Atrioventricular Nodal Reentrant Tachycardia (AVNRT) ablation is a minimally invasive procedure designed to correct a specific type of rapid heart rhythm originating in the heart’s center. AVNRT is the most common form of paroxysmal supraventricular tachycardia (SVT), causing sudden and often distressing episodes of a fast heartbeat. The procedure offers a high chance of a permanent cure by modifying a small area of the heart’s electrical wiring. This article explains the steps involved in this highly effective treatment, from initial preparation through the ablation process and recovery.
Understanding Atrioventricular Nodal Reentrant Tachycardia
AVNRT is caused by a functional “short circuit” within or near the atrioventricular (AV) node, which regulates electrical signals between the heart’s upper and lower chambers. Most people with AVNRT have two distinct electrical pathways in this area: a fast pathway and a slow pathway. The fast pathway conducts quickly but recovers slowly, while the slow pathway conducts slowly but recovers faster.
Under normal circumstances, the impulse travels down the fast pathway. A premature beat can find the fast pathway still recovering, forcing the signal down the slow pathway instead. This allows the impulse to travel backward up the fast pathway, creating a continuous, circular electrical loop—the reentrant circuit. This rapid, circular firing causes the heart rate to abruptly jump to between 120 and 280 beats per minute. Symptoms are experienced as sudden, pounding palpitations, dizziness, shortness of breath, or a fluttering sensation in the neck.
Preparing for the Ablation Procedure
Preparation for AVNRT ablation involves several logistical steps to ensure patient safety and optimize the procedure. Standard pre-procedure diagnostics usually include an electrocardiogram (ECG), blood work, and possibly an echocardiogram. These tests confirm the diagnosis and provide the medical team with a baseline of the patient’s cardiac health and function.
Patients are instructed to fast for at least six hours before the procedure. Specific instructions are given regarding blood-thinning medications, which may need adjustment or be temporarily stopped depending on the patient’s risk profile. Other regular medications are reviewed, and the patient is advised on which ones to take or hold on the morning of the procedure.
The Step-by-Step Ablation Process
The ablation procedure begins in a specialized cardiac catheterization lab. The patient is positioned on a table and given conscious sedation for comfort. Access to the heart is gained through a small puncture, typically in the femoral vein in the groin. Thin, flexible wires called catheters are inserted and guided to the heart using X-ray guidance.
These initial catheters conduct an Electrophysiology (EP) study, which is the mapping phase. The EP study precisely maps the heart’s electrical activity to locate the slow pathway responsible for the AVNRT circuit. Catheters deliver tiny electrical impulses to intentionally trigger the tachycardia, allowing physicians to identify the circuit and the precise area where the slow pathway connects to the AV node. The targeted site is usually located in the right posteroseptal region of the heart, known as the triangle of Koch.
Once the slow pathway is identified, the ablation catheter delivers energy to modify the tissue and interrupt the reentrant circuit. The most common method is radiofrequency (RF) ablation, which uses electrical current to heat and destroy the target tissue section. An alternative is cryoablation, which uses extreme cold to freeze the tissue. Cryoablation is sometimes preferred because its effect is reversible during initial application, offering an additional safety measure when working near the normal conduction system.
During energy delivery, the medical team monitors for junctional beats, a sign that the ablation is affecting the target tissue. The goal is to eliminate the slow pathway’s ability to participate in the circuit without damaging the adjacent fast pathway or the main AV node. Damage to the main AV node would lead to a serious complication called complete heart block.
Recovery and Long-Term Outcomes
Following successful ablation, the catheters are removed, and pressure is applied to the groin access site to prevent bleeding. The patient is required to lie flat for several hours to ensure the puncture site heals properly and minimize the risk of a hematoma. Most patients are monitored overnight in the hospital and are discharged the following day.
Recovery is quick, with most individuals resuming normal, non-strenuous activities within a few days. The long-term success rate for AVNRT ablation is exceptionally high, ranging from 97% to 99% after a single procedure. Recurrence is rare, occurring in a small percentage of patients who may necessitate a second procedure.
The primary, though rare, serious risk of AVNRT ablation is inadvertent damage to the normal conduction system, resulting in complete heart block, which requires a permanent pacemaker. The incidence of this complication is very low, less than 1% to 2.3% of procedures, especially when targeting the slow pathway. Patients are often able to return to a life free of the sudden, rapid heart episodes that prompted the procedure.