Approach to a patient with PR interval abnormality in ECG

The PR interval is the time from the onset of the P wave to the start of the QRS complex.
It reflects conduction through the AV node.
The normal PR interval is between 120 – 200 ms (0.12-0.20s) in duration (three to five small squares).
If the PR interval is > 200 ms, first degree heart block is said to be present.
PR interval < 120 ms suggests pre-excitation (the presence of an accessory pathway between the atria and ventricles) or AV nodal (junctional) rhythm.

1. Fundamentals of ECG
Approach to a patient with PR interval
abnormalities
Dr. Md.ToufiqurRahman
MBBS, FCPS, MD, FACC, FESC, FRCP, FSCAI,
FCCP,FAPSC, FAPSIC, FAHA,FACP
Professor & head of Cardiology
CMMC, Manikganj
Ex professor of cardiology,
NICVD, Dhaka

2. Fundamentals of ECG
PR interval abnormalities in ECG
The normal PR interval is between 120 –200 ms(0.12-0.20s) in
duration (three to five small squares).
If the PR interval is > 200 ms,first degree heart blockis said to be present.
PR interval < 120 mssuggestspre-excitation(the presence of an
accessory pathway between the atria and ventricles) orAV nodal
(junctional) rhythm.
ThePR intervalis the
time from the onset of
the P wave to the start
of the QRS complex.
It reflects conduction
through the AV node.

3. Fundamentals of ECG
PR interval abnormalities in ECG
Case-1: A 45 years old gentleman presented with
hypertension and taking beta blocker -atenolol for last 08
years. He had the following ECG.

4. Fundamentals of ECG
PR interval abnormalities in ECG
Case-2: A 45 years old gentleman diabetic, hypertensive and
smoker presented with severe central chest pain with
excessive sweating and vomiting for last 2 hours.On
emergency he had the following ECG.

5. Fundamentals of ECG
Case-3
A 15 years old boy presented with several episodes of sore
throat, palpitations and shortness of breath. His ASO titre
and CRP were raised. He had the following ECG.

6. Fundamentals of ECG
Causes of First Degree Heart Block
Increased vagal tone
Athletic training
Inferior MI
Mitral valve surgery
Myocarditis(e.g. Lyme disease)
Electrolyte disturbances (e.g.Hyperkalaemia)
AV nodal blocking drugs (beta-blockers,calcium
channelblockers,digoxin, amiodarone)
May be a normal variant

7. Fundamentals of ECG
Second degree AV block (MobitzI) with prolonged PR interval
Second degree heart block, Mobitztype I
(Wenckebachphenomenon).
The baseline PR interval is prolonged, and
then further prolongs with each successive
beat, until a QRS complex is dropped.
The PR interval before the dropped beat is
the longest (340ms), while the PR interval
after the dropped beat is the shortest
(280ms).

8. Fundamentals of ECG
Second degree AV block (MobitzI) with prolonged PR interval
Second degree heart block, Mobitztype I (Wenckebach
phenomenon).
The baseline PR interval is prolonged, and then further prolongs
with each successive beat, until a QRS complex is dropped.
The PR interval before the dropped beat is the longest (340ms),
while the PR interval after the dropped beat is the shortest
(280ms).
The P-P interval remains relatively constant
Thegreatest increasein PR interval duration is typicallybetween
the first and second beats of the cycle.
The RR interval progressively shortens with each beat of the cycle.
The Wenckebachpattern tends to repeat in P:QRS groups with
ratios of 3:2, 4:3 or 5:4.

9. Fundamentals of ECG
What are the causes of WenckebachPhenomenon?
Drugs:beta-blockers,calcium channel
blockers,digoxin, amiodarone
Increased vagal tone (e.g. athletes)
Inferior MI
Myocarditis
Following cardiac surgery (mitral valve
repair,Tetralogy of Fallotrepair)

10. Fundamentals of ECG
Short PR interval (<120ms)
A short PR interval is seen with:
Preexcitationsyndromes
AV nodal (junctional)
rhythm.

11. Fundamentals of ECG
Case-4
A 21 years old man was admitted in CCU with the diagnosis of
Supraventricular tachycardia (SVT) and was being treated with
intravenous adenosine and reverted to sinus rhythm. Now he has the
following ECG at sinus rhythm.

12. Fundamentals of ECG
Case-5
A 43 years old lady presented with palpitation and
chest discomfort. She had the following ECG.

13. Fundamentals of ECG
Pre-excitation syndromes
Wolff-Parkinson-White(WPW) andLown-Ganong-
Levine(LGL)syndromes.
Theseinvolvethepresenceofanaccessorypathway
connectingtheatriaandventricles.
Theaccessorypathwayconductsimpulsesfasterthannormal,
producingashortPRinterval.
Theaccessorypathwayalsoactsasananatomicalre-entry
circuit,makingpatientssusceptibletore-entry
tachyarrhythmias.
Patientspresentwithepisodesofparoxsymal
supraventriculartachycardia(SVT),specifically
atrioventricularre-entrytachycardia(AVRT),and
characteristicfeaturesontheresting12-leadECG.

14. Fundamentals of ECG
Pre-excitation syndromes
ECG showing Pre-excitation syndrome ( WPW
syndrome-short PR interval and delta wave)

15. Fundamentals of ECG
Wolff-Parkinson-White syndrome
The characteristic features ofWolff-Parkinson-White
syndromeare a short PR interval (<120ms), broad
QRS and a slurred upstroke to the QRS complex,
thedelta wave.

16. Fundamentals of ECG
Lown-Ganong-Levine syndrome
The features ofLown-Ganong-Levine syndromeLGL
syndromeare a very short PR interval with normal P
waves and QRS complexes and absent delta waves.

17. Fundamentals of ECG
Characteristics of Lown-Ganong-Levine syndrome
Accessory pathway composed ofJames fibres.
Short PR interval (<120ms);
normal P wave axis;
normal/narrow QRS morphology in the
presence of paroxysmal tachyarrhythmia.
Existence of LGL is disputed and the
condition may not actually exist…the term
should not be used in the absence of
paroxysmal tachycardia

18. Fundamentals of ECG
AV nodal (junctional) rhythm
oJunctionalrhythms are narrow complex, regular rhythms
arising from the AV node.
oP waves are either absent or abnormal (e.g. inverted)
with a short PR interval (=retrograde P waves).
oECG: Accelerated junctionalrhythm demonstrating
inverted P waves with a short PR interval (retrograde P
waves)

19. Fundamentals of ECG
AV nodal (junctional) rhythm
oJunctionalrhythms are narrow complex, regular rhythms
arising from the AV node.
oP waves are either absent or abnormal (e.g. inverted)
with a short PR interval (=retrograde P waves).
oECG: Accelerated junctionalrhythm demonstrating
inverted P waves with a short PR interval (retrograde P
waves)

20. Fundamentals of ECG
History of LGL syndrome
1921-1952–associationofparoxysmaltachycardia,shortAVconductiontime,
andnormalQRScomplexesreportedacross11cases,butusuallyattributedto
beingavariantofWolff-Parkinson-Whitesyndrome.
1938–Clerc,LevyandCritescofirstdescribedECGfindingsofashortPRinterval,
normalQRScomplex,andparoxysmaltachycardia.
1952–Lown,GanongandLevineperformedthefirststudycorrelatingthe
characteristicECGchangeswithclinicalfindings,whichdistinguishedpatients
withparoxysmaltachycardia,shortPRinterval,andnormalQRScomplexesfrom
Wolff-Parkinson-Whitecharacteristics.
1961–Jamesdescribedaccessorypathwayconnectionsbetweentheatriaand
distalatrioventricularnode,whichmayhavearoleinthepathophysiologyofLGL
syndrome
1975–Brechenmacherdescribedaccessorypathwaysbetweentheatriaand
bundleofHis,whichmayalsobeinvolvedinLGLsyndrome