ECG Quiz 49 – Discussion
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PP interval is half that of the RR interval. The P wave marked by red arrow is non conducted, while the P wave followed by the blue arrow is followed by a QRS complex. So it is a 2:1 AV conduction, the highest grade of second degree AV block. It is possible that longer recordings might show slight changes in P-QRS relationship so that it could even be complete AV block appearing as 2:1 AV block for a short period of time during the ECG recording. As the QRS complex is narrow, it is likely to be supra Hisian block at the AV nodal level rather than an infra Hisian block. Moreover, ECG shows features of hyperacute inferior wall myocardial infarction, which is associated with AV nodal block and not infra Hisian block.
Hyperacute inferior wall infarction is evidenced by the prominent upsloping ST elevation (Pardee’s sign) in the inferior leads (II, III and aVF) with upright T waves. ST elevation is significantly more in lead III than in lead II, suggesting that it is due to an occlusion of the right coronary artery rather than the left circumflex coronary artery. ST depression is seen in the anterior and lateral leads which could be either a reciprocal change or ischemia at a distance. Final proof will come from the coronary angio prior to primary angioplasty, which will be the therapeutic option of choice in this case. A temporary pacing wire will also be needed as there is a chance of development of complete heart block and symptomatic bradycardia.
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