Heart Disease

Third-degree atrioventricular nodal block, also known as third-degree heart block or complete heart block, occurs when no action potentials conduct through the AV node.

In second-degree type II AV nodal block (a.k.a. Mobitz Type II AV block), the AV node becomes completely refractory to conduction on an intermittent basis.

The ECG criteria for a right bundle branch block include the following:

The ECG criteria for a left bundle branch block include:

The TP segment is the portion of the ECG from the end of the T wave to the beginning of the P wave.

The QT interval is the time from the beginning of the QRS complex to the end of the T wave. Review the basics and see an ECG example.

The T wave occurs after the QRS complex and is a result of ventricular repolarization.

The S wave is the first downward deflection of the QRS complex that occurs after the R wave. However, a S wave may not be present in all ECG leads in a given patient.

The R wave is the first upward deflection after the P wave and part of the QRS complex. The R wave morphology itself is not of great clinical importance but can vary at times.