Heart 5

Question 1

From what do cardiac arrhythmias result?

Answer 1

Disturbances in impulse formation or impulse conduction (or both in combination).

Question 2

Define altered automaticity

Answer 2

Alterations in pacemaker rate that are mediated through changes in the pacemaker mechanisms that normally exist in pacemaker cells

Question 3

Tachycardia vs bradycardia

Answer 3

> 100 BPM vs

Question 4

Seven possible causes of tachy-dysrhythmias

Answer 4

1. Norepinephrine
2. Stimulants
3. Ischemia
4. Stretching
5. Sick sinus syndrome
6. Fever
7. Hyperthyroidism

Question 5

EKG manifestations in tachy-dysrhythmias

Answer 5

Sinus tachycardia, PAC’s, PVC’s, AT/VT, SVT

Question 6

Five possible causes of brady-dysrhythmias

Answer 6

1. Drugs
2. Barbiturates
3. Ischemia/infarct
4. Sick sinus syndrome
5. Aging

Question 7

EKG manifestations of brady-dysrhythmias

Answer 7

1. Sinus bradycardia

Question 8

Where can re-entry of excitation happen?

Answer 8

Anywhere in the heart

Question 9

What is the most common cause of dysrhythmias seen clinically?

Answer 9

Re-entry of excitation

Question 10

Three general requirements for re-entry of excitation to occur

Answer 10

1. Proper geometry for a conduction loop
2. Slow or delayed conduction
3. Unidirectional conduction block

Question 11

Possible causes of re-entry of excitation

Answer 11

Ischemia, infarct, congenital bypass tracts

Question 12

Possible EKG manifestations during episodes of re-entry of excitation

Answer 12

PVC's/PAC's
AT/VT
SVT
Atrial flutter
A-/V-fib

Question 13

Where in the heart can triggered activity happen?

Answer 13

In the atrial or ventricular tissues

Question 14

What is the cause of delayed afterdepolarization?

Answer 14

Abnormally elevated intracellular calcium concentration

Question 15

When are delayed afterdepolarizations clinically documented?

Answer 15

With dysrhythmias resulting from digitalis toxicity

Question 16

Possible causes of delayed afterdepolarizations

Answer 16

1. Digitalis toxicity
2. Elevated catecholamines
3. Rapid heart rate

Combination of all the above

Question 17

Possible manifestations from delayed afterdepolarizations

Answer 17

PAC/PVC’s

A-/V-tach

Question 18

Mechanism of delayed afterdepolarization (it’s a long one.)

Answer 18

• Elevated calcium is taken up by the SR
• After SR is overloaded, AP can trigger abnormal release of Ca after AP has ended
• Extra released Ca extruded by Na/Ca exchanger
• Net inward current produced by exchange
• Triggers DAD
• If DAD amplitude is large enough to reach threshold, an AP is generated*

Question 19

Early afterdepolarizations are related to . . .

Answer 19

prolongation of action potential duration.

Question 20

Mechanism of early afterdepolarizations

Answer 20

Still not certain, but could be due to abnormal re-activation of the slow inward calcium current

Question 21

To what else are early afterdepolarizations thought to be linked?

Answer 21

Prolonged Q-T syndrome

Question 22

Possible causes of early afterdepolarizations

Answer 22

1. Acidosis
2. Hypokalemia
3. Quinidine
4. Slow heart rates

Question 23

Possible EKG manifestations of early afterdepolarizations

Answer 23

PAC’s/PVC’s

A-/V-fib (torsades de pointes)

Question 24

What does the voltage graph look like during stimulation of Purkinje fibers in cesium solution?

Answer 24

Multiple repetitive triggered action potentials at CL>10 seconds

Question 25

What can single triggered action potentials result in?

Answer 25

Premature beats

Question 26

What can repetitive triggered action potentials result in?

Answer 26

Runs of tachycardia

Question 27

Anti-arrhythmic therapies

Answer 27

1. Drugs
2. Radio-frequency ablation
3. DC cardioversion
4. Implantable cardioverter-defibrillator

Question 28

Normal range for P-R interval

Answer 28

120-200 ms

Question 29

Normal range for QRS complex

Answer 29

70-100 ms

Question 30

Normal range for Q-T interval

Answer 30

250-430 ms