EGM, Electrocardiogram

1. Intracardiac Electrogram
Arief bk

2. Electrical System of the Heart
Purkinje fibers
Bundle of His
Sinoatrial node
Atrioventricular node
Pacemakers – Sinoatrial node, Atrioventricular node, Purkinje fibers

3. Pacemaker Activity
 Spontaneous time-dependent depolarization leading
to action potentials
 Pacemaker with highest frequency sets the heart
rate.
 SA node – 60 beats/min – smallest electrical region in
the heart, sum of 3 ion channels produces pacemaker
(ca, k, f)
 AV node – 40 beats/min – can take over for SA node,
pacemaker determined by same three channels as SA
node.
 Purkinje fibers –20 beats/min – unreliable pacemaker,
but great conducting system, pacemaker determined
by ‘f’ channels only.

4. INa+
rapid
depolarizing
(non-nodal)
IK+
repolarizing
(all myocytes)
ICa+
depolarizing
(nodal AP
and myocyte
contraction)
If
“funny channel” or HCN
Pacemaker current
(activated during hyperpolarization)
Hyperpolarization activated Cyclic
Nucleotide gated channel
Na+/K+
(activated during
depolarization)
MAJOR
MYOCYTE
ION CHANNELS
Which channel
is absent in SA and AV node?
Absent in ventricular myocytes?
Read-
Table 20-1

5. Pacemaker Action Potential

6. Cardiac Action Potential

7. Cardiac Muscle Depolarization

8. Ventricular Action Potential
5 Phases
0 – upstroke of AP
ICa+ – slow
ICa+/INa+ - fast
1 – rapid repolarization
Ik+ – activation
ICa+/INa+ - inactivation
2 – plateau phase
ICa+/INa+ - activated
3 – repolarization
Ik+
4 – diastolic potential
Ik+, ICa+, If
Produce pacemaker activity
SA/AV node, purkinje use If
Phase 1 and 2 not present in SA/AV node

9. Comparison of Slow Nodal and
ast Non-nodal Cardiac Action Potentia

11. Velocity of Electrical Conduction
Purkinje fibers
Bundle of His
(0.05 m/s)
(0.05 m/s)
(1.0-2.0 m/s)
(1 m/s)
(2.0-4.0 m/s)
Functionally, how might the speeds be important?
(0.3-1.0 m/s)
Ventricdular myocardium

12. Surface EKG Morphology

13. As the heart beats action
potentials on the heart cause an
electrical signal on the body
surface.
The larger the structure the
greater the voltage it induces.
This voltage pattern is called the
electrocardiogram

14. Atrial depolarization
gives rise to the P
wave

15. Conduction through
the small AV node is
associated with
virtually no electrical
signal on the skin.

16. Depolarization of
the ventricle
causes the QRS
complex.
QRS is
large
because the
ventricular
mass is
large
QRS is short
because
conduction
over the
ventricles is
very fast

17. Repolarization of the
ventricle causes the T
wave
Dispersion causes it to be
smaller and last longer than
the QRS complex.
Repolarization is not a
conducted wave.

18. HRA
His
RV
CS

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