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Normal Impulse Conduction
Sinoatrial node
AV node
Bundle of His
Bundle Branches
Purkinje fibers

Impulse Conduction & the ECG
Sinoatrial node
AV node
Bundle of His
Bundle Branches
Purkinje fibers

Ecg Sensor Recording cardiac Resting State
BIPOLARLEAD

The “PQRST”
• P wave - Atrial
depolarization
• T wave - Ventricular
repolarization
• QRS - Ventricular
depolarization

The PR Interval
Atrial depolarization
+
delay in AV junction
(AV node/Bundle of His)
(delay allows time for
the atria to contract
before the ventricles
contract)

The ECG Paper
• Horizontally
– One small box - 0.04 s
– One large box - 0.20 s
• Vertically
– One large box - 0.5 mV

The ECG Paper (cont)
• Every 3 seconds (15 large boxes) is
marked by a vertical line.
• This helps when calculating the heart
rate.
3 sec 3 sec

The 12-Lead ECG
• The 12-Lead ECG sees the heart
from 12 different views.
• Therefore, the 12-Lead ECG helps
you see what is happening in
different portions of the heart.

The 12-Leads
The 12-leads include:
–3 Limb leads
(I, II, III)
–3 Augmented leads
(aVR, aVL, aVF)
–6 Precordial leads
(V1- V6)

1st: ASSESS
CONNECTION & STANDERDIZATION
(voltage & timing)

Basics of 12 Lead ECG's
Determining AXIS
1. Leads 1 and AVF divide
the thorax into quadrants,
(Left, Normal, Right, No Man's)
2. If leads 1 and AVF are both
upright then the Axis is normal.
3. If lead 1 is upright and lead AVF
is downward the Axis is Left.
4. If lead AVF is upright and lead 1 is
downward then the Axis is Right
5. If both leads are downward then
the Axis is extreme Right Shoulder
and most often is Vent. Tachy

• Lead I = left thumb and aVF = right thumb
– If both I & aVF are up = Normal Axis
– If I is up but aVF is down = LAD
– If I is down but aVF is up = RAD
– If both I & aVF are down = Extreme RAD
– Clue: If aVR is positive = extreme
RAD
EKG Axis for Dummies!

Step 1: Determine regularity
• Look at the R-R distances (using a caliper or
markings on a pen or paper).
• Regular (are they equidistant apart)? Occasionally
irregular? Regularly irregular? Irregularly
irregular?
Interpretation?
Regular
R R

Step 2: Calculate Rate
• Option 1 (if rate regular)
Count the number of large boxes between R-
R interval. Then divided by 300
• Interpretation? 3003 =100

Step 2: Calculate Rate
• Option 2 (if rate irregular)
– Count the number of cardiac cycle(R –R
interval) in a 6 second rhythm strip, then
multiply by 10.
Interpretation? 9 x 10 = 90 bm
3 sec 3 sec

4th: ANALYSIS OF
waves, segments& intervals

The standard 12 Lead ECG
6 Limb Leads 6 Chest Leads (Precordial leads)
I, II, III, avR, avL, avF, V1, V2, V3, V4, V5 and V6
Rhythm Strip

Normal
ECG
PR interval0.12s-
0.2s(not>1 large sq)
QRS duration0.12s
(not>3 small squares)
PQRST
ST segmentisoelectric
T upright

EKG Basics: P Wave
• Normal
– Width < .1 secs
– Height .5 to 2.5 mm
– Morphology
• Flat
• Biphasic

EKG Basics: P Wave
• Abnormal
– Inversions
– Amplitude
• P-Pulmonale > 2.5 mm
– Duration
• P-Mitrale > .1 sec (or 2 ½ boxes)
– Absence

PR interval
• Normal: 0.12 - 0.20 seconds.
(3 - 5 small boxes)
Interpretation? 0.12 seconds

QRS
• Duration: .04 - .12 secs
• Amplitude: > 5mm;
< 20 mm in limb, < 25 in anterior leads
• Presence of Q waves < 0.04 msec and
< 2 mm

V1
V2
V3
V4
V5
V6
The R wave in the precordial leads must grow from V1 to at least V4

P
Q
T
S
All waves are negative in lead aVR

QRS Complex
May be too broad ( more than 0.12
seconds)
• A delay in the depolarisation of the
ventricles because the conduction
pathway is abnormal

Q Waves
Non Pathological Q waves
Q waves of less than 2mm are normal
Pathological Q waves
Q waves of more than 2mm
indicate full thickness myocardial
damage from an infarct
Late sign of MI (evolved)

ST Segment Depression
Can be characterised as:-
• Downsloping
• Upsloping
• Horizontal

ST Segment Depression
Downsloping ST segment depression:-
• Can be caused by digoxin.
Upward sloping ST segment depression:-
• Normal during exercise.

EKG Basics: T waves and
U waves
• T waves occur in
– Same direction as QRS
– Height: < 5 mm in limb leads, <10 mm in anterior
leads
– 0.18 – 0.22
• U waves
– After T wave
– Best seen in lead III
– Hypothermia/hypokalemia
QRS and T waves tend to have the same general direction in
the limb leads
The T wave must be upright in I, II, V2 to V6

I II III aVR aVL aVF V1 V2 V3 V4 V5 V6
The T wave must be upright in I, II, V2 to V6

Left Atrial Enlargement: Criteria
• P wave
• Notch in P wave
– Any lead
– Peaks > 0.04 secs
• V1
– Terminal portion of P wave > 1mm deep
and > 0.04 sec wide

P Wave: Left Atrial Enlargement

Right Bundle Branch Blocks
What QRS morphology is characteristic?
V1
For RBBB the wide QRS complex assumes a
unique, virtually diagnostic shape in those
leads overlying the right ventricle (V1 and V2).
“Rabbit Ears”

Myocardial layers
Epicardial, Middle, Subendocardial and
Endocardial
 Ischemia is a relative condition that depends on
the balance among:
1. Coronary blood supply
2. Oxygenation of the blood
3. Myocardial workload
 The myocardial area affected by ischemia
depends on:
1. Proximity to intracavitary blood supply
2. Distance from the major coronary arteries
3. Workload

ECG Changes & the Evolving MI
There are two
distinct patterns
of ECG change
depending if the
infarction is:
–ST Elevation (Transmural or Q-wave), or
–Non-ST Elevation (Subendocardial or non-Q-wave)
Non-ST Elevation
ST Elevation

sub
endocardial
vessels
sub epicardial
vessels
left
anterior
oblique
cross
section
of LV
Transmural
MI
SubendocardialMI
blockage

Origin of “pathological Q wave”

Stages of Ischemia & Infarction
• Ischemia during exercise: “ST-segment depression”
• usually indicative of subendocardial ischemia
J-point .08 seconds
Quantity or depth
of ST-segment
depression
Baseline

Reciprocal Changes
• Changes occurring on the opposite side
of the myocardium that is infarcting

Quick Quiz
Mr Jones is diagnosed as having had an
anterior MI. On which leads would you
expect to see the main changes?
(a) II, III and avL.
(b) I and avL.
(c) V2 - V4.

Quick Quiz
Mr Jackson has ECG changes suggestive
of an MI on leads II, III and avF. Which
surface of his heart is affected?
(a) The anterior surface.
(b) The lateral surface.
(c) The inferior surface.

Quick Quiz
Mrs Brown requires PTCA to her Circumflex
artery after complaining of unstable angina
symptoms. Her 12 lead ECG shows ST
depression and T wave inversion in what
leads?
(a) I, avL, V5 and V6
(b) II, III and avL
(c) V3 and V4

A 55 year old man with 4 hours of “crushing” chest
pain.
Acute inferior myocardial infarction (with reciprocal changes)
 ST elevation in the inferior leads II, III and aVF
 reciprocal ST depression in the anterior leads

A 63 Year Old woman with 10 hours of chest pain and
sweating
Can you guess her diagnosis?
Acute anterior-lateral myocardial infarction
ST elevation in the anterior leads V1 - 6, I and aVL
reciprocal ST depression in the inferior leads

RBBB + acute inferior MI + sinus
bradycardia (HR = 43 b/m)

 Consider the following:
1- Heart rate (tachy or brady).
2- Rhythm (regular or irregular < regular – irregular>).
3- P wave (Presence - Shape).
4- QRS (Normal or abnormal shape and size).
5- A-V conduction.
(Is there P wave for each QRS?)
(PR interval)

Arrhythmia Formation
Arrhythmias can arise from problems in
the:
• Sinus node
• Atrial cells
• AV junction
• Ventricular cells

SA Node Problems
The SA Node can:
• fire too slow
• fire too fast
Sinus Bradycardia
Sinus Tachycardia

Atrial Cell Problems
Atrial cells can:
• fire occasionally
from a focus
• fire continuously
Atrial premature beat
P .S .V .T
Atrial Flutter

Atrial Cell Problems
Atrial cells can also:
from multiple foci
Atrial Fibrillation

AV Junctional Problems
The AV junction can:
Fire (acting as
pacemaker)
• block impulses
coming from the
SA Node
Premature nodal beat
Paroxysmal SVT
AV Junctional Blocks

Ventricular Cell Problems
Fire occasionally
from a focus
Fire contanously
from a focus
Fire continuously
from multiple foci
Premature Ventricular
Contractions (PVCs)
Ventricular Tachycardia
Ventricular fibrillation

Sinus Bradycardia
30 bpm• Rate?
• Regularity? regular
normal
0.10 s
• P waves?
• PR interval? 0.12 s
• QRS duration?
Interpretation? Sinus Bradycardia

Sinus Bradycardia
• Deviation from NSR
- Rate < 60 bpm

Sinus Tachycardia
130 bpm• Rate?
normal
0.08 s
• P waves?
• QRS duration?
Interpretation? Sinus Tachycardia

Sinus Tachycardia
- Rate > 100 bpm

70 bpm• Rate?
• Regularity? occasionally irreg.
different contour
0.08
• P waves?
• QRS duration?
Interpretation? NSR with Premature Atrial
Contractions

–These ectopic beats come early than
the normal. QRS complex is normal
(narrow)= (0.04 - 0.12 s).

Sinus Rhythm with 1 PVC
60 bpm• Rate?
• Regularity? occasionally irreg.
none for 7th QRS
(wide)
• P waves?
• QRS duration?
Interpretation? Sinus Rhythm with 1 PVC

PVCs
– Ectopic beats originate in the ventricles
resulting in wide and bizarre QRS
complexes.
– When there are more than 1 premature
beats and look alike, they are called
“uniform”. When they look different, they are
called “multiform”.

Supraventricular Tachycardia
(PSVT)
74 150 bpm• Rate?
• Regularity? Regular
none
0.08 s
• P waves?
• PR interval? none
• QRS duration?
Interpretation? Paroxysmal Supraventricular
Tachycardia (PSVT)

70 bpm• Rate?
flutter waves (Saw teeth)
0.06 s
• P waves?
• QRS duration?
Interpretation? Atrial Flutter
Atrial Flutter

Atrial Flutter
–No P waves. Instead flutter waves (note
“sawtooth” pattern) are formed at a rate
of 250 - 350 bpm.
–Only some impulses conduct through
the AV node (usually every other
impulse).

Atrial Fibrillation
100 bpm• Rate?
• Regularity? irregularly irregular
none
0.06 s
• P waves?
• QRS duration?
Interpretation? Atrial Fibrillation

Atrial Fibrillation
Deviation from NSR
–No organized atrial depolarization, so
no normal P waves (impulses are not
originating from the sinus node). R-R
interval is irregular bec. AV node
allows some of the impulses to pass
through at variable intervals (so rhythm
is irregularly irregular).QRS is normal

160 bpm• Rate?
none
wide (> 0.12 sec)
• P waves?
• QRS duration?
Interpretation? Ventricular Tachycardia

–Impulse is originating in the ventricles
(no P waves, wide QRS).

Ventricular Fibrillation
none• Rate?
• Regularity? irregularly irreg.
none
wide, if recognizable
• P waves?
• QRS duration?
Interpretation? Ventricular Fibrillation

Ventricular Fibrillation
–Completely abnormal.

AV Nodal Blocks
• 1st Degree AV Block
• 2nd Degree AV Block, Type I
• 2nd Degree AV Block, Type II
• 3rd Degree AV Block

60 bpm• Rate?
normal
0.08 s
• P waves?
• QRS duration?
Interpretation? 1st Degree AV Block
1st Degree AV Block

1st Degree AV Block
–PR Interval > 0.20 s
(Prolonged conduction delay in the AV node).

2nd Degree AV Block, Type I
50 bpm• Rate?
• Regularity? regularly irregular
normal, but 4th no QRS
0.08 s
• P waves?
• PR interval? lengthens
• QRS duration?
Interpretation? 2nd Degree AV Block, Type I

2nd Degree AV Block, Type I
–PR interval progressively lengthens,
then the impulse is completely blocked
(P wave not followed by QRS).

2nd Degree AV Block, Type II
40 bpm• Rate?
nl, 2 of 3 no QRS
0.08 s
• P waves?
• QRS duration?
Interpretation? 2nd Degree AV Block, Type II

2nd Degree AV Block, Type II
–Occasional P waves are completely
blocked (P wave not followed by QRS).

3rd Degree AV Block
40 bpm• Rate?
no relation to QRS
wide (> 0.12 s)
• P waves?
• QRS duration?
Interpretation? 3rd Degree AV Block

3rd Degree AV Block
• Etiology: There is complete block of
conduction in the AV junction, so the
atria and ventricles form impulses
independently of each other. Without
impulses from the atria, the ventricles
own intrinsic pacemaker fires in at
around 30 - 45 beats/minute.

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