4.3 Anatomy of Cardiac Conduction System and Cardiac Electrophysiology

Question 1

On which side of the heart would you find the septomarginal trabecula? What is its role?

Answer 1

• Right side
• It plays a role in the delivery of electrical impulses to the right side of the heart

Question 2

Under what layer of the heart do the bundle branches and purkinje fibres run?

Answer 2

Under the endocardium (subendocardial)

Question 3

What coronary landmark is the av node located near? What is this larger area called?

Answer 3

• Located near coronary sinus opening into RA
• This is known as the triangle of koch

Question 4

Where do the bundle branches become the Prukinje fibres?

Answer 4

When the fibres reach the apex, and begin to branch off into cardiac muscle cells

Question 5

Approx cardiomyocyte resting membrane potential vs pacemaker cell

Answer 5

Cardiomyocyte: -90mV
Pacemaker: -60mV

Question 6

Mechanistically, how does autonomic stimulation influence heart rate in terms of electrical conduction?

Answer 6

By decreasing/increasing the resting membrane potential of the conduction system.

Question 7

Describe the different channels that open at different points in the cycle of a cardiac pacemaker cell.

Answer 7

• Sodium channels open
• T-type calcium channels
• L-type calcium channels
• Potassium channels open -> repolarization
• Sodium influx to correct hyperpolarisation

Question 8

List the phases of cardiomyocyte action potentials

Answer 8

Phase 4: Resting at -90mV
*Action potential lets some calcium in, up to -70mV)
Phase 0: Sodium channel opens, influx up to +20mV
Phase 1: Potassium outflow, decrease to 0mV
Phase 2: Calcium inflow, equilibrium
Phase 3: No more calcium inflow, repolarization