October 05, 2010

USMLE 2 Question 6

In a patient with Wolff Parkinson White syndrome, the most characteristic finding on an ECG is:

a) ST segment elevation
b) inversion of lead I
c) Q wave measuring 50% of QRS height
d) delta waves
e) ST segment depression


The correct answer is D


In WPW pre-ecxitation syndrome findings on the ECG include delta wave (initial slurring) of the QRS complex and short PR interval.

The combination of PR interval <0.12 sec, a delta wave at the beginning of the QRS complex, and a rapid, regular tachyarrhythmia has been termed the Wolff-Parkinson-White (WPW) syndrome.

The PR interval is short because the descending electrical impulse bypasses the normal AV nodal conduction delay. The delta wave is produced by slow intramyocardial conduction that results when the impulse, instead of being delivered to the ventricular myocardium via the normal conduction system, is delivered directly into the ventricular myocardium via an abnormal or anomalous bundle.

The QRS duration is prolonged because it begins too early.

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