2. OutlineOutline
• Ion current, action potential and cardiac
conduction
• Surface EKG
• Intracardiac mapping
• Mechanism and catheter ablation
3. Electrical System of the HeartElectrical System of the Heart
Purkinje fibers
Bundle of His
Sinoatrial node
Atrioventricular node
Pacemakers – Sinoatrial node, Atrioventricular node, Purkinje fibers
4. Pacemaker ActivityPacemaker 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.
5. 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
14. 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
16. Conduction throughConduction through
the small AV node isthe small AV node is
associated withassociated with
virtually no electricalvirtually no electrical
signal on the skin.signal on the skin.
17. Depolarization ofDepolarization of
the ventricle causesthe ventricle causes
the QRS complex.the QRS complex.
QRS is largeQRS is large
because thebecause the
ventricularventricular
mass is largemass is large
QRS is shortQRS is short
becausebecause
conduction overconduction over
the ventricles isthe ventricles is
very fastvery fast
18. 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.
29. 12 Lead-12 Directions12 Lead-12 Directions
Help to Analyze Gross Heart conductionHelp to Analyze Gross Heart conduction
30.
31. Limb Leads
• 1. R1 + SIII > 25 mm
• 2. R wave in aVL > 11 mm
• 3. R wave in aVF > 20 mm
• 4. S wave in aVR > 14 mm
Precordial Leads
• 5. R wave in V5 or V6 > 26 mm
• 6. R wave in V5 or V6 + S wave in V1 > 35 mm
• 7. Largest R wave + largest S wave in the
precodial leads > 45 min
Voltage Indicates Ventricular MassVoltage Indicates Ventricular Mass
-Left Ventricular Hypertrophy-Left Ventricular Hypertrophy
32. 12 Lead-12 Directions12 Lead-12 Directions
Help to Analyze Gross Heart conductionHelp to Analyze Gross Heart conduction
41. Distribution of AF triggerDistribution of AF trigger
Haissagurre et al. NEJM 1998Haissagurre et al. NEJM 1998 Chen et al. Circulation 1999Chen et al. Circulation 1999