How to recognize heart blocks on an ECG
Other platforms explain it with text and video. In VMS you practice it on the patient.
Heart blocks range from harmless to life-threatening. Telling them apart decides whether the patient needs only watching or urgent pacing.
Step by step
Check the patient
Look for dizziness, fainting, low blood pressure or chest pain. A slow rhythm with symptoms needs urgent care per ACLS. [1]
Measure the PR interval
Measure every PR interval in a long rhythm strip. Normal is 0.12 to 0.20 seconds. [2]
Match P waves to QRS
Check that every P wave is followed by a QRS. Look for P waves hidden in T waves. [2]
March out the P waves
Mark the distance between P waves and see if they keep coming regularly, even when no QRS follows. [2]
Name the pattern
Use the table below to match PR behavior and dropped beats to the type of block. [2]
Act on dangerous blocks
Second degree type II and third degree block can suddenly worsen. Place pads, call for help and prepare for pacing; atropine often does not work in these blocks. [1]
Common errors
- Confusing a blocked early atrial beat with a heart block.
- Missing P waves hidden in the T waves.
- Relying on atropine alone in type II or third degree block.
Heart block patterns [2]
| Block | PR interval | Dropped beats |
|---|---|---|
| First degree | Longer than 0.20 seconds, constant | None |
| Second degree type I (Wenckebach) | Gets longer each beat | Then one QRS drops and the cycle repeats |
| Second degree type II | Constant, normal or long | QRS drops suddenly without warning |
| Third degree (complete) | Varies; P waves and QRS are unrelated | Atria and ventricles beat on their own |
Practice it in VMS
In VMS you do this on the patient, not on paper: every step goes on the checklist with a score, and in Teach mode Blocky tells you what comes next.
VMS cases that train this skill
Sources
- AHA Guidelines for CPR and ECC
- NCCPA PANCE Content Blueprint
- AAMC Core Entrustable Professional Activities (Core EPAs)
Facts and steps follow AAMC Core Entrustable Professional Activities (Core EPAs); NCCPA PANCE Content Blueprint. VMS is not affiliated with these organizations. Updated: 2026-10-11.