Chest pain and diaphoresis. BP 80/50. Describe and interpret his ECG
Describe and interpret this ECG
ECG ANSWER and INTERPRETATION
This is a repeat ECG of the previous patient, demonstrating:
- Inferior STEMI — STE in II, III, aVF with reciprocal change in I and aVL.
- Evidence suggesting RV infarction — STE in III > II.
- Evidence confirming RV infarction — STE and hyperacute T wave in V4R.
- Evolving second degree AV block with alternating 2:1 block and 3:2 Wenckebach cycles.
This ECG pattern is diagnostic of a right coronary artery occlusion.
Rhythm Strip Explanation
- Arrows indicate the position of P waves.
- Black arrows indicate conducted P waves.
- Red arrows indicate non-conducted P waves — some of these are concealed within the preceding T wave, causing a small bump at the back of the T wave.
- Complexes cluster together in groups with either 2:1 conduction or as 3:2 Wenckebach cycles, with prolongation of the PR interval prior to the non-conducted P wave.
- The number above each P wave denotes its position in the sequence.
Bradycardia and AV Block in Inferior STEMI
Up to 20% of patients with inferior STEMI will develop either second- or third degree heart block.
There are two presumed mechanisms for this:
- The conduction block may develop either as a step-wise progression from 1st degree heart block via Wenckebach to complete heart block (in 50% of cases) or as abrupt onset of second or third-degree heart block (in the remaining 50%).
- Patients may also manifest signs of sinus node dysfunction, such as sinus bradycardia, sinus pauses, sinoatrial exit block and sinus arrest. Similarly to AV node dysfunction, this may result from increased vagal tone or ischaemia of the SA node (the SA nodal artery is supplied by the RCA in 60% of people).
- Bradyarrhythmias and AV block in the context of inferior STEMI are usually transient (lasting hours to days), respond well to atropine and do not require permanent pacing.