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Rhythm Disorders

Dr. Maged M. El Samady

MBBCh, MSc, MRCPCH, FRCP(UK)

Overview

• The Conduction System

• Rhythm Disorders:

Bradyarrhythmia

Tachyarrhythmia

THE CONDUCTION SYSTEM

Heart Beat Anatomy

Sinus Node

(SA Node)

• The Heart’s ‘Natural Pacemaker’

- 60-100 BPM at rest

SINUS NODE

Heart Beat Anatomy

AV NODE

Sinus Node

(SA Node)

Atrioventricular

Node (AV Node)

• Receives impulse from

SA Node

• Delivers impulse to the His-

Purkinje System

• 40-60 BPM if SA Node fails to

deliver an impulse

Heart Beat Anatomy

BUNDLE OF HIS

Sinus Node

(SA Node)

Atrioventricular

Node (AV Node)

Bundle of His

• Begins conduction to

the Ventricles

• AV Junctional Tissue:

40-60 BPM

Heart Beat Anatomy

Atrioventricular

Node (AV Node)

Sinus Node

(SA Node)

Bundle of His

Bundle Branches

Purkinje Fibers

• Bundle Branches

• Purkinje Fibers

• Moves the impulse through

the ventricles for contraction

• Provides ‘Escape Rhythm’:

20-40 BPM

THE PURKINJE NETWORK

Normal Sinus Rhythm

Click heart to

view animation

*Animation

Impulse Formation In SA Node

Atrial Depolarization

Delay At AV Node

Conduction Through Bundle Branches

Conduction Through Purkinje Fibers

Ventricular Depolarization

Plateau Phase of Repolarization

Final Rapid (Phase 3) Repolarization

Normal ECG Activation

Automaticity

Cardiac Cells have

AUTOMATICITY!

Automaticity

• Spontaneously depolarize

• Generally present in:

Cardiac Cells

• Upper (SA Node)

- 60-100 BPM

• Middle (AV Junction)

- 40-60 BPM

• Lower (Purkinje Network)

- 20–40 BPM

Automaticity

Once a pacemaker cell initiates an impulse,

its neighboring cells follow suit – like dominos!

STANDARD SURFACE 12

LEADS ECG

ECG LIMB LEADS

3 BIPOLAR LEADS:

I, II and III

3 UNIPOLAR LEADS:

aVR, aVL and aVF

LIMB LEADS I, II & III

LIMB LEADS aVR, aVL & aVF

LIMB LEADS

Limb Leads

CHEST LEADS

V1: Rt. 4th space

V2: Lt. 4th space

V3: In-between

V2&V4

V4: At apex

V5: Ant. Axillary line

V6: Mid. Axillary line

CHEST LEADS 2

ECG WAVES& INTERVALS

Reading ECGs

Normal Ranges in Milliseconds:

• PR Interval 120 – 200 ms

• QRS Complex 60 – 100 ms

• QT Interval 360 – 440 ms

Intervals and Timing

Developmental Changes in the ECG

• Gradual decrease in heart rate

• Gradual lengthening of the PR interval

• Gradual lengthening of the QRS

interval

• Shift from right to left ventricular

dominance

Rate and Intervals Based on Age

Adapted from: Benson, D.W. (1989 (

Reading ECG Squares

• Each square = 40 ms

• Each interval = 200 ms

Intervals and Timing

ECG INTERPRETATION

RATE

RHYTHM

AXIS

CHAMBERS HYPERTROPHY

S-T & T WAVE CHANGES

Question?

How do we measure heart rate?

BPM(Beats Per Minute)

Calculate Rate

• Option 1

– Count the # of R waves in a 6 second

rhythm strip, then multiply by 10.

– Reminder: all rhythm strips in the Modules

are 6 seconds in length.

Interpretation? 9 x 10 = 90 bpm

3 sec 3 sec

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.

R wave

•BPM to milliseconds (ms)

– If heart rate is measured in Beats Per Minute,

then we must divide the rate into _________

milliseconds to calculate the rate interval.

•60,000/rate (in BPM) = rate interval (in ms)

•60,000/100 BPM = 600 ms

60,000

•60,000/pacemaker interval (in ms) = rate (in BPM)

•60,000/500 ms = 120 BPM

•MS to BPM

Rate Conversions

Rate Conversions

How fast is this rhythm?

Milliseconds = ? 830 BPM = ? 72

60,000 / 830 = 72

Rate Conversions

How fast is this rhythm?

Milliseconds = ? 400 BPM = ? 150

60,000 / 400 = 150

Normal ECG for 1 day old infant

Normal ECG for 3 weeks old infant

Normal ECG for 3 months old infant

Normal ECG for 2 years old child

Normal ECG for 6 years old child

Normal ECG for 15 years old male

RHYTHM DISORDERS

Abnormally Slow = Bradycardia

• Failure due to disease

Excessively Rapid = Tachycardia

• Due to sympathetic nervous system

Mechanisms of Rhythm Disorders

Abnormal Automaticity

Slowed or Blocked Conduction

• Impulse generated normally

• Impulse slowed or blocked as it makes its way

through the conduction system


*Animation


ReentryConditions of Reentry


Reentry

Substrate + Trigger = Reentry


Reentry

RHYTHM DISORDERS

Bradyarrhythmias

• Failure of sinus node discharge

• Absence of atrial depolarization

• Periods of asystole

Sinus Arrest

*Animation

• Sinus Node emits energy very slowly

Sinus Bradycardia

• Intermittent episodes of slow and

fast rates from the SA node or atria

• Brady <60 BPM

• Tachy >100 BPM

Brady/Tachy Syndrome

• Transient block of impulses from the SA node

• Identified by P-P interval relationship

Exit Block

First-Degree AV Block

• PR interval > 200 ms

• Delayed conduction through the AV Node

- Example shows PR Interval = 320 ms

• Progressive prolongation of the PR interval until

there is failure to conduct and a ventricular beat

is dropped

Known as Wenckebach Block

Second-Degree AV Block - Mobitz I

*Animation

• Regularly dropped ventricular beats

– Ex: 2:1 block (2 P-waves to 1 QRS complex)

– Atrial rate = 75 BPM

– Ventricular rate = 42 BPM

Second-Degree AV Block – Mobitz II

• No impulse conduction from the atria to the ventricles

– Ventricular rate = 37 BPM

– Atrial rate = 130 BPM

– PR interval = variable

Third-Degree AV Block

*Animation

Summary

• Sinus Arrest

• Sinus Bradycardia

• Brady/Tachy

Syndrome

• Junctional Rhythm

• Idio-Ventricular

Rhythm

• Exit Block

• 1st Degree AV Block• 2nd Degree AV Block

-Mobitz I (Wenckebach Block)

-Mobitz II

• 3rd Degree AV Block

Impulse FormationDisorders

Impulse Conduction

Disorders

Bradyarrhythmia Classifications

RHYTHM DISORDERS

Tachyarrhythmias

•Paroxysmal

– Ectopic focus, sudden onset, abrupt cessation

•Sustained

– Duration of > 30 seconds

– Requires intervention to terminate

•Non-Sustained

– At least 6 beats or < 30 seconds

– Spontaneously terminates

•Recurrent

– Occurs periodically

– Periods of no tachycardia are longer than periods

of tachycardia

Terms Describing Tachycardias

• Incessant– Long periods of tachy, short periods of NSR

•Monomorphic– Single focus

– Complexes are similar with equal intervals

•Polymorphic– Multiple foci

– Complexes appear different with varied intervals

•SVT (Supraventricular Tachycardia)– Originating from above the ventricles

Terms Describing Tachycardias

Tachyarrhythmia Classifications

Classification Based on Disorder


TachycardiasImpulse Conduction

Disorders

Sinus Tachycardia

• Origin: Sinus Node

• Rate: 100-180 BPM

• Mechanism: Abnormal (Hyper) Automaticity

Atrial Tachycardia

• Origin: Atrium - Ectopic Focus

• Rate: >100 BPM

• Mechanism: Abnormal Automaticity

Premature Beats

Premature Atrial Contraction (PAC)

• Origin: Atrium (outside the Sinus Node)


• Characteristics: An abnormal P-wave occurring

earlier than expected, followed

by compensatory pause

Premature Junctional Contraction

• Origin: AV Node Junction


• Characteristics: A normally conducted complex with

an absent p-wave, followed by a

compensatory pause

Premature Beats

Premature Ventricular Contractions (PVCs)

• Origin: Ventricles


• Characteristics: A broad complex occurring earlier

than expected, followed by a

compensatory pause

Premature Beats

PVC Patterns

•Bigeminy

- Every other beat

•Trigeminy

- Every third beat

•Quadrigeminy

- Every fourth beat

• Origin: Varies within the Ventricle


• Characteristics: Each premature beat changes axis;

implies a different focus origin for

each beat

Multifocal PVC

Accelerated Idio-Junctional Rhythm

• Origin: AV Node or Junctional Tissue


• Characteristics: Occurs when cells depolarize at a

rate faster than the Sinus Node

Accelerated Idioventricular Rhythm

• Origin: Ventricle


• Rate: Ventricular rate >sinus rate, but <VT

• Characteristic: Dominates and takes over the rhythm

Sinus Rhythm being taken over by an Idioventricular Rhythm

Accelerated Idioventricular Rhythm

Atrial Flutter

• Origin: Right & Left Atrium

• Mechanism: Reentry

• Characteristics: Rapid, regular p-waves

*Animation

Atrial Fibrillation (AF)

• Origin: Right and/or left atrium

• Mechanism: Multiple wavelets of reentry

• Rate 400 BPM

• Characteristics: Random, chaotic rhythm;

atria quiver; associated with

irregular ventricular rhythm

*Animation

Atrial Fibrillation (AF)

Multifocal Firing

Other AF Mechanisms

• Mechanism: Abnormal Automaticity (multi-sites)

• Characteristics: Many depolarization waves;

activation occurs asynchronously;

not in rhythm with sinus node

• Mechanism: Abnormal Automaticity (single-

focus, usually in the Posterior

Left Atrium)

• Characteristics: Rapid discharge; single ectopic site

Other AF Mechanisms

Single Focus Firing

Atrial Flutter vs. Atrial Fibrillation

Atrial Flutter

Summary of Disease Characteristics

Underlying

Mechanism

Pattern

Atrial Rate

Ventricular Rate

Rhythm

Atrial Fibrillation

• Multiple wavelet reentry

• Multiple/single focus

firing

• Wavy baseline

• 400 BPM

• Varies w/conduction

• Grossly Irregular

• Reentry via macro

reentrant circuit

• Saw tooth baseline

• 250 to 400 BPM

• Varies w/conduction

• Usually regular

•Extra pathway + AV Node = reentry

•2 Types– Orthodromic

• A to V through node, then enters accessory pathway to loop

• Produces narrow complex SVT

– Antidromic

• A to V through accessory pathway, then enters node to loop

• Produces wide-complex SVT

•An SVT caused by the existence of an extra

pathway from the atria to the ventricles

AVRT

Orthodromic


• Rate: 180 - 260 BPM, sometimes faster

• Characteristics: Extra electrical pathway to ventricles

Wolf-Parkinson-White (WPW)

Syndrome is most common

AVRT

*Animation

Antidromic


• Rate: 180 - 260 BPM, sometimes faster

• Characteristics: Extra electrical pathway to ventricles;

produces wide complex tachycardia

AVRT

*Animation

• Accessory Pathway = Bundle of Kent

• Orthodromic - 90% - AV node – antegrade conduction;

- Extra pathway – retrograde conduction

• Antidromic – 10% - Extra pathway – antegrade conduction

- AV node – retrograde conduction

Wolff-Parkinson-White

• Origin: Outside the AV Node


• Rate: 180-260 BPM – can be faster

• Characteristics: Short PR Interval (< 120 ms),wide

QRS (> 110 ms), obvious delta wave

Wolff-Parkinson-White

• Origin: AV Node


• Rate: 150 - 230 BPM, faster in teenagers

• Characteristics: Normal QRS with absent P-waves;

most common SVT in adults

AVNRT

AVRT vs. AVNRT

AVRT

• 180 – 260 BPM

• Narrow QRS if orthodromic

• Wide QRS if antidromic

• Delta wave + in SR

• PR < 120 ms

• 1:1 Conduction

AVNRT• 150 – 230 BPM

• Narrow QRS

• Short RP interval

• No delta waves

• Initiating PR long

• P-waves buried in QRS

• Conduction 1:1, or 2:1when distal block present

AVRT vs. AVNRT

• Origin: Ventricles (Single Focus)

• Mechanism: Reentry Initiated by abnormal

Automaticity or Triggered activity

• Characteristics: Rapid, wide, and regular QRS

EKG Characteristics

Monomorphic VT

*Animation

• Origin: Ventricles (Wandering Single Focus)

• Mechanism: Reentry with movement in the circuit

Initiated by Abnormal Automaticity or

Triggered activity

• Characteristics: Wide and irregular QRS Complex that

changes in axis

Polymorphic VT

*Animation


• Mechanism: Reentry (movement in focus)

• Rate: 200 – 250 BPM

• Characteristics: Associated with Long QT interval;

QRS changes axis & morphology with alternating positive/negative complexes

Torsades de Pointes


• Mechanism: Multiple Wavelets of reentry

• Characteristics: Irregular with no discrete QRS

Ventricular Fibrillation (VF)

*Animation


Summary


Impulse Conduction

Disorders

• Atrial Flutter

• Atrial Fibrillation

• AVRT

•AVNRT

• Ventricular Tachycardia

• Ventricular Fibrillation

• Sinus Tachycardia• Atrial Tachycardia

• Premature Contractions

• Accelerated Idio-

Junctional Rhythm

• Accelerated

Idioventricular

Rhythm (AIVR)

Based on origin

• Sinus Tachycardia

• Atrial Tachycardia

• Accelerated Idio-Junctional Rhythm

• Atrial Flutter

• Atrial Fibrillation

• AVRT

• AVNRT


• Accelerated Idioventricular

Rhythm (AIVR)

• Ventricular Fibrillation (VF)

• Ventricular Tachycardia (VT)

RHYTHM DISORDERS

Common Causes

Causes of Rhythm Disorders

Congenital

• Present at birth due to genetics,

environment

Heart Disease

• Myocardial Infarction, Cardiomyopathy,

High Blood Pressure

Chemically Induced

• Diet Pills, Cold Medicine, Illegal Drugs,

Caffeine, Tobacco, Alcohol

Causes of Rhythm Disorders

Secondary to other conditions

• Hyper-Thyroid

• Neurocardiogenic Syncope

- Hypersensitive Carotid Sinus Syndrome (CSS)

- Vasovagal Syncope (VS)

Thank You

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