Cardiac Pacemaker Activity Quiz
Biomedical Engineering - Cardiac Electrophysiology
1
Which of the following is the primary pacemaker of the heart under normal conditions?
Atrioventricular (AV) node
Sinoatrial (SA) node
Purkinje fibers
Bundle of His
2
What is the typical intrinsic firing rate of the SA node in a healthy adult?
40-60 beats per minute
60-100 beats per minute
20-40 beats per minute
100-120 beats per minute
3
The pacemaker potential (phase 4 depolarization) in SA nodal cells is primarily due to:
Inward calcium current (I
Ca
)
Funny current (I
f
) and decreasing potassium efflux
Rapid sodium influx (I
Na
)
Chloride ion movement
4
Which ion channel is responsible for the "funny current" (I
f
) in pacemaker cells?
Voltage-gated sodium channels
Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels
L-type calcium channels
Delayed rectifier potassium channels
5
What is the normal delay at the AV node and why is it important?
Approximately 0.22 seconds; allows for ventricular filling
Approximately 0.12 seconds; ensures simultaneous atrial and ventricular contraction
Approximately 0.04 seconds; minimizes the QRS complex duration
Approximately 0.15 seconds; allows for atrial repolarization
6
In the hierarchy of cardiac pacemakers, if the SA node fails, which structure typically takes over as the primary pacemaker?
Bundle of His
Atrioventricular (AV) node
Purkinje fibers
Bachmann's bundle
7
What is the typical intrinsic firing rate of the Purkinje fibers?
15-40 beats per minute
40-60 beats per minute
60-80 beats per minute
80-100 beats per minute
8
Which of the following best describes "overdrive suppression" in cardiac pacemaker cells?
Faster pacemakers inhibit slower ones through Na+/K+ ATPase activation
Slower pacemakers accelerate to match the fastest pacemaker's rate
Pacemaker cells become fatigued and fire more slowly over time
The SA node takes over from ectopic foci through electrical resetting
9
How does sympathetic stimulation affect pacemaker activity?
Increases slope of phase 4 depolarization and increases heart rate
Decreases slope of phase 4 depolarization and decreases heart rate
Increases the threshold potential, making cells harder to depolarize
Has no direct effect on pacemaker cells
10
From an engineering perspective, how do artificial pacemakers mimic the natural pacemaker system?
They generate action potentials using the same ionic mechanisms as SA nodal cells
They deliver precisely timed electrical pulses to initiate depolarization
They chemically stimulate beta-adrenergic receptors to increase heart rate
They physically compress the SA node to regulate its firing rate
11
Which characteristic differentiates pacemaker action potentials from ventricular myocyte action potentials?
Pacemaker cells have a stable resting membrane potential
Pacemaker cells lack a plateau phase (phase 2)
Pacemaker cells have rapid depolarization via fast sodium channels
Pacemaker cells have a shorter action potential duration
12
What is the primary mechanism by which parasympathetic stimulation (vagal tone) slows heart rate?
Increases funny current (I
f
) activation
Increases potassium conductance, hyperpolarizing the cell
Decreases calcium channel availability
Activates sodium-potassium pumps
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