Third Degree Heart Block ECG Interpretation

Description Part 1

• Third Degree Heart Block is also known as “Complete Heart Block”.
• This name more accurately describes the electrical event or problem occurring within the heart.
• As a result of disease or tissue death, there is a blockage preventing electrical impulses within the atria from entering the ventricular conduction system.
• The outcome of 3rd degree heart block ECG are two independently functioning pacemakers within the heart (typically one is supraventricular, the other is ventricular).
• Essentially, the atria and ventricles are electrically separated (dissociated) from one another.

Description Part 2

• What will be seen are regularly occurring P waves and QRS complexes, but at two distinctly different rates.
• The QRS complexes may occur as a result of impulses coming from the His bundle or the Purkinje network.
• Morphology and rate will often provide clues regarding the locus of ventricular impulse stimulation. A more narrow appearing QRS with a rate greater than 40 generally would indicate the impulse formation is coming from the His bundle. A wide, bizarre QRS with a rate of 40 or less indicates the impulses are originating in the Purkinje network.
• Complete heart block presents with Regular P to P and R to R intervals and a variable P-R interval.

ECG Practice Strip

Analyze this tracing using the five steps of rhythm analysis.