Criteria for Determining a Second-Degree Type 1 Heart Block
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Article at a Glance
- Second-degree heart block Type I (Wenckebach) is characterized by:
- Regularity: R to R irregular with grouped beats
- Rate: Usually slower than normal
- P Wave: P waves are uniform but not always followed by QRS
- PR Interval: Becomes progressively longer until a P wave is blocked and the QRS is dropped
- QRS Complex: < 0.12 seconds
Criteria to Determine a Second-Degree Type I Heart Block
First, look at the relationship between the P wave and the QRS complex. In a second-degree Type I heart block, you’ll find an increasingly longer PR interval until the QRS complex drops off, unlike a first degree heart block where the PR interval is consistently prolonged but every QRS is conducted.
Related Video – ECG and the Cardiac Cycle Basics
The PR interval becomes increasingly longer until the QRS complex drops off.
In the image above, the second PR interval is longer than the first and so on. The QRS complex drops off, and then it starts over. It’s the telltale sign for a second-degree type 1 heart block.
Summary
To diagnose a second-degree heart block, providers must interpret an ECG diagram, paying close attention to the P waves, PR interval, and QRS complex. During a second-degree type 1 heart block, the PR interval increases until the QRS complex drops off.
Related Video – What are Atrioventricular Blocks?
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