Cardiovascular Physiology Lecture 2 & 3

Question 1

Slow Response Action Potentials

3 Phases

Answer 1

a. Phase 0 occurs as L-type Ca2+ channels are activated.
b. Phase 3 is repolarization as L-type Ca2+ channels are inactivated and
K+ exits through IK channels.
c. Phase 4 defines the spontaneous depolarization phase caused by
K+, Ca2+ and funny (If) currents.

Question 2

Current conduction pathways in the heart

Answer 2

SA node > AV node > Bundle of His > Purkinje fibers > ventricular muscle cells.

SA node is the pacemaker, sets pace for beating of the heart

Sinus rhythm = normal heart rate.

Question 3

Primary pacemaker, and what happens if it changes?

Answer 3

SA node is the primary pacemaker, sets pace for beating of the heart. Can become the AV node which makes heart beat a bit slower. Both SA and AV make up slow response action potentials, and if pacemaker goes to Bundle of His, purkinje, or ventricular, it becomes way more slower and is from fast response action potentials.

Question 4

Electrocardiogram (EKG)

Answer 4

Records mean electrical activity of heart over time.

Question 5

Components of the EKG

P wave, PR interval, QRS complex, QT interval, T wave

Answer 5

P wave: atrial depolarization
PR interval: AV conduction
QRS complex: ventricular depolarization
QT interval: 0.4 sec
T wave: ventricular repolarization

Question 6

Cardiac Arrhythmias

Answer 6

Enhanced automaticity: increased heart rate, increase in slope of phase 4 of slow response AP.

Abnormal automaticity: Ectopic pacemaker cells responsible for premature atrial contractions, etc.

Question 7

First degree AV block

Answer 7

PR interval prolonged, more than .2 sec.

Question 8

Second degree AV block

Answer 8

Not all P waves are followed by QRS complexes. P wave: QRS complex ratios = 2:1, 3:1, or 3:2.

Dropping QRS, no R wave. Skipping whole depolarization of ventricle.

Question 9

Third Degree AV block

Answer 9

Electrical activity of atria and ventricle are dissociated from each other, each are doing their own thing.

Bundle branch block: Right: wider and split QRS.
Left: Wide QRS too.

Question 10

Re-entry excitation concept in cardiac arrhythmias

Causes this:

Atrial fibrillation, Ventricular fibrillation characteristics.

Answer 10

Must have a block, must have a conduction speed difference, and difference in refractiveness

Atrial fibrillation: no p waves. blood clot formation

Ventricular fibrillation: chaotic ECG, absense of ventricular contractions, no perfusion, bp falls. Death within minutes. Must do defibrillation