Heart Disease

Left axis deviation occurs when the QRS axis falls between -30 and -90. There are a variety of causes, including left anterior fascicular block and left ventricular hypertrophy. See the ECG basics section on determining axis for details.

In second-degree atrioventricular nodal block — also known as Wenckebach block or Mobitz Type I AV block — varying failure of conduction through the AV node occurs, such that some P waves may not be followed by a QRS complex.

Wellen's phenomenon occurs when biphasic T waves are seen in leads V1-V3, or deep symmetric inverted T waves are seen in the precordial leads.

When right atrial enlargement occurs, it does not take longer for cardiac action potentials to travel through the atrial myocardium (similar to left atrial enlargement).

The Lown-Ganong-Levine (LGL) syndrome occurs when an accessory pathway is congenitally present that directly connects the atria to the ventricles, bypassing the AV node similar to the Wolff-Parkinson-White (WPW) syndrome.

Chapman’s sign is used to diagnose an acute myocardial infarction in the setting of a left bundle branch block and consists of a notch in the upslope of the R wave in lead I, aVL or V6.

Dextrocardia occurs when the heart is positioned in the right side of the chest instead of the left.