Around the Block

These three ECGs are from a 70 year old man. The first ECG (ECG_A) was taken 6 months before the next two ECGs. The last two ECGs  were taken after an episode of syncope. 

Figure 1. ECG_A taken 6 months before the current presentation

Figure 1. ECG_A taken 6 months before the current presentation

Figure 2. ECG_B_1 taken on arrival at 1800

Figure 2. ECG_B_1 taken on arrival at 1800

Figure 3. ECG_B_2 taken on arrival at 1842

Figure 3. ECG_B_2 taken on arrival at 1842

What are the main abnormalities in each ECG?

Comments on ECG_A

The main findings are:  

  • Leads I, II, aVR, aVL , V1 and V2 are not horizontal, but  have a gentle downwards slope from left to right that is annoying but does not interfere with assessment of the tracing.
  • Rhythm and rate: Sinus rhythm is present, with an atrial and ventricular rate of about 75 beats per minute
  • PR interval: This is 0.20 seconds
  • QRS morphology and axis: qR complexes are present in I and aVL, and there is left axis deviation. This indicates that there is a left anterior fascicular block (LAFB).   A complete right bundle branch block (RBBB) is also present.  
  • There is positive concordance in V1 to V5 (i.e. the dominant deflection is upright in these leads. This has no diagnostic implications in this case, but  in broad complex tachycardias the presence of concordance favours a ventricular site for the tachycardia).
  • The T waves are upright in V2 and V3 rather than the expected secondary change in RBBB of T inversion.  

 

Comments on ECG_B_2

The main findings are

  • P waves are present, with an  atrial rate slightly faster than 100 beats per minute. The ventricular rate is  about 35 beats per minute, and AV dissociation is present. The patient has developed complete heart block.
  • The  QRS complexes have a RBBB pattern with positive concordance in the precordial leads, and there is right axis deviation suggesting a left posterior fascicular block.

 

Comments on ECG_B_2

The main findings are

  • Complete heart block is present, with an atrial rate of about 88 beats per minute and  a ventricular rate of about 35 meats per minute.
  • The  QRS complexes have a RBBB pattern with left axis deviation. The  morphology of the ventricular complexes in this ECG differs from that in the previous ECG, even though both are consistent with RBBB.

 

The development of complete heart block means that the patient will need a pacemaker. The changes in the complexes in Leads I, II and III in the three ECGs are shown in Figure 4, and show left axis deviation, right axis deviation and then left axis deviation.

Figure 4. Comparison of  leads I to III  from the ECGs of Case C_0004. A: ECG taken 6 months before presentation. B: ECG taken at 1800 on presentation. C: ECG taken at 1842 on presentation

Figure 4. Comparison of  leads I to III  from the ECGs of Case C_0004. A: ECG taken 6 months before presentation. B: ECG taken at 1800 on presentation. C: ECG taken at 1842 on presentation

The change in axis over a short time interval after the development of complete heart block  could be explained by a (escape) pacemaker located  in the left anterior fascicle at 1800, and an (escape) pacemaker located  in the left posterior fascicle at 1842.