2020.06.05 ECG basics

ECG basics presentation

1. ECG - Basics Saurabh Bhardwaj , MD Cardiology Trainee National Heart Institute New Delhi,

2. Outline Introduction Utility Standardisation & technical features of ECG machine How to record Genesis of waveform Intervals /Segments ECG interpretation Summary

3. What is an Electrocardiogram? An ECG is the recording (gram) of the electrical activity ( electro ), generated by the cells of the heart(cardio) that reaches the body surface . P rovides a time-voltage chart of the heartbeat . It records cardiac electrical currents (voltages or potentials ) by means of sensors, called electrodes , selectively positioned on the surface of the body.

4. Alexander Muirhead in 1869, first recorded an ECG in humans A. D. Waller in 1878, recorded the first human ECG and labeled the deflections as “V1” and “V2” W. Einthoven in 1895, recorded an improved ECG and later named he deflections as “PQRST” By 1910, ECG emerged from the research laboratory into the clinic and became the most commonly used cardiac diagnostic test . Although other techniques have evolved to assess cardiac structure and mechanical function, the ECG remains the fundamental method to assess the heart's electrical activity.

5. Evolution of ECG machine….. Circa. 1911

6. 1940s-70s Current & Future

7. Utility of ECG Reliable tool for diagnosis and management of the cause chest pain- Acute coronary syndromes Pericarditis Cardiac arrythmias It can help with diagnosis of the cause of breathlessness or palpitations or syncope It can be used for assessing- Electrolyte disorders Drug effects Toxicity

8. STANDARDISATION ECG graphs: 1 mm squares 5 mm squares Paper Speed: 25 mm/sec Voltage Calibration: 10 mm/mV

9. ECG Leads A pair of electrodes that constitute an ECG lead All the leads are equidistant from the heart (greater than 15cms ) Record differences in electro-magnetic potentials & have positive and negative poles • Two types - Bipolar -record potential between two surface electrodes -Limb Leads I, II and III are bipolar leads -Unipolar -record potential between a surface electrode and an electrode with zero potential(central terminal of Wilson) -as these leads record small potentials, it needs to be augmented called Augmented Leads ( aVR , aVL & aVF ) (developed by Goldberger, 1942)

10. The standard ECG has 12 leads: 3 Standard Limb Leads 3 Augmented Limb Leads 6 Precordial Leads

11. Standard Limb Leads Einthoven Triangle The potential in lead II equals the vectorial sum of potentials sensed in leads I and III; I + III = II

12. All Limb Leads The hexaxial reference system constructed from the lead axes of the six frontal plane leads . The lead axes of the six frontal plane leads have been rearranged so that their centers overlie one another .

13. Precordial Leads

14. Precordial Leads In frontal plane

15. Anatomic Groups (Summary)

16. ECG recording by computerized systems involves several steps : signal acquisition, data transformation , waveform recognition, and feature extraction , diagnostic classification, and display of the final ECG.

17. The Normal Conduction System

18. 3 distinct waves are produced during a cardiac cycle P wave caused by atrial depolarization QRS complex caused by ventricular depolarization T wave results from ventricular repolarization U wave represents Purkinje repolarization ECG waves 13-63

19. P wave : Depolarization of both atria Duration less than 120msec Shape and duration indicates atrial enlargement Relationship between P and QRS helps distinguish various cardiac arrhythmias

20. QRS complex : Ventricular depolarization Larger than P wave because of greater muscle mass of ventricles Normal duration = 0.08-0.12 seconds Its duration, amplitude, and morphology are useful in diagnosing cardiac arrhythmias, ventricular hypertrophy, MI, electrolyte derangement, etc. Q wave greater than 1/3 the height of the R wave, greater than 0.04 sec are abnormal and may represent MI

21. T wave : Represents repolarization or recovery of ventricles A normal T wave has an asymmetrical shape; that is, its peak is closer to the end of the wave than to the beginning. Duration -within 40msec Abnormalities seen myocardial ischemia, septal hypertrophy, hyperkalemia, etc

22. Dome- or hump-shaped wave or notch that appears at the end of the QRS complex and that has the same polarity as the preceding QRS complex. Normal variant or Pathologic conditions- hypothermia ( Osborn wave) , J wave syndromes ( Brugada patterns and the early repolarization pattern.) Origin postulated to be associated with a prominent notch in phase 1 of the action potentials on the epicardium but not on the endocardium , creating a transmural potential gradient leading to QRS notching and ST elevation. J

23. U wave : Small rounded deflection that occurs immediately after the T wave Best seen V2- to V4, with slow heart rates usually less than 0.1 mV in amplitude, normally has the same polarity as the preceding T wave Caused by delayed repolarization in areas of the ventricle that undergo late mechanical relaxation or late repolarization of the Purkinje fibers Prominent in hypokalemia, drug effects ( sotalol , quinidine, phenothiazines ) or in some patients of cerebrovascular accident .

24. Waveforms and Intervals

25. PR segment: Time taken by impulse to travel from AV node, through His bundle, and to the ventricles is represented by the PR segment. PR segment is the usually isoelectric region beginning with the end of the P wave and ending with the onset of the QRS complex . S erves as the temporal bridge between atrial activation and ventricular activation. Includes atrial repolarization and slow conduction within the AV node plus the more rapid conduction through the ventricular conduction system. The segment ends when enough ventricular myocardium has been activated to initiate the QRS complex.

26. ST segment : Connects the QRS complex and T wave. Represents early phase of ventricular repolarization . Duration of 0.08-0.12 sec (80-120 msec ) Low-amplitude , slowly changing wave gradually evolves into the T wave. Onset of ST-T wave is the junction or J point, and is normally isoelectric. Recommendations- in V2 and V3 < 0.2 mV for men (≥40y), <0.25 mV for men(<40y), and <0.15 mV for women. In other leads the recommended upper limit is 0.1 mV for men and women.

27. TP segment: End of the T wave to beginning of the P wave. Represents the electrical resting state. Used as the baseline reference from which to assess PR and ST deviations in conditions such as acute pericarditis and acute myocardial ischemia , respectively.

28. PR interval : From onset of P wave to onset of QRS Normal duration = 0.12-2.0 sec (120-200 ms ) (3-5 horizontal boxes) Represents atria to ventricular conduction time (through His bundle )\ Kind of physiologic delay which allows the ventricles to fill fully with blood before ventricular depolarization occurs , to optimize cardiac output. Prolonged PR interval may indicate various types of heart block. Short PR interval in Pre-excitation (WPW syndrome)

29. QT Interval: Measured from beginning of QRS to the end of the T wave Represents total duration of ventricular activation and recovery Best seen a lead with initial q-wave like I, II, aVL , V5, V6 Normal range of QTc = 350ms to 430ms

30. The normal QT interval is rate dependent, decreasing as heart rate increases. This corresponds to rate related changes in the duration of the normal ventricular action potential . Numerous formulas have been proposed to correct the measured QT interval for this rate effect. Bazett’s formula: QTc =QT / Hodges method: QTc = QT + 1.75 (HR- 60) Fridericia's formula: QTc= QT/ (RR)  

31. Causes of QT interval prolongation During sleep Hypothermia Hypocalcemia Acute myocarditis Hypertrophic cardiomyopathy Advanced or complete AV block, ‘ torsades d pointes’ Cerebral injury Drug effects-quinidine, procainamide, TCAs, chloroquine >HCQS. Congenital long QT syndromes

32. Causes of shortened QTc Hyperthermia Vagal stimulation Hypercalcemia Digitalis effect Congenital short QT syndrome

33. ECG interpretation- Practical Approach Clinical profile/history Rate Rhythm Axis P wave morphology PR interval QRS voltage/width ST segment/ J point T wave morphology QT interval Compare with prior ECG, if available.

34. Summary The technology ECG has continuously evolved since the invention of string galvanometer by Einthoven in 1901 and it is still the most commonly used cardiac diagnostic test. It is the final outcome of a complex series of physiologic and technologic processes recorded by placing electrodes over body. Uniquely provides essential information about the electrical properties of the heart with potentially life-threatening conditions such as brady - and tachyarrhythmia , ischemia, hyperkalemia, etc. The clinical effectiveness of the ECG as a diagnostic tool depends on numerous “real world” factors such as the appropriateness of the procedure, proper recording technique, and the skills of the interpreter .

35. Thanks “Perfection is unattainable, But if we chase perfection we can catch excellence……”