ECGs

1. ECGs

2. ECG Basics • Normally 25mm/sec. 1 small square = 0.04sec (40ms), 1 large square = 0.2sec (200ms) • PR: Includes atrial depolarization, conduction through internodalpathways,AV node (slow), Bundle of His, Bundle branches and Purkinje fibres (0.12-0.2sec) • QRS: Ventricular depolarization (<0.12sec) • ST: Ventricular mass depolarized (plateau phase of action potential), absoluterefractory period) • T wave: Ventricular repolarization (in reverse direction from depolarization) • QT: Beginning of QRS to end of T wave (approx 0.4sec)

3. ECG Basics (cont.)

4. Stress ECG’s • Useful for confirming ECG pathology (but don’t want to/can’t perform more conclusive tests like angiograms) • Two types of stress ECG: • Exercise stress: you put the patient on a treadmill and gradually increase the difficulty of the run until they tire out/reach desired heart rate • Dobutamine stress: inject dobutamine (a sympathomimetic) to increase heart contractility and accentuate ECG’s

5. Exercise Stress ECG • Follow the Bruce Protocol: • Determine the patient’s maximal heart rate for exercise: (220-age) x 85% • Get baseline heart rate, BP and ECG • Start the patient on Stage 1 • After 3 every minutes, increase intensity and measure heart rate, BP and ECG again • When maximal heart rate is achieved, maintain exercise until patient tires • You can then get the patient off the treadmill, and measure the HR, BP and ECG while resting

6. Exercise Stress ECG (cont.) • Contraindications to Exercise Stress: • Aortic stenosis • Pacemakers • Patient cannot exericse

7. Dobutamine Stress ECG • Use Dobutamine (a sympathomimetic) to increase contractility • Contraindications: • Severe HTN (>200mmHg sys) • AF, VF • Tachycardias • Glaucoma

8. ECG Interpretation

9. The Approach to ECG Reading • Interpret the heart rate (check distance between QRS complexes) – checks for tachy- and bradycardias, arrhythmias etc • Check the distance between the P waves – checks for 2nd degree heart block • Check for the P waves and their character • Check the PR interval (3-5 small squares; 120-200ms) • Check the Q wave (pathological Q waves are noticeably deep) • Check the QRS interval (3 small squares) and its shape • Check the ST interval’s shape • Check the QT interval (duration depends on HR) • Check the T wave – check for inversions,

11. ECG Examples

12. Normal ECG

13. Pacemaker Artifact • Appears as a spike that is followed by a QRS complex Atrial demand pacemaker Ventricular demand pacemaker

14. Atrial Fibrillation • P-waves are either non-existent or very jittery • Heart rate is random

15. Atrial Flutter • Has a clear saw-tooth P-wave pattern

16. Ventricular Tachycardia • The waves are regular but very fast (100-250bpm)

17. Ventricular Fibrillation • All of the waves are completely random • Variation in size of waves • No obvious P waves

18. Torsades de Pointes • ‘Turning of the points’ – the ECG shows tachycardia but they form beads • Associated with prolonged QT intervals (e.g. from quinidine, amiodarone, sotalol, erythromycin use, hypokalaemia, hypocalcaemia etc)

19. Pathological Q Waves • Many causes of unusual Q waves: • Myocardial injury or replacement • Ventricular enlargement • Altered ventricular conduction

20. Wolff-Parkinson White Syndrome • Has a distinct triad of findings: • Short PR • Delta wave • Widened QRS • May see pathological Q waves

21. Heart Blocks • 1st Degree: Prolonged PR interval (>0.2sec) • Causes: drugs (e.g. B-blockers, Ca channel blockers, digoxin) • 2nd Degree, Type 1: Prolonged PR interval (that keeps on increasing), P-P interval becomes increasingly smaller (pattern resets) • Causes: B-blockers, digoxin, acute MI • 2nd Degree, Type 2: P waves don’t get linked to a QRS interval • Causes: acute MI (can evolve into 3rd degree block) • 3rd Degree: P waves have a random rhythm • Causes: digoxin, acute MI

22. Heart Blocks 1st Degree – Prolonged PR interval, all regular 2nd Degree , Type 1 – Prolonged PR interval that keeps on increasing 2nd Degree , Type 2 – Prolonged PR interval, occasionally one of the P waves is not linked to a QRS interval 3rd Degree – Prolonged PR interval; P waves are completely independent to QRS

23. Prolonged QT Interval • QTc = QT interval ÷ square root of the RR interval (in sec) • If QTc > 0.44sec, then it’s prolonged • Can be caused by: drugs (e.g. TCA’s, amiodarone, erythromycin etc), hypothyroidism, Long QT Syndrome (congenital)

24. STEMI • The leads that show the STEMI pattern can tell you where the infarct has occurred • V1-V2 — anteroseptal • V3-V4 — anteroapical • V5-V6 — anterolateral • 1, aVL — lateral • 2, 3, aVF — inferior • Can often see pathological Q waves and T wave inversion in prior STEMI • However, if the infarct is in the posterior, then the T waves are actually upright (with STEMI patterns being inverted)

25. STEMI (cont.) • Subendocardial infarctions are an inverted version of STEMI V4-V6 have STEMI pattern indicates subendocardial infarction

26. STEMI (cont.) ST Segment Depression in V3-V6 and T wave inversions (suggests the patient has had subendocardial infarction, at anterior wall, in the past)

27. STEMI (cont.) ST Segment Depression in V1-4; ST elevation in II, III , aVF and V6 (suggests an infarct that has spread to the posterior)

28. STEMI (cont.) ST Segment elevation in V4-V6

29. Testing your ECG Skills • http://www.ecglibrary.com/ecghome.html? • http://ekgreview.com/

30. References • Harrison’s Principles of Internal Medicine 18th edition • Clinician’s Pocket Reference • Oxford’s Handbook of Clinical Medicine • UptoDate