Catheter ablation for idiopathic left fascicular VT

Idiopathic left fascicular ventricular tachycardia (ILFVT), also known as verapamil-sensitive VT or Belhassen tachycardia, is a reentrant ventricular arrhythmia that usually arises in a structurally normal heart. Its circuit involves the left ventricular Purkinje system rather than scar, myocarditis or an ischaemic substrate. The condition typically presents in adolescents and young adults, with palpitations, dizziness or syncope, although a minority present after cardiac arrest.

Diagnosis and treatment sit within the subspecialty of cardiac electrophysiology. Verapamil can terminate an acute episode, yet recurrent symptomatic ILFVT is usually treated with catheter ablation because it targets the arrhythmogenic fascicle and offers a durable alternative to lifelong medication. Mapping must distinguish the classic left posterior fascicular circuit from other idiopathic ventricular arrhythmias and from ventricular tachycardia caused by structural disease.

Recognising the arrhythmia and excluding structural disease

Clinical clues begin with the electrocardiogram. The common left posterior fascicular pattern has a relatively narrow QRS, right bundle branch block morphology and left-axis deviation; left anterior and upper septal variants produce other axis and conduction patterns. Exercise, emotional stress and premature ventricular beats can initiate the arrhythmia. A resting ECG may be normal, so ambulatory monitoring and exercise testing can be more informative than a single tracing.

Structural assessment is essential before the tachycardia is labelled idiopathic. Clinicians generally review echocardiography, coronary status when clinically indicated, family history and arrhythmic burden, with cardiac MRI reserved for concerning features such as regional wall abnormalities, cardiomyopathy or suspected scar. Blood pressure, medication use and electrolyte abnormalities should also be assessed, because acquired abnormalities can trigger ventricular arrhythmias that mimic fascicular VT.

Presentation does not always indicate severity. Some patients have brief, tolerated runs, whereas others have syncope or sustained episodes with haemodynamic compromise. In Australian emergency departments in cities such as Sydney and Melbourne, recurrent episodes may be evaluated during an acute admission; outpatient review should then establish the rhythm mechanism rather than treating every wide-complex tachycardia as idiopathic.

Electrophysiology and circuit mapping

An electrophysiology study defines the mechanism and permits catheter ablation during the same session. Atrial pacing or programmed ventricular stimulation may induce ILFVT, while an isoproterenol or procainamide challenge can expose fascicular reentry in difficult cases. Verapamil sensitivity supports the diagnosis but is not independently diagnostic, since Purkinje-related arrhythmias and some accessory-pathway tachycardias can respond similarly.

During mapping, the operator looks for a Purkinje or fascicular potential that precedes the surface QRS and for an earliest ventricular activation site consistent with the exit of the circuit. The earliest site may lie in the left posterior fascicle, the left anterior fascicle or the upper septal region. Entrainment can test participation of the mapped structure, while activation and refractory-period observations help distinguish a small focal reentrant circuit from an automatic focus.

Correlation with the surface ECG is particularly valuable. A right bundle branch block pattern with marked left-axis deviation usually suggests the left posterior fascicular exit, whereas a superior-axis pattern suggests the anterior fascicle. Focal ablation at Purkinje potentials that are inseparable from the earliest ventricular electrogram is favoured. Failure to identify the target, or ablation too close to the His bundle, risks either recurrence or unwanted conduction block.

Ablation routes, targets and endpoints

The standard technique uses a retrograde transaortic approach. A catheter is advanced from the femoral artery through the aortic valve into the left ventricle, allowing direct mapping of the posterior fascicle and its Purkinje network. Radiofrequency energy is delivered at the selected site, with success judged by elimination of the target electrogram and non-inducibility under a predefined stimulation protocol. This method has a long record of high success, but arterial access and aortic manipulation introduce specific risks.

A transseptal approach provides an alternative route from the right atrium to the left atrium and mitral valve, then into the left ventricular outflow tract or papillary region. It can be useful when aortic access is unsuitable or when the operator needs a different catheter orientation, although transseptal puncture adds septal, atrial and mitral-valve considerations. In selected left posterior fascicular arrhythmias, a retrograde transvenous route through the coronary sinus may reach an eligible fascicular target, but this technique requires specialist experience and careful awareness of coronary venous injury.

Target selection matters more than route alone. The endpoint is usually abolition of the clinical VT and all clinically relevant fascicular morphologies, supported by disappearance of the local target potential and failure to re-induce tachycardia with ventricular extrastimulation and, where appropriate, pharmacological provocation. Irrigated radiofrequency is commonly used when a firm, stable substrate is sought; cryothermal ablation may be considered for selected targets, although its evidence base in fascicular VT is smaller. Lesions should spare the normal His-Purkinje system whenever possible.

Success, recurrence and procedural risk

Reported outcomes are favourable when the diagnosis is correct and the reentrant circuit is completely identified. Many published series report immediate procedural success above 90%, and long-term freedom from recurrence in roughly 85–95% of patients, with the precise figures varying by follow-up duration, stimulation protocol and the proportion with genuinely idiopathic disease. Reasonable follow-up includes early clinical review and ambulatory monitoring because patient-reported symptoms may not capture brief recurrent episodes.

Recurrence may follow incomplete lesion formation, target misidentification, multiple fascicular reentries or the presence of occult structural disease. A change in QRS morphology should prompt renewed evaluation rather than immediate repeat ablation. Outcomes also depend on operator experience and the completeness of mapping. ILFVT generally carries a good prognosis in the absence of structural heart disease, so implantable cardioverter-defibrillators are not routinely required for recurrent fascicular VT; they may be considered when the mechanism is atypical, ventricular fibrillation has occurred, or additional cardiac disease is present.

Procedural complications are uncommon in experienced centres but include vascular injury, aortic regurgitation, coronary artery injury, perforation with tamponade, stroke, conduction block and, with transseptal access, atrial or mitral injury. Comparable age and comorbidity considerations are discussed in outcomes in older adults, which is useful when weighing these risks against expected benefit in an individual patient.

Australian pathways, training and research

Australian care is delivered through a mixture of tertiary public hospitals and private electrophysiology services, with complex ablation concentrated in major centres in Sydney, Melbourne, Brisbane, Adelaide and Perth. Referral pathways may involve a cardiologist, an electrophysiology specialist and a centre familiar with ventricular arrhythmia mapping. Public waiting lists can influence the timing of elective ablation, while private cover and hospital policies determine where investigation and treatment occur. Rural patients may need travel and remote monitoring arranged around a metropolitan procedure.

The local device market supplies modern mapping systems, radiofrequency generators, irrigated and solid-tip catheters, and cryoablation consoles from international manufacturers through Australian distributors. Hospital procurement, maintenance and consumable costs influence which technologies are available, so access should be discussed with the treating centre rather than assumed. Medicare Benefits Schedule itemisation, private-insurance funding and hospital admission status can affect where and when the procedure occurs. Australian anaesthetic, anticoagulation and infection-prevention protocols frame the procedural pathway, while regional guidelines and institutional protocols support reproducible electrical endpoints and complication surveillance.

Training is strengthened by supervised electrophysiology, journal clubs and the educational activities of the Asia Pacific Heart Rhythm Society and Japanese Heart Rhythm Society. The Journal of Arrhythmia is the official publication of both societies and provides an open-access venue for clinical and translational research. The journal information and submissions page explains its scope, editorial policies and manuscript routes for Australian and international contributors. Original data on mapping, follow-up and complications are particularly valuable because treatment volumes vary across centres and because findings from elsewhere may not reflect local patient selection.

Patients with recurrent symptomatic left fascicular VT benefit from early referral for electrophysiological assessment, especially after syncope, sustained episodes or a failed medical trial. Clinicians should document the tachycardia morphology, arrange appropriate structural assessment and provide a discharge plan for recurrent wide-complex tachycardia. Readers can use the linked evidence to guide referral and counselling, while clinicians and researchers are encouraged to submit relevant case series, systematic reviews and original ablation studies to the journal.