Ecg Principles

Question 1

Definition

Answer 1

Records of the myocardial potential changes during the cardiac cycle (sum of the action potential
of all myocardial muscle fibers)
Via electrodes placed on body surface as body fluid act as a good conductor

Skin has high electrical resistance,
An electrolyte jelly (NaCl, KCl) is rubbed
to remove the oil and
form a conducting surface between the skin & metal electrode

Question 2

ECG Paper

Answer 2

is divided in 1x1 mm squares, each 5 small squares are bounded by heavier line.
Each horizontal small square (1mm) = 0.04 sec
Each vertical 10 small squares = 1 mV
Recording paper move at 25mm/sec

Question 3

What is the clinical importance of ecg

Answer 3

Diagnose and monitor conditions affecting the heart.
Used to investigate symptoms of a possible cardiac problem, as chest pain, palpitations
(suddenly noticeable heartbeats), dizziness and shortness of breath

Question 4

P wave

Answer 4

Time: < 0.1 (2.5 ss)
Amplitude: < 0.25 mv
Represent - significance (importance) mention 1 abnormality: Atrial depolarization (spread of wave from SAN to atria)
Atrial repolarization (very small wave) is masked by
Large wave of ventricular depolarization

Question 5

PR-segment & PR-interval

Answer 5

Time: 0.06- 0.1 & 0.12- 0.2 (3-5ss)
Represent - significance (importance) mention 1 abnormality: Conduction through AV node (delay) (isoelectric)
From end of P wave to beginning of qrs
Atrial depolarization & conduction through AV node
From beginning of P wave to beginning of QRS

Question 6

QRS complex

Answer 6

Time: < 0.08 (2ss)

Amplitude: 1 mv in limb leads
3 mv in chest leads

Represent - significance (importance) mention 1 abnormality: Ventricular depolarization

Question 7

ST-segment

Answer 7

Time: 0.16

Represent - significance (importance) mention 1 abnormalities: Plateau of Ventricular repolarization (isoelectreic)
From end of QRS to beginning of T wave

Question 8

T wave

Answer 8

Time: 0.16 (4ss)

Amplitude: < 0.5 mv in limb leads
< 1 mv in chest leads

Represent - significance (importance) mention 1 abnormality: Ventricular repolarization (final rapid)

Question 9

QT interval

Answer 9

Time: 0.2-0.4

Represent - significance (importance) mention 1 abnormality: Ventricular depolarization & ventricular repolarization (AP)
From beginning of QRS to end of T wave
Depends on heart rate
At high heart rate→ AP shorten & shorter QT

Question 10

U wave

Answer 10

Amplitude: small positive wave

Represent - significance (importance) mention 1 abnormality: May not appear normally due to its small size
origin →uncertain ,may be repolarization of papillary muscle