electrocardiogram (ecg) prof. sultan ayoub meo mbbs, m.phil, ph.d (pak), pg dip med ed, m med ed...
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ELECTROCARDIOGRAM (ECG)ELECTROCARDIOGRAM (ECG)
Prof. Sultan Ayoub MeoMBBS, M.Phil, Ph.D (Pak), PG Dip Med Ed, M Med Ed (Scotland)
FRCP (London), FRCP (Dublin), FRCP (Glasgow), FRCP (Edinburgh)Professor and Consultant, Department of Physiology,
College of Medicine, King Saud University, Riyadh, Saudi Arabia
LECTURE OBJECTIVES
Define ECG
Identify waves of ECG and the physiological cause of each
Define the normal intervals and segments
Discuss the bipolar and un ipolar leads and their locations
Discuss the bipolar limb lead and the cardiac axis
INTRODUCTION
Cardiac impulse passes through the heart, electrical current spreads
from heart into adjacent tissues surrounding the heart. Current
spreads all the way to the surface of the body. If electrodes are
placed on the chest, opposite sides of the heart, electrical potentials
generated by the current can be recorded; the recording is known as
an electrocardiogram
A record of the waves (impulses) of electrical excitation in the heart
is called ECG.
It helps in the diagnosis of muscle damage or electrical problems in
the heart.
NORMAL IMPULSE CONDUCTIONNORMAL IMPULSE CONDUCTION
Sinoatrial node
AV node
Bundle of His
Bundle Branches
Purkinje fibers
TYPES OF PATHOLOGY IDENTIFY AND STUDY FROM ECGS?
•Arrhythmias•Myocardial ischemia and infarction
•Pericarditis•Chamber hypertrophy
•Electrolyte disturbances (i.e. hyperkalemia, hypokalemia)
•Drug toxicity (i.e. digoxin and drugs which prolong the QT interval)
NORMAL ECGThe normal ECG is composed of: P wave QRS complex T wave
The separate waves:
Q wave, the R wave, and the S wave.
P wave: Atria depolarize before atrial contraction begins
QRS complex: Ventricles depolarize before contraction. P wave and the components of the QRS complex are depolarization waves.The T wave: Ventricles recover from the state of depolarization This process normally occurs in ventricular muscle 0.25 to 0.35 second after depolarization and the T wave is known as a repolarization wave
The ECG Paper
P wave:
Atrial depolarization (completed in 0.1 seconds )
• Irregular or absent P waves may indicate arrhythmia.
• The shape of the P waves may indicate atrial problems
QTPR
0.12-0.2 s approx. 0.44 s
Atrial muscledepolarization
P
Q
R
S
T
PR interval: Atrial depolarization & conductive time Measured from the P wave to the beginning of the QRS complex .Through the AV node /0.18 seconds (N. R. 0.12 to 0.2 s)
QTPR
0.12-0.2 s approx. 0.44 s
Atrial muscledepolarization
P
Q
R
S
T
QRS complex: Ventrical depolarization
Equal 0.08-0.12 s (max time 0.1seconds)
Very wide and deep Q waves indicate myocardial infarction
QTPR
0.12-0.2 s approx. 0.44 s
Atrial muscledepolarization
Ventricular muscledepolarization
P
Q
QRS
S
T
QT interval: Ventricular depolarization & re-polarization (equal . 0.4 seconds
QTPR
0.12-0.2 s approx. 0.44 s
Atrial muscledepolarization
Ventricular muscledepolarization
Ventricular muscle repolarization
P
Q
R
S
T
ST segment:(QT – QRS) Ventricular depolarization (equal . 0.32 seconds )
QTPR
0.12-0.2 s approx. 0.44 s
Atrial muscledepolarization
Ventricular muscledepolarization
Ventricular musclerepolarization
P
Q
R
S
T
ECG LEADS
Leads are electrodes which measure the difference in electrical potential between either:
1. Two different points on the body (bipolar leads)1. Two different points on the body (bipolar leads)
2. One point on the body and a virtual reference point 2. One point on the body and a virtual reference point with zero electrical potential, located in the center of with zero electrical potential, located in the center of the heart (unipolar leads)the heart (unipolar leads)
ECG LEADS
The standard ECG has 12 leads: 3 Standard Limb Leads
3 Augmented Limb Leads
6 Precordial Leads
The axis of a particular lead represents the viewpoint from The axis of a particular lead represents the viewpoint from
which it looks at the heart.which it looks at the heart.
STANDARD LIMB LEADS
STANDARD LIMB LEADS AUGMENTED LIMB LEADS
ALL LIMB LEADS
PRECORDIAL LEADS
SUMMARY OF LEADS
Limb LeadsLimb Leads Precordial LeadsPrecordial Leads
BipolarBipolar I, II, IIII, II, III(standard limb leads)(standard limb leads)
--
UnipolarUnipolar aVR, aVL, aVF aVR, aVL, aVF (augmented limb leads)(augmented limb leads)
VV11-V-V66
ARRANGEMENT OF LEADS ON THE ECG
ANATOMICAL REPRESENTATION(SEPTUM)
ANATOMIC PRESENTATION(ANTERIOR WALL)
ANATOMICAL PRESENTATION(LATERAL WALL)
ANATOMICAL PRESENTATION (INFERIOR WALL)
ANATOMICAL PRESENTATION(SUMMARY)
RULE OF 300
Take the number of “big boxes” between neighboring QRS complexes, and divide this into 300. The result will be approximately equal to the heart rate
Although fast, this method only works for regular rhythms.
DETERMINING THE HEART RATE
1. Rule of 3002. 10 Second Rule
WHAT IS THE HEART RATE?
(300 / 6) = 50 bpm
(300 / 4) = 75 bpm
(300 / 1.5) = 200 bpm
10 Second Rule
As most ECGs record 10 seconds of rhythm per page, one can simply count the number of beats present on the ECG and multiply by 6 to get the number of beats per 60 seconds.
This method works well for irregular rhythms.
WHAT IS THE HEART RATE?
33 x 6 = 198 bpm
The Alan E. Lindsay ECG Learning Center ; http://medstat.med.utah.edu/kw/ecg/
The QRS Axis
The QRS axis represents the net overall direction of the heart’s electrical activity.
Abnormalities of axis can hint at:
Ventricular enlargement
Conduction blocks (i.e. hemiblocks)
The QRS Axis
By near-consensus, the normal QRS axis is defined as ranging from -30° to +90°.
-30° to -90° is referred to as a left axis deviation (LAD)
+90° to +180° is referred to as a right axis deviation (RAD)
•The QRS Axis
ST Elevation - Acute MI or AnginaST depression >1 mm - Ischemia/Angina (flat), digoxin (sloping)Q waves in 2 or more leads - Previous MI (Transmural)Diffuse ST elevation with PR depression – PericarditisT wave inversions and non-specific ST changes - Can be seen both in normal cases and in many diseases, therefore not useful for diagnosis.Tall P waves - Right atrial hypertrophyBroad (and often bifid) P waves - Left atrial hypertrophyPeaked T waves or loss of P wave – HyperkalemiaU waves - Hypokalemia ('Hump' at the end of T wave)Prolonged QT interval – HypocalcemiaShortened QT interval - Hypercalcemi
Clinical Significance of different waves and segments of ECG