BASICS OF ECGBASICS OF ECGBASICS OF ECGBASICS OF ECG
- 1. BASICS OF ECG D R A M B I L Y S YA M
- 2. The electrocardiogram (ECG) is a representation of the electrical events of the cardiac cycle. Each event has a distinctive waveform, the study of waveform can lead to greater insight into a patient’s cardiac patho physiology
- 3. • P wave – atrial depolarisation • PR interval- atrial depolarisation+ AV nodal conductance. • QRS complex -Ventricular depolarisation • T wave- Ventricular repolarisation • U wave- After depolarisation
- 4. ECG CAN IDENTIFY • 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)
- 5. ECG PAPER • Horizontally • One small box - 0.04 s • One large box - 0.20 s • Vertically • One large box - 0.5 mV
- 6. NORMAL ECG
- 7. Standardization (calibration) and technical features (including lead placement and artifacts) Rhythm Heart rate, PR interval/AV conduction QRS interval QT/QTc interval Mean QRS electrical axis P waves QRS voltages Precordial R-wave progression Abnormal Q waves ST segments T waves U waves
- 8. STANDARDIZATION The first step while reading ECG is to look for whether standardization is properly done. Look for the vertical mark and see that the mark exactly covers two big squares(10 mm or 1mV) on the graph. Standard calibration 25 mm/s 0.1 mV/mm
- 10. RHYTHM Evaluate the rhythm strip at the bottom of the 12-lead for the following- Is the rhythm regular or irregular? Is there a P wave before every QRS complex? Are there any abnormal beats?
- 11. 1.Rule of 300/1500(Regular rhythm) 2.10 Second Rule • Count the number of “big boxes” between two QRS complexes, and divide 300 by this. (smaller boxes with 1500) for regular rhythms. • Count the number of beats present on the ECG during 10 seconds ie 50 big squares. • Multiply them by 6 • For irregular rhythms.
- 13. P wave • Atrial contraction • Duration-< 3small sq • Amplitude <2.5 small sq • Always positive in lead 1 and 2 • Commonly biphasic in lead V1 • Right atrial enlargement- tall >2.5mm pointed p wave- p pulmonale • Left atrial enlargement- notched/ bifid/ M shaped P wave- p mitrale
- 14. PR interval Atrial depolarization + delay in AV junction (AV node/Bundle of His) (delay allows time for the atria to contract before the ventricles contract) 0.12 to 0.20 s (3 - 5 small squares). Short PR – Wolff-Parkinson-White. Long PR – 1st Degree AV block
- 15. Long PR interval • First degree Heart Block
- 17. ABNORMAL PR RR INTERVAL REGULAR IRREGULAR 2ND DEGREE HEART BLOCK REGULAR PR INTERVAL 1ST DEGREE HEART BLOCK IRREGULAR PR INTERVAL 3RD DEGREE HEART BLOCK IRREGULAR PR MOBITZ TYPE 1 REGULAR PR MOBITZ TYPE 2
- 18. QRS INTERVAL(DURATION) Normal QRS duration is 110-120 msec. Intrinsic impairment of conduction in either the right or the left bundle system (intra ventricular conduction disturbances) leads to prolongation of the QRS interval. With complete bundle branch blocks, the QRS interval exceeds 120 ms in duration; with incomplete blocks, the QRS interval is between 110 and 120 msec.
- 19. Bundle branch blocks • Conduction in the Bundle Branches and Purkinje fibers are seen as the QRS complex on the ECG. • Therefore, a conduction block of the Bundle Branches would be reflected as a change in the QRS complex.
- 20. RBBB • For RBBB the wide QRS complex assumes a unique, virtually diagnostic shape in those leads overlying the right ventricle (V1 and V2). V1
- 21. • For LBBB the wide QRS complex assumes a characteristic change in shape in those leads opposite the left ventricle (right ventricular leads - V1 and V2). Broad and deep S waves.
- 22. QT interval It includes the total duration of ventricular activation and recovery. When the interval is to be measured from a single lead, the lead in which the interval is the longest, most commonly lead Avl, V2 or V3, and in which a prominent U wave is absent should be used. The normal range for the QT interval is rate-dependent A commonly used formula was developed by Bazett in 1920. The result is a corrected QT interval, or QTc, defined by the following equation: QTc=QT / RR
- 23. • The upper normal limit be set at 450 or even 460 msec. • The Bazett formula remains significantly affected by heart rate and that as many as 30% of normal ECGs would be diagnosed as having a prolonged QT interval when this formula is used. • One formula that has been shown to be relatively insensitive to heart rate is- QTc= QT +1.75(HR-60)
- 24. Prolonged QTc During sleep Hypocalcemia Acute myocarditis Acute Myocardial Injury Drugs like quinidine, procainamide, tricyclic antidepressants Hypothermia HOCM Advanced AV block or high degree AV block Jervell-Lange –Neilson syndrome Romano-ward syndrome
- 26. ST segment ST Segment is flat (isoelectric) Elevation or depression of ST segment by 1 mm or more is significant. “J” (Junction) point is the point between QRS and ST segment
- 27. T wave Normal T wave is asymmetrical, first half having a gradual slope than the second. Should be at least 1/8 but less than 2/3 of the amplitude of the R. T wave amplitude rarely exceeds 10 mm. Abnormal T waves are symmetrical, tall, peaked, biphasic or inverted. T wave follows the direction of the QRS deflection.
- 29. U wave U wave related to afterdepolarizations which follow repolarization U waves are small, round, symmetrical and positive in lead II, with amplitude < 2 mm U wave direction is the same as T wave More prominent at slow heart rates