ELECTROCARDIOGRAM (ECG)

1. ELECTROCARDIOGRAM (ECG) Prof. Sultan Ayoub Meo MBBS, M.Phil, Ph.D (Pak), PG Dip Med Ed, M Med Ed (Scotland) FRCP (London), FRCP (Dublin), FRCP (Glasgow), FRCP (Edinburgh) Professor and Consultant, Department of Physiology, College of Medicine, King Saud University, Riyadh, Saudi Arabia

2. LECTURE OBJECTIVES Define ECG Identify waves of ECG and the physiological cause of each Define the normal intervals and segments Discuss the bipolar and un ipolar leads and their locations Discuss the bipolar limb lead and the cardiac axis

3. INTRODUCTION Cardiac impulse passes through the heart, electrical current spreads from heart into adjacent tissues surrounding the heart. Current spreads all the way to the surface of the body. If electrodes are placed on the chest, opposite sides of the heart, electrical potentials generated by the current can be recorded; the recording is known as an electrocardiogram A record of the waves (impulses) of electrical excitation in the heart is called ECG. It helps in the diagnosis of muscle damage or electrical problems in the heart.

4. NORMAL IMPULSE CONDUCTION Sinoatrial node AV node Bundle of His Bundle Branches Purkinje fibers

5. Arrhythmias Myocardial ischemia and infarction Pericarditis Chamber hypertrophy Electrolyte disturbances (i.e. hyperkalemia, hypokalemia) Drug toxicity (i.e. digoxin and drugs which prolong the QT interval) TYPES OF PATHOLOGY IDENTIFY AND STUDY FROM ECGS?

6. NORMAL ECG The normal ECG is composed of: P wave QRS complex T wave The separate waves: Q wave, the R wave, and the S wave. P wave: Atria depolarize before atrial contraction begins QRS complex: Ventricles depolarize before contraction. P wave and the components of the QRS complex are depolarization waves. The T wave: Ventricles recover from the state of depolarization This process normally occurs in ventricular muscle 0.25 to 0.35 second after depolarization and the T wave is known as a repolarization wave

8. The ECG Paper

9. approx. 0.44 s 0.12-0.2 s QT PR R T Atrial muscle depolarization P Q S P wave: Atrial depolarization (completed in 0.1 seconds ) • Irregular or absent P waves may indicate arrhythmia. • The shape of the P waves may indicate atrial problems

10. approx. 0.44 s 0.12-0.2 s QT PR R T P Atrial muscle depolarization Q S PR interval: Atrial depolarization & conductive time Measured from the P wave to the beginning of the QRS complex . Through the AV node /0.18 seconds (N. R. 0.12 to 0.2 s)

11. approx. 0.44 s 0.12-0.2 s QT PR QRS T Atrial muscle depolarization P Q S Ventricular muscle depolarization QRS complex: Ventrical depolarization Equal 0.08-0.12 s (max time 0.1seconds) Very wide and deep Q waves indicate myocardial infarction

12. approx. 0.44 s 0.12-0.2 s QT PR R T Atrial muscle depolarization P Q S Ventricular muscle repolarization Ventricular muscle depolarization QT interval: Ventricular depolarization & re-polarization (equal . 0.4 seconds

13. approx. 0.44 s 0.12-0.2 s QT PR R Atrial muscle depolarization T P Q S Ventricular muscle repolarization Ventricular muscle depolarization ST segment: (QT – QRS) Ventricular depolarization (equal . 0.32 seconds )

14. Leads are electrodes which measure the difference in electrical potential between either: ECG LEADS 1. Two different points on the body (bipolar leads) 2. One point on the body and a virtual reference point with zero electrical potential, located in the center of the heart (unipolar leads)

15. The standard ECG has 12 leads: ECG LEADS 3 Standard Limb Leads 3 Augmented Limb Leads 6 Precordial Leads The axis of a particular lead represents the viewpoint from which it looks at the heart.

16. STANDARD LIMB LEADS

17. STANDARD LIMB LEADS AUGMENTED LIMB LEADS

18. ALL LIMB LEADS

19. PRECORDIAL LEADS

20. SUMMARY OF LEADS

21. ARRANGEMENT OF LEADS ON THE ECG

22. ANATOMICAL REPRESENTATION(SEPTUM)

23. ANATOMIC PRESENTATION(ANTERIOR WALL)

24. ANATOMICAL PRESENTATION(LATERAL WALL)

25. ANATOMICAL PRESENTATION (INFERIOR WALL)

26. ANATOMICAL PRESENTATION(SUMMARY)

27. Take the number of “big boxes” between neighboring QRS complexes, and divide this into 300. The result will be approximately equal to the heart rate Although fast, this method only works for regular rhythms. RULE OF 300 DETERMINING THE HEART RATE 1. Rule of 300 2. 10 Second Rule

28. WHAT IS THE HEART RATE? (300 / 6) = 50 bpm (300 / 4) = 75 bpm (300 / 1.5) = 200 bpm

29. As most ECGs record 10 seconds of rhythm per page, one can simply count the number of beats present on the ECG and multiply by 6 to get the number of beats per 60 seconds. This method works well for irregular rhythms. 10 Second Rule

30. WHAT IS THE HEART RATE? The Alan E. Lindsay ECG Learning Center ; http://medstat.med.utah.edu/kw/ecg/ 33 x 6 = 198 bpm

31. The QRS axis represents the net overall direction of the heart’s electrical activity. Abnormalities of axis can hint at: Ventricular enlargement Conduction blocks (i.e. hemiblocks) The QRS Axis

32. The QRS Axis By near-consensus, the normal QRS axis is defined as ranging from -30° to +90°. -30° to -90° is referred to as a left axis deviation (LAD) +90° to +180° is referred to as a right axis deviation (RAD)

33. The QRS Axis

35. Clinical Significance of different waves and segments of ECG ST Elevation - Acute MI or AnginaST depression >1 mm - Ischemia/Angina (flat), digoxin (sloping) Q waves in 2 or more leads - Previous MI (Transmural)Diffuse ST elevation with PR depression – PericarditisT wave inversions and non-specific ST changes - Can be seen both in normal cases and in many diseases, therefore not useful for diagnosis. Tall P waves - Right atrial hypertrophyBroad (and often bifid) P waves - Left atrial hypertrophyPeaked T waves or loss of P wave – HyperkalemiaU waves - Hypokalemia ('Hump' at the end of T wave)Prolonged QT interval – HypocalcemiaShortened QT interval - Hypercalcemi