cardiac arrhythmias dr. ahmad hersi. myocardium muscle action potential
TRANSCRIPT
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Cardiac Arrhythmias
Dr. Ahmad Hersi
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Action Potential of a Myocardial Cell+25
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-25
-50
-75
-100
Resting P otential - 90 m v
O vershoot +10 m v
N a+ C a++
K +
0
1
2
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Active TransportNa+ out K+ back in
A R P R R P S N P
C orrespond ing E C G O verlay
Myocardium Muscle Action Potential
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Normal Cardiac Cycle
Systole Diastole
Electrical Depolarization
“activate”
Repolarization
“recovery”
Mechanical Contract
“empty”
Relax
“fill”
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What does it tell us?• the electrical conduction through the heart• areas of ischemia or myocardial damage• LV Hypertrophy• electrolyte disturbances / drug toxicity
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The Electrical System of the Heart
AV Node
Posterior Inferior Fascicle
Anterior Superior Fascicle
Septal Depolarization Fibers
Purkinjie Fibers
Inter- nodal Tracts
Bundle of HIS
Left Bundle Branch
Right Bundle Branch
SA Node
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SA Node
AV Node
Inter-nodal Tract
Bundle of Kent
James Fibers
Conduction System of the Heart:
A Conceptual Model for Illustration
Bundle of HIS
Right Bundle Branch
Left Bundle Branch
Septal Depolarization Fibers
Anterior Superior Fascicle
Posterior Inferior Fascicle
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SA Node – “pacemaker” of
the heart (60-100bpm)
AV Node – junction of the
atria and ventricles (40-60bpm)
Bundles – Bundle of His
connects the AV node to the
bundle branches (20-40bpm)
AV Node
Inter- nodal Tracts
Bundle of HIS
SA Node
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What Is In Each Beat? (the cardiac cycle in waves, complexes, and intervals)
• P Wave – atrial contraction or depolarization, (usually upright)
• QRS Complex – time for ventricular contraction or depolarization (usually upright) (0.04 - 0.12sec) (delays in the bundle branches will widen the QRS)
• T Wave – ventricular repolarization “recharging” (usually upright)
• PR Interval – time between atrial depolarization to ventricular depolarization (beginning of P wave to beginning of QRS)(0.12 - 0.20sec) (prolonged PR = delays in the AV node conduction)
• QT Interval – represents one complete ventricular depolarization and repolarization (beginning of QRS to the end of the T wave) (0.32 – 0.44sec) (disturbances are usually due to electrolyte disturbances or drug effects)
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The ECG Complex with Interval and Segment Measurements
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ECG Paper and related Heart Rate & Voltage Computations
Memorize These 2
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Reading a Rhythm StripWhat Do I Look For?
► Regularity - What is the R – R Interval?
► Rate - Is the rate normal (60-100), slow, or fast? ***Six-second strip method - (30 big boxes) & multiply
times ten
► P Wave – Is there a P wave before every QRS? Is it upright?
► QRS Complex – Is there a normal QRS complex following each P wave? Wide or normal?
► T wave – How does your T wave look? Upright?
► Measure your intervals – PR Interval, QRS, QT
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Tehran Arrhythmia Center
Pacemakers of the Heart
• SA Node - Dominant pacemaker with an intrinsic rate of 60 - 100 beats/minute.
• AV Node - Back-up pacemaker with an intrinsic rate of 40 - 60 beats/minute.
• Ventricular cells - Back-up pacemaker with an intrinsic rate of 20 - 45 bpm.
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Rhythm Analysis
• Step 1: Calculate rate.
• Step 2: Determine regularity.
• Step 3: Assess the P waves.
• Step 4: Determine PR interval.
• Step 5: Determine QRS duration.
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Step 1: Calculate Rate
Option 1– Count the # of R waves in a 6 second rhythm
strip, then multiply by 10.
Interpretation? 9 x 10 = 90 bpm
3 sec 3 sec
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Step 1: Calculate Rate
• Option 2 – Find a R wave that lands on a bold line.– Count the # of large boxes to the next R wave. If
the second R wave is 1 large box away the rate is 300, 2 boxes - 150, 3 boxes - 100, 4 boxes - 75, etc. (cont)
R wave
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Step 1: Calculate Rate
• Option 2 (cont) – Memorize the sequence:
300 - 150 - 100 - 75 - 60 - 50
Interpretation?
300
150
100
75
60
50
Approx. 1 box less than 100 = 95 bpm
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Step 2: Determine regularity
• Look at the R-R distances (using a caliper or markings on a pen or paper).
• Regular (are they equidistant apart)? Occasionally irregular? Regularly irregular? Irregularly irregular?
Interpretation? Regular
R R
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Step 3: Assess the P waves
• Are there P waves?
• Do the P waves all look alike?
• Do the P waves occur at a regular rate?
• Is there one P wave before each QRS?
Interpretation? Normal P waves with 1 P wave for every QRS
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Step 4: Determine PR interval
• Normal: 0.12 - 0.20 seconds.
(3 - 5 boxes)
Interpretation? 0.12 seconds
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Step 5: QRS duration
• Normal: 0.04 - 0.12 seconds.
(1 - 3 boxes)
Interpretation? 0.08 seconds
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Rhythm Summary
• Rate 90-95 bpm• Regularity Regular• P waves Normal• PR interval 0.12 s• QRS duration 0.08 s
Interpretation? Normal Sinus Rhythm
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Normal Sinus Rhythm
• Normal and constant P wave contours
• Normal P wave axis
• Rate between 60 and 100 bpm
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Anatomical Aspects of Normal Sinus Node
• Located at the superior anterolateral portion of right atrium near its border with the superior vena cava
• It is an epicardial structure near sulcus terminalis
• From endocardial approach the closest approach is near the superior end of crista terminalis
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Sinus Node Function
• The dominant cardiac pacemaker
• Highly responsive to autonomic influences
• Decreasing rate with vagal stimulation
• Increasing rate with sympathetic activity
• Normal sinus rate under basal conditions is 60-100 bpm.
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Sinus Tachycardia
130 bpm• Rate?• Regularity? Regular
Normal
0.08 s
• P waves?
• PR interval? 0.16 s• QRS duration?
Interpretation? Sinus Tachycardia
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Sinus Tachycardia
• Sinus rhythm exceeding 100 bpm in adults
• Usually between 100 and 180 bpm but may be higher with extreme exertion
• Maximum heart arte decreases wit age from near 200 bpm to less than 140 bpm
• Gradual onset and termination
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Sinus Tachycardia
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Sinus TachycardiaCauses
• Common in infancy and childhood• Normal response to a variety of physiological and
pathological stresses– Exertion, anxiety
– Hypovolemia, anemia
– Fever
– Congestive heart failure
– Myocardial ischemia
– Thyrotoxicosis
• Drugs• Inflammation
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Sinus Bradycardia
30 bpm• Rate?• Regularity? Regular
normal
0.10 s
• P waves?
• PR interval? 0.12 s• QRS duration?
Interpretation? Sinus Bradycardia
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Sinus Bradycardia
• Sinus rhythm at a rate less than 60 bpm
• Can result from excessive vagal or decreased sympathetic tone as well as anatomic changes in sinus node
• Frequently occurs in healthy young adults, particularly well-trained athletes
• Sinus arrhythmia often coexists
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Sinus Bradycardia
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Sinus BradycardiaJunctional Escape Beats
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Sinus Bradycardia Causes
• Hypothyroidism
• Drugs
• During vomiting or vasovagal syncope
• Increased intracranial pressure
• Hypoxia, hypothermia
• Depression
• Jaundice
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Sinus Arrhythmia
50-75 bpm• Rate?• Regularity? Phasic variations
normal
0.10 s
• P waves?
• PR interval? 0.12 s• QRS duration?
Interpretation? Sinus Arrhythmia
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Sinus Pause
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Sick Sinus Syndrome•A combination of symptoms (dizziness,
fatigue, confusion, syncope and congestive heart failure) caused by sinus node dysfunction
•Atrial tachyarrhythmias may accompany sinus node dysfunction
<bradycardia-tachycardia syndrome>
Tehran Arrhythmia Center
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AV BlockTypes
• First degree AV block
• Second degree AV block– Mobitz type I (Wenckebach)– Mobitz type II
• Third degree AV block (Complete heart block)
• High degree (advanced) AV block
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First Degree AV Block
60 bpm• Rate?• Regularity? Regular
Normal
0.08 s
• P waves?
• PR interval? 0.36 s• QRS duration?
Interpretation? 1st Degree AV Block
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PR Interval
PR interval
AV nodal blocksNormalHigh catecholamine
states
Wolff-Parkinson-White
> 0.20 s0.12-0.20 s< 0.12 s
Wolff-Parkinson-White 1st Degree AV Block
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First Degree AV Block
• Conduction time is prolonged but all impulses are conducted.
• PR interval exceeds 0.2 sec in adults
• Site of conduction delay may be in the AV node (most commonly), in the His-Purkinje system or both.
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First Degree AV Block
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Wenckebach AV Block
50 bpm• Rate?• Regularity? Regularly irregular
Nl, but 4th no QRS
0.08 s
• P waves?
• PR interval? Lengthens• QRS duration?
Interpretation? 2nd Degree AV Block, Type I
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Mobitz Type I Second Degree AV Block
• Also called Wenckebach block
• Typical type characterized by progressive PR prolongation culminating in a non-conducted P wave
• Narrow QRS in most cases
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WB
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Wenckebach Block
• Atypical pattern in over half the cases
• The site of block is almost always in the AV node.
• Generally benign and does not advance to more advanced AV block
• Can occur in normal children and well-trained athletes
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Mobitz Type II AV Block
40 bpm• Rate?• Regularity? Regular
Nl, 5th P no QRS
0.11 s
• P waves?
• PR interval? 0.18 s• QRS duration?
Interpretation? 2nd Degree AV Block, Type II
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Mobitz Type II Second Degree AV Block
• PR interval remains constant prior to the blocked P wave
• Commonly associated with bundle branch blocks
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2:1 AV Block
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2:1 AV BlockAV Nodal Level
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2:1 AV BlockInfra-nodal Level
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2:1 AV block Infra-nodal Level
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Complete Heart Block
40 bpm• Rate?• Regularity? Regular
No relation to QRS
Wide (> 0.12 s)
• P waves?
• PR interval? None• QRS duration?
Interpretation? 3rd Degree AV Block
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Complete AV block
• No atrial activity conducts to the ventricles• AV dissociation is present. The atria and
ventricles are controlled by independent pacemakers.
• Ventricular focus is usually located just below the site of block.
• Higher sites are more stable with a more faster escape rate.
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Complete AV block
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Remember• When an impulse originates in a ventricle,
conduction through the ventricles will be inefficient and the QRS will be wide and bizarre.
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AV Conduction DisturbancesEtiology
• Degenerative diseases are the most common causes
• A variety of other diseases may be responsible: myocardial infarction, drugs, acute infections, infiltrative diseases, neoplasms, etc.
• Hypervagotonia
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Premature Beats
• Premature Atrial Contractions (PACs)
• Premature Ventricular Contractions (PVCs)
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Tehran Arrhythmia Center
PAC
70 bpm• Rate?• Regularity? Occasionally irreg.
2/7 different contour
0.08 s
• P waves?
• PR interval? 0.14 s (except 2/7)• QRS duration?
Interpretation? NSR with Premature Atrial Contractions
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Tehran Arrhythmia Center
Narrow QRS Beats
• When an impulse originates anywhere in the atria (SA node, atrial cells, AV node, Bundle of His) and then is conducted normally through the ventricles, the QRS will be narrow (0.04 - 0.12 s).
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Tehran Arrhythmia Center
PVC
60 bpm• Rate?• Regularity? Occasionally irreg.
None for 7th QRS
0.08 s (7th wide)
• P waves?
• PR interval? 0.14 s• QRS duration?
Interpretation? Sinus Rhythm with 1 PVC
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Tehran Arrhythmia Center
Wide QRS Beats
• When an impulse originates in a ventricle, conduction through the ventricles will be inefficient and the QRS will be wide and bizarre.
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Tehran Arrhythmia Center
Ventricular Conduction
NormalSignal moves rapidly through the ventricles
AbnormalSignal moves slowly through the ventricles
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Tehran Arrhythmia Center
Ventricular Premature Complexes
Compensatory Pause
Interpolated VPC
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Tehran Arrhythmia Center
Atrial Fibrillation
100 bpm• Rate?• Regularity? Irregularly irregular
None
0.06 s
• P waves?
• PR interval? None• QRS duration?
Interpretation? Atrial Fibrillation
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Tehran Arrhythmia Center
Atrial Fibrillation
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Tehran Arrhythmia Center
Atrial Fibrillation
• The most common sustained arrhythmia
• Incidence increases progressively with age.
• Prevalence: 0.4% of overall population
• Mortality rate double that of control
• AF is characterized by disorganized atrial activity without discrete P waves
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Tehran Arrhythmia Center
Atrial Fibrillation
• Undulating baseline or atrial deflections of varying amplitude and frequency ranging from 350 to 600 bpm.
• Irregularly irregular ventricular response.
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Tehran Arrhythmia Center
Atrial Fibrillation
• Morbidity related to:– Excessive ventricular rate– Pause following cessation of AF– Systemic embolization– Loss of atrial kick– Anxiety secondary to palpitations– Irregular ventricular rate
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Tehran Arrhythmia Center
Atrial Fibrillation• Persistent AF usually in patients with
cardiovascular disease– Valvular heart disease
– Hypertensive heart disease
– Congenital heart disease
• Paroxysmal AF may occur with acute hypoxia, hypercapnia or metabolic or hemodynamic derangements
• Normal people with emotional stress or surgery or acute alcoholic intoxication
• Lone AF
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Tehran Arrhythmia Center
Atrial Fibrillation
• Therapeutic Goals:– Control of ventricular rate– Restoration and maintenance of sinus rhythm– Prevention of thromboembolism
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Tehran Arrhythmia Center
CHADS2 Score and Risk of Stroke
JAMA 2001;285:2864
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Tehran Arrhythmia Center
Atrial Flutter
70 bpm• Rate?• Regularity? Regular
Flutter waves
0.06 s
• P waves?
• PR interval? None• QRS duration?
Interpretation? Atrial Flutter
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Tehran Arrhythmia Center
Atrial Flutter
• Regular atrial tachyarrhythmia with atrial rate between 250-350 bpm.
• Flutter waves are seen as saw-tooth like atrial activity
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Tehran Arrhythmia Center
Atrial Flutter
• Atrial Flutter is a form of atrial reentry localized to right atrium.
• Typically the ventricular rate is half the atrial rate, but the ventricular response may be 4:1, 2:1, 1:1 etc.
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Tehran Arrhythmia Center
Atrial Flutter Circuit
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Tehran Arrhythmia Center
Atrial Flutter• Most often in patients with organic heart
disease
• Usually less long-lived than AF and may convert to AF.
• Control of ventricular rate is difficult in atrial flutter
• The most effective treatment is DC cardioversion
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Tehran Arrhythmia Center
PSVT
74 148 bpm• Rate?• Regularity? Regular regular
Normal none
0.08 s
• P waves?
• PR interval? 0.16 s none• QRS duration?
Interpretation? Paroxysmal Supraventricular Tachycardia
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Tehran Arrhythmia Center
Paroxysmal Supraventricular Tachycardia (PSVT)
• Usually at a rate of 150-250 bpm
• No organic heart disease in the majority
• Presentations– Palpitations– Chest discomfort,dyspnea, lightheadedness– Frank syncope– SCD
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Tehran Arrhythmia Center
Preexcitation
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Tehran Arrhythmia Center
VT
160 bpm• Rate?• Regularity? Regular
None
Wide (> 0.12 sec)
• P waves?
• PR interval? None• QRS duration?
Interpretation? Ventricular Tachycardia
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Tehran Arrhythmia Center
Ventricular ArrhythmiasDefinitions
• Premature Ventricular beats– Single beats– Ventricular Bigeminy, the appearance of one PVC after each sinus
beat– Couplets, two consecutive premature beats– Triplets, three consecutive premature beats– Salvos, runs of 3-10 premature beats
• Accelerated Idioventricular Rhythm (Slow VT), rate 60-100 bpm
• Ventricular Tachycardia (VT), rate over 100 bpm • Ventricular Flutter, regular large oscillations at a rate of
150-300 bpm• Ventricular Fibrillation (VF), irregular undulations of
varying contour and amplitude
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Tehran Arrhythmia Center
Ventricular TachycardiaClassification
• Duration– Sustained VT defined as VT that persists for than 30 s
or requires termination because of hemodynamic collapse
– Nonsustained VT, 3 beats to 30 s
• Morphology– Monomorphic
– Polymorphic
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Tehran Arrhythmia Center
Salvos
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Tehran Arrhythmia Center
Sustained Monomorphic VT
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Tehran Arrhythmia Center
Sustained Polymorphic VT
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Tehran Arrhythmia Center
VT Etiology
• VT generally accompanies some form of structural heart disease most commonly:– Ischemic heart disease– Cardiomyopathies
• Primary electrical abnormalities– Long QT syndromes– Brugada syndrome
• Idiopathic VT
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Tehran Arrhythmia Center
VF
None• Rate?• Regularity? Irregularly irreg.
None
Wide, if recognizable
• P waves?
• PR interval? None• QRS duration?
Interpretation? Ventricular Fibrillation
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Tehran Arrhythmia Center
Sudden Death Syndrome
• Incidence– 400,000 - 500,000/year in U.S.– Only 2% - 15% reach the
hospital– Half of these die before
discharge
• High recurrence rate
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Tehran Arrhythmia Center
Clinical Substrates Associated with VF Arrest
• Coronary artery disease• Idiopathic cardiomyopathy• Hypertrophic cardiomyopathy• Long QT syndrome• RV dysplasia• Rarely: WPW syndrome