Electrocardiography

part 2

.

QRS complex

Normal values

Duration: < 2.5 mm.

Morphology: progressionfrom Short R and deep S (rS) in V1 to tall R and short S in V6 with small Q in V5-6 (qRs).

Abnormalities: 1. Wide QRS complex

Bundle branch block.

Ventricular rhythm

Tall R in V1

RVH.

RBBB.

Posterior MI.

WPW syndrome.

3. Abnormal Q wave

[ > 25% of R wave]

MI.

Hypertrophiccardiomyopathy.

Normal variant

RBBB

VT

ECG IN bundle branch block

Normal Q wave

Q wave in MI

Q wave in septal hypertrophy

ST- segment

Normally it's isoelectric.

[i.e. at same level of PR segment]

Abnormalities:

1. ST elevation: Acute MI.

Prinzmetal angina.

Acute pericarditis.

Early repolarization.

2. ST depression:

Ischemia.

Ventricular strain.

BBB.

Hypokalemia.

Digoxin effect

ST-segment abnormality

T-waveNormal values. 1. Polarity: Always up in I,II,V4-5 Always down in aVR. Variable in III, aVL,

aVF, V1-3.

2. amplitude: < 10mm inthe chest leads.

Abnormalities: 1. Peaked T-wave: Hyper-acute MI. Hyperkalemia. Normal variant. 2. T- inversion: Ischemia. Myocardial infarction. Myocarditis Ventricular strain BBB. Hypokalemia. Digoxin effect

QT-Interval

Definition: Time interval between beginning of

QRS complex to the end of T wave.

Normally: At normal HR: QT ≤ 11mm (0.44 sec)

Abnormalities:

1. Prolonged QT interval: hypocalcemia and congenital long QT syndrome.

2. Short QT interval: hypercalcemia

ECG in IHD

ECG IN STEMIHyper acute T wave

ST segment elevation

• development of Q waves

• ST segment returns to the baseline

• T waves become inverted

This changes should follow either surface or specificartery

Evolution of ECG changes in MI

ECG in other IHD (NSTEMI ,

unstable angina , angina pectoris)

• ST segment depression

• T waves become inverted

• may be normal

NSTEMI

ECG IN ARRYTHMIAS

Tachyrythmias

Narrow complex QRS

Rate >100 with narrow QRS

Broad complex QRS

Rate >100 with broad QRS

Sinus tachycardia

Paroxysmal supraventricular tachycardia(regular tachycardia with normal QRS complex and absent P wave)

PSVT

Atrial fibrillation (fine)

(VT)(regular tachycardia with wide QRS complex and absent P wave)

2. Bradyarrythmias

Sinus bradycardia being defined as a sinus rhythmwith a rate below 60 beats per minute

Sinus Arrest

Sudden disappearance of P waves

ATRIOVENTRICULAR (AV) BLOCK

delay or interruption in the transmission of an impulse

from the atria to the ventricles

The conduction disturbance can be transient or

permanent

First degree heart block

In this condition AV conduction is delayed so the PR

interval is prolonged ( > 0.20 s) it rarely causes symptoms.

Second degree heart block

Mobitz type 1 there is progressive lengthening of

successive PR intervals endding in a dropped beat. Thecycle then repeats itself . this is known as Wenchebach's phenomenon .

.

Mobitz type 2

the PR interval of the conducted impulses remainsconstant but some P waves are not conducted .

Third degree (complete ) heart block When AV conduction fails completely , the atria and ventricles beat independently ( AV dissociation )

Ventricular activity is maintained by an escape rhythm

arising in the AV node or bundle of His or the distal Purkinje tissues.

ECG in ventricular hypertrophy

LVH ➢

R(v6 or v5)+S(v1+v2) > 3.5 mv(7 LS)

Or R(v6 or v5)> 2.5 mv(5 LS)

RVH ➢

R(v1)≥ 0.5 mv

R/S (v1)≥ 1

S(v5)≥ 0.5 mv