Approach to a patient with PR interval abnormality in ECG
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The document discusses the fundamentals of ECG interpretation focusing on PR interval abnormalities, including definitions of normal PR intervals and conditions such as first-degree heart block, Mobitz type I second-degree block, and pre-excitation syndromes. It provides case studies to illustrate these abnormalities and their clinical implications, as well as historical context regarding the Lown-Ganong-Levine syndrome. The effects of various factors like medications and vagal tone on these conditions are also examined.
Approach to a patient with PR interval abnormality in ECG
- 1. Fundamentals of ECG Approach to a patient with PR interval abnormalities Dr. Md.Toufiqur Rahman 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 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. 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.
- 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 channel blockers, digoxin, amiodarone) May be a normal variant
- 7. Fundamentals of ECG Second degree AV block (Mobitz I) with prolonged PR interval Second degree heart block, Mobitz type 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).
- 8. Fundamentals of ECG Second degree AV block (Mobitz I) with prolonged PR interval Second degree heart block, Mobitz type 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 The greatest increase in PR interval duration is typically between the first and second beats of the cycle. The RR interval progressively shortens with each beat of the cycle. The Wenckebach pattern 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 Wenckebach Phenomenon? 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 Fallot repair)
- 10. Fundamentals of ECG Short PR interval (<120ms) A short PR interval is seen with: Preexcitation syndromes 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) and Lown-Ganong- Levine (LGL) syndromes. These involve the presence of an accessory pathway connecting the atria and ventricles. The accessory pathway conducts impulses faster than normal, producing a short PR interval. The accessory pathway also acts as an anatomical re-entry circuit, making patients susceptible to re-entry tachyarrhythmias. Patients present with episodes of paroxsymal supraventricular tachycardia (SVT), specifically atrioventricular re-entry tachycardia (AVRT), and characteristic features on the resting 12-lead ECG.
- 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 of Wolff-Parkinson-White syndrome are a short PR interval (<120ms), broad QRS and a slurred upstroke to the QRS complex, the delta wave.
- 16. Fundamentals of ECG Lown-Ganong-Levine syndrome The features of Lown-Ganong-Levine syndrome LGL syndrome are 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 of James 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 o Junctional rhythms are narrow complex, regular rhythms arising from the AV node. o P waves are either absent or abnormal (e.g. inverted) with a short PR interval (=retrograde P waves). o ECG: Accelerated junctional rhythm demonstrating inverted P waves with a short PR interval (retrograde P waves)
- 19. Fundamentals of ECG AV nodal (junctional) rhythm o Junctional rhythms are narrow complex, regular rhythms arising from the AV node. o P waves are either absent or abnormal (e.g. inverted) with a short PR interval (=retrograde P waves). o ECG: Accelerated junctional rhythm demonstrating inverted P waves with a short PR interval (retrograde P waves)
- 20. Fundamentals of ECG History of LGL syndrome 1921-1952 – association of paroxysmal tachycardia, short AV conduction time, and normal QRS complexes reported across 11 cases, but usually attributed to being a variant of Wolff-Parkinson-White syndrome. 1938 – Clerc, Levy and Critesco first described ECG findings of a short PR interval, normal QRS complex, and paroxysmal tachycardia. 1952 – Lown, Ganong and Levine performed the first study correlating the characteristic ECG changes with clinical findings, which distinguished patients with paroxysmal tachycardia, short PR interval, and normal QRS complexes from Wolff-Parkinson-White characteristics. 1961 – James described accessory pathway connections between the atria and distal atrioventricular node, which may have a role in the pathophysiology of LGL syndrome 1975 – Brechenmacher described accessory pathways between the atria and bundle of His, which may also be involved in LGL syndrome