Pseudo-S and Pseudo-R’ Waves

As we have seen, the P wave in the junctional rhythms can be inverted and can occur slightly after the QRS complex. In junctional tachycardias, that retrograde P wave can look just like a slurred S wave in leads II, III, and aVF and an R or R’ wave in lead V1. To differentiate these waves from “true” S and R’ waves, they are known as pseudo-S and pseudo-R (or pseudo-R’) waves (Figures 24-2 and 24-3). The “pseudo” part is added to reflect the fact that these appear to be S waves and R waves but are not true waves; rather, they are merely an electrocardiographic reflection caused by the retrograde P waves.

A rhythm strip from lead 2 shows a sharp peak of the QRS complex, a small and subtle dip of the pseudo S wave, and a wide and curved peak of the T wave. P wave is missing.

Figure 24-2 Pseudo-S wave in lead II, commonly found in junctional tachycardias.

© Jones & Bartlett Learning.

A rhythm strip from lead V1 shows a sharp dip of the QRS complex, a small and subtle peak of the pseudo R prime wave, and a wide and curved dip of the T wave. P wave is missing.

Figure 24-3 Pseudo-R’ wave in lead V1, commonly found in junctional tachycardias.

© Jones & Bartlett Learning.

These pseudo waves sometimes cause confusion when interpreting an ECG. But, they can also add a great clue to the correct arrhythmic diagnosis. Whenever you see a narrow-complex tachycardia with no obvious P waves but an s wave in the inferior leads and a small r’ in lead V1, think of an accelerated junctional rhythm, a junctional tachycardia, or AV nodal reentry tachycardia (which we will discuss in the next chapter).

ARRHYTHMIA RECOGNITION

Accelerated Junctional Rhythm

Rate: > 60 to 100 BPM
Regularity: Regular
P wave:

Morphology:

Upright in II, III, and aVF:

 Variable

Different, if present

No
P:QRS ratio: Variable
PR interval: Variable
QRS width: Normal
Grouping: None
Dropped beats: None

ARRHYTHMIA RECOGNITION

Junctional Tachycardia

Rate: > 100 to 200 BPM
Regularity: Regular
P wave:

Morphology:

Upright in II, III, and aVF:

 Variable

Different, if present

No
P:QRS ratio: Variable
PR interval: Variable
QRS width: Normal
Grouping: None
Dropped beats: None

DIFFERENTIAL DIAGNOSIS

Accelerated Junctional Rhythm and Junctional Tachycardia

  1. Ischemic heart disease, acute myocardial infarction (AMI)
  2. Intracardiac surgery
  3. Digitalis toxicity
  4. Myocarditis
  5. Electrolyte disorders

This list is not all-inclusive.