3-LEAD ECG CRASH COURSE. Mrs Dagmar Muhlbauer NDip AET; BTech EMC; MTech EMC August 2016

Transcription

1 3-LEAD ECG CRASH COURSE Mrs Dagmar Muhlbauer NDip AET; BTech EMC; MTech EMC August 2016

2 Anatomy & Physiology Recap: Heart sits in middle of chest at a slight angle pointing downward, to the left and slightly anterior. RV dominates the anterior view RV dominates visual view LV dominates electrical view CO = HR x SV HR is the most important variable in maintaining CO

3 Anatomy & Physiology Recap: AV septum is non-conductive tissue between the atria and ventricles Acts like a firewall The only electrical communication between the atria and ventricles is the AV node.

4 Anatomy & Physiology Recap: Main pacemaker of the heart is the SA node found in RA (60-100bpm) Internodal pathways AV node (RA) slows down conduction from atria to ventricles to allow for atrial contraction to occur (45-50bpm) Bundle of His gives rise to left and right bundle branches in RA and intraventricular septum Left and right bundle branches (40-45bpm) Purkinje system initiate ventricular depolarization (35-40bpm)

5 Components of the ECG: P wave: Atrial depolarization Wave starts when SA node fires Includes transmission through three internodal pathways, Bachman bundle and atrial myocytes 0.06 to 0.12 seconds

6 Components of the ECG: Tp wave: Atrial repolarization Not seen as occurs at the same time as the QRS

7 Components of the ECG: PR segment: End of P wave to the start of the QRS

8 Components of the ECG: PR interval: Time period from start of P wave to QRS Includes P wave and PR segment Covers all events from initiation of electrical impulse in SA node up to ventricular depolarisation seconds

9 Components of the ECG: QRS complex: Ventricular depolarization Q = first negative deflection R = first positive deflection after P S = first negative deflection after R seconds or half of the PR interval Pathological Q wave: Height is equal to or greater than ⅓ the height of the R wave

10 Components of the ECG: ST segment: End of QRS to beginning of T wave Electrically neutral time for heart between ventricular depolarization and repolarization J-Point: Point where QRS ends and ST begins

11 Components of the ECG: T wave: Ventricular depolarization

12 Components of the ECG: QT interval: QRS complex + ST segment + T wave Ventricular depolarization to ventricular repolarization

13 ECG paper: Little box = 0.04 seconds Big box = 0.20 seconds (5 x little boxes) Big boxes x 5 = 1 second Small marks along bottom of strip every 3 seconds

14 ECG tools: Calipers ECG ruler Straight edge (paper)

15 Calculating rate: Remember that the P wave rate (atrial) may be different to QRS rate (ventricular). Find a QRS that starts on a thick line which is the starting point Then go to exact spot of next QRS (end point). Count the thick lines between the 2 spots.

16 Calculating rate: Print a 6 second strip 30 large boxes = 6 seconds Count the number of complexes x 10 = rate/min

17 Terminology recap: Chronotrope: Change in HR Positive chronotrope causes increase in HR Negative chronotrope causes decrease in HR Dromotrope: Change in speed of conduction through AV junction Positive dromotrope causes increase in AV node conduct velocity Negative dromotrope causes decrease in AV node conduct velocity Inotrope: Change in myocardial contractility Positive inotrope causes increase in myocardial contractility Negative inotrope causes decrease in myocardial contractility

18 ECG Leads: Lead I: +ve L clavicle -ve R clavicle Provides info about left lateral wall of heart Lead II: +ve electrode just below L pectoral muscle -ve R clavicle Provides info about inferior wall of heart Lead III: +ve electrode just below L pectoral muscle -ve L clavicle

19 ECG Leads: Lead II commonly used for cardiac monitoring The positioning of the +ve and ve electrodes in this lead most closely resembles the pathway of current flow in normal atrial and ventricular depolarization.

20 Steps to analyse a strip: 1. Rate (atrial & ventricular)? 2. Regular / irregular? If irregular, is it regularly irregular or irregularly irregular? 3. P waves? Present? Uniform? P wave before each QRS? 4. PR interval? Within normal limits? Constant?

21 Steps to analyse a strip: 5. QRS complexes? P waves and QRS associated with each other? Narrow? 0.10 seconds (supraventricular) Wide? > 0.12 seconds (ventricular) QRS uniform throughout? Any dropped beats?

22 Arrhythmia zones of the heart: Sinus Node Arrhythmias: Supraventricular When the heart functions normally, SA node acts as a primary pacemaker The autonomic nervous system innervates the SA node through the vagus nerve Stimulation of vagus: firing of SA node Stimulation of SNS it

23 Arrhythmia zones of the heart: Atrial Arrhythmias: Supraventricular Result from impulses originating in areas outside the SA node

24 Arrhythmia zones of the heart: Junctional Arrhythmias: Supraventricular Originate in the AV junction (area around AV node and bundle of His) Occurs when SA node is suppressed and fails to conduct impulses or when a block in conduction occurs

25 Arrhythmia zones of the heart: Ventricular Arrhythmias: Originate in the ventricles below the bundle of His Occur when electrical impulses depolarize the myocardium using a different pathway from normal impulses QRS complex will be wider because of prolonged conduction through ventricles

26 Normal Sinus Rhythm: Impulse starts in SA node & progresses to ventricles through normal conduction pathway Rhythm: Regular Rate: Normal P wave: P wave for every QRS; similar in size and shape QRS complexes: Similar in size and shape ( seconds) PR interval: Normal ( seconds) QT interval: Normal ST segment: Normal T waves: Normal

27 Sinus Bradycardia: Normal response to demand for blood flow. Vagal stimulation & sympathetic stimulation Automaticity in SA node Rhythm: Regular Rate: <60bpm P wave: P wave for every QRS; similar in size and shape QRS complexes: Similar in size and shape ( seconds) PR interval: Normal ( seconds) QT interval: Normal ST segment: Normal T waves: Normal

28 Sinus Tachycardia: Results in reduced CO Rhythm: Regular Rate: >100 but <160bpm (except during exercise) P wave: P wave for every QRS; similar in size and shape QRS complexes: Similar in size and shape ( seconds) PR interval: Normal ( seconds) QT interval: Normal ST segment: Normal T waves: Normal

29 Sinus Arrhythmia: Pacemaker cells of SA node fire irregularly Rhythm is irregular & corresponds with respiratory cycle During inspiration: An increase in the flow of blood back to the heart reduces vagal tone which HR P-P interval shortens During expiration: VR decreases which increases vagal tone and HR P-P interval lengthens Cyclic irregular rhythm that varies with respiratory cycle

30 Sinus Arrest: Disorder of impulse formation Due to lack of electrical activity in the atrium (atrial standstill) Atria aren t stimulated and an entire PQRST complex is missing Sinus pause: Atrial standstill when 1 or 2 beats aren t formed Sinus arrest: When 3 or more beats aren t formed SA node fails to generate an impulse Causes: Acute infection Heart disease Vagal stimulation

31 Premature Atrial Contraction: Originate outside the SA node Result from irritable focus in the atria that takes over as pacemaker for one or more beats SA node fires an impulse but then irritable focus jumps in, firing its own impulse before SA node fires again Baseline rhythm is regular Rhythm: Irregular Rate: Depends P wave: Present but abnormal QRS complexes: Normal. Similar in size and shape ( seconds) PR interval: Normal ( seconds) QT interval: Normal ST segment: Normal T waves: Normal or abnormal with some embedded P waves

32 Atrial Tachycardia: Supraventricular tachycardia Rhythm originates above the ventricles Rhythm: Regular Rate: Atrial rate of bpm P wave: Almost hidden in T wave QRS complexes: Normal. Similar in size and shape ( seconds) PR interval: Normal ( seconds) QT interval: Normal ST segment: Normal T waves: Distorted by P wave

33 Multifocal Atrial Tachycardia: Supraventricular tachycardia Numerous atrial foci firing intermittently Produces varying P waves Rhythm: Irregular Rate: Atrial rate of bpm P wave: Configuration varies QRS complexes: Normal. Similar in size and shape ( seconds) PR interval: Varies QT interval: Normal ST segment: Normal T waves: Distorted by P wave

34 Wandering Atrial Pacemaker: Irregular rhythm Pacemaker changes its focus from the SA node to another area above the ventricles Origin of impulse wanders beat-to-beat from the SA node to other atrial sites or to AV junction Multifocal atrial tachycardia is a tachycardic version of Wandering Atrial Pacemaker Rhythm: Irregular Rate: Normal P wave: Configuration varies QRS complexes: Normal PR interval: Varies QT interval: Normal ST segment: Normal T waves: Normal

35 Atrial Flutter: Supraventricular tachycardia Originates in a single atrial focus. AV node fails to allow conduction of all the impulses to the ventricles Due to this, the ventricular rate is slower Rhythm: Atrial is regular and Ventricular is irregular Rate: Atrial rate of bpm & Ventricular rate is slower P wave: Classic saw-toothed experience QRS complexes: Normal PR interval: Unmeasurable QT interval: Unidentifiable ST segment: Normal T waves: Unidentifiable

36 Atrial Fibrillation: Chaotic, asynchronous, electrical activity in atrial tissue Stems from the firing of a number of impulses in re-entry pathways Ectopic impulses may fire at a rate of bpm, causing atria to quiver instead of contract Ventricles only respond to those impulses that make it through AV node Rhythm: Irregularly irregular Rate: Atrial rate is indiscernible & ventricular rate is slower P wave: Absent, replaced with fine fibrillatory waves QRS complexes: Normal PR interval: Indiscernible QT interval: Unmeasurable ST segment: Normal T waves: Indiscernible

37 Premature Junctional Contraction: An ectopic beat occurs when an irritable location within the AV junction acts as a pacemaker and fires prematurely or out of sequence The atria are depolarized in retrograde fashion causing an inverted P wave Ventricles depolarized normally PJC appears as an early beat Rhythm: Irregular Rate: Depends on underlying rhythm P wave: Inverted and precedes the QRS complex with PJC, otherwise normal QRS complexes: Normal PR interval: Normal for underlying rhythm and 0.06secs for PJC QT interval: Normal ST segment: Normal T waves: Normal

38 Junctional Escape Beat: A beat that occurs after a conduction delay from the atria Normal intrinsic firing rate of cells in AV junction is 40-60bpm AV junction can take over as the pacemaker if the SA node slows down or fails to conduct Prevents ventricular standstill Rhythm: Irregular Rate: Depends on underlying rhythm but usually slow P wave: Underlying rhythm may be normal but JEB has inverted or no P wave QRS complexes: Normal PR interval: Normal QT interval: Normal ST segment: Normal T waves: Normal

39 Junctional: String of beats that occurs after a conduction delay from the atria Normal intrinsic firing rate of cells in AV junction is 40-60bpm AV junction can take over as the pacemaker if the SA node slows down or fails to conduct Prevents ventricular standstill Rhythm: Regular Rate: 40-60bpm P wave: Absent or inverted and preceding each QRS QRS complexes: Normal PR interval: Not present or normal QT interval: Normal ST segment: Normal T waves: Normal

40 Accelerated Junctional: Irritable focus in the AV junction that speeds up to take over as the heart s pacemaker The atria are depolarized by means of a retrograde conduction and the ventricles function normally Rhythm: Regular Rate: bpm P wave: Absent QRS complexes: Normal PR interval: Unmeasurable QT interval: Normal ST segment: Normal T waves: Normal

41 Junctional Tachycardia: 3 or more PJCs occur in a row An irritable focus from the AV junction has enhanced automaticity, overriding the SA node to function as the pacemaker Rhythm: Regular Rate: bpm P wave: Inverted or absent QRS complexes: Normal PR interval: Unmeasurable or normal if present and inverted QT interval: Normal ST segment: Normal T waves: Normal

42 Premature Ventricular Contraction: Ectopic beat Electrical irritability in the ventricular conduction system or muscle tissue Rhythm: Irregular Rate: Depends on underlying rhythm P wave: Absent with PVC but present with other QRS complexes QRS complexes: Wide & bizarre for PVC; normal for underlying rhythm PR interval: None in PVC; normal in underlying rhythm QT interval: Normal ST segment: Normal T waves: Normal

43 Premature Ventricular Contraction: Couplets: 2 PVCs in a row Salvo: 3 or more PVCs in a row Considered a run of VT (dangerous) Multiform: PVCs that look different from one another Arise from different sites Bigeminy / Trigeminy: PVC every other beat = bigeminy PVC every third beat = trigeminy

44 Premature Ventricular Contraction: Treatment: Lignocaine Hydrochloride: Control of haemodynamically compromising PVCs, i.e. complex ventricular ectopy (symptomatic / unstable patient) associated with AMI / ACS: Multiform (multifocal) Repetitive (couplets, salvos, or > 3) R on T pattern Complex ventricular ectopy in the setting of myocardial ischemia or causing haemodynamic instability should be suppressed. (Only in the setting of symptomatic, complex ectopy is lignocaine likely to benefit a patient having an AMI / ACS). Loading dose: 1mg/kg slowly IVI Repeat loading dose: 0.5mg/kg every 5 minutes Maximum dose: 3mg/kg Follow with maintenance infusion of 1-4mg/min upon restoration of a stable rhythm 100mg/5ml (2%) ampoule

45 Ventricular Escape Beat: Ventricular escape beats occur when the rate of electrical discharge reaching the ventricles falls below the rate of ventricular depolarisation Escape beat usually occurs 2-3 seconds after an electrical impulse has failed to reach the ventricles Acts to prevent cardiac arrest Rhythm: Irregular Rate: Depends on underlying rhythm but usually bradycardic P wave: Absent with PVC but present with other QRS complexes QRS complexes: Wide & bizarre for PVC; normal for underlying rhythm PR interval: None in PVC; normal in underlying rhythm QT interval: Normal ST segment: Normal T waves: Normal

46 Idioventricular: Rhythms of last resort Act as safety mechanism to prevent ventricular standstill when no impulses are conducted to the ventricles from above the bundle of His The cells of the His-Purkinje system take over and act as the heart s pacemaker Rhythm: Regular Rate: 20-40bpm P wave: Absent QRS complexes: Wide & bizarre PR interval: Unmeasurable QT interval: 0.60 seconds ST segment: Absent T waves: Normal

47 Accelerated Idioventricular: Same characteristics as idioventricular, just faster Rhythm: Regular Rate: bpm P wave: Absent QRS complexes: Wide & bizarre PR interval: Unmeasurable QT interval: 0.60 seconds ST segment: Absent T waves: Normal

48 Ventricular Tachycardia: Three or more PVCs occur in a row Ventricular rate exceeds 100bpm Results from increased myocardial irritability Monomorphic or Polymorphic Rhythm: Regular Rate: bpm P wave: Absent QRS complexes: Wide & bizarre PR interval: Unmeasurable QT interval: Unmeasurable ST segment: Absent T waves: Opposite direction of QRS

49 Torsades de Pointes: Twisting about the points Special form of polymorphic VT QRS complexes rotate about the baseline deflecting downward and upward for several beats Rhythm: Irregular Rate: bpm P wave: Absent QRS complexes: Wide with changing amplitude PR interval: Unmeasurable QT interval: 0.60 seconds ST segment: Absent T waves: Normal

50 Torsades de Pointes: Treatment: Pulseless = Defibrillation & CPR Pulse: Magnesium Sulphate 1 2g (2 to 4 ml of a 50% solution) Dilute 1g/2ml vial to 10ml with sterile water = 10% solution. Give slowly, not exceeding 1.5ml/min, with continuous careful monitoring. Lignocaine hydrochloride if Magnesium not available or ineffective Cardioversion

51 Ventricular Fibrillation: Chaotic pattern of electrical activity in the ventricles in which electrical impulses arise from many different foci Produces no effective muscular contraction and no CO Rhythm: Irregulary irregular Rate: Undetermined P wave: Absent QRS complexes: Indiscernible PR interval: Unmeasurable QT interval: N/A ST segment: Absent T waves: Indiscernible

52 AV Blocks: Interruption in the conduction of impulses between the atria and ventricles Block can occur at AV node, bundle of His or bundle branches

53 1 st Degree AV Block: Impulses from the atria are consistently delayed during conduction through AV node Conduction eventually occurs, it just takes longer than normal E.g. people walking in line through a doorway, but each person hesitates before crossing the threshold Rhythm: Regular Rate: Based on underlying rhythm P wave: Normal QRS complexes: Normal PR interval: >0.20 seconds QT interval: Normal ST segment: Normal T waves: Normal

54 2 nd Degree Type I AV Block: Occurs when each successive impulse from the SA node is delayed slightly longer than the previous impulse Pattern continues until an impulse fails to be conducted to the ventricles Then cycle repeats E.g. line of people trying to get through a doorway, each one taking longer and longer until finally one cant get through Rhythm: Atrial regular and ventricular irregular Rate: Atrial rate and ventricular rate will differ with atrial rate being faster P wave: Normal QRS complexes: Normal PR interval: Gradually longer with each successive beat until a P wave fails to conduct to ventricles QT interval: Normal ST segment: Normal T waves: Normal

55 2 nd Degree Type II AV Block: Occasional impulses from the SA node fail to conduct to the ventricles You wont see the PR interval lengthen before the impulse fails to conduct E.g. people passing through a doorway at the same speed, except that, periodically, one of them just cant get through Rhythm: Atrial regular and ventricular irregular Rate: Atrial rate and ventricular rate will differ with atrial rate being faster P wave: Normal, but some not followed by a QRS QRS complexes: Normal PR interval: Constant but may be normal or prolonged QT interval: Normal ST segment: Normal T waves: Normal

56 3 rd Degree AV Block: Impulses from atria are completely blocked at the AV node and cant be conducted to the ventricles E.g. line of people waiting to go through a doorway but no one can go through Atria and ventricles act independently Atria remain under control of SA node (60-100bpm) Ventricles originate from AV node (40-60bpm) Rhythm: Regular Rate: Atrial rate and ventricular rate will differ P wave: Normal QRS complexes: Normal / Wide PR interval: Varies QT interval: Normal ST segment: Normal T waves: Normal

57 Agonal Rhythm: Similar in appearance to an idioventricular rhythm But occurs at a rate of < 20bpm Dying heart Basically asystole with an occasional P wave or QRS complex QRS complexes are very wide and very bizarre Treat as asystole

58 Asystole: Ventricular standstill No electrical activity in the heart and no CO Rhythm: N/A Rate: Undetermined P wave: Absent QRS complexes: Absent PR interval: Unmeasurable QT interval: N/A ST segment: Absent T waves: Absent

59 Pacemakers: Atrial Pacemakers: Ventricular Pacemakers: Loss of capture:

60 References: 1. ECGs Made Easy; B Aehlert, RN; Mosby Lifeline; Arrhythmia Recognition: The Art of Interpretation; TB Garcia, MD, FACEP & GT Miller, NREMT-P; Jones & Bartlett; ECG Interpretation Made Incredibly Easy, 5 th Edition; Lippincott Williams & Wilkins; Wolters Kluwer; 2011.