Cardiovascular Physiology and Electrocardiogram: Normal and Pathological States

Learning Objectives: Electrocardiogram

• Characterize EKG of normal states.
• Calculate heart rate from an EKG.
• Characterize EKG of pathological states.

Electrocardiogram (ECG)/Electrokardiogram (EKG)

AVR
VI
aVL
V5
V6

Limb Leads vs. 12 Lead

Lead I
(-)
(+)
(+)
(+)
(-)
aVR
I
Lead II
(-)
Lead III
aVF
(+)
V1
V2
V6
V3 V4 V5
Ground
(a)
(b)

Einthoven's Triangle

-)
(-)
aVL

Limb Leads vs. 12 Lead Analysis

Limb Leads Orientation

-90
-120°
-60
o
-150
-30°
aVR
aVL
Lateral
V2
AVL.
Inferior
AVF
V3
Coronary Anatomy & ECG Leads http://rebelem.com/rebel-reviews/
Lateral Leads
I, aVL, V5 - V6
LCx or Diagonal of LAD
Inferior Leads
II, III, aVF
RCA and/or LCx
Anterior/Septal Leads
aVF
Lateral
AVR
V1
Anterior/Septal
Lateral
+180
1 0
o
o
+30
+150
II
o
o
+60
+120
V1 - V4
LAD

EKG Waveform Components

RR interval
R
mm/sec.
PR
ST
segment
T
P
U
PR
interval
S
ST interval
S
ORS
interval
QT interval
segment
mm/mV 1 square = 0.04 sec/0.1mV

Electrical Conduction of the Heart

SA Node and Atrial Excitation

SA node (pacemaker cells)
Generates spontaneous AP
1
AP spreads to the atria (P wave)
1
Atria fully depolarized (PR segment)
1
AP travels to AV node
1
AP travels through Bundle of His
(atria relaxes; QRS)
AP travels to R/L Bundle Branches
& Purkinje Fibers (QRS)
AP travels to ventricles (QRS)
1
Ventricle depolarizes
(QRS -> ST segment)
1
Ventricle repolarizes (T wave)
Atrial excitation
Ventricular excitation
Ventricular relaxation
Begins
Complete
Begins
Complete
SA node
AV node
Atrial
relaxation
Time
Time
Time
Time
Time
Electrocardiogram

Electrical Conduction of the Heart: EKG Waveforms

R
T
P
J-point
Qs
CM1 Bjana

AP, EKG, Contraction Relationship

R
T
EKG
S
Action potential
recorded with
surface electrode
action potential
150 mV
Action potential
recorded intra-
cellularly
0.5 g
contraction
ARP
RRP
Mechanical
response
0
100
200
300
ms

Learning Objectives: EKG Interpretation

• Characterize EKG of normal states.
• Calculate heart rate from an EKG.
• Characterize EKG of pathological states.

How to Measure Heart Rate

300
100
60
Start
150
75
50
5 large squares = 1 s
here
1 large square = 0.2 s
1 small square = 0.04 s

Learning Objectives: EKG States

• Characterize EKG of normal states.
• Calculate heart rate from an EKG.
• Characterize EKG of pathological states.

Normal Sinus Rhythm

NORMAL SINUS RHYTHM
Impulses originate at S-A node at normal rate
S-A node
1 mV
1
1.0s
All complexes normal, evenly spaced. Rate 60 - 100/min.

Sinus Tachycardia

SINUS TACHYCARDIA
Impulses originate at S-A node at rapid rate
1
1
S
All complexes normal, evenly spaced. Rate >100/min.
CAUSE: STIMULANTS
TREATMENT: BETA BLOCKER, CARDIOVERSION

Atrioventricular Nodal Reentrant Tachycardia (AVNRT)

TYPE OF SUPRAVENTRICULAR TACHYCARDIA (SVT)
CAUSE: RE-ENTRY CIRCUIT
EKG: ABSENT P WAVES
TREATMENT: CARDIOVERSION
In most cases the P-wave is hidden
in the QRS complex.
Atrium
Atrium
Reentry
circuit
AV
node
AV
bode
Slow pathway
Fast pathway
His Bundle
His Bundle
T
Ventricles
Ventricles

Wolf-Parkinson-White (WPW) Syndrome

TYPE OF SUPRAVENTRICULAR TACHYCARDIA (SVT)
BUNDLE OF KENT
EKG: DELTA WAVE
TREATMENT: ABLATION
His bundle
SA node
Accessory pathways
--
Lead II
AV node
Right bundle branch
Left bundle branch
Normal electrical pathway
Wolff-Parkinson-White syndrome
Delta wave
Delta wave

Sinus Bradycardia

SINUS BRADYCARDIA
Impulses originate at S-A node at slow rate
1
All complexes normal, evenly spaced. Rate < 60/min.
TREATMENT: WITHDRAW CAUSE, PACEMAKER

Sinus Arrhythmia

SINUS ARRHYTHMIA
Impulses originate at S-A node at varying rate
1
MEDULLA
ADI AMPATA
All complexes normal, rhythm is irregular
Longest R-R interval exceeds shortest > 0.16 s
TREATMENT: BETA BLOCKER, CARDIOVERSION, ABLATION

Atrial Fibrillation (AFib)

ATRIAL FIBRILLATION
Impulses have chaotic, random pathways in atria
3
Baseline irregular, ventricular response irregular
Ventricular filling incomplete
TREATMENT: BETA BLOCKER, ELECTRIC CARDIOVERSION

Ventricular Fibrillation

EKG: IRREGULAR RHYTHM
TREATMENT: CARDIOVERSION
Steady rhythm and rate
Normal Sinus Rhythm
Chaotic rhythm and rate
Ventricular Fibrillation
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Ventricular Fibrillation EKG

avR
V1
IV4
Nv
aVL
W2
IV5
Un
E
AVF
IV6

First Degree AV Block

A-V BLOCK, FIRST DEGREE
Atrioventricular conduction lengthened
1
Partial
block
R
P
T
P-R
P-wave precedes each QRS-complex but interval is > 0.2 s
TREATMENT: BENIGN, WITHHOLDING OFFENDING MEDICATION

Electrical Conduction of the Heart: Conduction Velocity

Conduction Velocity
Atria
1 m/sec
0
50
50
Right
atrium
Left
atrium
90
SLOWEST
AV node
0.01-0.05 m/sec
60
70
Bundle of His
(common bundle)-210-
160
220
190
190
Right bundle branch
Right
ventricle
Loft
ventricle
Left bundle branch
FASTEST
His-Purkinje 2-4 m/sec
170
170
Purkinje fibers
200
Time (msec)
Sinoatrial node
Atrioventricular node
Ventricle
1 m/sec

Second Degree AV Block

A-V BLOCK, SECOND DEGREE
Sudden dropped QRS-complex
QRS
absent
R
QRS
absent
₽
₽
P
2
S
-
Partial
block
Intermittently skipped ventricular beat

Second Degree AV Block Types

Mobitz I or Wenckebach

Mobitz I or Wenckebach
CAUSE: ELECTRICAL PATHWAY
TREATMENT: BENIGN, WITHHOLDING
OFFENDING MEDICATION
EKG: PROGRESSIVELY LENGTHENING PR
INTERVAL BEFORE A DROPPED QRS

Mobitz II

Mobitz II
CAUSE: ELECTRICAL PATHWAY
TREATMENT: PACEMAKER
EKG: CONSTANT PR INTERVALS WITH
INTERMITTENT DROPPED QRS

Third Degree AV Block

A-V BLOCK, THIRD DEGREE
Impulses originate at AV-node and proceed to ventricles
Atrial and ventricular activities are not synchronous
1
Total
block
R-R
R-R
R
R
R
P
T
P
TP
PT
5
5
-
+
P-P
R-P
P-P
P-P interval normal and constant,
QRS complexes normal, rate constant, 20 - 55 /min
CAUSE: 1°/2° HEART BLOCK
TREATMENT: PACEMAKER

Review Question: QT Interval

1. What will be the effect on the QT interval of a
drug that effectively blocks K+ current during
phase 3?
A. Prolong the QT interval
B. Shorten the QT interval
C. Not change the QT interval

Review Question: ECG Trace and Ventricular Action Potential

2. Which part of the ECG trace most closely
reflects phase 0 of the ventricular action
potential?
A. T-wave
B. QRS-complex
C. P-wave
D. PR-interval
E. ST-segment

Review Questions: Pacemaker Location

3. A person's electrocardiogram (ECG) has no P wave, but has
a normal QRS complex and a normal T wave. Therefore, his
pacemaker is located in the:
a. Sinoatrial (SA) node
b. Atrioventricular (AV) node
c. Bundle of His
d. Purkinje system
e. Ventricular muscle

Review Questions: Ventricular Depolarization

4. The ventricles are completely depolarized during which
isoelectric portion of the electrocardiogram (ECG)?
a. PR interval
b. QRS complex
c. QT interval
d. ST segment
e. T wave

Review Questions: ECG Pattern Interpretation

5. A person's electrocardiogram (ECG) shows two P waves
preceding each QRS complex. The interpretation of this pattern
is:
a. Decreased firing rate of the pacemaker in the sinoatrial (SA)
node
b. Decreased firing of the pacemaker in the atrioventricular AV)
node
c. Increased firing rate of the pacemaker in the SA node
d. Decreased conduction through the AV node
e. Increased conduction through the His-Purkinje system

Answers to Review Questions

1. A
2. B
3. B
4. D
5. D