Fascicular TachycardiaEdit
Fascicular tachycardia is a distinctive form of idiopathic left ventricular tachycardia that arises from the specialized conduction tissue within the left ventricle. It typically occurs in people with structurally normal hearts, often young or middle-aged adults, and manifests as episodes of palpitations, dizziness, or short bursts of rapid heart rate. The arrhythmia is notable for its relative responsiveness to calcium channel blockade and for the high success rate of targeted ablation therapy. The term encompasses several variants linked to different fascicles of the left bundle branch system, including the left posterior and left anterior fascicles, and is sometimes described in the broader context of verapamil-sensitive fascicular tachycardias. Purkinje fibers Purkinje network Idiopathic left ventricular tachycardia Verapamil Catheter ablation Electrophysiology study
Pathophysiology
Fascicular tachycardias are reentrant arrhythmias that use the left ventricular Purkinje network as part of the circuit. In most cases, the reentry involves a slow conduction pathway within or adjacent to a fascicle of the left bundle branch, with the fast and slow limbs forming a circuit that sustains rapid ventricular activation. The tachycardia is classically described as verapamil-sensitive, meaning that calcium channel blockade can interrupt the reentrant loop and terminate the rhythm. This sensitivity helps distinguish fascicular tachycardia from other forms of ventricular tachycardia in patients with structurally normal hearts. Left bundle branch Purkinje fibers Verapamil Calcium channel blocker
The main variants reflect involvement of specific fascicles: - left posterior fascicular tachycardia, the most common form, and - left anterior fascicular tachycardia, which is less common and can have a different electrical signature.
In all variants, meticulous intracardiac mapping during electrophysiology studies can reveal the earliest Purkinje potentials and delineate the circuit, guiding targeted therapy. Left posterior fascicular Left anterior fascicular Electrophysiology study Purkinje potentials
Epidemiology and clinical presentation
Fascicular tachycardia most often affects individuals without structural heart disease. It is frequently observed in younger patients but can occur across a wide adult age range. Symptoms include palpitations, awareness of a rapid heartbeat, lightheadedness, or brief episodes of presyncope. Episodes may be self-terminating or recurrent, and in some patients occur with varying frequency, from occasional to daily. The absence of overt structural heart disease helps distinguish fascicular tachycardia from scar-related ventricular tachycardias seen in cardiomyopathy or prior infarction. Idiopathic left ventricular tachycardia Cardiac conduction system Tachycardia Palpitations
Diagnosis
Diagnosis rests on clinical history, electrocardiography during tachycardia, and targeted electrophysiology testing when needed. Key diagnostic clues include a tachycardia with a relatively regular rhythm and a QRS morphology that resembles a bundle-branch block pattern, reflecting activation through the Purkinje system rather than a ventricular scar. Verapamil often terminates the tachycardia or suppresses its inducibility, a feature that supports the diagnosis of a fascicular, calcium channel–sensitive mechanism. When noninvasive testing is inconclusive, an electrophysiology study with intracardiac mapping can confirm the diagnosis by identifying the reentrant circuit and guiding ablation. Electrocardiography Verapamil Adenosine Electrophysiology study Purkinje fibers
Differential diagnosis includes other idiopathic left ventricular tachycardias, right ventricular outflow tract tachycardia, and supraventricular tachycardias with aberrant conduction. Distinguishing features on ECG and during pacing maneuvers help separate fascicular tachycardia from these alternatives. Idiopathic left ventricular tachycardia Ventricular tachycardia Atrial tachycardia Supraventricular tachycardia
Treatment
Management can be divided into acute termination and long-term suppression or cure.
Acute termination and stabilization: Intravenous verapamil is the hallmark for terminating acute episodes of fascicular tachycardia in hemodynamically stable patients. If the patient is unstable or verapamil is ineffective or contraindicated, electrical cardioversion may be required. Adenosine is typically less effective for fascicular VT than for some other tachycardias, but may be attempted in a monitored setting. Verapamil Electrical cardioversion Adenosine Calcium channel blocker
Long-term therapy and cure: For recurrent episodes or in patients seeking a definitive solution, catheter ablation of the involved fascicular pathway is highly effective, with high success rates and relatively low risk when performed by experienced operators. Ablation targets the left fascicular network implicated in the reentrant circuit, aiming to eliminate the substrate for tachycardia while preserving overall conduction. Medication options include ongoing calcium channel blockade (e.g., verapamil or diltiazem) or, less commonly, antiarrhythmic drugs, but these are generally considered secondary to ablation in patients with recurrent symptoms or objective arrhythmia burden. Catheter ablation Verapamil Antiarrhythmic drug Electrophysiology study
Controversies and practice debates: Clinicians discuss the balance between early ablation versus initial medical therapy, weighing the high success and low recurrence of ablation against procedural risks and costs. Debates also center on patient selection, the appropriate use of invasive testing, and the management of asymptomatic individuals with sporadic episodes. In practice, many centers favor ablation for patients with recurrent episodes or those whose quality of life is affected, while others may start with medical management in patients with infrequent symptoms. Catheter ablation Idiopathic left ventricular tachycardia Electrophysiology study
Prognosis
In the absence of structural heart disease, fascicular tachycardia generally carries an excellent long-term prognosis. Episodes are typically arrhythmic and non-life-threatening; the main clinical impact is symptom burden and, in some cases, reduced quality of life due to recurrent tachycardias. Successful catheter ablation offers a durable solution for many patients, with low risk of recurrence after a well-executed procedure and a small, procedure-related risk of inadvertent conduction disturbance. Prognosis Catheter ablation