2nd part ECG basics PR interval and heart block
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This document discusses PR interval and heart block. It defines the PR interval as the time from the beginning of the P wave to the beginning of the QRS complex, normally ranging from 120-200ms. Abnormal PR intervals can be shortened or prolonged. A shortened PR interval may indicate preexcitation syndromes like WPW syndrome or AV junctional rhythms. A prolonged PR interval suggests different degrees of heart block, from first degree block with a constant delay, to second degree blocks like Mobitz I and II, and third degree or complete heart block where there is no relationship between P waves and QRS complexes.
2nd part ECG basics PR interval and heart block
- 1. ECG BASICSECG BASICS 22ndnd LectureLecture PR interval and Heart BlockPR interval and Heart Block By Salah Mabruok Khalaf South Egypt Cancer Institute 2017 Course of Medical Oncology Medical Oncology department
- 2. PR interval
- 3. PR interval • Definition: from the beginning of the P-wave to the beginning of the QRS complex . • PR = Atr Depolar + AVN Delay = P wave + isoelectric line = 2.5 + (0.5-2.5) = 3-5 ss
- 4. Abnormal PR interval • It is an interval • So its abnormalities either 1- Shortened OR 2- Prolonged According impulse passage through natural block (AVN) AVN Atrium Ventricle
- 5. Short PR: < 3 ss 1-Preexcitation syndromes: – WPW (Wolff-Parkinson-White) Syndrome. – LGL (Lown-Ganong-Levine) 2-AV Junctional Rhythms. 3-Ectopic atrial rhythms originating near the AV node. 4-Normal variant
- 6. WPW Syndrome • An accessory pathway (called the "Kent" bundle) connects the right atrium to the right ventricle (see diagram below) or the left atrium to the left ventricle, and this permits early activation of the ventricles causing: • 1-short PR interval. • 2- delta wave • 3- Tall R wave • 4- Wide QRS
- 7. • Localising the accessory pathway • An accessory pathway, bundle of Kent, exists between atria and ventricles and causes early depolarisation of the ventricle. The location of the pathway may be deduced as follows:- • LOCATION V1 V2 QRS axis left posteroseptal (type A) +ve +ve left right lateral (type B) -ve -ve left left lateral (type C) +ve +ve inferior (90) right posteroseptal -ve -ve left anteroseptal -ve -ve normal
- 8. LGL (Lown-Ganong-Levine( • An AV nodal bypass track into the His bundle exists, and this permits early activation of the ventricles without a delta-wave because the ventricular activation sequence is normal. Atrium VentricleAVN
- 9. Lown Ganong Levine Syndrome short PR interval, less than 3 small squares (120 ms( nodelta wave
- 10. AV Junctional Rhythms with retrograde atrial activation (inverted P waves in II, III, aVF): Retrograde P waves may occur before the QRS complex (usually with a short PR interval):
- 11. Ectopic atrial rhythms originating near the AV node (the PR interval is short because atrial activation originates close to the AV node; the P wave morphology is different from the sinus P)
- 12. II- Prolonged PR • >0.20s > 5 ss • In Heart block = AVN block: • First degree AV block • Second degree AV block – Type I (Wenckebach) – Type II (Mobitz) • Third degree AV block = complete heart block
- 13. First Degree AV Block • PR interval is constant = same delay in each one but there is still one P-wave per QRS.
- 14. First Degree AV Block
- 15. Second degree AV Block: • Mobitz I Block (Wenckebach phenomenon): Here there is progressive PR interval prolongation until a P wave fails to conduct. NO QRS P P PPP
- 16. Mobitz I Block
- 17. Mobitz II Block: sudden absent QRS complex P PPPP
- 18. Mobitz II Block • 2:1 or 3:1 Block: Occurs when every second or third P wave conducts to the ventricles. P- R interval remains normal in the conducted beats.
- 19. Mobitz II Block
- 20. Third degree (complete) AV Block: There will be no relationship between P-wave (atrial) rate and QRS complex (ventricular) rate (AV Dissociation). QRS complexes tend to be abnormally shaped due to abnormal spreading of depolarization across the ventricles.
- 21. 40 bpm• Rate? • Regularity? regular no relation to QRS wide (> 0.12 s) • P waves? • PR interval? none • QRS duration? Interpretation? 3rd Degree AV Block