Understanding basics of EKG

By Alula A.(R III)

www.le.ac.uk

Topic for discussion

• Understanding of cellular electrophysiology

• Basics – Rate

– Rhythm

– Axis

– Intervals

– P wave

– QRS

– ST/T wave

Abnormal EKGs

Understanding electrophysiology

• The EKG is nothing more than a recording

of the heart's electrical activity

Cardiac cells

•Resting state(mme pump)

•Depolarization

/Repolarization

The Cells of the Heart and action potential

EKG basics

Electrode placement

Right precordial leads V1: right 4th intercostal space

V2: left 4th intercostal space

V3: halfway between V2 and V4

Left Precordial leads

V4: left 5th intercostal space, MCL

V5: horizontal to V4, anterior axillary

V6: horizontal to V5, mid-axillary line

Limb leads

EKG grid • The wave on EKG primarily reflect the electrical

activity of myocardial cell

• Three chief characteristics of the waves.

– Duration

– Amplitude

– Configuration

EKG strip

Einthoven's Triangle

The Six Precordial Leads

• Record forces moving

anteriorly and posteriorly

12

Order of depolarization

Follow the way

Interpretation steps

RRAI- P-QRS-T • Rate

• Rhythm

• Axis

• Intervals

• P wave

• QRS

• T

Rate • Atrial/ Ventricular rate 60 - 90 bpm

•Regular RR; 1500/small box or 300/large box

•Irregular RR –# of QRS waves in 6 sec X 10

–# of QRS on the whole EKG(10 Sec) X6

Rhythm •Normal sinus Rhythm( originated from SA)

The P waves in leads I and II –upright

Same morphology before each QRS

Read on the rhythm strip at lead II if not V1

Axis

• Two technique; I. Identification of isoelectric lead or

II. Look for lead I and aVF

• If needed look for lead II

• QRS axis Frontal Plane QRS Axis: +90 o to -30 o (in the adult)

Normal Axis

Left axis

- LA fascicular block

- Inferior MI

- Pacemaker

lead I +ve and

aVF -ve

Look lead II

+ve = normal axis

-ve = left axis deviation

Right axis

- RVH

- Left posterior fascicular block

- PE

lead I - ve and

aVF +ve

Intervals

• PR interval

– Normal 0.12 - 0.20 sec

• QT interval QTc < 0.40 sec

– Bazett's Formula: QTc = (QT)/SqRoot RR (in

seconds)

P wave • Bi atrial activation

Right to left

Lead II or V1

- duration < 0.12 sec

- 3 blocks wide - amplitude < 2.5 mm

2.5 blocks high

P wave Normal

• Up in lead II

• Down in aVR

• Biphasic, up or down in V1, III

• Same morphology and PR before each QRS

Abnormal

• too wide, too tall, different, unclear, funny (i.e. LAE, RAE, wandering pacemaker/MAT, a fib respectfully)

Wandering Pacemaker

at least 3 different P wave morphologies in a Ventricular response is irregularly irregular , COPD

QRS – Duration < 0.10 sec

– QRS amplitude - variable from lead to lead and

from person to person

– Comment: pathologic Q waves, abnormal voltage

QRS • Q wave

– Narrow (<0.04s duration) and

– Small (<25% the amplitude of the R wave)≈ 0.1mv

– Often seen in

leads I and aVL when the QRS axis is to the left of +60o, and

leads II, III, aVF when the QRS axis is to the right of +60o.

• R-waves begin in V1 or V2 and progress in size to V5. R-V6 < R-V5.

• In reverse, the S-waves begin in V6 or V5 and progress in size to V2. S-V1 is usually smaller than S-V2

• The usual transition from S>R in the right precordial leads to R>S in the left precordial leads is V3 or V4

ST wave

• Normal V1-V3 concave upwards

ST / ST- T wave

• Abnormal ST elevation and/or Depression

• ST elevation

– **compare J point to the TP level not PR**

Early repolarization- concave upwards

ST elevation

Convex or straight upward ST

ST segment depression

abnormal but non specific

T wave

•The normal T wave is usually in the same

direction as the QRS except in the right

precordial leads( V1-V3)

•T wave amplitude is 1/3-2/3 of R wave

• Always upright in leads I, II, V3-6, and

• Always inverted in lead aVR

U wave

• Afterdepolarizations which interrupt or follow repolarization

• U wave amplitude is usually < 1/3 T wave amplitude in same lead

• U wave direction is the same as T wave direction in that lead

• more prominent at slow heart rates and usually best seen in the right precordial leads

Conclusion ECG interpretations

i. Measurements

ii. Rhythm analysis

iii. Conduction analysis

iv. Waveform description

v. ECG interpretation

(normal, abnormal, bordeline)

i. Comparison with previous ECG (if any)

• Remember “RRAI P-QRS-T”

Provided by The Leicester Gondar Link

Collaborative Teaching Project

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