cardiac electrophysiology

Basic Arrhythmias Basic Arrhythmias InterpretationInterpretation

Cardiac Cardiac ElectrophysiologyElectrophysiology

Natalie Bermudez, RN, BSN, MSNatalie Bermudez, RN, BSN, MSClinical Educator for TelemetryClinical Educator for Telemetry

Myocardial Cardiac Cell TypesMyocardial Cardiac Cell Types

P Cells • Pacemaker cells

– Responsible for generation of action potentials

– electrical activity

Cardiomyocytes• Myocardial Cells

– Contractile cells that generate force– Mechanical activity

Cardiac Cell ActivityCardiac Cell ActivityElectrical activity ALWAYS precedes mechanical activity

Electrical activity can occur without a mechanical response

(i.e. pulse).

This is known as pulseless electrical activity (PEA).

Primary Characteristics of Cardiac Cells

Automaticity

Excitability

Conductivity

ContractilityECG Workout Textbook: p. 10

Is it GOOD or BAD???ALL ELECTRICAL CARDIAC CELLS ARE

CAPABLE OF AUTOMATICITY!!!

IRRITABILITY!!!

AutomaticityAutomaticity

It is definitelyREALLYGOOD

THING!!

But it can alsobe a

REALLYBAD THING!!

Electrolytes and Cardiac Cells

• Electrolyte solution surrounds cardiac cells

• K+ primary intracellular ion

• Na+ primary extracellular ion

• Ready State: Inside of the cell

more negative

• Cell stimulated; membrane permeability changes

PolarizationPolarization

DepolarizationDepolarization

RepolarizationRepolarization

Electrical Activity at the Cellular LevelElectrical Activity at the Cellular Level

Cardiac Action Potential• As cardiac cells reverse polarity, the electrical

impulse generated during that event creates an energy stimulus that travels across the cell membrane

• High-speed, self-producing current (heart only)

Slow-Response Cells

• SA node & AV node

• Spontaneously depolarize slowly

• Shorter, non-prominent plateau phase with slower repolarization period

Fast-Response Cells

• Purkinje cells and working myocardial cells

• Rapid depolarization

• Then, a period of sustained depolarization – plateau phase

Phases of Action Potential

Phase 0 • Cellular depolarization is initiated as + ions enter the cell

(Na+ and Ca++)• Working cells rapidly depolarize as Na+ enters the cells

through Na+ fast channels (fast response)• SA/AV node depolarize as Ca++ enters the cell through

Ca++ slow channels (slow-response)


Phase 1 • Small, early, rapid repolarization as K+ exits the

intracellular space

Phase 2• The plateau phase as Ca++ ions enter the intracellular

space


Phase 3 • Completion of repolarization and return of cell to

resting state

Phase 4• Resting phase before the next depolarization (Na+

out, K+ in)

POLARIZATIONPOLARIZATION

Electrical charges are balanced and ready for discharge.

The discharge of energy that accompanies the transfer of electrical charges across

the membrane.

The process of electrical discharge and flow

of electrical activity.

An electrical event that can be recorded on

an EKG or rhythm strip.

DEPOLARIZATIONDEPOLARIZATION

The return of electrical charges across the cell membrane.

REPOLARIZATIONREPOLARIZATION

Refractory PeriodRefractory Period

Absolute: The brief period during repolarization when the cell CAN’T respond to any stimulus,

no matter how strong.

*Relative: The brief period during repolarization when excitability is depressed. If stimulated, the

cell may respond, but a stronger than usual stimulus is required.

Supernormal: The cells will respond to a weaker than normal stimulus (this period occurs just before the cells have completely repolarized)

What is an EKG?

• Think of it as a map that shows the road traveled by an electrical impulse

• Each waveform indicates the location of the electrical impulse and if has traveled through that location “normally”

Isoelectric Line & WaveformsIsoelectric Line & WaveformsIsoelectric Line:

electrically neutral baseline of an EKG complex.

Waveform: any part of the EKG tracing that moves away from & returns to the isoelectric line (baseline)

DeflectionsDeflectionsDeflection: a waveform

on an EKG strip that denotes electrical activity; may be positive (upright) and/or negative (downward).

Monophasic or Biphasic

See Overhead slide 1-0

Positive & Negative PolesPositive & Negative Poles

Electrical activity that travels towards a

positive pole appears upright on an EKG

appears and is called a positive deflection.

Electrical activity that travels towards a

negative pole appears inverted

(downward) on an EKG and is called a negative deflection

Positive & Negative PolesPositive & Negative PolesSee Overhead Slide 1-1

Cardiac Monitors

Electrodes, Poles, Wires, Leads, and Electrode Placement

Five-Leadwire System

Electrode Pad PlacementElectrode Pad Placement

Electrode

An electrode pad is the medium through electrical activity is registered/recorded

Proper placement of the electrode pad is the most important step in obtaining a good quality and accurate EKG tracing

An EKG lead provides a view of the heart’s electrical activity between two points or poles (one positive & one negative)

The EKG waveforms are recorded via an electrode/wire system – i.e. five-leadwire system

Poles & Lead IIPoles & Lead II

Lead II consists of the following electrode

placement:

•Right Limb Lead (negative pole): the 2nd intercostal space on the right

•Left Limb Lead (positive pole): the 8th intercostal space on the left

•Grounding Lead: 8th intercostal space to the right

LEAD II

Lead II is used alone quite frequently. Normal rhythms present with a prominent

P wave and a tall QRS.

Irritability versus EscapeIrritability versus Escape

Irritability – a site that speeds up and takes over as the pacemaker.

Escape – when the normal pacemaker slows down or fails and a lower site assumes pace making responsibility.

Either of these may exist as a beat or rhythm!

More EKG Terminology

Focus, Ectopy, Aberrancy, Artifact

Important TerminologyImportant Terminology

Focus - The starting point of an electrical impulse

Ectopic – An impulse that originates from a focus other than the primary pacemaker.

AberrancyAberrancy

Aberrancy – abnormal conduction of an electrical impulse

Aberrant Ventricular Conduction – An impulse that originates from the SA node, atria, or AV junction that is abnormally conducted through the ventricles producing a wider than normal

QRS complex: a.k.a “aberrancy”

ArtifactArtifactElectrical activity displayed on graph

paper that is superimposed on cardiac tracings, interfering with interpretation of the rhythm.

Can be caused by outside electrical soures, muscle tremors, patient movement; also called interference.

Cardiac Electrophysiology

The Electrical Conduction Pathway

Nervous System StimulationNervous System Stimulation

Sympathetic Nervous System: causes an increase in heart rate, increase in AV conduction , and increase in ventricular

contractility

The increase is caused a release of norepinephrine

(catecholamine/neurotransmitter)

Nervous System StimulationNervous System Stimulation

Parasympathetic Nervous System: (from the vagus nerve) causes a slowing of the heart rate, a decrease in AV conduction, and a slight decrease in ventricular contractility

The decrease is caused a release of acetylcholine

(catecholamine/neurotransmitter)

PacemakerPacemakerPacemaker – the SA node is the natural/normal

pacemaker of the heart.

Latent Pacemaker Cells – Cells in the electrical conduction system located below the SA node with the property of automaticity

These cells hold the property of automaticity in reserve in case the SA node fails to function properly or electrical impulses fail to be conducted.

a.k.a. – Subsidiary pacemaker cells

The Electrical Conduction Pathway

SA Node

• ie. Sinoatrial Node or Sinus Node

• Posesses the highest level of automaticity

• SA Node is the primary pacemaker of the heart

• If it fails to fire or slows down less than its inherent firing rate (60 – 100), another pacemaker that is lower in the conduction system will take over

AV Node (The Gatekeeper)

Three main functions:

• Slows conduction to allow time for the atria to contract & empty its contents (atrial kick) before the ventricles contract

• Secondary pacemaker (40 – 59 bpm)

• Blocks some of the impulses from being conducted to the ventricles when atrial rate is rapid

AV Node (The Gatekeeper)

Three Regions:

• Atrial-Nodal (upper region)

Pacemaker cells

• Nodal (middle region)

No pacemaker cells (area responsible

for delay)

• Nodal-His (lower region)

Pacemaker cells

Ventricular Conduction

Impulses moves rapidly through the ventricles:

• Bundle of His• Left & Right Bundle branches (LBB divides

into the anterior fascicle and posterior fascicle)

• Purkinje fibers

Tertiary pacemaker (20 – 39)

EKG COMPLEXEKG COMPLEX

PQRST = One EKG complex = One Cardiac CycleTotal Duration of a Cardiac Cycle = ___________ seconds

P WaveP Wave• Depicts the firing of

the SA node and atrial depolarization (contraction).

• P waves are upright & rounded (in Lead II).

• Precedes a QRS

• Both atria depolarize simultaneously.

P Wave AbnormalitiesP Wave Abnormalitiesp mitrale = Wide & Notched P wave

______________________________________________________________________

p pulmonale = Tall, peaked P wave

________________________________________________________________________

PR SegmentPR Segment

The PR segment represents delay in the AV node

Flat = Baseline

QRS ComplexQRS Complex

Depicts the electrical impulse traveling through the ventricles and ventricular depolarization

(contraction).

Not all QRS complexes have a Q, R, and S.

QRS ComplexQRS ComplexQ wave is the FIRST negative

deflection

R wave is the FIRST positive deflection

S wave is the negative deflection that follows the R

wave

J Point is the point where the QRS complex endsSee Overhead Slide 1-3

QRS Complex VariationsQRS Complex VariationsOverhead Slide 1-2

ST-SegmentST-Segment

The ST-segment represents ventricular contraction and period before ventricular

repolarization. No electricity is flowing. The ST segment is therefore usually even with the

baseline.

ST-Segment Elevation & ST-Segment Elevation & DepressionDepression

To be considered a significant elevation or depression the ST must deviate at least 1 mm

above or below the baseline (in at least 2 or more correlating leads)

ST-Segment DepressionST-Segment Depression

Most often seen with acute myocardial ischemia

Other Causes:

Left and right ventricular hypertrophyLeft and Right BBB

HypokalemiaDrug Effects (i.e. digitalis)

ST-Segment ElevationST-Segment Elevation

Most often seen with acute myocardial injury or infarction

Other Causes:

Coronary vasospasm (Prinzmetal’s Angina)

Pericarditis

Ventricular Aneurysm

Hyperkalemia

Early repolarization (a normal variant)

T WaveT Wave

Depicts ventricular repolarization

Refractory Period

T WavesT WavesPositive Deflection

(above baseline < 5 mm)

Should appear rounded and symmetrical

Peak is closer to the end of the wave

Elevated T WavesElevated T WavesPositive Deflection

(above baseline > 5 mm)

Tall, peaked (tented)

HYPERKALEMIA

or MYOCARDIAL INJURY

Inverted T WavesInverted T WavesNegative Deflection

(below baseline)

Causes:

Myocardial Ischemia

Myocardial Infarction

Pericarditis

Ventricular Enlargement

Bundle Branch Block

Subarachnoid Hemorrhage

Certain Drugs (quinidine or procainamide)

U WaveU Wave

Depicts last phase of ventricular repolarization or endocardial

repolarization???

U WaveU WaveU Wave < 2 mm

Seen most commonly with BRADYCARDIC rate

Can cause inaccuracies when measuring QT intervals

U WaveU WaveU Wave < 2 mm

Large = hypokalemia, cardiomyopathy, LV enlargement

Some drugs may cause a large U wave

May cause Torsades de Pointes

Atrial Repolarization ???Atrial Repolarization ???

Hidden beneath the QRS complex.

EKG Graph PaperEKG Graph Paper

Waveform Measurements

PR IntervalPR Interval

Measurement:0.12 – 0.20 seconds

Represents the time from SA node firing to the end of AV

node delay

PRI AbnormalitiesPRI Abnormalities

Prolonged or Inconsistent PRI’s may indicate a type of heart

block:

1st degree AVBMobitz 1 or Mobitz 2

Complete AVB

PRI AbnormalitiesPRI AbnormalitiesShortened or

Nonexistent PRI’s may indicate:

Tachycardic Rhythms WPW Syndrome

Junctional RhythmsEctopic Atrial Rhythms

Ventricular Rhythms

PRI AbnormalitiesPRI AbnormalitiesSee Overhead Slide 1-4

PR IntervalPR Interval

PRI=

PRI=

QRS DurationQRS Duration

Measurement:0.04 – 0.10seconds

Represents the travel time of

electrical activity through the ventricles

QRS Complex VariationsQRS Complex Variations

Wide and/or notched QRS complexes:

- BBB’s - Aberrant ventricular conductivity- Rhythms with Ventricular Focus

Aberrant QRS ComplexAberrant QRS Complex

See Overhead Slide 1-5

QRS DurationQRS Duration

QRS=

QRS=

QT IntervalQT IntervalMeasurement:

< ½ the distance of the preceding R-R interval

Represents travel time through ventricles to the

end of ventricular repolarization

Normally varies according to age, sex,

and particularly heart rate

QT Rate CorrectedQT Rate Corrected

HR ↑ = QT interval ↓

HR ↓ = QT interval ↑

QTc = QT + 1.75 (ventricular rate – 60)

QT IntervalQT Interval

QT= QTc=

QT= QTc=

Prolonged QT IntervalsProlonged QT IntervalsRepresents a

prolonged time to repolarization

May lead to R-on-T

Phenomenon and ventricular

dysrhythmias!!!

Basics to Interpreting StripsBasics to Interpreting Strips

Rhythm

Rate

P Wave

PR Interval (PRI)

QRS Duration

RHYTHMRHYTHM

Determine regularity or irregularity

Use calipers for accuracy

Measure distance from R-R wave

Regular Rhythm = R-R distance does not vary (less than 3 small boxes of variation does not count)

Irregular Rhythm = R-R distance varies (3 small small boxes or greater)

HEART RATEHEART RATE

Use 1500-rule and the 6-second rule for all regular rhythms

6-second rule only for irregular rhythms

Calculating Heart RatesCalculating Heart Rates

The 6-Second Rule

The Rule of 300’s

The 1500 Rule

6-Second Strip6-Second Strip

Count number of R waves in a 6-second strip and multiply by 10

A.K.A. Rapid Rate Calculation

HR = # R waves x 10

• Not very accurate• Used only for very quick estimate

Rule of 300’sRule of 300’sCount number of large

squares between 2 consecutive R waves and

divide into 300.

HR = 300 / # large squares

• Very quick• Used only with regular

rhythms• Not very accurate with

fast rates

Rule of 300’sRule of 300’s

Scale of 300Scale of 3001 large square = 300 bpm

2 large squares = 150 bpm





1500 Rule1500 RuleCount number of small squares between 2

consecutive R waves and divide into 1500

A.K.A. – Precise Rate Calculation

• Most accurate

• Used only with regular rhythms

• Time-consuming

P WavesP Waves

• Upright

• Uniform

• Precedes each QRS complex

• Any extra P waves

PRIPRI

• Measure from beginning of P wave to the end of the PR

segment• 0.12 – 0.20 seconds

• Constant

QRS ComplexQRS Complex

• Measure from beginning to the end of QRS complex (1st deflection from

baseline after the PR segment to the beginning of the ST segment)

• 0.04 – 0.10 seconds

• Notched???, Wide, etc.

QT Interval or QTcQT Interval or QTc

• QT Interval = Count the # of small boxes from beginning QRS complex to the end of the T wave. Should be less than ½ the distance of the preceding

R-R interval

• QTc = QT + 1.75 (ventricular rate – 60)

Extras???Extras???

• P waves without QRS complexes

• ST-segment depression or elevation

ReferencesReferencesChernecky, C., et al. (2002). Real world nursing survival guide: ECG’s & the heart. United States

of America: W. B. Saunders Company.

Garcia, T. B., & Holtz, N. E. (2001). 12-lead ecg: The art of interpretation. Sudbury, MA: Jones and Bartlett Publishers.

Huff, J. (2006). ECG workout: Exercises in arrhythmia interpretation (5th ed.). United States of America: Lippincott, Williams & Wilkins.

Smeltzer, S. C., et al. (2008). Brunner and suddarth’s testbook of medical-surgical nursing, (11th ed.). Philadelphia, PA: Lippincott, Williams & Wilkins.

Walraven, G. (1999). Basic arrhythmias (5th ed.). United States of America: Prentice-Hall, Inc.

Woods, S. L., et al. (2005). Cardiac nursing, (5th ed.). Philadelphia, PA: Lippincott, Williams & Wilkins.

www.madsci.com/manu/ekg_rhy.htm

cardiac electrophysiology

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