Lecture 9 - Cardiac Arrhythmias

Question 1

What is tachycardia?

What are potential causes?

Answer 1

-elevated heart rate of >100bpm

Causes:

• elevated body temperature (~increase of 10bpm per degree F or 18 bpm for degree C)
• sympathetic nerve stimulation (loss of blood or state of shock)
• toxic condition of the heart

Question 2

What is characteristic of endogenously mediated tachycardia?

Answer 2

• cardiac output increases
• filling time reduced
• sympathetic stimulation increases contractility and maintains stroke volume
• systolic interval reduced; diastolic filing time increased
• increased venous return

Question 3

What is characteristic of pathologically mediated tachycardia?

Answer 3

• cardiac output decreases
• mean atrial pressure decreases activating sympathetic response; occurs too late to compensate
• no increase in venous return

Question 4

What is bradycardia? What are potential causes?

Answer 4

-decreased heart rate of <60 bpm

Causes:

• athletic heart
• vagal stimulation
• sensitive carotid baroreceptors

Question 5

What is the cause of respiratory arrhythmia?

Answer 5

-spillover signals from medullary respiratory center during respiratory cycles increasing and decreasing sympathetic and vagus nerve signals

Question 6

What is an SA block?

Answer 6

• cessation of P waves
• standstill of atria
• ventricles pick up rhythm from AV node which slower

Question 7

What is a first degree AV block?

Answer 7

-PR interval greater than 0.20 seconds

Question 8

What is a second degree AV block

Answer 8

• PR interval is 0.25-0.45 seconds

- can result in dropped QRS segments

Question 9

What is a complete AV block?

Answer 9

• no relation between atrial contraction and ventricle contraction
• after loss of AV conduction ventricles may not establish a rhythm for another 5-30 seconds
• resumption of ventricular beats is called ventricular escape
• fainting spells, Stokes-Adams syndrome, can occur

Question 10

What is a partial intraventricular block?

Answer 10

• referred to as electrical alternans

- alternation in the amplitude of P waves, QRS complexes, or T waves

Question 11

What are premature contractions?

Answer 11

• premature contraction of the atrium (PAC) or the ventricle (PVC)
• result of an ectopic foci such as ischemic areas, calcified plaques, or irritation of the conduction systems

Question 12

What is paroxysmal tachycardia?

Answer 12

• heart rate becomes rapid in paroxysms lasting seconds to hours
• paroxysms end suddenly with pacemaker shifting back to SA node

Question 13

What is fibrillation?

Answer 13

• twitching of muscle fibers
• normal ventricular or atrial depolarization wave dies out because cardiac muscle is in refractory period
• caused by circus movements

Question 14

What are the causes of circus movements?

Answer 14

• pathway around the circle is too long
• velocity of conduction slows
• refractory period is shortened

Question 15

What is a circus movement?

Answer 15

-by the time a wave of depolarization goes all the way around the circle, the initial tissue is out of its refractory period and depolarizes again

Question 16

What are causes of atrial fibrillation?

Answer 16

• enlargement of the atrium (i.e., due to valve lesions)

- inadequate emptying of the ventricles causing build up of blood in the atrium