Heart Blocks on ECG

By behereaxum

Summary

Heart blocks look intimidating on an ECG. But once you know what to watch for, each one tells a clear story.

Chapters

  1. Heart blocks look intimidating on an (0s)
  2. Normally, every P wave conducts through (6s)
  3. First degree block: every beat still (13s)
  4. Second degree, Mobitz one: the PR (22s)
  5. Mobitz two: the PR interval stays (31s)
  6. Third degree, complete block: no P (41s)
  7. Check the PR interval, look for (52s)

Transcript

Heart blocks look intimidating on an ECG. But once you know what to watch for, each one tells a clear story. Normally, every P wave conducts through the AV node to a QRS, with a steady PR interval under two hundred milliseconds. First degree block: every beat still conducts, but the PR interval is fixed and long, over two hundred milliseconds. No beats are dropped. Second degree, Mobitz one: the PR interval lengthens beat after beat, until one P wave fails and a QRS is dropped. Then the cycle resets. Mobitz two: the PR interval stays constant, then suddenly a QRS drops without warning. Because it can progress rapidly to complete block, this rhythm is far more dangerous. Third degree, complete block: no P wave conducts at all. P waves and QRS complexes march completely independently, at their own rates. The atria and ventricles are fully dissociated. Check the PR interval, look for dropped beats, and you'll recognize every block.