From the Guidelines
AVRT and AVNRT are two distinct types of supraventricular tachycardias with different anatomical pathways and characteristics, with AVRT involving an accessory pathway outside the AV node and AVNRT occurring entirely within the AV node itself. AVRT (Atrioventricular Reciprocating Tachycardia) involves an accessory pathway that connects the atria and ventricles, creating a reentry circuit, as described in the 2015 ACC/AHA/HRS guideline for the management of adult patients with supraventricular tachycardia 1. This accessory pathway can conduct either antegrade (Wolff-Parkinson-White syndrome) or retrograde only (concealed pathway). In contrast, AVNRT (Atrioventricular Nodal Reentrant Tachycardia) occurs entirely within the AV node itself, utilizing dual pathways within the node - a fast pathway and a slow pathway, as outlined in the same guideline 1.
Key Differences
- AVRT typically shows a longer RP interval with visible retrograde P waves on ECG
- AVNRT often displays very short RP intervals with P waves hidden within or just after the QRS complex
- AVRT is more common in younger patients and may be associated with pre-excitation syndromes
- AVNRT is the most common SVT in adults, especially middle-aged women
Treatment
Treatment for both conditions includes vagal maneuvers and adenosine for acute termination, as recommended in the 2015 ACC/AHA/HRS guideline 2. Long-term management may involve calcium channel blockers, beta-blockers, or catheter ablation, with ablation targeting the accessory pathway in AVRT and typically the slow pathway in AVNRT. According to the guideline, vagal maneuvers and/or IV adenosine are recommended as the first line of treatment for AVNRT (Class I) 2.
Management Considerations
- AVRT and AVNRT have different responses to treatment, with AVRT often requiring ablation of the accessory pathway
- AVNRT can be managed with calcium channel blockers, beta-blockers, or catheter ablation of the slow pathway
- The choice of treatment depends on the patient's age, symptoms, and underlying heart disease, as well as the presence of any pre-excitation syndromes 1, 2.
From the Research
Difference between AVRT and AVNRT
- AVRT (Atrioventricular Reentrant Tachycardia) and AVNRT (Atrioventricular Nodal Reentrant Tachycardia) are two types of supraventricular tachycardia (SVT) that occur in the heart 3.
- The main difference between AVRT and AVNRT is the mechanism by which they develop: + AVNRT occurs due to intranodal reentry via fast and slow conduction pathways within the atrioventricular junction 3. + AVRT occurs due to reentrant tachycardia across accessory pathways, which can be associated with preexcitation 3.
Characteristics of AVRT and AVNRT
- AVRT is often associated with Wolff-Parkinson-White syndrome, which can lead to a potentially lethal type of atrial fibrillation if not treated properly 3.
- AVNRT is the most common paroxysmal supraventricular tachycardia among adults and accounts for considerable morbidity 4.
- The concept of dual pathway physiology is useful in understanding AVNRT, although it is likely due to functional properties of anisotropic tissue within the triangle of Koch rather than anatomically distinct tracts of conduction 4.
Treatment and Management
- Electrocardiographic cues can help differentiate between AVNRT and AVRT, and treatments range from emergency cardioversion to administration of intravenous agents such as adenosine 3.
- Catheter ablation is a definitive therapy for both AVRT and AVNRT, with a high success rate and is recommended as the first-line method for long-term management of recurrent, symptomatic paroxysmal SVT 4, 5.
- Pharmacological therapy, such as beta-blockers and calcium channel blockers, can also be used to manage AVRT and AVNRT, especially in patients who are not candidates for catheter ablation 6, 5.