Mori Quartet Part 2 - "Repetitions"

This is the second of four ECGs that have been kindly provided by Dr Alfredo Mori, an Emergency Physician from Melbourne, Australia.

Figure 1

This is the ECG of a 36 year old man who presented with a spontaneous pneumothorax. 

+ Describe the main findings in this ECG

The major change involves the heart rhythm, with the R-R intervals increasing and then decreasing. Figure 2 shows the rhythm strip from the 12 lead ECG

Figure 2

There are 9 complexes in the rhythm strip.

  • The first complex has a normal P wave, the PR interval is 0.16 seconds and the QRS complex and the ST-T wave segments are normal.
  • Complexes 2 to 5 have R-R intervals which progressively decrease from 1360 msec to 840 msec. Complexes 3 to 5 seem to lack P waves, but when we check the QRS complexes in the other limb leads that are inscribed at the same time as the complexes in the (Lead II) rhythm strip we find that they have P waves e.g the second complex in Lead I (upright P wave) and the second complex in Lead III (inverted P wave), and the complexes in Leads aVR to aVF (all have upright P waves). The absence of a visible P wave in complexes 3 to 5 is explained by a shift in the P wave axis from (about) + 60 degrees in complex 1 to (about) - 30 degrees in complexes 3 to 5.

The ventricular rate between complexes 1 to 3 is about 40 beats per minute, and betweem complexes 3 to 5 is about 60 beats per minute.

Complexes 5 to 8 are all preceded by a P wave and have the same R-R interval (800 - 840 msec), the ventricular rate between complexes 5 and 8 is about 80 beats per minute.

The R-R interval between complex 8 and 9 has increased to 1360 msec, and a P wave is not seen before complex 9 but is seen in the corresponding complexes in Leads V4 to V6.

Main Points:

  • The ventricular rate of 40 to 80 beats per minute is slow in the setting of a spontaneous pneumothorax. This may be due to increased vagal tone.
  • The rhythm is irregular, with a sequence of slow → fast → slow. This is consistent with sinus arrhythmia.
  • The marked changes in the P wave axis during the sinus arrhythmia could be due to displacement/shift of the atria because of presence of a spontaneous pneumothorax.


The British band Blueneck released their album Repetitions in 2011, which included a song called "Pneumothorax"