Generation of action potential
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Transcript of Generation of action potential
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Generation of action potential
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ECG Graph paper
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Unipolar precordial leads
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Normal ECG
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Guide in Reading ECG
• Standardization & technique• Rhythm• Rate: atrial & ventricular• P wave morphology & duration• P-R interval• QRS complex morphology & duration• ST segment• T-wave• U wave• Q-T interval• Hypertrophy and enlargement• arrhythmias
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Standardization
Heart rate 60 - 100 beats/minbradycardia < 60 tachycardia > 100
PR interval 0.12 – 0.20 secQRS < 0.12 secQRS axis - 30º to + 110ºQTc < 0.47 sec males
< 0.48 sec females
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Guide in Reading ECG
• Standardization & technique• Rhythm• Rate: atrial & ventricular• Axis• P wave morphology & duration• P-R interval• QRS complex morphology & duration• ST segment• T-wave• U wave• Q-T interval• Hypertrophy and enlargement• arrhythmias
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Rhythm
SA node – sinus
AV node – junctional
Ventricular rhythm
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Rhythm
Are there p waves? sinus, atrial fibrillation
Do they look similar? MFAT, wandering pacemaker
Are they regular? AF
Does a QRS complex follow each p wave? SVT, junctional rhythm, ventricular rhythm
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Guide in Reading ECG
• Standardization & technique• Rhythm• Rate: atrial & ventricular• Axis• P wave morphology & duration• P-R interval• QRS complex morphology & duration• ST segment• T-wave• U wave• Q-T interval• Hypertrophy and enlargement• arrhythmias
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Heart rate assessment by “rule of 300”
Determination of Heart Rate
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Measurement of Rate
• Formula 1: 300 # big squares between R-R
• Formula 2: 1500
# small squares between R-R
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Determination of Heart Rate• Is the atrial rate same as ventricular
rate?– PVC’s, PAC’s, 3rd degree AV block
• Is there normal-looking QRS complex after each p wave?
• What if there are no p waves?– Six second strip heart rate
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RATE
1. Sinus Bradycardia2. Sinus Tachycardia3. AV junctional rhythm
- Inherent rate of 40-60/min- No p waves- Normal looking QRS complex
4. Ventricular rhythm- Inherent rate of 20-40/min- No p waves- Bizaare-looking QRS complex
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Guide in Reading ECG
• Standardization & technique• Rhythm• Rate: atrial & ventricular• Axis• P wave morphology & duration• P-R interval• QRS complex morphology & duration• ST segment• T-wave• U wave• Q-T interval• Hypertrophy and enlargement• arrhythmias
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Hexaxial System
Determination of Axis
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QRS axis
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Vectorial Analysis
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Determination of Axis
Axis = 90 x QRS in AVF
QRS in [ I] + QRS in [AVF]
Special cases: • negative QRS deflection in I
– Add 90 to result
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Guide in Reading ECG
• Standardization & technique• Rhythm• Rate: atrial & ventricular• Axis• P wave morphology & duration• P-R interval• QRS complex morphology & duration• ST segment• T-wave• U wave• Q-T interval• Hypertrophy and enlargement• arrhythmias
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P wave morphology and duration
• No p waves– Atrial fibrillation
• Multiple p waves– Multifocal atrial tachycardia– Wandering pacemaker
• Notched p wave– Left atrial enlargement
• Peaked p wave– Right atrial enlargement
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Guide in Reading ECG
• Standardization & technique• Rhythm• Rate: atrial & ventricular• Axis• P wave morphology & duration• P-R interval• QRS complex morphology & duration• ST segment• T-wave• U wave• Q-T interval• Hypertrophy and enlargement• arrhythmias
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P-R Interval
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P-R interval
• Prolongation– Hypokalemia– 1st degree AV block
• Shortening– Wolff-Parkinson White
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Guide in Reading ECG
• Standardization & technique• Rhythm• Rate: atrial & ventricular• Axis• P wave morphology & duration• P-R interval• QRS complex morphology & duration• ST segment• T-wave• U wave• Q-T interval• Hypertrophy and enlargement• arrhythmias
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QRS morphology and duration
• Normal looking– Supraventricular origin
• Bizarre looking– Ventricular in origin– Paced rhythm
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Guide in Reading ECG
• Standardization & technique• Rhythm• Rate: atrial & ventricular• Axis• P wave morphology & duration• P-R interval• QRS complex morphology & duration• ST segment• T-wave• U wave• Q-T interval• Hypertrophy and enlargement• arrhythmias
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ST segment
• Elevation– Infarction
• >1mm in limb leads• >2 mm in chest leads
• depression– Ischemia
• >1 mm in all leads from the J point
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Guide in Reading ECG
• Standardization & technique• Rhythm• Rate: atrial & ventricular• Axis• P wave morphology & duration• P-R interval• QRS complex morphology & duration• ST segment• T-wave• U wave• Q-T interval• Hypertrophy and enlargement• arrhythmias
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T and U waves
• T wave – Hypokalemia– 1st degree AV block
• Shortening– Wolff-Parkinson White
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Guide in Reading ECG
• Standardization & technique• Rhythm• Rate: atrial & ventricular• Axis• P wave morphology & duration• P-R interval• QRS complex morphology & duration• ST segment• T-wave• U wave• Q-T interval• Hypertrophy and enlargement• arrhythmias
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Determination of QT interval
Corrected QT interval = QT (actual)
R-R
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QT interval
• prolongation– hypocalcemia
• shortening– hypercalcemia
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Chamber Enlargement
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Atrial Enlargement (due to chronic lung disease or pulmonay embolus
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Atrial Enlargement (commonly seen in mitral valve disease)
II V1
B
V1
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Ventricular Enlargement
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Ventricular Enlargement
Right Ventricular HypertrophyR in V1 + S in V5-V6 >11 mmR in V1 >7mmR:S in V1 >1RAD > +90 degrees
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Ischemic Heart Disease
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Anatomy of Myocardial Infarction
Infarction area
ECG leads Coronary Artery
Branch
Extensive anterior
A, AVL, V1 – V6 Left, LM LAD, LCX
Anteroseptal V1 – V4 Left LAD Anterolateral I, AVL, V3 – V6 Left LCX
Inferior II, III, AVF Right 80% Left 20%
PDA
True posterior V1 – V2 (reciprocal)
Variable left/right
LCX PL
Anterior V3 – V4 Left LAD
*LAD = left anterior descending aretery; LCX = left circumflex arteryLM = left main artery; PDA = posterior descending artery; PL = posterolateral branches
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Evolution of Infarct
1. ST segment elevation2. Progressive decrease in ST segment elevation3. Q wave formation4. T wave flattening/inversion5. Q wave with upright T wave
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Significant Q wave
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RULES on Q waves
• Not significant in aVR• Ignored in V1 unless with abnormalities in
other precordial leads• Ignored in III unless with abnormalities in
II, AVFmore reliable if with St-T segment changes
• Not significant if located in V1-V3 in LBBB• Significant in V1-V2 in the presence of
RBBB• Pathologic if >= 0.04 sec and >25% of R
wave amplitude
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RHYTHM DISORDERS
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ATRIAL Arrhythmias
1. Atrial fibrillation2. Atrial flutter3. Wandering Pacemaker4. Multifocal Atrial tachycardia
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ATRIAL FIBRILLATION
- Most common sustained arrhythmia associated with increased CV mortality and morbidity
- Prevalence increasing with age, doubling with each successive decade, 70% in ages 65-85
- Multiplier effect on risk- 3-5x stroke- 3x CHF- 1.5-3x death
- Associated with heart disease but ~30% are without underlying heart disease
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ATRIAL FIBRILLATION
- Rapid and irregular atrial fibrillatory waves at a rate of 350 to 600/minute
- CRITERIA- Absent P waves- F waves vary in amplitude, morphology and
intervals- R-R intervals are irregularly irregular- Ventricular rate usually ranges from 90-170- QRS complexes are narrow unless AV
conduction is abnormal - Hypothesized to be due to multiple wavelets in
the atrium competing for the conduction to the AV node
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ATRIAL FIBRILLATION
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ATRIAL FLUTTER
- Atrial rate of 220 to 350/minute- CRITERIA
- Absent p waves- Biphasic saw-toothed flutter waves, fairly
regular- F waves vary in amplitude, morphology and
intervals- R-R intervals are irregularly irregular- Ventricular rate usually ranges from 90-170- QRS complexes are narrow unless AV
conduction is abnormal - Hypothesized to be due to multiple wavelets in
the atrium competing for the conduction to the AV node
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ATRIAL FLUTTER
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Escape Rhythm/Beat
1. Atrial - Sinus arrest causing escape rhythm- With p’ waves
2. Junctional- No P waves- 40-60/min inherent rate- Produces a series of lone QRS complexes
3. Ventricular- may occur in complete AV block
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Escape Rhythm/Beat
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Sinoatrial block
- Complete failure of a P wave to appear- A cycle appears which is twice the
anticipated P-P interval- Transient doubling of P-P interval
- SA exit block- No visible P-QRST complex for more than 1 cycle- Normal P wave morphology, before and after the
pause- Pause is preceded and followed by a normal P-P
cycle- P-P interval is a mutliple of the normal P-P interval
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SA block
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SINUS ARREST vs SINUS PAUSE
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Wandering Pacemaker
- Impulses originate from different foci in the atrium and even AV node
- Sinus node may still be dominant- >= 3 P wave morphologies, with varying
P-R intervals, resulting in varying R-R intervals
- Heart rate <100- May be seen in
- Increased vagal tone- Digitalis effect- Organic heart disease
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Wandering Pacemaker
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Multifocal Atrial Tachycardia
- Irregular atrial rate > 100- P wave shows >= 3 different morphologic
patterns and varying PR intervals- Varying P-P and P-R intervals result in
avrying R-R intervals
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Multifocal Atrial Tachycardia
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HEART BLOCKS
1. 1st degree2. 2nd degree
- Type 1 Wenkeboch- Type 2 Mobitz II
3. Complete AV block4. Bundle Branch Block
- Right bundle branch block- Left bundle branch block
5. Hemiblocks- Left anterior hemiblock- Left posterior hemiblock
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• 1st degree– PR interval > 0.20s
• 2nd degree (type1 and 2)– Type 1 – PR interval becomes longer until depolarization is
not conducted anymore– Type 2 – AV conduction is blocked
• 3rd degree– AV dissociation– Variable PR and RP intervals– QRS rate is usually constant and lies within the range of 15-
70 beats /min
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Trifascicular Conduction System
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Right Bundle Branch Block
• Lead V1 late intrinsicoid, M-shaped QRS (RSR pattern)
• Lead V6 early intrinsicoid, wide S wave• Lead I wide S wave
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Right Bundle Branch Block
• Associated with– RHD– Cor pulmonale/RVH– Myocarditis– IHD– Degenerative disease of the conduction system– Pulmonary embolus– ASD
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Right Bundle Branch Block
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Left Bundle Branch Block
• Lead V1 QS or rS• Lead V6 late intrinsicoid, no Q waves,
monophasic R• Lead I monophasis R, no Q wave
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Left Bundle Branch Block
• Associated with – CAD– HHD– Dilated cardiomyopathy
-- unusual for LBBB to exist in the absence of organic disease
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Left Bundle Branch Block
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Left Anterior Hemiblock
• LAD (usually -30 to -60 degrees)• Small Q in leads I and aVL, small R in II, III and aVF• Usually normal QRS duration• Late intrinsicoid deflection in aVL• Increased QRS voltage in limb leads
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Left Anterior Hemiblock
• Usually benign in the absence of apparent organic heart disease and not associated with block in the other fascicles
• Can also occur in– CAD– Chagas disease– Infiltrative and inflammatory diseases– CHDs– Sclerodegenerative disorder
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Left Anterior Hemiblock
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Left Posterior Hemiblock
• RAD (usually + 120 degrees)• Small R in leads I and aVL, small Q in II, III and aVF• Usually normal QRS duration• Late intrinsicoid deflection in aVF• Increased QRS voltage in limb leads• No evidence of RVH
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Left Posterior Hemiblock
• Can occur in– Cardiomyopathies– Myocarditis– Hyperkalemia– Acute cor pulmonale– chronic degeneerative and fibrotic processes of the
conducting system– Aretriosclerotic cardiovascular disease
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Left Posterior Hemiblock
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Bifascicular Block
• Complete LBBB• RBBB with either LAHB or LPHB• Duration of QRS complex is prolonged to 0.12s
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Bifascicular Block
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Trifascicular Block
• Bifascicular block associated with 1st degree AV block
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Trifascicular Block
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Premature Complexes
1. Premature Atrial Complex2. Junctional Premature Beats3. Ventricular Premature Beats
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Premature Complexes - PACs
- Premature atrial activation arising from a site other than the sinus node
- P wave occuring relatively early in the cardiac cyle
- with a different morphology from the sinus P wave
- PR interval different from that during the sinus rhythm
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Premature Complexes - PACs
- Not life-threatening by themselves- But may also start a VT- May be asymptomatic or cause a
sensationof “skipping” or palpitations- May be associated with normal conduction
or aberrant conduction
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Premature Complexes - PACs
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Premature Complexes – Junctional Premature Beats
- Arise from the AV node or in the His bundle
- A premature normal QRS complex is closely accompanied by an “upside down” P wave
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Premature Complexes – Ventricular Premature Beats
- Duration of more than 0.12s- Bizarre morphology T wave in the
opposite direction from the QRS vector- A fully compensatory pause- Ventricular bigeminy, trigeminy,
quadrigeminy, couplet
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Premature Complexes – Ventricular Premature Beats
- May be present in - Normal individuals- MVP- Hypertension and LVH- Chronic HD- Acute MI- cardiomyopathy
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Miscellaneous• Poor R wave progression
– < 3mm R wave in V3
• Low QRS– < 5mm QRS amplitude in limb leads– <10mm QRS amplitude in chest leads
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