Basic ECG Interpretation Workshop
King Fahad Medical City Academic and training Affaires Nursing Education Department
Basic ECG Interpretation Workshop Presented by: Adel Hasanein, RN, BSN Nurse Clinician Supervised by: Usama Saleh, RN, PhD Head,Nursing Education Department
Outline 1. Definition of the ECG 2. Types of pathology can we identify and study from ECGs 3. Review of the conduction system 4. ECG Leads 5. ECG waveforms and intervals 6. Determining heart rate 7. ECG-common rhythm abnormalities
What is an ECG? • An Electrocardiogram (ECG or EKG) is a test that records the electrical activity of the heart. • ECG is used to measure the rate and regularity of heartbeats as well as the size and position of the chambers, the presence of any damage to the heart, and the effects of drugs or devices used to regulate the heart (such as a pacemaker).
How does it works… •
The heart is a muscle with wellcoordinated electrical activity, so the electrical activity within the heart can be easily detected from outside of the body.
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After the appropriate leads are attached to the body, a heated stylus moves upward with positive voltage and downward for negative voltage.
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On the moving heat-sensitive paper, voltage is traced out.
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The test takes about five minutes, and it is fairly painless.
THE CARDIAC CYCLE Systole
Diastole
What types of pathology can we identify and study from ECGs? • • • • •
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)
The Normal Conduction System
The Normal Conduction System • SA node: – Impulse formation is initiated – Dominant pacemaker of the heart.
• Internodal Pathways: – Carry the impulse from the SA node to the AV node
• AV node: – Protects the ventricles from: • run away atrial rates and delays conduction allowing for ventricular filling time.
– Receives oxygenated blood from the RCA (60%)
• Bundle Branches – Right and Left bundle branches.. – The bundle branches receive virtually all their oxygenated blood from the LCx.
• Purkinje fibers: – The bundles divides numerous times into the Purkinje fibers. • Final pathways of conduction to the ventricles
Types of ECG lead • There are two basic types of ECG leads: • Bipolar leads (standard limb leads) utilize a single positive and a single negative electrode between which electrical potentials are measured. • Unipolar leads (augmented leads and chest leads) have a single positive recording electrode and utilize a combination of the other electrodes to serve as a composite negative electrode
Lead Position • A typical ECG report shows the cardiac cycle from 12 different vantage points (I, II, III, aVR, aVL, aVF, V1-V6). • Lead I represents activity that is going from the right arm to the left arm • Lead II represents activity that is going from the right arm to the left leg • Lead III represents activity that is going from the left arm to the left leg
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aVL is placed on the left arm (or shoulder) aVF is placed on the left leg (or hip) aVR is placed on the right arm (or shoulder) V1- 4th intercostal space to the right of sternum V2- 4th intercostal space to the left of sternum V3- halfway between V2 and V4 V4- 5th intercostal space in the left mid-clavicular line V5- 5th intercostal space in the left anterior axillary line V6- 5th intercostal space in the left mid axillary line
Summary of Leads
Bipolar
Limb Leads
Precordial Leads
I, II, III
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(standard limb leads)
Unipolar
aVR, aVL, aVF (augmented limb leads)
V1-V6
Arrangement of Leads on the ECG
Components of the ECG Tracing • • • • • •
P wave PR interval QRS complex ST segment T wave U wave
P wave : atrial depolarization the 1st up right wave round in shape the amplitude not more than 2.5mm & up to 0.12 second in duration .
Q wave : the 1st downward deflection below isoelectric line following the p wave , if present its depth not exceeds one third R wave ( 2mm)
R wave : the 2nd upward deflection S wave : the 2nd downward deflection
• The QRS should not exceed 0.12 sec in duration
ST segment : the isoelectric line between the end of QRS and the beginning of T wave
QT interval : the interval between the beginning of Q wave and the end of T wave , it measures ( 0.32 – 0.40 ) second
• Vertically each large square = 0.5 mv , so each small square = 0.1 mv . • Horizontally each large square = 0.04 second , so each small square = 0.2 second Speed 25
• We have many ways to measure the heart rate 1- to count number of small boxes between 2 R waves , then to divide 1500 by number of small boxes . 2- to count number of large boxes between 2 R waves , then divide 300 by number of large boxes .
What is the heart rate?
www.uptodate.com
What is the heart rate?
www.uptodate.com
What is the heart rate?
The Rule of 300 It may be easiest to memorize the following table: # of big boxes 1
Rate
2
150
3
100
4
75
5
60
6
50
300
The 12 leads ECG
Old Fashion
Why is that important? • Electrical impulse must travel to all parts of the ventricle quickly so that all parts of the ventricle contract simultaneously • The normal QRS is narrow (less than 0.12 seconds), meaning that the impulse has depolarized all parts of the ventricle in less than 0.12 second • Wide QRS indicates a delay in conduction, either because of block in one of the bundle branches or because the impulse is not traveling through the specialized conducting system
Quiz Question: • What is the width of the normal QRS complex in little squares?
What will happen if there is a block in the conducting system? • Block at or near the AV node causes AV block (delay will cause a long PR interval, first degree AV block)
• Block in the left or right bundle causes LBBB or RBBB
Why do we care about Bundle Branch Block? • Block may be congenital or due to degeneration of the conducting system without serious heart disease OR
• May be a sign of serious heart disease: ischemia or infarction, cardiomyopathy
Wide QRS beat? • If preceded by a sinus p wave at the appropriate PR interval, this is a sinus beat which is wide due to a block in the left or right bundle • If no p wave, beat originates in the ventricle either prematurely (PVC) or because no other beat came along (ventricular escape beat)
Time for a stretch?
Fundamentals of ECG Interpretation • Rate • Rhythm and conduction • P wave morphology • PR interval • QRS width • QRS axis • QRS - Initial deflection in each lead - Up? Down? • QRS Voltage • QRS morphology • ST segment – Up? Down? Isoelectric? • T wave – Up? Down? Flat?
Initial deflection: Is there a Q wave? • The earliest part of the left ventricle to depolarize is the septum which depolarizes from left to right. • This will lead to a small upright deflection in V1V2 and a small negative deflection in the left leads I, aVL, and (V4-V6) as well as sometimes in the inferior leads. • These normal Q waves are narrow (< 0.04 seconds) and usually not deep and are known as septal Q’s.
Q waves of Myocardial Infarction • “Pathologic” Q waves are considered the hallmark of myocardial infarction • Q must be >.04 seconds in width and/or more than 25% of the height of the R wave in the same lead • aVR doesn’t count • Q in III alone doesn’t count
T wave • T waves are normally upright in most leads but are always negative in aVR and often negative in leads III and V1 • The T wave axis should be similar to the QRS axis • T waves should be symmetrical • Abnormal T waves can be caused by ischemia or infarction, hypertrophy, abnormal conduction patterns, drugs, metabolic changes, CNS events, etc.
Abnormal T waves • Inverted or flat where they should be upright • Often asymmetric • Often associated with abnormal ST segments (ST/T changes)
Causes of non-specific ST/T changes • Acute illness – hypoxia, anemia, fever, acidosis, acute abdomen – look at the date of the ECG and what happened on that date • Endocrine/metabolic abnormalities – hypokalemia, hypothyroidism • Drugs especially psychiatric drugs • Myocardial disease – ischemia, myocarditis, hypertrophy, cardiomyopathy • Normal? Athletic heart syndrome
Causes of dramatic T wave changes • Severe ischemia, myocardial infarction • LVH, hypertrophic cardiomyopathy • Athlete’s heart??? Prove it!
The QT interval
Long QT syndrome â&#x20AC;˘ A disorder of myocardial repolarization characterized by prolongation of the QT interval on the ECG â&#x20AC;˘ Associated with a life-threatening cardiac arrhythmia, Torsade de Pointes
â&#x20AC;˘ Acquired form due to various prescription drugs, often in combination, metabolic disturbances, eating disorders
When to worry about long QT? • When the ECG shows a QT interval greater than0.44 seconds •When there is a family history of sudden cardiac death at a young age • Personal or family history of unexplained syncope or seizures at a young age • Personal or family history of syncope or cardiac arrest with exercise (especially swimming) or with emotional stress
â&#x20AC;˘ Occurs when the SA node discharge an impulses regularly at a rate less than 60 bpm , the complexes and intervals remain within normal time duration
1- RHYTHM : regular 2-RATE : less than 55 bpm . 3- P WAVE : normal (up right ,rounded ) 4-PR INTERVAL : normal 5- QRS COMPLEX : normal 6-ST SEGMENT: isoelectric 7- T WAVE : normal ( symmetric , rounded ) 8-CONDUCTION : normal electrical path
CAUSES : 1- vagal stimulation 2- increased intra cranial pressure 3- myocardial infarction 4- use of beta blockers
Occurs when the SA node discharges an impulses in a rate of more than 100 bpm , some times the rate can be as high as 180 bpm
1- RHYTHM : regular 2-RATE : more than 100bpm . 3- P WAVE : normal (up right ,rounded ) 4-PR INTERVAL : normal 5- QRS COMPLEX : normal duration 6-ST SEGMENT: isoelectric 7- T WAVE : normal ( symmetric , rounded ) 8-CONDUCTION : normal electrical path way
CAUSES : 1-fever 2- anxiety 3-hypo volemia 4- congestive heart failure
• The rate usually increase with inspiration & decrease with expiration . • During expiration the parasympathetic vagal tone activated , so the heart rate decreased . • During inspiration the stretch receptors in the lung stimulate the cardioinhibitary centers in the medulla via fibers in the vagus nerve , so the heart rate increased .
1- RHYTHM : rate increased with inspiration ,decreased with expiration 2-RATE : varies between 50 -100 bpm . 3- P WAVE : normal (up right ,rounded ) 4-PR INTERVAL : normal 5- QRS COMPLEX : normal duration 6-ST SEGMENT: isoelectric 7- T WAVE : normal ( symmetric , rounded ) 8-CONDUCTION : normal electrical path way
CAUSES : During inspiration venous blood returning to the heart increases and vagal tone decreases resulting on tachy cardia & vice versa
â&#x20AC;˘ Occur when an ectopic atrial focus discharge an impulse before the next anticipated sinus node activation , these ectopic Ps have a bizarre appearance and can be pointed , inverted or notched
1- RHYTHM : regular except for ectopic beat 2-RATE : normal except for ectopic beat 3- P WAVE :normal ,pointed in atrial ectopic beat 4-PR INTERVAL : normal except for ectopic beat 5- QRS COMPLEX : normal duration
6-ST SEGMENT: isoelectric 7- T WAVE : normal ( symmetric , rounded ) 8-CONDUCTION : normal electrical path way after passing the AV junction
â&#x20AC;˘ Occurs when multiple irritable focuses in both atria started to initiate impulses that resulting in chaotic , irregular excitation of the atrium . â&#x20AC;˘ Its characterized by the appearance of numerous irregular fibrillatory waves on the rhythm strip , the ventricular wave also irregular depending on the conduction of the atrial impulses conduction through the AV junction .
• 1- RHYTHM: irregular for both atrium & ventricles . • 2- RATE : atrial ( 400-500 )bpm , ventricular ( 80 -180 ) bpm ( varies upon conduction . • 3- PR INTERVAL : absent . • 4- QRS COMPLEX : normal shape & duration • 5-CONDUCTION : bizarre atrial conduction , normal conduction after AV junction .
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occurs when there is a rapid but regular excitation from an ectopic focus in the atrium at rate of 300 bpm . The ventricular waves are regular , the ratio between atrial and ventricular rate varies between ( 2:1 & 3:1& 4:1 ) .
1- RHYTHM : atrial rhythm is regular ,ventricular rhythm regular & depend on the conduction . 2-RATE : atrial 288 bpm , ventricular 96 bpm . Ratio 3: 1 . 3- P WAVE : saw-tooth ; no true p waves , only flutter or F waves . 4- PR INTERVAL : absent .
5- QRS COMPLEX : normal shape & duration . 6- T WAVE : difficult to define . 7- CONDUCTION : ectopic atrial foci , impulses follow normal path way after AV junction .
â&#x20AC;˘ During an episode of SVT the heart beat is not controlled by SA node , another part of the heart overrides this role with faster impulses . â&#x20AC;˘ The source of the impulse is some where above ventricles , but the impulse then spread to the ventricles so the heart beats faster than normal .
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1- RATE: between (140 – 200) bpm . 2- RHYTHM : R-R interval regular . 3- P WAVE : absent . 4- P-R INTERVAL : absent .
• 5- QRS COMPLEX : narrow < 0.06 second . • 6- T WAVE : peaked T wave . • 7- CONDUCTION : the ventricles is stimulated from some where in the atria .
VENTRICULAR TACHYCARDIA
Develops when there is more than 3 consequences VEBs and the heart rate exceeds 100 bpm , such activity is due to enhanced automaticity and re-entry within the purkinji fibers . P wave not visible because its hidden in the QRS complex .
• 1- RHYTHM :regular . • 2-RATE : ventricular 180 bpm , it range is ( 100-200) bpm . • 3-P WAVE : not present , or hidden in the QRS complex . • 4-P-R INTERVAL : not present . • 5- QRS COMPLEX : uniform configuration . • 6- CONDUCTION : the ventricles are directly stimulated by an ectopic focus within the purkinji fibers network .
chaotic un coordinated ventricular depolarization , usually initiated by the R wave of a VEB striking the peak of the T wave of preceding beat . Because of chaotic activity the muscle mass on quivers & cardiac out put falls rapidly .
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1- RHYTHM : irregular , chaotic . 2-RATE : cannot be determined . 3- P WAVE : absent . 4- P-R INTERVAL : absent . 5- QRS COMPLEX : replaced by f wave . 6- CONDUCTION : un coordinated ventricular depolarization .
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Occurs when there is a delay in the transmission of electrical impulse through the AV node to the ventricles
1- RHYTHM : regular . 2- RATE : 45 bpm < 50bpm 3- P WAVE : normal . 4- P-R INTERVAL : 0.28 seconds 5- QRS COMPLEX : normal . 6- CONDUCTION : follow normal conduction pathway but there is a delay in the process .
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Occurs when conduction through the AV junction become progressively difficult with each successive impulse until finally a ventricular depolarization doesnâ&#x20AC;&#x2122;t occur .
• 1-RATE :ventricular = 68 bpm , atrial = 75 bpm . • 2- RHYTHM : atrial regular , but ventricular irregular . • 3- P WAVE : normal . • 4-P-R INTERVAL : lengthening with each successive beat . • 5-QRS COMPLEX :normal .
â&#x20AC;˘ 6- CONDUCTION : some of the impulses from the atria are blocked . P-R interval gets progressively longer until one P wave is not followed by QRST .
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In this arrhythmia 2 or more atrial impulses conducted normally , then the next impulse blocked without warning . Block may occur occasionally or at regular intervals . ( for every third beat ) ( 3:1) .
• 1- RATE : atrial 64 bpm , but ventricular depend on conduction . • 2- RHYTHM : P-P interval regular , R-R interval irregular . • 3- P WAVE : normal . • 4- P-R INTERVAL : 0.16 sec , absent in missed beats .
• 5- QRS COMPLEX : normal, some dropped beats . • 6- T WAVE : normal , some dropped as QRS • 7- CONDUCTION : Third atrial impulse is blocked .
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Occurs when the electrical impulses above the AV node are blocked , therefore no impulses conducted to the ventricles , if SA node blocked the junctional arises , if the block involve the junctional tissue , the idiodventricular rhythm arises .
• 1-RATE : atrial rate ( 60-100) bpm, ventricular rate (30-40) bpm . • 2- RHYTHM : P-P interval regular , R-R interval regular . • 3-P WAVE : normal . • 4-P-R INTERVAL : absent ( no relation between atria& ventricles )
• 5- QRS COMPLEX : depend on the site of pace maker , ( wide = purkinji fibers ) ( normal =junctional tissue ) • 6- T WAVE : absent . • 7- CONDUCTION : the atria & ventricles have independent pacemaker ,so there is no relationship between both .
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