Vent. rate 64 bpm
PR interval 122ms
QSR duration 120ms
What do you think this is?
1: left bundle branch block
2: right bundle branch block
3: true posterior wall MI
4: some other interpretation
Do you think this ECG is helpful in explaining the probable cause of this patient's symptoms?
This is ventricular pre-excitation (WPW)
This ECG shows sinus rhythm at a rate just over 60 bpm. In measuring the intervals, two results stand out. First, the PR interval is short. The computer measures it at 122 ms (0.122 sec) which would be just inside the normal range. It is actually shorter than that. Look at V2 for an example. The PR is just a hair over 80ms. The other abnormal interval is the QRS duration of 120ms (0.12 sec). Whenever the QRS duration is 120 ms or greater during sinus rhythm, the next goal is to determine why.
The most common choice is between complete right bundle branch block or left bundle branch block. This isn't LBBB because the QRS is upright in V1. It could therefore be RBBB as RBBB results in tall R-waves in V1 or RSR' complexes in V1. However the broad terminal S-waves of RBBB, typically seen in leads I and V6, are not seen in this ECG. Some other explanation is required.
This is the VENTRICULAR PRE-EXCITATION pattern of Wolff-Parkinson-White Syndrome or WPW. It is characterized by a short PR-interval, a broadened QRS and Delta waves. The slurred upstroke of the QRS, called a delta wave, is best seen in leads V2-V6. The reason they are not seen well in the limb leads is that the delta wave vector has resulted in nearly isoelectric delta waves in those leads. Delta waves are actually caused by rapid transmission of the electrical impulse via an anomalous, acessory pathway. The electrocardiogropher can predict the location of this accessory pathway by plotting the mean direction of the delta wave vector.
Accessory pathways make an individual susceptible to PSVT (paroxysmal supraventricular tachycardia) by providing a made-to-order means of reentry. Therefore, the probable cause of this patient's presenting symptoms was well explained by his resting electrocardiogram (palpitation due to PSVT).
Subsequent electrophysiologic studies demonstrated a postero-lateral bypass tract which was successfully ablated with radiofrequency electrical energy. He no longer has attacks of palpitation, and (factoid) his first heart sound is a little softer than it was before.
HAPPY LEARNING :-)
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