What is His-Purkinje system disease, its clinical presentation, and recommended management?

His-Purkinje System Disease: Overview and Management

His-Purkinje system disease encompasses conduction disorders and arrhythmias involving the specialized cardiac conduction system distal to the AV node, including the His bundle, right and left bundle branches, and fascicles. 1

Anatomy and Pathophysiology

The His-Purkinje system consists of the His bundle dividing into right and left bundle branches, with the left bundle further dividing into anterior and posterior fascicles. 1 Disease processes affecting this system may be:

• Developmental, hereditary/genetic, metabolic, infectious, inflammatory, infiltrative, traumatic, ischemic, malignant, or degenerative 1
• Static or progressive in nature 1

Clinical Presentations

Conduction Disorders

Isolated fascicular and bundle branch blocks are rarely symptomatic on their own, though they serve as markers for underlying structural heart disease. 1 Key presentations include:

• Bifascicular block (right bundle branch block plus left anterior or posterior fascicle block, or complete left bundle branch block) 1
• Symptoms of intermittent bradycardia (lightheadedness, syncope) when progression to higher-degree block occurs 1
• Left bundle branch block (LBBB) may cause symptoms particularly with reduced left ventricular function due to cardiac dyssynchrony 1

Arrhythmias Involving the His-Purkinje System

Bundle branch reentrant ventricular tachycardia occurs in patients with structural heart disease and preexisting conduction abnormalities, utilizing the His-Purkinje system as a macroreentrant circuit. 1, 2, 3

Idiopathic left ventricular tachycardia (fascicular VT) presents with right bundle branch block morphology and superior axis, involving reentry through the left posterior fascicle and Purkinje network in structurally normal hearts. 1, 2, 4

Focal Purkinje triggers can initiate idiopathic ventricular fibrillation in patients without structural heart disease. 2, 4

Diagnostic Evaluation

For Conduction Disorders

In patients with newly detected LBBB, obtain transthoracic echocardiography to exclude structural heart disease (Class I, Level B-NR). 1

In symptomatic patients with conduction system disease where AV block is suspected, ambulatory ECG monitoring is indicated (Class I, Level C-LD). 1

For patients with symptoms suggestive of intermittent bradycardia (lightheadedness, syncope) and documented conduction system disease without demonstrated AV block, electrophysiology study (EPS) is reasonable (Class IIa, Level B-NR). 1

Electrophysiology Study Protocol

When His-Purkinje block is suspected, EPS should include: 1

• Measurement of HV interval at baseline (normal <55 ms; prolonged >55 ms; markedly prolonged ≥100 ms) 1
• Assessment of His-Purkinje conduction with incremental atrial pacing 1
• Pharmacological provocation with ajmaline (1 mg/kg IV), procainamide (10 mg/kg IV), or disopyramide (2 mg/kg IV) if baseline study is inconclusive 1

EPS is diagnostic when: 1

• Baseline HV interval ≥100 ms in bifascicular block 1
• Second- or third-degree His-Purkinje block demonstrated during incremental atrial pacing 1
• High-degree His-Purkinje block provoked by pharmacological challenge 1

For Ventricular Arrhythmias

In patients with suspected His-Purkinje-related VT, look for QRS morphology during tachycardia that resembles the baseline conduction abnormality. 3

Obtain 12-lead ECG, echocardiography, and consider cardiac MRI when structural heart disease is suspected. 5

Management Strategies

Conduction Disorders

The primary management decision is whether permanent pacing is indicated based on symptoms and degree of conduction abnormality. 1

Patients with bifascicular block and prolonged HV interval (>55 ms) have increased risk of progression to complete heart block, though annual incidence remains low (2-3%, higher if HV >100 ms). 1

Bundle Branch Reentrant VT

Catheter ablation of the right bundle branch is curative for bundle branch reentrant VT (success rate >90%). 2, 3 However:

• Ablation produces complete heart block requiring permanent pacing in approximately 30% of cases 3
• Many patients (60%) have additional VT circuits through myocardial scar requiring ICD implantation 3
• Prognosis depends primarily on the severity of underlying structural heart disease 2

Idiopathic Left Ventricular (Fascicular) Tachycardia

For acute termination of hemodynamically stable verapamil-sensitive idiopathic LVT, intravenous verapamil is recommended (Class I, Level B-NR). 1

For chronic management of recurrent verapamil-sensitive idiopathic LVT, oral verapamil is reasonable (Class IIa, Level C-LD). 1

Catheter ablation targeting the distal insertion of the Purkinje system along the inferior LV septum is highly effective (>90% acute success, ~10% recurrence) and should be considered for symptomatic patients. 1, 2

Purkinje-Triggered Ventricular Fibrillation

For patients with recurrent idiopathic VF initiated by PVCs with consistent QRS morphology, catheter ablation of the Purkinje trigger is useful (Class I, Level B-NR). 1

ICD implantation is recommended for survivors of sudden cardiac arrest due to idiopathic polymorphic VT/VF if meaningful survival >1 year is expected (Class I, Level B-NR). 1

Critical Pitfalls to Avoid

Do not assume normal EPS excludes arrhythmic cause of syncope when clinical suspicion is high; consider prolonged monitoring with loop recorder. 1

Do not use calcium channel blockers for wide-complex tachycardia of uncertain origin, especially with known myocardial dysfunction. 5

Recognize that ablation of His-Purkinje-related VT often requires subsequent pacemaker and/or ICD implantation due to induced conduction abnormalities and coexisting myocardial scar-related VT circuits. 3

In patients with structural heart disease and His-Purkinje VT, focus on optimizing heart failure therapy and assessing ICD indication rather than relying solely on ablation. 5, 3