## Distinguishing AVNRT from AVRT ### Key Anatomical Difference **Key Point:** The fundamental discriminator between AVNRT and AVRT is the presence or absence of an accessory pathway (AP). AVRT requires an AP; AVNRT does not. ### Comparison Table | Feature | AVNRT | AVRT | |---------|-------|------| | **Accessory Pathway** | Absent | Present (WPW or concealed) | | **Reentry Circuit** | Dual AV nodal pathways (slow & fast) | AP + AV node + atrium | | **P Wave Location** | Buried in QRS or immediately after | Often visible before QRS (orthodromic) | | **Heart Rate** | 140–250 bpm (typically 180–200) | 140–300 bpm (often >200) | | **Adenosine Response** | Abrupt termination | Abrupt termination | | **Definitive Diagnosis** | Electrophysiological study (EPS) | EPS + AP localization | ### Why This Matters Clinically **Clinical Pearl:** The presence of an accessory pathway on EPS is the gold standard that definitively separates AVRT from AVNRT. Both arrhythmias respond identically to adenosine and have similar heart rates, making clinical features alone insufficient. **High-Yield:** AVRT with an overt AP (WPW syndrome) shows a short PR interval and delta wave on baseline ECG. Concealed AVRT (AP conducting only retrograde) has a normal baseline ECG but an AP is still demonstrable on EPS. ### Diagnostic Approach Electrophysiological study is the definitive diagnostic modality: - Dual AV nodal physiology (jump in AV nodal conduction) → AVNRT - Accessory pathway conduction (earliest retrograde atrial activation outside the CS) → AVRT **Mnemonic: AVRT = Accessory pathway; AVNRT = Nodal (dual pathways)** [cite:Harrison 21e Ch 226]
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.