erwinanto div. of cardiology, dept. of internal medicine padjadjaran university school of medicine...

Erwinanto

Div. Of Cardiology, Dept. of Internal Medicine Padjadjaran University School of Medicine

Hasan Sadikin Hospital

Bandung

What medical problems can be diagnosed with an ECG?

• Enlargement of cardiac chambers

• Hypertrophy of cardiac muscle

• Cardiac arrhythmias

• Insufficient coronary blood flow

• Death of heart muscle and its location

• Electrolyte abnormality

What is an Electrocardiogram?

An ECG is the recording (“gram”) of the

electrical activity (“electro”) of the cells

of the heart (“cardio”) that reaches the

body surface

Initiates the heart muscle to contract, to

pump blood to the tissues

What does an ECG actually measure?

An ECG records voltage on its vertical

axis against time on its horizontal axis

• Measurement along the vertical axis

indicates “summation” of the electrical

activation of all of the cardiac cells

• Measurement along the horizontal axis

indicates heart rate, regularity, and the time

intervals required for electrical activity to

move from one part of the heart to another

– ––+ +

++– ––+ +

++– ––+ +

++– ––+ +

++

– ––+ +

++– ––+ +

++– ––+ +

+++ ++– ––

– ––

+ ++– ––

– ––+ ++– ––

– ––+ ++– ––

– ––+ ++– ––

– ––

+ ++– ––

– ––+ ++– ––

– ––+ ++– ––

– ––+ ++– ––

– ––

+ ++– ––

– ––+ ++– ––

– ––+ ++– ––

– ––– ––+ +

++

– ––+ +

++– ––+ +

++– ––+ +

++– ––+ +

++

0+

–

– ––

+ +

++

– ––

+ +

++

+ ++

– ––

– ––

+

–

Systole Diastole

Activation Recovery

Electrical Excitation Recovery

Depolarization Repolarization

Shortening Lengthening

Mechanical Contraction Relaxation

Emptying Filling

Terms describing cardiac cycle

(SAN)

(AVN)

(BB)

(BB)

(HB)RA

LA

V

V

SAN

RALA

AVN

HB

BB

V

RECORDING ELECTRODES AND LEADS

1. Bipolar limb leads:

record the potential differences between two limbs

2. Unipolar precordial leads:

record the absolute electrical potential at each of

designated torso sites

3. Augmented unipolar limb leads:

is designed to increase the amplitude of the output

of limb leads

BIPOLAR LIMBS LEADS

Lead I Left arm

Lead II Left leg

Lead III Left leg

AUGMENTED UNIPOLAR LIMBS LEADS

aVR Right arm

aVL Left arm

aVF Left leg

PRECORDIAL LEADS

V1 Right sternal margin, 4th intercostal space

V2 Left sternal margin, 4th intercostal space

V3 Midway between V2 and V4

V4 Left midclavicular line, 5th intercostal space

V5 Left anterior axillary line

V6 Left midaxillary line

Positive

input

Positive

input

R R R

SQ

R

Q S QS

R

S

R’

Systematic evaluation of the ECG

1. Rate and regularity

2. P-wave morphology

3. PR interval

4. QRS-complex morphology

5. ST-segment morphology

6. T-wave morphology

7. U-wave morphology

8. QTc interval

9. Rythm

Rate and regularity

P waves and QRS complexes are used to determine cardiac rate and regularity

Over a particular interval of time, normally, there are same numbers of P waves and QRS complexes

Heart rate:

* 1500 divided by number of small squares between successive P waves or QRS complexes

* 300 divided by number of large squares between successive P waves or QRS complexes

Normal heart rate: 60-100 beats per minute (bpm)

P-wave morphology

1. The contour: is normally smooth and monophasic

(entirely positive or negative) in all leads except V1

or occasionally V2

2. Upright or positive P waves are normally seen in

leads I, aVL, aVF, V4-V6 and downward in lead aVR.

P wave in lead III may be either upright or downward.

3. P-wave duration is normally less than 0.12 seconds

4. The maximal amplitude is normally no more than 0.2

mv

Abnormal P waves

The PR interval

1. The PR interval measures the time required

for an electrical impulse to travel from the

atrial myocardium adjacent to the SA node

to the ventricular myocardium adjacent to

the fibers of the Purkinye network

2. The duration is normally from 0.11 to 0.20

seconds

3. PR interval varies with the heart rate. The

faster the heart rate, the shorter the PR

interval

Abnormal PR interval

Morphology of the QRS

complex

1. Q waves.

• The presence of Q waves in leads V1, V2,

and V3 should be consider abnormal.

• The absence of small Q waves in leads

V5 and V6 should be consider abnormal

• A Q wave of any size is normal in leads

III and avR

• In all other leads, a “normal” Q wave

would be very small (less than 0.04 second

and its voltage is less than 25% of the R-

wave)

Anbormal Q waves

2. R waves

The positive R wave normally increases in

amplitude and duration from lead V1 to V4

or V5.

Loss of normal R-wave progression is

considered

abnormal

3. S wave

S wave should be large in V1 and then

progressively smaller to V6

4. Ratio of R/S amplitude in V1 and V2 is

normally less than 1

Abnormal R wave in V1

5. Duration of the QRS complex (QRS interval)

It normally ranges from 0.07 second to 0.11

second (less than 0.12 second). The QRS

interval has no lower limit that indicates

abnormality

6. Amplitude of QRS complex

There is no arbitrary upper limit for normal

voltage of the QRS complex. An abnormally

low QRS complex when the amplitude is no

more than 0.5 mV in any limb leads and no

more than 1.0 mV in any of the precordial

leads

Abnormal QRS interval

0.19 s

7. The axis of QRS complex

• Normal axis: between –30 degrees and

+90 degrees

• Right axis deviation (RAD): between

+90 degrees and ± 180 degrees

• Left axis deviation (LAD): between –30

degrees and –120 degrees

Right axis deviation (RAD)

Left axis deviation (LAD)

Morphology of the ST

segment

1. The ST segment represents the period

during which the ventricular myocardium

remains in an activated or depolarized state

2. ST segment normally located at the same

horizontal level with the PR segment

3. Normal variations:

• Slight upsloping, downsloping, or

horizontal depresion

• Early repolarization: displacement of ST

segment by as much as 0.1 mV in the

direction of the ensuing T wave

4. ST segment may be altered when there is

prolonged QRS complex

Normal ST segment

Normal ST-segment deviation

Morphology of the T

and

U waves

The T wave

• The T waves are positively directed in all

leads except aVR (negative) and V1

(biphasic)

• T waves do not normally exceed 0.5 mV in

any limb lead or 1.5 mV in any precordial

lead The U wave

U wave is either absent or present as a small

wave following the T wave and is usually most

prominent in leads V1 and V2. Increased

prominence of the U wave indicates the

possibility of hypokalemia

The QTc interval

1. The QT interval measures the duration of electrical activation and recovery of the ventricular myocardium

2. The QT interval decreases as the heart rate increases and therefore should be corrected for cardiac rate (QTc interval)

3. QTc= QT/RR interval (in seconds)The upper limit of QTc is 0.46 second (slightly longer in in females)

4. QT interval varies among different leads. The longest QT interval measured in multiple leads should therefore be considered the true QT interval