Lec 6 ECG.pptx cardiopulmonary physical therapy

ECG

1. Electrocardiography ECG

2. INTRODUCTION The heart is a vital link in the oxygen transport system , pumping blood to the pulmonary and peripheral circulation systems to supply oxygen and other nutrients required for metabolism in all tissues. The beating heart generates rhythmic, electrical impulses that cause mechanical contraction, or the pumping action, of cardiac muscle. Some of the electrical current produced by these rhythmic impulses is detectable by electrodes that may be placed on the surface of the skin. Current flow during the cardiac cycle is then recorded as the characteristic waveforms of the electrocardiogram(ECG). Mechanical events such as contraction and relaxation of the myocardium are inferred from the waveforms produced by the ECG.

3. Electrocardiogram (ECG) An ECG is the recording (gram) of the electrical activity (electro) generated by the cells of the heart (cardio) over time. Useful in diagnosis of… Cardiac Arrhythmias (gold standard) Myocardial ischemia and infarction Pericarditis Electrolyte disturbances Drug effects and toxicity Non-cardiac diseases (e.g. pulmonary embolism)

4. Basic Electrophysiological Principles Electrical stimulation makes the cell membrane more permeable to the flow of ions. As there is a predominance of potassium (K+) on inside of the cell and sodium (Na+) on outside , Electrical stimulation makes the membrane more permeable to the sodium ions = they flow inward , creating a change in the resting state of the cells of the cardiac muscle from a negative to a positive charge on the interior. Sodium flow is referred to as the fast channel Potassium flow is referred to as the slow channel

5. As the cell becomes positive on interior , the myocardial cells are stimulated to contract. The electrical stimulation of the specialized cells that cause contraction is called depolarization Depolarization – repolarization --contraction – relaxation of heart muscle.

6. The Conduction System The primary pacemaker that initiates the electrical impulse for the cardiac muscle is the SA node . The wave of atrial depolarization ( atrial contraction) is represented on the ECG as the P wave . Impulse then reaches the AV node , AV node delays the conduction= P-R segment

7. Impulse then passes from the AV node into the His bundle and then to the bundle branches . The bundle branches consist of a left and right division and are located in the interventricular septum Impulses spread down the bundle branches and terminate in Purkinje fibers , stimulate muscle contraction from the apex upward toward the base of the heart. Ventricular depolarization as the QRS complex

8. Repolarization begins when ventricular contraction ends. T wave represents the ventricular repolarization .

9. ECG leads 12 leads ECG include: 6 limb leads ( 3 standard leads, 3 unipolar leads) 6 chest or precordial leads Each lead incorporates two electrodes measuring the potential or voltage difference between them. The positive electrodes detects the electrical impulse while neutral electrodes completes the circuit. The ECG monitor placed in the circuit detects electrical activity.

10. Standard limb leads Lead I: Exploring electrode is attached to left arm and neutral to the right arm Lead II: Exploring electrode to the left leg and the neutral electrode to the right arm Lead III: Exploring electrode to the left leg and the neutral electrode to the left arm. ASSESSMENT: Lead I: Anterior surface of the heart Lead II: Inferior surface of the heart Lead III: Inferior surface of the heart

11. Unipolar limb leads Exploring electrode is on the rt leg and neutral electrode on all the other limbs Lead AvR attached to right arm Lead AvL attached to left arm Lead AvF attached to left leg A= augmented. ASSESSMENT: AvR - (R) side of the heart AvL - (L) side of the heart AvF – Inferior aspect of the heart

12. Chest leads V1 4 th IC space (R) V2 4 th IC space (L) V3 b/w V2 and V4 V4 5 th IC space mid-clavicular line V5 5 th IC space anterior axillary line V6 5th IC space mid-axillary line ASSESSMENT: V1 and V2 assess the right ventricle V3 and V4 interventricular septum V5 and V6 Left side of the heart

13. ECG LEADS To obtain a 12-lead ECG, four wires are attached to each limb and six wires are attached at different locations on the chest. The total of ten wires provides twelve views ( 12 leads). Electrodes are placed on the right arm (RA), left arm (LA), right leg (RL), and left leg (LL). With only four electrodes, six leads are viewed.

14. The Electrocardiogram Recording The electrocardiogram is recorded on ruled graph paper, with the smallest divisions (or squares) being 1 mm long and 1 mm high. Time is represented on the graph paper by 0.04 second between each small square 0.2 second between the large square The paper speed is set at 25 mm/second.

15. ECG 1  small box   represents  0.04 seconds or 1mm 1  large box represents 0.2 seconds or 5mm 5 large box   = 1 second 25mm 30 large box = 6sec 300 large box  = 1 minute PR interval (0.20sec) = 1 big box QRS complex (0.10 sec) = 3 small boxes The normal running speed for recording an ECG is 25mm/sec

16. COMPONENTS OF THE ECG P – Wave: Represents atrial depolarization Duration: b/w 0.08 - 0.12 sec QRS complex: Represents depolarization of ventricles Duration: b/w 0.06 to 0.10 second. T – wave: Represents ventricular repolarization U – wave: Represents late repolarization after the T – wave Of little importance but needs to be recognized so as not to confuse it with other components

17. COMPONENTS OF THE ECG P – R interval: Starts at the beginning of the P wave and ends at the onset of the QRS The P-R interval is normally 0.12 to 0.20 second (or up to five small squares on the ECG paper). This period of time represents the atrial depolarization and the slowing of electrical conduction through the AV node. S – T segment: Starts from the end of the QRS and terminates at the onset of the T wave.  Following completion of ventricular depolarization, there is a period of electrical inactivity represented by the S – T segment.

18. Measuring Heart Rate F ind an R-wave located on or near a heavy vertical line. Proceeding to the left of that R wave, for each subsequent heavy vertical line, assign the following numbers: 300 for the first heavy line encountered, 150 for the next followed by 100, 75, 60, 50. In the following figure , the rate would be estimated as falling between 100 and 75, or close to 80 beats per minute (BPM).

19. Heart Rate

20. Another method for measuring heart rate : Count the number of R-waves within the 6-second recording, and multiply by lO . In Figure The rate of this irregular rhythm is estimated at 60 BPM.

21. Interpretation of Heart Rhythm

22. Normal Sinus Rhythm All P waves are upright, normal in appearance, and identical in configuration; a P wave exists before every QRS complex. • The P-R interval is between 0.12 and 0.20 second. • The QRS complexes are identical. • The QRS duration is between 0.06 and 0.10 second. • The R-R interval is regular (or if irregular, the difference between shortest and longest intervals is less than 0.12 second). • The heart rate is between 60 and 100 beats per minute.

23. Sinus Bradycardia All P waves are upright, normal in appearance, and identical in configuration; a P wave exists before every QRS complex. The P-R interval is between 0.12 and 0.20 second. The QRS complexes are identical. The QRS duration is between 0.06 and 0.10 second. The R-R interval is regular. The heart rate is less 60 beats per minute.

24. Sinus bradycardia is usually non–life-threatening. The underlying cause should be sought. Some possible causes include beta-blocking medications and second- or third-degree AV block (not benign). Trained athletes with an increased resting and exercise stroke volume may also exhibit bradycardia .

25. Sinus tachycardia All P waves are upright, normal in appearance, and identical in configuration; a P wave exists before every QRS complex. The P-R interval is between 0.12 and 0.20 second. The QRS complexes are identical. The QRS duration is between 0.06 and 0.10 second. The R-R interval is regular. The heart rate is greater then 100 beats per minute.

26. S upraventricular tachycardia (SVT) The tachycardia may be sustained, lasting hours or even days, or may be "paroxysmal" (PSVT), appearing abruptly and spontaneously reconverting to the previous rhythm within seconds or minutes. Symptoms associated with inadequate cardiac output, such as dizziness, lightheadedness, and syncope may ensue. The causes of PAT can include emotional factors; overexertion; hyperventilation; potassium depletion; caffeine, nicotine, and aspirin sensitivity; rheumatic heart disease; mitral valve dysfunction, particularly mitral valve prolapse ; digitalis toxicity; and pulmonary embolus.

27. • P waves may be present but may be merged with the previous T wave. • The P-R intervals may be difficult to determine but are less than 0.20 second. • The QRS complexes are identical unless there is aberration. • The QRS duration is between 0.06 and 0.10 second. • The R-R intervals are usually regular and may show starting and stopping of the PAT. • The ST segment may be elevated or depressed, yet the magnitude of change is not diagnostically reliable. • The heart rate is very rapid, often greater than 160 beats per minute.

28. SVT Figure 11-13 demonstrates supraventricular tachycardia at a rate of 190 BPM.

29. Atrial fibrillation Twitching of the atrial muscle caused by multiple ectopic foci in the atria that emit electrical impulses constantly. None of the ectopic foci actually depolarizes the atria, so no true P waves are found in atrial fibrillation. The atria, are not pumping effectively which cause impair ventricular contraction. Figure atrial fibrillation with a "controlled," that is, less than 100 BPM, ventricular response. Pulse monitoring of an individual in atrial fibrillation reveals an irregularly irregular pattern. Symptoms occur only if the ventricular response is too rapid, which causes cardiac output decompensation .

30. Atrial Fibrillation

31. The characteristics of atrial fibrillation include the following: • P waves are absent, thus leaving a flat or wavy baseline. • The QRS duration is between 0.06 and 0.10 second. • The R-R interval is characteristically defined as irregularly irregular. • The rate varies but is called “ventricular response.”

32. Atrial flutter Rapid succession of atrial depolarization at a rate of 250 to 350 times per minute P-waves have a distinctive morphology often referred to as a "saw tooth" or "picket fence" appearance. Of clinical importance is the ratio of atrial to ventricular conduction. The conduction ratios may vary from 2 : 1 up to 8 : 1 ,whether or not the patient is hemodynamically stable. 

33. Atrial Flutter

34. Ventricular tachycardia An emergency situation because cardiac output is greatly diminished. Ventricular tachycardia is defined as a series of three or more PVCs in a row. P waves are absent. QRS complexes of the ventricular tachycardia are wide and bizarre, greater then 0.12 s Ventricular rate of ventricular tachycardia is between 100 and 250 beats per minute.

35. VT

36. Ventricular fibrillation Ventricular fibrillation is defined as an erratic quivering of the ventricular muscle resulting in no cardiac output. As in atrial fibrillation, multiple ectopic foci fire, creating asynchrony. The ECG results in a picture of grossly irregular up and down fluctuations of the baseline in an irregular zigzag pattern Treatment is defibrillation as quickly as possible followed by cardiopulmonary resuscitation, supplemental oxygen, and injection of medications If not successfully treated, v-fib may further degenerate into asystole, which indicates complete absence of ventricular electrical activity.

37. VF

38. Conduction Blocks The propagation of a cardiac impulse may be inhibited or terminated along the conduction pathway. Blockage can occur at the sinus node, between the atria and ventricles, Or within the ventricular conduction system. Sinus block occurs if the impulse cannot propagate beyond the sinus node. In this case, the AV junction usually takes over as the pacemaker, and a junctional rhythm is seen with the absence of P-waves. More common are the AV blocks. They are ranked as first-, second, or third-degree, depending on the extent of delay or obstruction of the cardiac impulse between the atria and ventricles.

39. First-degree A V block First-degree AV block occurs when the impulse is initiated in the SA node but is delayed on the way to the AV node; or it may be initiated in the AV node itself, and the AV conduction time is prolonged. This results in a lengthening of the P-R interval only and a normal QRS complex. Thus for each P wave, there is a QRS complex; therefore the conduction ratio is 1: 1.

40. • A P wave is present and with normal configuration before every QRS complex. • The P-R interval is prolonged (greater than 0.20 second). • The R-R intervals are regular. • The heart rate is usually within normal limits (60 to 100 beats per minute) but may be lower than 60 beats per minute.

41. First-degree A V block

42. Second-degree A V block If the ventricles do not respond to atrial stimuli the P wave is not followed by QRS complex The typical appearance of second-degree block is a progressive prolongation of the P-R interval until finally one impulse is not conducted through to the ventricles (no QRS complex following a P wave). If there is 2 P wave deflections to every ventricular deflections this is known as 2:1 block. 

43. Second-degree A V block The typical appearance of type I ( Wenckebach ) second-degree block is a progressive prolongation of the P-R interval until finally one impulse is not conducted through to the ventricles (no QRS complex following a P wave).

44. The characteristics of second-degree type I include the following: • Initially a P wave precedes each QRS complex, but eventually a P wave may stand alone (conduction is blocked). • Progressive lengthening of the P-R interval occurs in progressive order. • As the P-R interval increases, a QRS complex will be dropped. • This progressive lengthening of the P-R interval followed by a dropped QRS complex occurs in a repetitive cycle. • The QRS configuration is normal, and the duration is between 0.06 and 0.10 second. • Because of the dropping of the QRS complex, the R-R interval is irregular (regularly irregular). • The heart rate varies.

45. SECOND DEGREE AV BLOCK

46. Second-Degree Atrioventricular Block, Type II Second-degree AV block, type II ( Mobitz II), is defined as nonconduction of an impulse to the ventricles without a change in the P-R interval. The characteristics of second-degree AV block type II include the following: • A ratio of P waves to QRS complexes that is greater than 1 : 1 and may vary from 2 to 4 P waves for every QRS complex. • The QRS duration is between 0.06 and 0.10 second. • The QRS configuration is normal. • The R-R intervals may vary depending on the amount of blocking that is occurring. • The heart rate is usually below 100 and may be below 60 beats per minute.

47. Third degree A V block Complete heart block is a medical emergency. All impulses that are initiated above the ventricle are not conducted to the ventricle No communication between the atria and the ventricles and creating complete independence of the two systems. Thus, there is no relationship between P-waves or QRS complexes. Treatment for complete heart block involves permanent pacemaker insertion, with atropine and isoproterenol injection or infusion used in the acute situation. In Figure, the needlelike spikes indicate that an artificial pacemaker is depolarizing the ventricles at a rate of 60 BPM.

48. The characteristics of complete heart block include the following: • P waves are present, regular, and of identical configuration. • The P waves have no relationship to the QRS complex because the atria are firing at their own inherent rate. • The QRS complexes are regular in that the R-R intervals are regular. • The QRS duration may be wider than 0.10 second if the latent pacemaker is in the ventricles. • The heart rate depends on the latent ventricular pacemaker and may range from 30 to 50 beats per minute.

49. THIRD DEGREE AV BLOCK

50. MYOCARDIAL ISCHEMIA OR INFARCTION During myocardial ischemia, blood flow to a portion of myocardium is compromised, resulting in alteration of myocardial metabolism. If full thickness of heart wall commonly of left ventricle is depleted of its perfusion this is transmural infarction, S-T segment shift has significant diagnostic value. For example S-T segment elevation is associated with transmural Ml.

51. MYOCARDIAL ISCHEMIA OR INFARCTION

52. MYOCARDIAL ISCHEMIA OR INFARCTION Whereas S-T segment depression is associated with non transmural or subendocardial MI where percentage of wall is effected Onset of S-T segment depression during activity is often considered diagnostic of myocardial ischemia.

53. ST DEPRESSION

54. MYOCARDIAL ISCHEMIA OR INFARCTION A prominent, pathological Q-wave is indicative of a transmural MI (Lilly, 1993). “Non-Q " is synonymous with nontransmural concerning MI. The presence of a prominent Q-wave (Figure 11-28) does not, however, distinguish between an old or an acute event.  The T-wave may also undergo changes during myocardial ischemia or MI. During ischemia, for example, the T-wave may invert as a result of prolongation of repolarization (Guyton, 1991). Similarly, during MI, changes in the T - wave may "evolve" with the infarct, at first becoming indistinguishable within an elevated S-T segment, then inverting, then perhaps reverting to original configuration following the passage of time.

55. Q – WAVE

56. MI ECG changes The change that occur on the ECG depict the changing state of myocardium: Within minutes or hours, the ST segment becomes elevated in the leads facing the infarction. Within hours or days, there is development of broad deep Q –waves with R wave reduction and an inverting T wave. Abnormal Q wave is the definitive diagnosis for transmural infarction. W ithin a week or more, there is return of S-T segment to baseline but the other signs remain same. Months later, there is a possible gradual return of the T wave but persistent abnormal Q waves.

57. BUNDLE BRANCH BLOCK There is disturbance in the intraventricular conduction. QRS complex wide 2 peaks on R – wave P – wave, P-R intervals and heart rate normal. Depending on which leads demonstrates the changes, it can be established if the block is a left or right bundle branch block

58. Ventricular Hypertrophy Left ventricular hypertrophy a deep S wave occurs in V1 and a large R wave in V5 Signs of right ventricular hypertrophy are noted by changes found in lead V1 that include a large R wave and an S wave smaller than the R wave S wave in V1 (in mm) is added to the height of the R wave in V5 (in mm) the resulting number is greater than 35, then left ventricular hypertrophy is present.

59. Ventricular Hypertrophy

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