Ecg interpritation
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ECG
HISTORY
1842- Carlo Matteucci -electricity is a/w heart beat
1876- Marey - electric pattern of frog’s heart
1895 - William Einthoven - invention of EKG
1924 - Noble prize - Einthoven for EKG
1938 -AHA & Cardiac society of great Britain
defined position of chest leads
1942 -Goldberger increased Wilson’s Unipolar lead
voltage by 50% & made Augmented leads
ELECTROCARDIOGRAM
Is a recording of electrical activity of heart conducted thru ions in body to surface
ECG INTERPRITATION STEPS
Rate Rhythm Cardiac Axis P – wave PR - interval QRS Complex ST Segment QT interval (T & U wave) Other ECG signs
CARDIAC ELECTROPHYSIOLOGY
Electrical activity is governed by multiple trans
membrane ion conductance changes
3 types of cardiac cells
1. Pacemaker cells - SA node, AV node
2. Specialized conducting tissue -
Purkinje fibres
3. Cardiac myocytes
WAVEFORMS AND INTERVALS
ECG GRAPH PAPER
Runs at a paper speed of 25 mm/sec
Each small block of ECG paper is 1 mm2
At speed of 25 mm/s, 1 small block = 0.04 s
Voltage: 1 mm = 0.1 mV between each individual
block vertically
5 mm
1 mm
0.1 mV
0.04 sec
0.2 sec
Speed = rate
Voltage ~Mass
ECG GRAPH PAPER
ECG LEADS
Leads are electrodes which measure the difference in electrical potential between either:
1. Two different points on the body (bipolar leads)
2. One point on the body and a virtual reference point with zero electrical potential, located in the center of the heart (unipolar leads)
+-
RA
RA
LL+
+
--LA
LL
LA
LEAD II
LEAD I
LEAD III
Remember, the RLis always the ground
• By changing the arrangement of which arms or legs are positive or negative, three unipolar leads (I, II & III ) can be derived giving three "pictures" of the heart's electrical activity from 3 angles.
The Concept of a “Lead”
Leads I, II, and III
I
II III
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 which it looks at the heart.
ECG LEADS
Gold Berger :aV frontal leads
Wilson & co-workwers :chest leads
STANDARD LIMB LEADS
PRECORDIAL LEADS
PRECORDIAL LEADS
STANDARDIZATION
300 number of BIG SQUARE b/w R-R
Rate =
1500 number of SMALL SQUARE b/w R-R
OR
Rate =
RATE
RATE
RHYTHM
P -QRS relationships- Lead II is commonly used
Regular or irregular?
Ventricular rhythm – measured by R-R interval
Atrial rhythm - measured P-P interval.
ECG rhythm -usual rate as per age of child, every P
wave must be followed by a QRS & every QRS is
preceded by P wave.
P wave is upright in leads I and II
Normal Sinus Rhythm
NORMAL SINUS RYTHM
Originates in the sinus node Rate between 60 and 100 beats per min P wave axis of +45 to +65 degrees (Tallest p
waves in Lead II) Monomorphic P waves Normal PR interval of 120 to 200 msec Normal relationship between P and QRS Some sinus arrhythmia is normal
AXIS
Axis refers to general direction of heart's
depolarization wave front (or mean electrical
vector) in the frontal plane.
In healthy conducting system - axis is related to
where the major muscle bulk of heart lies.
William Einthoven developed a system capable of
recording small signals & recorded 1st ECG.
Leads were based on Einthoven triangle a/w limb
leads.
Leads put heart in middle of a triangle
EINTHOVEN TRIANGLE
AXIS
1. Lead I & aVF divide
thorax into quadrants,
(Lt, N , Rt, No Man's)
2. If Lead I & aVF are both upright- Axis is normal.
3. If lead I is upright & lead aVF is downward - Axis is Left.
AXIS
4. If lead aVF is upright & lead I is downward - Axis is Rt
5. If both leads are downward - Axis is extreme Right Shoulder & most often is Vent. Tachy
Cardiac
Axis
Causes
LAD Pregnancy, obesity; Ascites ,
abdominal distention, tumour ;
LAH, LVH
RAD N finding in children & tall thin
adults, COPD, RVH, Anterolateral
MI.
North
West
Emphysema, Hyperkalaemia ,
Lead transposition, Artificial
cardiac pacing, VT
P WAVE
Depolarization of both atria
Relationship b/w P & QRS - distinguish various
arrhythmias
Shape & duration of P - indicate atrial
enlargement
P WAVE
Always +ve in lead I & II
Always -ve in lead aVR
<2 small sqs - duration
<2 small sqs - amplitude
Biphasic in lead V1
Best seen in lead II
P-PULMONALE P-MITRALE
PR INTERVAL
Onset of P wave to onset of QRS
• Normal = 0.12 - 2.0 sec
• Represents A to V conduction time (via His
bundle)
Prolonged PR interval indicate AV block
PR INTERVAL
Onset of P wave to onset of QRS
• Normal = 0.12 - 2.0 sec
• Represents A to V conduction time (via His
bundle)
Prolonged PR interval indicate AV block
VENTRICULAR DEPOLARIZATION
Includes Bundle of His Bundle Branches
Right Left
SeptalAnteriorPosterior
Terminal Purkinjie fibers
Ventricular Waves
Q wave – 1st downward deflection after P wave
Rwave – 1st upward deflection after Q wave
S wave – 1st downward deflection after R wave
QRS COMPLEX
Ventricular depolarization
• Is > P wave d/t > Ventricular mass
• Normal duration = 0.08 - 0.12 secs
ST SAGMENT
Connects QRS complex & T wave
Duration = 0.08 - 0.12 sec
T WAVE
“small to moderate” size +ve deflection wave
after QRS complex,
Ht is 1/3rd - 2/3rd that of corresponding R wave
U WAVE
Septal repolarization (not always seen on ECG)
QT INTERVAL
Beginning of QRS to end of T wave
Normal QT is usually about 0.40 sec
QT varies based on HR- faster HR ,shorter QT
Bazett’s formula: QTC = QT / √ RR
Fredericia’s formula: QTC = QT / RR 1/3
Framingham formula: QTC = QT + 0.154 (1 – RR)
Hodges formula: QTC = QT + 1.75 (HR– 60)
PROLONGED QT INTERVAL
CAD Cardiomyopathy Severe Bradycardia, High-Grade AV Block Anti-Arrhythmics Psychotropic Drugs Hypocalcemia Autonomic dysfunction Hypothyroid Hypothermia Congenital Long QT Syndrome
SHORT QT INTERVAL
Digitalis effect Hypercalcemia Hyperthermia Vagal stimulation
VENTRICULAR HYPERTROPHY
RVH = R in V1 + S in V6
LVH = S in VI + R in V6
THANK YOU