How is the reentry mechanism in cardiac arrhythmias best managed?

Management of Reentry Mechanism in Cardiac Arrhythmias

Catheter ablation is the definitive first-line therapy for most reentrant arrhythmias and should be offered when feasible, as it provides curative treatment by eliminating the reentry circuit. 1

Understanding the Reentry Mechanism

Reentry is the most common mechanism underlying sustained ventricular and supraventricular arrhythmias, particularly in structural heart disease. 2 The circuit requires three critical elements:

• Unidirectional conduction block in one limb of the circuit, which is essential for reentry initiation 1
• Slow conduction through at least one pathway, necessary for both initiation and maintenance 1
• Recovery of excitability in the initially blocked pathway to allow retrograde activation and complete the circuit 1

The substrate develops from any disturbance of cardiac architecture—myocardial fibrosis, inflammation, hypertrophy, or cellular necrosis from conditions like hypertension, coronary artery disease, valvular disease, and cardiomyopathies. 2, 1

Acute Management Algorithm

For Hemodynamically Unstable Patients

Immediate synchronized cardioversion is the definitive treatment for any hemodynamically unstable reentrant arrhythmia. 1

For Hemodynamically Stable Patients with AV Nodal-Dependent Reentry

Step 1: Vagal Maneuvers

• Attempt Valsalva maneuver or carotid massage first for stable patients with AV nodal-dependent reentry (AVNRT, AVRT). 1

Step 2: Adenosine

• Administer adenosine 6-12 mg IV rapid push if vagal maneuvers fail, which transiently blocks AV nodal conduction. 1

Step 3: IV Calcium Channel Blockers or Beta-Blockers

• Use IV diltiazem, verapamil, or beta-blockers if adenosine fails. 1

For Verapamil-Sensitive Interfascicular Reentrant VT (Belhassen Tachycardia)

Intravenous verapamil is recommended for VT termination in patients with sustained hemodynamically tolerated verapamil-sensitive idiopathic left ventricular tachycardia related to interfascicular reentry. 2 This specific reentry involves the left posterior fascicle as the retrograde limb and LV tissue with verapamil-sensitive slow conduction as the anterograde limb. 2

For Atrial Flutter

Electrical cardioversion or radiofrequency catheter ablation are often required for termination, as pharmacologic agents are less effective. 1

Definitive Management: Catheter Ablation

Catheter ablation should be offered as first-line treatment when feasible for most reentrant arrhythmias, as it provides definitive cure by eliminating the reentry circuit. 1

Specific Ablation Targets by Arrhythmia Type:

Typical Atrial Flutter:

• Cavotricuspid isthmus ablation has high success rates and prevents recurrence. 1

Interfascicular Reentrant VT:

• Target the distal insertion of the anterograde limb along the inferior LV septum near the left posterior fascicle junction. 2
• Acutely successful in >90% of patients with ~10% recurrence risk. 2

AVRT (Accessory Pathway-Mediated):

• Accessory pathway ablation provides excellent prognosis and cure. 1

Scar-Related Ventricular Tachycardia:

• The existence of structural reentrant substrates around fixed anatomical obstacles (post-MI scar, surgical scars) provides the rationale for VT ablation. 2

Chronic Pharmacologic Suppression

When ablation is not feasible, declined by patient, or as bridge therapy:

For Supraventricular Reentry:

• Oral beta-blockers, verapamil, or diltiazem may be used for chronic suppression. 1

For Verapamil-Sensitive Idiopathic LVT:

• Chronic oral verapamil can be useful for controlling recurrent episodes. 2

For Ventricular Arrhythmias:

• Class IC agents (flecainide, propafenone) are FDA-approved for prevention of paroxysmal supraventricular tachycardias including AVNRT and AVRT in patients without structural heart disease. 3, 4
• Critical caveat: Flecainide and propafenone should not be used in patients with recent myocardial infarction or structural heart disease due to proarrhythmic risk. 3

Important Clinical Pitfalls

Avoid Class IC antiarrhythmics in structural heart disease: Flecainide and propafenone are contraindicated in patients with coronary disease, prior MI, or left ventricular dysfunction due to increased mortality risk. 3

Recognize verapamil-sensitive VT: This specific entity responds dramatically to verapamil, unlike most ventricular tachycardias, making correct diagnosis critical for appropriate acute management. 2

Monitor for proarrhythmia: All antiarrhythmic drugs can paradoxically worsen arrhythmias, particularly at higher plasma levels (>0.7-1 mcg/mL for flecainide). 3

Hospitalize for syncope with suspected VA: Patients presenting with syncope for which ventricular arrhythmia is documented or thought likely should be hospitalized for evaluation, monitoring, and management. 2