Arrythmias mechanism

1. • Cardiac myocytes exhibit a characteristically long
action potential (200–400 ms) .
• The action potential profile is sculpted by the
orchestrated activity of multiple distinctive time-
and voltage-dependent ionic currents:
(ion channels, pumps, exchangers)
• The most abundant superfamily of ion channels
expressed in the heart is voltage gated
3

2. 4

3. 5

4. 6

5. MECHANISMS OF CARDIAC ARRHYTHMIAS
• Cardiac arrhythmias result from abnormalities of
electrical impulse generation or conduction
• Bradyarrhythmias typically arise from
disturbances in impulse formation at the level of
the sinoatrial node or from disturbances in
impulse propagation at any level.
7

6. • Tachyarrhythmias can be classified according to
mechanism:
• Enhanced automaticity :spontaneous
depolarization of atrial, junctional, or ventricular
pacemakers.
• Triggered arrhythmias :initiated by
afterdepolarizations occurring during or
immediately after cardiac repolarization, during
phase 3 or 4 of the action potential.
• Reentry : circus propagation of a depolarizing
wavefront.
8

7. Automaticity Trigger Reentry
Abnormal Impulse generation Abnormal Impulse conduction
enhanced Abnormal EAD DAD Anatomic Functional Anisotropy
Mechanisms of Arrhythmias
9

8. Altered Automaticity
A- Enhanced normal automaticity by cathecholamines and occurs in pace maker cells
B- Abnormal automaticity is due to ishemia or injury and may occur anywhere in the heart
10

9. Altered Automaticity
A- Enhanced normal automaticity by cathecholamines and occurs in pace maker cells
B- Abnormal automaticity is due to ishemia or injury and may occur anywhere in the heart
10

10. Triggered activity
11

11. 12

12. Reentry
• Two parallel conducting pathways
( limb A and B) connected
proximally and distally
• Different refractory periods
between A and B
• Different conduction velocities
between A and B
A
B
13

13. Reentry
• Unidirectional conduction block
• Inexcitable tissue in the center
of the circuit
• Excitable tissue ahead of the
traveling impulse
A
B
14

14. 15