Cardiac Arrhythmias Dr. Ahmad Hersi. Myocardium Muscle Action Potential.

Cardiac Arrhythmias

Dr. Ahmad Hersi

Action Potential of a Myocardial Cell+25

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Myocardium Muscle Action Potential

Normal Cardiac Cycle

Systole Diastole

Electrical Depolarization

“activate”

Repolarization

“recovery”

Mechanical Contract

“empty”

Relax

“fill”

What does it tell us?• the electrical conduction through the heart• areas of ischemia or myocardial damage• LV Hypertrophy• electrolyte disturbances / drug toxicity

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

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

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

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)

The ECG Complex with Interval and Segment Measurements

ECG Paper and related Heart Rate & Voltage Computations

Memorize These 2

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

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.


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.


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



• 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



• 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


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


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


Step 4: Determine PR interval

• Normal: 0.12 - 0.20 seconds.

(3 - 5 boxes)

Interpretation? 0.12 seconds


Step 5: QRS duration

• Normal: 0.04 - 0.12 seconds.

(1 - 3 boxes)

Interpretation? 0.08 seconds


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


Normal Sinus Rhythm

• Normal and constant P wave contours

• Normal P wave axis

• Rate between 60 and 100 bpm


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


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.


Sinus Tachycardia

130 bpm• Rate?• Regularity? Regular

Normal

0.08 s

• P waves?

• PR interval? 0.16 s• QRS duration?

Interpretation? Sinus Tachycardia


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


Sinus Tachycardia


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


Sinus Bradycardia


normal

0.10 s

• P waves?


Interpretation? Sinus Bradycardia


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


Sinus Bradycardia


Sinus BradycardiaJunctional Escape Beats


Sinus Bradycardia Causes

• Hypothyroidism

• Drugs

• During vomiting or vasovagal syncope

• Increased intracranial pressure

• Hypoxia, hypothermia

• Depression

• Jaundice


Sinus Arrhythmia

50-75 bpm• Rate?• Regularity? Phasic variations

normal

0.10 s

• P waves?


Interpretation? Sinus Arrhythmia


Sinus Pause

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>



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


First Degree AV Block


Normal

0.08 s

• P waves?


Interpretation? 1st Degree AV Block


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



• 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.


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


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


WB


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


Mobitz Type II AV Block


Nl, 5th P no QRS

0.11 s

• P waves?


Interpretation? 2nd Degree AV Block, Type II


Mobitz Type II Second Degree AV Block

• PR interval remains constant prior to the blocked P wave

• Commonly associated with bundle branch blocks


2:1 AV Block


2:1 AV BlockAV Nodal Level


2:1 AV BlockInfra-nodal Level


2:1 AV block Infra-nodal Level


Complete Heart Block


No relation to QRS

Wide (> 0.12 s)

• P waves?

• PR interval? None• QRS duration?

Interpretation? 3rd Degree AV Block


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.


Complete AV block


Remember• When an impulse originates in a ventricle,

conduction through the ventricles will be inefficient and the QRS will be wide and bizarre.


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


Premature Beats

• Premature Atrial Contractions (PACs)

• Premature Ventricular Contractions (PVCs)


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


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).


PVC

60 bpm• Rate?• Regularity? Occasionally irreg.

None for 7th QRS

0.08 s (7th wide)

• P waves?


Interpretation? Sinus Rhythm with 1 PVC


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.


Ventricular Conduction

NormalSignal moves rapidly through the ventricles

AbnormalSignal moves slowly through the ventricles


Ventricular Premature Complexes

Compensatory Pause

Interpolated VPC


Atrial Fibrillation

100 bpm• Rate?• Regularity? Irregularly irregular

None

0.06 s

• P waves?


Interpretation? Atrial Fibrillation


Atrial Fibrillation


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


Atrial Fibrillation

• Undulating baseline or atrial deflections of varying amplitude and frequency ranging from 350 to 600 bpm.

• Irregularly irregular ventricular response.


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


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


Atrial Fibrillation

• Therapeutic Goals:– Control of ventricular rate– Restoration and maintenance of sinus rhythm– Prevention of thromboembolism


CHADS2 Score and Risk of Stroke

JAMA 2001;285:2864


Atrial Flutter


Flutter waves

0.06 s

• P waves?


Interpretation? Atrial Flutter


Atrial Flutter

• Regular atrial tachyarrhythmia with atrial rate between 250-350 bpm.

• Flutter waves are seen as saw-tooth like atrial activity


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.


Atrial Flutter Circuit


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


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


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


Preexcitation


VT


None

Wide (> 0.12 sec)

• P waves?


Interpretation? Ventricular Tachycardia


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


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


Salvos


Sustained Monomorphic VT


Sustained Polymorphic VT


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


VF

None• Rate?• Regularity? Irregularly irreg.

None

Wide, if recognizable

• P waves?


Interpretation? Ventricular Fibrillation


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


Clinical Substrates Associated with VF Arrest

• Coronary artery disease• Idiopathic cardiomyopathy• Hypertrophic cardiomyopathy• Long QT syndrome• RV dysplasia• Rarely: WPW syndrome

Cardiac Arrhythmias Dr. Ahmad Hersi. Myocardium Muscle Action Potential.

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