ELECTROPHYSIOLOGY OF HEART EXPLAINED BRIEFLY.

1. Dr Vijesha Soni,
Pharm.D,
Executive Clinical Pharmacist (Dept. of Pharmacology),
Artemis Hospital, Gurugram.

2. What’s Cardiac Electrophysiology?
• Cardiac electrophysiology – study of elucidating, diagnosing, and
treating the electrical activities of the heart.
• to assess arrhythmias,
• elucidate symptoms,
• evaluate abnormal electrocardiograms,
• assess risk of developing arrhythmias in the future,
• design treatment.

3. Normal heart
• An electrical impulse stimulates the heart
muscle to contract.
• The normal electrical conduction starts in
the sino-atrial (SA) node sending an impulse
through the atria to the atrio-ventricular
(AV) node, which is the relay station of the
heart.
• It sends the electrical impulses to the
ventricles.

4. The cardiac action potential
• The cardiac action potential, the basic unit of electrical activity in the
heart, produces cardiac contractions.
• Cardiac myocytes, like other types of muscle cells, have a negative
potential difference (-90 mV) at rest between the cell membrane and
extra-cellular space (ie, they are polarized).
• Under the influence of trigger events, potassium, sodium, and
calcium ions cross the cell membrane, thereby generating discrete
ion currents

5. Phases of cardiac action potential
Divided into 5:
• Phase 0 (Opening of Na+ channels)
• Phase 1 (Opening of K+ channels)
• Phase 2 (Opening of Ca++ channels)
• Phase 3 (Opening of K+ channels)
• Phase 4 (Return to resting membrane potential)

6. Phase 0
• Also known as “rapid
depolarization phase”
• Resting membrane potential in a
myocardial cell is -90 mV
• With opening of Na+ channels 
rapid influx of sodium ions into
myocardial cells  depolarization
occurs  Phase 0 begins.

7. Phase 1
• Inactivation of sodium
channels
• Activation/opening of
potassium channels
• Action potential reduces.
• Slight downward
deflection of action
potential.

8. Phase 2
• Also known as “plateau phase”
• In this phase  calcium channels
get opened
• In this phase:
1. Inward movement of calcium
ions
2. Outward movement of
potassium ions.
• Since there is a balance between
inward movement of calcium &
outward movement of potassium
 this phase is also known as
“plateau phase”.

9. Phase 3
In this phase:
1. Calcium channels close
2. Potassium channels still remain
open
3. Due to above changes 
repolarization occurs
4. When membrane potential
reaches -80 to -85 mV  K+
channels close.

10. Phase 4
• Also known as “Resting Membrane
Potential”(RMP)
• Associated with diastole
• Certain myocardial cells  have
potential to undergo spontaneous
depolarization  generate action
potential without any stimulus
(automaticity)
• Spontaneous depolarization 
fastest in SA node  hence it is
also known as “pacemaker”
• From SA node  electrical activity
begins  propagates to the rest of
the heart.