Sometimes an electrocardiogram (ECG) reader will mention an rSR’ on the ECG reading. Sounds really important, doesn’t it? In reality, most of the time it is a benign finding. Here, I will tell you what is an rSR prime (rSR’), and some of the common and uncommon etiologies.
First, The QRS Complex
Not to belittle anyone, but to understand what an rSR’ is, we first need to know the components of the QRS complex.
- Q-wave: The first downward deflection before the R-wave
- R-wave: The first upward deflection of a QRS complex
- S-wave: The first downward deflection after the R-wave
- R prime (R’): The second upward deflection of a QRS complex
- S prime (S’): The second downward deflection after the R-wave
- Subsequent upward deflections: R double prime (R”), R triple prime (R”’), and so on
- Subsequent downward deflections: S double prime (S”), S triple prime (S”’), and so on
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Here are some examples of QRS complexes:
What is an rSR prime (rSR’)?
Now that we know the parts of the QRS complex, an rSR’ is simple. It is an R-wave, followed by an S-wave, followed by another R-wave. In other words, an upward deflection, followed by a downward deflection, followed by another upward deflection. Voila! That’s it. When an ECG reader mentions it, though, he/she is referring to an rSR’ in leads V1 and/or V2. An rSR’ in other leads is typically insignificant. Additionally, this finding typically implies that the QRS interval is normal (0.08 – 0.10 seconds) or only mildly prolonged (0.11 seconds). There is little to no significance if this is seen in the other leads.
Another tidbit is that the reader may write a small “r” or a large “R” to denote which upward deflection is bigger. For example, rSR’ suggests a small R-wave, followed by an S-wave, followed by a large R-wave. Likewise, RSr’ suggests a large R-wave, followed by an S-wave, followed by a small R-wave.
What is the significance of an rSR’ in leads V1 and/or V2?
As mentioned above, most of the time an ECG reader mentions an rSR’ pattern on the ECG, the QRS complex is narrow or only mildly prolonged. A majority of the time this finding is a benign finding from abnormally high lead placement of V1 and V2, a normal variant seen due to normal depolarization of the intraventricular septum, or an incomplete right bundle branch block. Additionally, this pattern can be seen in athletes or people with sunken chests (pectus excavatum) (1). In some cases, the rSR’ is significant. Pathological conditions causing this include Brugada Syndrome, right ventricular enlargement, right ventricular hypertrophy, or abnormal conduction through a bypass tract with preexcitation or Wolff Parkinson White (WPW) (1). In these cases, hopefully, the ECG interpreter is able to tease these diagnoses out and be more specific with his/her reading.
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rSR’ in V1 or V2 with a Wide QRS Complex
An rSR’ in V1 or V2 in a widened QRS complex is abnormal. This may be due to a right bundle branch block (RBBB), preexcitation or Wolff Parkinson White (WPW), or a ventricular beat.
What do I do with a reading of an rSR’?
As you may have guessed by now, most of the time, and rSR’ is a benign finding. It is often from lead misplacement, is a normal variant, or may indicate a slight right ventricular conduction delay. Clinically this finding is insignificant and does not affect the patient’s prognosis. Remember that this finding is really only mentioned with regard to leads V1 and V2. When I read an ECG, I comment further if the rSR’ represents significant or possible significant pathology. I hope that other ECG readers do the same.
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References:
(1) https://onlinelibrary.wiley.com/doi/epdf/10.1111/anec.12241
Baranchuk, A., Enriquez, A., García-Niebla, J., Bayés-Genís, A., Villuendas, R. and Bayés de Luna, A. (2015), Differential Diagnosis of rSr’ Pattern in Leads V1-V2. Comprehensive Review and Proposed Algorithm. Ann Noninvasive Electrocardiol, 20: 7-17. https://doi.org/10.1111/anec.12241
