A sinus tachycardia is present with a frequency of 112 beats/min (PP interval 540 ms). At that sinus rate, the PR interval measures 240 ms and is therefore definitely prolonged. In addition, as indicated under lead aVF, in the middle of the tracing there is sudden doubling of the PP interval (1080 ms), suggesting a 2:1 sinoatrial block. The P wave after the pause is conducted to the ventricle and followed by an atrial premature beat after 400 ms, which is not conducted to the ventricle; 700 ms later, a sinus P wave is conducted to the ventricle but with a QRS complex showing a left bundle branch block configuration. That QRS complex, labeled C in Figure 1
under lead V6
, occurs 1100 ms after the previous narrow QRS complex, labeled B (the B-C interval). QRS complex B is preceded by a narrow QRS complex by 940 ms (the A-B interval). Therefore, the occurrence of left bundle branch block in QRS complex C can be explained by bradycardia-related phase 4 block in the left bundle branch (B-C interval > A-B interval). This is not an unusual finding during bradycardia in inferior myocardial infarction (IMI).
- Lie K.I.
- Wellens H.J.
- Schuilenburg R.M.
- Durrer D.
Mechanism and significance of widened QRS complexes during atrioventricular block in acute inferior myocardial infarction.