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PR segment

Instructors' Collection ECG: Sinus Tachycardia

Wed, 10/09/2019 - 20:42 -- Dawn

This ECG is from a collection of tracings that, sadly, have no patient information.  It is interesting nonetheless, and we would love to hear your thoughts on it.

ECG Findings:  The rhythm is sinus tachycardia, at a rate of 120 bpm.  The QRS is narrow at .08 seconds (82 ms).  While the PR interval is normal, at .14 seconds (140 ms), the PR segment is very short. The PR segment is the line between the end of the P wave to the beginning of the QRS complex.  This can indicate the presence of an accessory pathway that bypasses the AV node, or of faster conduction within the AV node. The P waves in the inferior leads II, III, and aVF barely meet voltage criteria for right atrial enlargement,  but the P waves in V1 do not have the usual prominent positive deflection one would expect with RAE.  Even with the short PR segment, the segment appears to be elevated in the inferior leads, without any reciprocal PR depression.  The PR segment is where atrial repolarization occurs (the atrial “T” wave). There are many conditions that can elevate or depress PR segments, and without a patient story here, we can’t guess at the cause.  If you are an instructor, this would be a good ECG to illustrate why we use the TP segment to determine the “isoelectric line”, rather than the PR segment.

The inferior ST segments are very flat, which is not normal, while the rest of the ST segments display the normal concave up “smile” shape.  Serial ECGs would no doubt be helpful here, to recognize changes in the ST segments.

Bottom Line:  It would be much easier to make a determination about the causes of these subtle changes if we had patient information.  However, this ECG is still valuable as an exercise in measuring intervals, and as an example of short PR segment. It is also a good example of a fairly fast sinus tachycardia.  We would love to hear our visitors’ thoughts on this tracing.

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