Causes

  Right bundle branch blockRight bundle branch block (most common).

  Right ventricular hypertrophy

  Posterior myocardial infarction

  Wolff-Parkinson-White (WPW) syndrome

  Dextrocardia

  Hypertrophic cardiomyopathy

  Misplacement of the chest electrodes

  Normal variant




Reference

  Am J Emergency Medicine 2001;19:504-513.





ECG 1. The compact ECG above is from a 51 years-old man. Two years ago, he had experienced acute posterior myocardial
infarction due to total occlusion of the dominant Circumflex (Cx) coronary artery.
The R wave in leads V1 and V2 are taller (and wider) than expected.





ECG 2a. The ECG above belongs to a 46 years-old man with mild mitral stenosis and frequent attacks of palpitation.
At first glance, the q waves in inferior leads and tall R waves in lead V1 suggest a diagnosis of old inferoposterior
myocardial infarction. The delta waves in some patients with WPW syndrome may imitate q waves suggesting old myocardial
infarction.
In the above ECG,
lead V3 shows a giant delta wave, while leads V4 and aVL show subtle delta waves.

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ECG 2b. The above ECG was recorded during one of his palpitation attacks.
During the tachycardia, AV-node, His bundle and Purkinje fibers are used for conduction to the ventricles
and the accessory pathway is used for re-exciting the atria:
orthodromic AVRT (AV Reciprocating Tachycardia).
Because of this, delta wave is not seen during the tachycardia.
Because of this, tall R wave in lead V1 is not seen during the tachycardia.
Because of this, the ECG above looks very similar to the post-ablation resting ECG below (ECG 9c).

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ECG 2c. Electrophysiologic study showed left posterolateral accessory pathway in this patient.
The above ECG was recorded after ablation of the accessory pathway.
Inferior leads do not show q waves anymore. No more suggestion of old inferoposterior myocardial infarction.
Lead V3, V4 and aVL also do not show delta waves any more.

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