Cardiac Electrophysiology Quiz

Study Notes

Cardiac Action Potential:
- Propagation: Action potentials spread throughout the heart, enabling coordinated contraction.
- Excitability: The ability of heart cells to respond to a stimulus and generate an action potential.
- Refractory Period: The period following an action potential where the cell is unresponsive to further stimulation.

Pacemaker of the Heart: The SA Node initiates the electrical impulse that triggers each heartbeat.
Spontaneous Discharge: The SA Node can generate action potentials independently, setting the heart's rhythm.
Sympathetic Nervous System: Increases the rate of discharge from the SA Node, speeding up the heart rate.
Parasympathetic Nervous System: Decreases the rate of discharge from the SA Node, slowing down the heart rate.

Prepotential (Unstable Resting Membrane Potential): A gradual depolarization leading to the action potential.
Prepotential Mechanisms:
- Decreased Potassium Efflux: Potassium ions leak out of the cell more slowly during the prepotential, contributing to depolarization.
- Calcium Influx: Calcium ions enter the cell through T-type calcium channels, further depolarizing the membrane.
- Funny Current: A mixed sodium and potassium influx through funny channels, also playing a role in prepotential development.
Sympathetic Stimulation: Makes the prepotential steeper, increasing the rate of discharge.
Parasympathetic Stimulation: Makes the prepotential more horizontal, decreasing the rate of discharge.

Location: Situated above the fibrous ring, connecting the atria to the ventricles via the bundle of His.
Slowest Conduction Velocity: The AV Node conducts impulses slowly (0.02 to 0.05 m/sec) due to gap junctions, contributing to a delay in conduction.
Conduction Delay (0.1 sec): This delay protects the ventricles from rapid atrial rhythms (e.g., atrial fibrillation) by preventing excessively fast ventricular contractions.

Location: Crosses the fibrous ring, carrying the electrical impulse from the AV Node to the ventricles.

Location: Branch off from the bundle of His, conveying the impulse to the left and right ventricles.

Fastest Conduction Velocity: Purkinje fibers conduct impulses very rapidly (4-5 m/sec), ensuring efficient and synchronized ventricular contraction.

Interventricular Septum: The impulse travels through the interventricular septum, spreading from left to right.

Electrical Activity of the Heart: The ECG records the electrical activity generated by the heart.
Summation of Action Potentials: The ECG represents the sum of all action potentials occurring in the heart at any given time.
Electrodes: Ten electrodes are used for ECG recording.
- Nine active electrodes placed on the chest and limbs.
- One inactive electrode on the right leg.
Electrocardiograph: This device is a modified voltmeter used to record the ECG.
ECG lead types:
- Unipolar lead: Uses one active electrode and an inactive electrode, resulting in nine unipolar leads.
- Bipolar lead: Uses two active electrodes and an inactive electrode, resulting in three bipolar leads.
Standard ECG: Consists of 12 leads:
- 3 bipolar limb leads.
- 3 augmented limb leads.
- 6 chest leads.