Atrioventricular nodal reentrant tachycardia, commonly known as AVNRT, is a type of supraventricular tachycardia characterized by rapid heartbeats originating from the atrioventricular node. Patients with AVNRT often experience palpitations, dizziness, chest discomfort, or shortness of breath. While medications can help control symptoms, catheter ablation has become a definitive treatment option for many patients. Ablation involves carefully targeting specific areas within the heart to interrupt the abnormal electrical pathway responsible for the tachycardia. Understanding where to ablate for AVNRT is crucial for achieving successful outcomes and minimizing complications.
Understanding AVNRT
AVNRT occurs due to a reentrant circuit within or around the atrioventricular (AV) node. In a typical AVNRT, there are two pathways a fast pathway and a slow pathway. The electrical impulse may travel down one pathway and return through the other, creating a loop that results in rapid heartbeats. The slow pathway is usually targeted during ablation, as eliminating its conduction can prevent the reentrant circuit without compromising normal AV nodal function. Proper identification of these pathways is essential to safely perform ablation and avoid unintended damage to the heart’s electrical system.
Symptoms of AVNRT
Recognizing AVNRT symptoms helps determine when ablation may be necessary. Common symptoms include
- Rapid heart rate that starts and stops suddenly
- Palpitations or pounding in the chest
- Lightheadedness or dizziness
- Shortness of breath
- Chest discomfort or pressure
Symptoms can vary in frequency and intensity. Some patients experience brief episodes, while others may have sustained tachycardia. When episodes are recurrent or severely impact daily life, catheter ablation may be considered as a long-term solution.
Indications for Ablation
Not all patients with AVNRT require ablation. Indications for the procedure typically include
- Frequent or symptomatic episodes despite medical therapy
- Intolerance to medications used to control heart rate or rhythm
- Patient preference for a potential curative procedure over long-term medication
- Evidence of tachycardia causing structural or functional cardiac issues
Electrophysiology studies are often performed to map the heart’s electrical pathways and confirm the diagnosis before ablation is recommended.
Electrophysiology Study and Mapping
An electrophysiology (EP) study is a crucial step before ablation. During this study, specialized catheters are inserted through veins into the heart to record electrical signals and identify the pathways responsible for AVNRT. Mapping helps locate the slow pathway, which is typically targeted during ablation. Accurate mapping is essential to ensure that ablation effectively eliminates the tachycardia without affecting the fast pathway or normal AV nodal function.
Identifying the Slow Pathway
The slow pathway is usually found in the posterior-inferior region of the right atrium near the tricuspid valve and close to the coronary sinus ostium. Specific anatomical landmarks and electrical signals guide the electrophysiologist to this area. Ablation at this location aims to modify or eliminate the slow pathway, thereby interrupting the reentrant circuit while preserving normal AV conduction.
Ablation Technique for AVNRT
Radiofrequency ablation is the most common method used to treat AVNRT. The procedure involves delivering controlled energy through a catheter to the slow pathway region. Key steps include
- Inserting catheters into the heart through the femoral vein
- Mapping electrical activity to locate the slow pathway precisely
- Delivering radiofrequency energy to modify or eliminate the slow pathway
- Monitoring the heart’s response to ensure normal conduction is maintained
Some centers may use cryoablation, which involves freezing the tissue instead of using heat. Cryoablation is often preferred in cases where there is a higher risk of damaging the AV node, as it allows for temporary testing before permanent tissue modification.
Success Rates and Risks
Catheter ablation for AVNRT is highly effective, with success rates exceeding 95% in most studies. Patients often experience complete resolution of tachycardia after the procedure. However, as with any invasive procedure, there are potential risks
- Damage to the AV node, which may require a pacemaker in rare cases
- Vascular complications at the catheter insertion site
- Pericardial effusion or cardiac tamponade, though uncommon
- Recurrence of AVNRT, requiring repeat ablation in a small percentage of patients
Careful technique, proper mapping, and experience significantly reduce these risks, making ablation a safe and effective treatment for most patients.
Post-Ablation Care
After ablation, patients are usually monitored for a few hours to ensure stability. Some mild discomfort or bruising at the catheter site is common. Post-procedure care includes
- Avoiding strenuous activity for several days
- Monitoring for signs of infection or unusual symptoms
- Follow-up visits with the electrophysiologist to assess success and heart rhythm
Most patients can resume normal activities within a short period and may no longer require medications for AVNRT.
Ablation for AVNRT targets the slow pathway in the posterior-inferior region of the right atrium near the coronary sinus ostium. Understanding the anatomy, performing careful electrophysiology mapping, and using precise ablation techniques ensure high success rates and minimize risks. For patients with recurrent or symptomatic AVNRT, catheter ablation offers a potentially curative solution, eliminating rapid heartbeats and improving quality of life. Awareness of procedure indications, techniques, and post-procedure care helps patients and healthcare providers achieve optimal outcomes while maintaining the safety and integrity of the heart’s electrical conduction system.