Electrocardiograph analysis

ELECTROCARDIOGRAPHELECTROCARDIOGRAPHANALYSISANALYSIS

Reported by:Reported by:AGNES PurwidyantriAGNES Purwidyantri

BIOMEDICAL ENGINEERING DEPTBIOMEDICAL ENGINEERING DEPT

ECG interpretation - step-by-step

• Rate• Rhythm• Cardiac Axis• P – wave• PR - interval• QRS Complex• ST Segment• QT interval (T & U wave)• Other ECG signs

Cardiac Cardiac ElectrophysiologyElectrophysiology

• Electrical activity is governed by multiple transmembrane ion conductance changes

• 3 types of cardiac cells– 1. Pacemaker cells- SA

node, AV node– 2. Specialised conducting

tissue – (Purkinjee Fibers)– 3. Cardiac myocytes

•SA Node - Dominant pacemaker -intrinsic rate of 60 - 100 beats/minute.•AV Node - 40 - 60 beats/minute.•Ventricular cells - 20 - 45 beats/minute.

Pacemakers of Heart

ELEMENTS OF ECGELEMENTS OF ECG

S Allen 2003

The Normal Conduction System

Electrocardiogram• Is a recording of electrical activity of heart conducted

through ions in body to surface

13-60

EKG Distributions

• Anteroseptal: V1, V2, V3, V4• Anterior: V1–V4• Anterolateral: V4–V6, I, aVL• Lateral: I and aVL• Inferior: II, III, and aVF• Inferolateral: II, III, aVF, and V5

and V6

Rate• HR of 60-100 per minute is normal• HR > 100 = tachycardia• HR < 60 = bradycardia• Rule of 300- Divide 300 by the number of boxes

between each QRS = rate Number of big boxes

Rate

1 300

2 150

3 100

4 75

5 60

6 50

Differential Diagnosis of Tachycardia

Tachycardia

Narrow Complex

Wide Complex

Regular STSVTAtrial flutter

ST w/ aberrancySVT w/ aberrancy

VT

Irregular A-fibA-flutter w/ variable conductionMAT

A-fib w/ aberrancy

A-fib w/ WPWVT

What is the heart rate?

(300 / 6) = 50 bpm

www.uptodate.com

Rhythm

• Sinus – Originating from SA

node– P wave before

every QRS– P wave in same

direction as QRS

What is this rhythm?

Normal sinus rhythm

Normal Intervals

• PR– 0.20 sec (less than one

large box)• QRS

– 0.08 – 0.10 sec (1-2 small boxes)

• QT– 450 ms in men, 460 ms in

women– Based on sex / heart rate– Half the R-R interval with

normal HR

Waveforms & Intervals

Depolarization of both atria• Relationship b/w P & QRS - distinguish various arrhythmias• Shape & duration of P - indicate atrial enlargement

P Wave P Wave

Onset of P wave to onset of QRS• Normal = 0.12 - 2.0 sec• Represents A to V conduction time (via His bundle)• Prolonged PR interval indicate AV block

PR INTERVAL PR INTERVAL

Short PR Interval•WPW SxAccessory pathway (Bundle of Kent) - early activation of the ventricle (delta wave & short PR interval)

Long PR Interval

• 1st degree Heart Block

Ventricular Depolarization

Includes• Bundle of His• Bundle Branches

– Right– Left

• Septal• Anterior• Posterior

• Terminal Purkinjie fibers

What is the axis?

Normal- QRS up in I and aVF

Hypertrophy

Add the larger S wave of V1 or V2 in mm, to the larger R wave of V5 or V6.

Sum is > 35mm = LVH

Ischemia

• Usually indicated by ST changes– Elevation = Acute infarction– Depression = Ischemia

• Can manifest as T wave changes• Remote ischemia shown by q waves

Lead Placement

aVF

All Limb Leads

Precordial Leads

Ventricular depolarization• Is > P wave d/t > Ventricular mass• Normal duration = 0.08 - 0.12 secs Q wave >1/3 the height of R wave, >0.04 sec –abnormal; may represent MI

QRS COMPLEXQRS COMPLEX

• Connects QRS complex & T wave

• Duration = 0.08 - 0.12 sec

ST Segment ST Segment

–“small to moderate” size +ve deflection wave after QRS complex,–Ht is 1/3rd - 2/3rd that of corresponding R wave

–Septal repolarization (not always seen on ECG)

T Wave T Wave

U Wave U Wave

•Beginning of QRS to end of T wave• Normal QT is usually about 0.40 sec• QT varies based on HR- faster HR ,shorter QT . •Hence QTc.

Bazett’s formula: QTC = QT / √ RRFredericia’s formula: QTC = QT / RR 1/3

Framingham formula: QTC = QT + 0.154 (1 – RR)Hodges formula: QTC = QT + 1.75 (HR– 60)

QT Interval QT Interval

CALCULATING RATE

300Rate =

Eg

3150015

Rate =or

Rate = 100 beats/minute

Rhythm irregular- # of beats in a 6-sec X by 10

CALCULATING RATE

1 2 3 4 5 6 7 8

= (Number of waves in 6-sec strips) x 10= 8 x 10= 80 bpm

Rate

There are 8 waves in this 6-seconds strip.

References

• The EKG made easy-John R. Hampton• An Introduction to Electrocardiography – Leo

Schamroth • Marriot’s Practical Electrocardiography. • www.ambulancetechnicianstudy.co.uk• www.learntheheart.com