Retrograde P-waves in Supraventricular Tachycardias

Characteristics of 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, according to the American Heart Association 1, 2
These retrograde P-waves typically appear as a narrow negative deflection in the inferior leads or a slightly positive deflection at the end of the QRS complex in lead V1, as noted by the American College of Cardiology 1, 3
The RP interval is very short (RP < 90 ms from the surface ECG), creating what is known as a "short RP" tachycardia, with a strength of evidence level of IIa, as recommended by the European Society of Cardiology 3, 4

In orthodromic AVRT, retrograde P-waves are usually clearly visible in the early part of the ST-T segment, with the American Heart Association stating that this occurs in 90-95% of AVRT episodes 1, 2
The retrograde conduction occurs over the accessory pathway, with the P-wave typically appearing separate from the QRS complex, as described by the Heart Rhythm Society 1, 3
The RP interval is longer than in typical AVNRT but still creates a "short RP" tachycardia (RP < PR), with a level of evidence of IIb, as noted by the American College of Cardiology 3, 4

In atypical forms of AVNRT, the P-wave is closer to the subsequent QRS complex, creating a "long RP" tachycardia, as stated by the European Society of Cardiology 1, 2
In the permanent form of junctional reciprocating tachycardia (PJRT), the accessory pathway has decremental conduction properties that result in delayed atrial activation and a long RP interval, with the American Heart Association recommending consideration of this diagnosis in patients with long RP intervals 1, 5
PJRT typically shows deeply inverted retrograde P-waves in leads II, III, and aVF, as described by the Heart Rhythm Society 5, 6

When evaluating narrow QRS tachycardias, the relationship between the P-wave and QRS complex (RP versus PR intervals) is crucial for determining the mechanism, with the American College of Cardiology stating that this is a key factor in diagnosis 7
In patients with bundle branch block, retrograde P-waves may be more difficult to discern in both types of tachycardia, as noted by the European Society of Cardiology 1, 2