Are retrograde P-waves (atrial depolarizations) present in Atrioventricular Reentrant Tachycardia (AVRT) or Atrioventricular Nodal Reentrant Tachycardia (AVNRT)?

Retrograde P-waves in AVRT and AVNRT

Yes, retrograde P-waves are present in both AVRT and AVNRT, but they appear differently on ECG and have distinct characteristics that help differentiate between these two types of supraventricular tachycardias.

Retrograde P-waves in AVNRT

• In typical AVNRT, atrial activation occurs nearly simultaneously with ventricular activation, resulting in retrograde P-waves that are often buried within or appear at the end of the QRS complex 1
• These retrograde P-waves typically appear as:
  • A narrow negative deflection in the inferior leads (pseudo S wave) 1
  • A slightly positive deflection at the end of the QRS complex in lead V1 (pseudo R' wave) 1
• The RP interval is very short (RP < 90 ms from the surface ECG), creating what is known as a "short RP" tachycardia 1
• In some cases, especially in elderly patients, the P-waves may be visible after the QRS complex due to delayed nodal retrograde conduction 2

Retrograde P-waves in AVRT

• In orthodromic AVRT (the most common form, accounting for 90-95% of AVRT episodes), retrograde P-waves are usually clearly visible in the early part of the ST-T segment 1
• The retrograde conduction occurs over the accessory pathway, with the P-wave typically appearing separate from the QRS complex 1
• The RP interval is longer than in typical AVNRT but still creates a "short RP" tachycardia (RP < PR) 1
• P-waves are visible in 100% of AVRT cases, compared to only 16% of typical AVNRT cases 2

Special Variants and Exceptions

• In atypical forms of AVNRT (such as "fast-slow"), the P-wave is closer to the subsequent QRS complex, creating a "long RP" tachycardia 1
• In the permanent form of junctional reciprocating tachycardia (PJRT), which is an uncommon form of AVRT, the accessory pathway has decremental conduction properties that result in delayed atrial activation and a long RP interval 1
• PJRT typically shows deeply inverted retrograde P-waves in leads II, III, and aVF 1

Differentiating Between AVNRT and AVRT

• The amplitude of retrograde P-waves can help differentiate between slow-slow AVNRT and AVRT through a posteroseptal accessory pathway:
  • Deeper negative deflection of retrograde P-waves in the inferior leads (particularly lead aVF) suggests slow-slow AVNRT 3
  • A cutoff value of -0.16 mV in lead aVF has 93% sensitivity and 88% specificity for distinguishing between these two mechanisms 3
• The presence of a pseudo r' wave in lead V1 or a pseudo S wave in leads II, III, aVF indicates anterior-type AVNRT with high accuracy 4
• Gender and age can influence the presentation:
  • AVNRT is more common in women (91%) than in men (72%) 2
  • Elderly patients with AVNRT are more likely to have visible P-waves (29%) compared to younger patients (12%) 2

Clinical Pearls

• When evaluating narrow QRS tachycardias, the relationship between the P-wave and QRS complex (RP versus PR intervals) is crucial for determining the mechanism 5
• The absence of visible P-waves or the presence of pseudo R' in V1/pseudo S in inferior leads strongly suggests AVNRT 2
• Visible P-waves after the QRS complex can occur in both AVRT and AVNRT, but are more common in AVRT 1, 2
• In patients with bundle branch block, retrograde P-waves may be more difficult to discern in both types of tachycardia 1