Cardio VII

Question 1

All the muscle cells in the heart are sorted into two classes of action potentials: […] and […].

Answer 1

fast and slow.

Question 2

Where in the heart are slow and fast action potentials found respectively?

Answer 2

Slow: SA node, AV node
Fast: ventricular muscle, atrial muscles, bundle of His, bundle branches, Purkinje fibers

Question 3

How does the upstroke rate compare between fast and slow action potentials?

Answer 3

Slow: 1-10 V/sec
Fast: 100-1000 V/sec

Question 4

How does the speed of depolarization compare between fast and slow action potentials?

Answer 4

Fast: 0.5-5 m/sec
Slow: 0.01-0.05 m/sec

Question 5

What is the physiological function of having both slow and fast action potentials in different parts of the heart?

Answer 5

The purpose is physiological delay between the depolarization of the atria and the ventricles. If the ventricles and the atria contracted at the same time, since the pressure of the ventricles is much stronger, it is likely that blood would squirt back up the atria.

Question 6

At what point on the ECG does the upstroke of the atrial action potential occur?

Answer 6

Around halfway through the P-wave (line 1).

Question 7

At what point on the ECG does the upstroke of the ventricular action potential occur?

Answer 7

Right before the peak of the QRS complex (line 2)

Question 8

How does the duration of the ventricular action potential compare to that of the atrial action potential?

Answer 8

The duration of the atrial action potential is much shorter than the ventricular action potential.

Question 9

What is normal sinus rhythm? State the range of values that fall within a normal rhythm.

Answer 9

It is the normal heart rhythm that creates the typical ECG wave. A heart rate between 60 bpm and 100 bpm (inclusive) is considered normal.

Question 10

What is sinus bradycardia? Is it pathological or physiological?

Answer 10

It is when heart rate is less than 60 bpm. It can be physiological when we sleep, as the heart rate slows, or pathological otherwise

Question 11

What is sinus tachycardia? Is it physiological or pathological?

Answer 11

It is when heart rate is greater than 100 bpm. We get a physiologic sinus tachycardia when we exercise. Athletes often have resting heart rates than are less than 60, which is technically a bradycardia. Otherwise, it is pathological.

Question 12

What is sinus arrythmia? Is it physiological or pathological?

Answer 12

It is when heart rate increases on inspiration and decreases on expiration. This is completely normal (physiological). They gradually go away with age.

Question 13

What is the appearance of the ECG when someone has a 2:1 atrioventricular block

Answer 13

Has very large QRS complex, only has QRS complex after every other P-wave

Question 14

What is happening in the heart during a 2:1 atrioventricular block?

Answer 14

When another P-wave follows the T-wave (instead of a QRS complex), this means that the atria were activated, but that the action potential didn’t make it down to the ventricles. Only the atria beat. This occurs for every other beat.

Question 15

Where are the possible locations of a block that can cause a 2:1 atrioventricular block?

Answer 15

• Could be in the AV node, where action potentials might enter but not be able to leave
• Bundle of His
• Both bundle branches.

Question 16

Why is a 2:1 atrioventricular block problematic?

Answer 16

If there’s something wrong with the AV node, you can go from a 2:1 block to a 3:1 block etc. to eventually a complete block, where no APs will get through.

Question 17

What does the ECG look like for a complete atrioventricular block?

Answer 17

Only P-waves are visible and there are no more QRS complexes.

Question 18

What is happening during a complete atrioventricular block?

Answer 18

The ventricles are not contracting at all, only the atria.

Question 19

What is the treatment for a complete atrioventricular block?

Answer 19

The solution would be to implant an electronic pacemaker that generates a current once per second and picks up the ECG. If it sees something abnormal for long enough, it will inject current into the ventricles of the heart, thus pacing the ventricles.

Question 20

What is the ECG look like for a premature ventricular contraction?

Answer 20

You see a premature complex/ectopic QRS that is large and occurs before the previous beat is over.

Question 21

What is happening during premature ventricular contraction?

Answer 21

The patient’s ventricles have an area that is sending off action potentials, causing premature ventricular contraction.

Question 22

What is an ectopic beat? When does it occur?

Answer 22

An ectopic beat occurs when there is a pacemaker in the wrong place in the heart. You might see an ectopic beat during premature ventricular contraction.

Question 23

What does the ECG look like for ventricular tachycardia?

Answer 23

There is an almost sinusoidal alternation as the ventricles beat extremely quickly (5 times per second(.

Question 24

What is happening to the patient during ventricular tachycardia and fibrillation? What is the effect on blood circulation?

Answer 24

After a premature ventricular contraction, the Q, R, S, and T waves all merge together and the ventricles are beating several times per second. Because the ventricles have no time to fill with blood, the stroke volume and cardiac output go to zero, as will the blood pressure. The patient will faint.

Question 25

What does the ECG look like for ventricular fibrillation?

Answer 25

Similar to ventricular tachycardia, where there is rapid oscillation, but the amplitude is smaller and the frequency is faster.

Question 26

How does entering into ventricular fibrillation affect the arterial pulse?

Answer 26

There’s no blood pressure and no perfusion of any organs.

Question 27

What is the treatment for ventricular fibrillation?

Answer 27

You have to defibrillate the patient using an AED. It generates a big shock that should hopefully put them back into a normal sinus rhythm.

Question 28

The tool used to map cardiac electrical activity is the […]

Answer 28

epicardial sock array

Question 29

What does the ECG look like for reentrant ventricular tachycardia?

Answer 29

QRS complexes just happen over and over without degenerating into fibrillation.

Question 30

What is happening during reentrant ventricular tachycardia?

Answer 30

The action potential is continuously circulating counterclockwise around the ventricles, assuming it has an anatomical obstacle to circulate around.

Question 31

By what process does reentrant ventricular tachycardia turn into ventricular fibrillation?

Answer 31

The action potential is zipping around extremely quickly and the refractory period of the cells increases as they become more and more tired. Eventually, the wavefront will come back around when the next cells are still in the refractory period. When they meet, the AP will no longer propagate. The wavefront will break off into two wavelets and propagate into two directions. This is thought to be the cause of the transition from v tach to v fib. In v fib there are many wavelets circulating in a random way.

Question 32

The circulation of the action potential during reentrant ventricular tachycardia is called […]

Answer 32

circus movement reentry

Question 33

What is the cure for reentrant ventricular tachycardia?

Answer 33

Remove the scar tissue that is serving as the anatomical obstacle.

Question 34

What is a possible cause for the creation of an anatomical obstacles in the heart?

Answer 34

A heart attack can create scar tissue (and thus reentrant ventricular tachycardia), because once cardiac cells die, they get replaced by scar tissue.

Question 35

What does the ECG look like for atrial fibrillation?

Answer 35

You can observe irregular fibrillation waves (not P-waves) that are inconsistently followed by QRS complexes. Looks like many P-waves with the occasional QRS complex.

Question 36

What is happening during atrial fibrillation?

Answer 36

There is a continual circulation of several wavelets coming from the AV node. This leads to irregular fibrillation waves (these are not P-waves). The ventricles respond to that irregular output - their action is also irregular.

Question 37

What is the cause of atrial fibrillation? What is the point of origin?

Answer 37

Atrial fibrillation is often triggered by a premature atrial contraction. The point of origin is usually one of the pulmonary veins leading into the atrium.

Question 38

What is the treatment for atrial fibrillation? Explain how it works.

Answer 38

Pulmonary vein isolation. They go into the heart freeze or burn the tissue around the vein, and the vein is isolated. A few days later, the muscle will be dead and replaced by fibrous tissue, so the AP triggered in the pulmonary vein will not be able to travel.