anand ecgppt, basics and application,in humans

ECG in human body ,basics and application

1. INTERPRETATION OF NORMAL ECG PRESENTOR- DR.ANAND MODERATOR-DR.PALLAVI

2. The ecg is a transthoracic interpretation of the electrical activity of the heart -Is a graph that represents the electric activity Vs time -Device used to obtain and display the conventional ECG is called electrocardiograph

3. DEPOLARISATION Spread of electrical signals through atria and ventricles following stimulation REPOLARISATION Return of heart muscles cells to their resting state following stimulation Depolarization begins at the SA node(60-100) Spreads across the atria Reaches AV node and the accessory bundle(40-55) bundle of His(25-40) Right and left bundle branches(25-50) Purkinje fibres(25-50) Ventricle

4. ECG GRAPH PAPER P-QRS-T sequence is usually recorded on special ECG graph paper that is divided into grid like boxes. Paper moves at the speed of 25mm/sec Each of small boxes is 1 mmsquare Horizontally each unit represents 0.04 sec, each 5mm unit corresponds to 0.2 sec

5. CALIBARATION/ STANDARDIZATION 1mV signal produces a 10mm deflection The standardization mark - square(rectangular) wave 10mm tall. Some ECGs do not display calibration pulse , instead they print the paper speed and standardization at the bottom of ECG paper.(25mm/sec,10mm/mV ). IMPORTANCE OF CALIBERATION large deflections - take ECG at one half standardization Small ECG complexes - Double the standardization

6. Upward deflection or wave is called positive Downward deflection or wave is called negative Biphasic complex is seen if mean direction of wave is at right angles to the lead. Deflection or wave that rests on the baseline is said to be isoelectric

7. ECG LEADS Way of recording the voltages from the heart is with the 12 standard ECG leads They show the difference in voltage among electrodes placed on surface of the body. BIPOLAR AUGMENTED V1 to V6 I aVL II aVR III aVF

8. EINTHOVEN’S TRIANGLE

9. CALCULATION OF HEART RATE Vary according to cardiac rhythm , regular or irregular 1. When HR is regular Count the no of small boxes between successive R waves and divide 1500 by that number. Count the no of large boxes between 2 successive QRS complexes and divide 300 by that number. 2.When HR is irregular Count the no of R in 30 large squares(it is equivalent to 6sec) then multiply this by 10 (it becomes rate in 1 minute) HR <60 bpm – Bradycardia HR > 100 bpm - Tachycardia

10. Systematic Interpretation of ECG Rhythm Features of sinus rhythm are: Each P wave should be followed by QRS complex. P-R interval should be normal and constant. P wave morphology should be normal. R-R interval should be equal, if it is irregular, then it is called irregular rhythm. Causes of Irregular Rhythm Physiological: Sinus arrhythmia Pathological: Atrial fibrillation Ventricular fibrillation

11. ELECTRICAL AXIS AND AXIS DEVIATION ECG electrode record only the average current flow at any given moment , each leads record only the instantaneous average of these forces i.e resultant of these forces is called VECTOR Or ELECTRICAL axis The normal electrical axis of the heart ( -30deg and +100deg) If the axis is more negative than -30deg it is called LEFT AXIS DEVIATION. If the axis is more positive than +100 deg called RIGHT AXIS DEVIATION

12. Einthovens triangle and axis

13. P waves The P wave is the first positive deflection on the ECG It represents  atrial depolarization-its identification is important for determination of sinus rhythm Normal duration: < 0.12 s (< 120ms or 3 small squares Morphology Monophasic  in lead II and lateral leads Biphasic  in V1( ocassionally V2)

14. P waves should be upright in leads I and II, inverted in aVR Amplitude < 2.5 mm (0.25mV) in the limb leads < 1.5 mm (0.15mV) in the precordial leads Atrial abnormalities are most easily seen in the inferior leads (II, III and aVF ) and lead V1, as the P waves are most prominent in these leads.

15. P wave The combined depolarisation wave, the P wave, is less than 120 ms wide and less than 2.5 mm high

16. P wave The combined depolarisation wave, the P wave, is less than 120 ms wide and less than 2.5 mm high

17. The Atrial Waveform – Relationship to the P wave Atrial depolarisation proceeds sequentially from right to left, with the right atrium activated before the left atrium The right and left atrial waveforms summate to form the P wave The first 1/3 of the P wave corresponds to right atrial activation, the final 1/3 corresponds to left atrial activation; the middle 1/3 is a combination of the two In most leads (e.g. lead II), the right and left atrial waveforms move in the same direction, forming a monophasic P wave However, in lead V1 the right and left atrial waveforms move in opposite directions. This produces a biphasic P wave with the initial positive deflection corresponding to right atrial activation and the subsequent negative deflection denoting left atrial activation

18. PR interval The  PR interval  is the time from the onset of the P wave to the start of the QRS complex. It reflects activation of AV node , bundle of H is,bundle branch,interventricular conduction system.most of the conduction delay is due to AV nodeal delay. 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 .

19. QRS Its pattern lead represents the sum of all electrical forces emanating from the wave front propogation of ventricular electrical excitation aimed at the direction of that lead. The excitation spreads from bundle of His to purkinje fibers,which disperse throughout the entire endocardial surfaces of both ventricles. The excitation of the purkinje –ventricular muscle junction the proceeds by conduction from muscle cell to cell (activating the entire ventricle)towards epicardium.

20. Its it a manifestation of activation of free walls of left and right ventricular.(generally represents the left ventricular activity-due to larger muscle mass than right,with its main vector moving from right to left in axial plane and anterior, followed by posterior vectors in horizontal plane –R wave followed by a small S wave in left sided leads) Main vector of QRS is used to calculate the axis of the heart,which is normally -30 to +90 degree.

21. QRS QRS Width Normal QRS width is <120 ms ,The QRS width is useful in determining the origin of each QRS complex (e.g. sinus, atrial, junctional or ventricular). Narrow complexes  (QRS < 120 ms ) are  supraventricular  in origin. Broad complexes  (QRS > 120 ms ) may be either  ventricular  in origin, or due to  aberrant conduction  of supraventricular complexes (e.g. due to bundle branch block, hyperkalaemia or sodium-channel blockade)

22. Q waves The Q wave represents the normal (vector oriented from left-to-right in frontal plane and anteriorly in horizontal plane) depolarisation of the interventricular septum( produces an initial small positive wave in right sided leads- aV R and V1). Small ‘septal’ Q waves are typically seen in the left-sided leads (I, aVL , V5 and V6) Q waves in different leads Small Q waves(less than 40 ms ) are normal in most leads Deeper Q waves (>2 mm) may be seen in leads III and aVR as a normal variant

23. Pathological Q Waves Q waves are considered pathological if: > 40 ms (1 mm) wide > 2 mm deep > 25% of depth of QRS complex Seen in leads V1-V3 Loss of normal Q waves The absence of small septal Q waves in leads V5-6 should be considered abnormal. Absent Q waves in V5-6 is most commonly due to  LBBB .

24. T wave Normal T wave characteristics Repolerisation of the ventricles generate the ST segment and T wave . Because the endocardial action potential lasts longer than that of its overlying epicardium,repolerisation of the epicardium often starts earlier than in the endocardium. Upright in all leads except aVR and V1 Amplitude < 5mm in limb leads, < 10mm in precordial leads (10mm males, 8mm females) Duration relates to  QT interval

25. ST segment The  ST segment  is the flat, isoelectric section of the ECG between the end of the S wave (the J point) and the beginning of the T wave. The ST Segment represents the interval between ventricular depolarization and repolarization. The most important cause of ST segment abnormality (elevation or depression) is  myocardial ischaemia  or  infarction .

26. QT interval Time from the start of the Q wave to the end of the T wave Represents time taken for ventricular depolarisation and repolarisation , effectively the period of ventricular systole from ventricular isovolumetric contraction to isovolumetric relaxation The QT interval is inversely proportional to heart rate: An abnormally prolonged QT is associated with an increased risk of ventricular arrhythmias, especially  Torsades de Pointes Congenital short QT syndrome  has been found to be associated with an increased risk of paroxysmal atrial and ventricular fibrillation and sudden cardiac death

27. U wave The U wave is a small (0.5 mm) deflection immediately following the T wave U wave is usually in the same direction as the T wave. U wave is best seen in leads V2 and V3. Source of the U wave The source of the U wave is unknown. Three common theories regarding its origin are: Delayed repolarisation of Purkinje fibres After-potentials resulting from mechanical forces in the ventricular wall

28. Features of Normal U waves The U wave normally goes in the same direction as the T wave U -wave size is inversely proportional to heart rate: the U wave grows bigger as the heart rate slows down U waves generally become visible when the heart rate falls below 65 bpm The voltage of the U wave is normally < 25% of the T-wave voltage: disproportionally large U waves are abnormal Maximum normal amplitude of the U wave is 1-2 mm

29. The J point The  J point  is the the junction between the termination of the QRS complex and the beginning of the ST segment. It represents the approximate end of depolarization and the beginning of repolarization as determined by the surface ECG. There is an overlap of around 10ms. The J point marks the end of the QRS complex, and is often situated above the baseline, particularly in healthy young males. The J point may deviate from the baseline in early repolarization, epicardial or endocardial ischaemia or injury, pericarditis, RBBB, LBBB, RVH, LVH or digitalis effect.

30. Electrolyte Imbalances Hyperkalemia Key characteristics includes: T wave peaking Flattened P waves First degree AV heart block Widened QRS complex Deepened S waves Merging of S and T waves Hypokalemia ST segment depression Flattening of the T wave Appearance of U wave

31. Hypocalcemia QT interval slightly prolonged Prolonged ST segment Hypercalcemia Shortened ST segment Widened T wave

32. Hypomagnesemia Tall T wave ST depression Hypermagnesemia Prolonged PR interval QRS widening

33. REFERENCE GOLDBERGER’S CLINICAL ELECTROCARDIOGRAPHY-8 TH EDITION THE ECG MADE EASY – JOHN R HAMPTON ANAESTHESIA AND CO-EXISTING DIASEASE-STOELTING’S 7 TH EDITION