The Telltale Tall R Waves

Philip J. Podrid, MD


October 02, 2018

Figure 2. Courtesy of Dr Podrid


The diagnosis is sinus tachycardia, short PR interval (enhanced AV conduction), and Duchenne muscular dystrophy.

The rhythm is regular at a rate of 100 beats/min. A P wave occurs before each QRS complex (+) with a stable but short PR interval (0.12 sec). The PR interval is shorter than what would be expected for a sinus tachycardia of 100 beats/min, and probably represents enhanced AV nodal conduction. This may be caused by either a rapidly conducting (slick) AV node or a bypass tract of the AV node. Because the QRS complex duration is normal (0.08 sec), indicating conduction to the ventricle via the normal His-Purkinje system, this would be termed a Lown-Ganong-Levine (LGL) pattern caused by an accessory pathway (bypassing conduction through the AV node), known as a "bundle of James."

The QRS complex duration is normal with a normal axis between 0° and +90° (positive QRS complex in leads I and aVF). However, the QRS complex morphology is not normal, with prominent (although not very wide) Q waves in leads I, aVL, and V4-V6 (^), suggesting a lateral wall MI. There is also a tall R wave in lead V1 (←). The possible causes for this finding include:

  • Right ventricular hypertrophy (usually associated with a right axis and P-pulmonale);

  • A posterior wall MI (usually associated with an inferior wall MI);

  • Dextrocardia (with reverse R-wave progression and what looks like right arm/left arm lead switch with a right axis and also negative P and T waves in leads I and aVL);

  • Right-sided leads (with reverse R-wave progression);

  • V1-V3 lead switch (misplaced leads);

  • Wolff-Parkinson-White pattern (with short PR interval and delta wave);

  • Significant counterclockwise rotation of the electrical axis in the horizontal plane;

  • Hypertrophic cardiomyopathy; or

  • Duchenne muscular dystrophy (with a posterolateral infarction pattern).

Because this ECG shows a posterolateral infarction pattern, this is from a patient with Duchenne muscular dystrophy.


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