with the urgency. In polymorphic forms synchronization may not be reliable, and electrical treatment must follow the specific indications of the rhythm and circulatory situation.

The 2025 European recommendations favor electrical cardioversion also in stable monomorphic tachycardia with structural heart disease or when the underlying myocardial injury has not been clarified. Drug therapy may be considered in selected stable patients, for example when sedation or anesthesia carries greater risks. The choice takes account of ventricular function, blood pressure, QT and drug availability. Initial stability does not mean that an effective treatment can be postponed indefinitely.

Intravenous antiarrhythmic drugs must be selected according to mechanism and context. Procainamide, amiodarone and other options are not interchangeable in every patient; some are inappropriate in particular conditions of ventricular function or repolarization. Verapamil may be useful in correctly identified fascicular tachycardia, but may be dangerous if given empirically in an undiagnosed wide-complex tachycardia. The response of a single episode should not replace assessment of the substrate.

In torsades de pointes, causes of long QT, drugs and electrolytes are corrected and magnesium is used when indicated; in acquired pause-dependent forms it may be necessary to increase the heart rate with appropriate measures. Ischemic polymorphic tachycardia instead requires particular attention to reperfusion and treatment of ischemia. Catecholaminergic arrhythmias have a different pathophysiology in which adrenergic stimulation may worsen the condition. Confusing these phenotypes may make an otherwise useful therapy harmful.

Electrical storm requires coordinated management of arrhythmias, ischemia, electrolytes, sympathetic activation and devices. Sedation, drug therapy, review of device programming and ablation may be required according to the mechanism. Repeated shocks may fuel stress and instability without by themselves resolving the cause of recurrences. Transfer to an experienced center is considered when control is inadequate or procedures and support not locally available are required.

Long-term prevention, ablation and prognosis

The implantable cardioverter-defibrillator protects against major ventricular rhythms in patients with an appropriate indication, often for secondary prevention after events not attributable to a completely reversible cause. Preserved ventricular function does not exclude this need in certain settings. The choice also considers life expectancy, comorbidities and preferences. The device treats recognized episodes, but it does not correct the heart disease and does not eliminate every possible cause of sudden death.

Catheter ablation can treat scar-related circuits or idiopathic foci and reduce recurrences and device therapies. The likelihood of success differs between an accessible focus and a cardiomyopathy with an intramural or diffuse substrate. In many heart diseases, ablation complements, without automatically replacing, protection by the implantable cardioverter-defibrillator. In well-defined idiopathic forms, however, it may have a central therapeutic role, with decisions based on symptoms, risk and anatomical characteristics.

Treatment of the underlying heart disease includes management of heart failure, ischemia and modifiable factors, as well as disease-specific interventions for inherited disorders. Antiarrhythmic drugs may reduce episode burden but require safety monitoring and do not by themselves guarantee a mortality benefit. Cardiomyopathy induced or worsened by tachycardia may improve after rhythm control; function should be reassessed to distinguish recovery from residual substrate.

Prognosis is heterogeneous and dynamic. Some idiopathic tachycardias have a favorable course after appropriate diagnosis and treatment, whereas progressive heart disease or extensive scars maintain a risk of recurrence. A satisfactory initial procedural result does not exclude disease progression. A change in morphology, syncope, worsening of heart failure or new family findings require reassessment of the condition, not merely an empirical increase in a drug.

Follow-up integrates clinical review, device assessment when present, ventricular function and quality of life. Fear of recurrences or shocks may limit activity and adherence and deserves specific attention. Advice on exercise, work and other activities is individualized according to diagnosis and risk, with a clear plan for future episodes. The aim is to reduce dangerous events and symptoms while maintaining a functionally satisfactory life, beyond mere suppression of recorded runs.