Lecture 08 Cardiac Arrhythmias

Question 0

What can cause tachycardia?

Answer 0

Increased body temperature - increase 10 beats/F degree
Stimulation of the heart by sympathetic nerves - due to loss of blood and/or state of shock
Toxic conditions of the heart - weakening of myocardium

Question 1

What is tachycardia?

Answer 1

Fast heart rate greater than 100 beats/min

Question 2

What is bradycardia?

Answer 2

Slow heart rate less than 60 beats/min

Question 3

What are causes of bradycardia?

Answer 3

Athletic heart
Vagal stimulation
Extremely sensitive carotid baroreceptors in carotid sinus syndrome

Question 4

What are spillover signals?

Answer 4

From medullary respiratory center into vasomotor center during inspiratory and expiratory respiratory cycles these signals alternately increase and decrease number of impulses transmitted through sympathetic and vagus nerves to the heart

Question 5

What is sinus arrhythmia caused by?

Answer 5

Spillover signals

Question 6

What is Sinoatrial block?

Answer 6

Sudden cessation of P waves
Resultant standstill of atria
Ventricles pick up a new rhythm, usually originating in the AV node
Rate of QRS is slowed but not otherwise altered

Question 7

What are conditions causing atrioventricular block?

Answer 7

Ischemia of AV node or AV bundle fibers through coronary insufficiency
Compression of AV bundle by scar tissue or calcified portions of the heart
Inflammation of the AV node or bundle
Extreme stimulation of the heart by the vagus nerves

Question 8

What is incomplete atrioventricular block first degree?

Answer 8

Normal P-R time interval = .16 sec
When P-R interval increases to greater than .20 seconds (slower heart beat), then the P-R interval is prolonged and has first degree block

Question 9

What is second -degree block?

Answer 9

P-R interval time increases to .25 to .45 seconds
Atrial P wave is present but QRS-T wave may be missing, resulting in dropped beats of the ventricle
2:1 rhythm or other variations may develop

Question 10

What is complete AV block?

Answer 10

Ventricles establish their own signal
No relation between the rate of the P waves and rate of QRS - T complexes.
Duration of the block is highly variable (seconds to weeks)
After AV conduction ceases, ventricles may not start beating on their own for 5 to 30 seconds

Question 11

What is ventricular escape?

Answer 11

When there is a resumption of the ventricular beat that may be due to parts of the Purkinje system acting as the ectopic pacemaker

Question 12

What is Stokes-Adams syndrome?

Answer 12

After a complete AV block occurs, patients will often faint due to lack of blood to the brain until the ventricles escape and the periodic fainting spells are referred to the syndrome

Question 13

What is partial intraventricular block referred to as?

Answer 13

Electrical alternanas

Question 14

What does electrical alternans mean?

Answer 14

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

Question 15

What are causes of premature contractions?

Answer 15

Ectopic foci
Local ischemic areas
Calcified plaques
Irritation of the conduction system or nodes

Question 16

What is paroxysmal tachycardia?

Answer 16

Heart becomes rapid in paroxysms and begins suddenly and lasts for a few seconds, minutes, hours or longer
They end suddenly
Pacemaker of the heart instantly shifts back to the sinus node

Question 17

What does electroshock defibrillation do?

Answer 17

Sends a very strong voltage throughout the heart that stops everything and gives the SA node a chance to recuperate and restart the rhythm

Question 18

Why in a normal ventricular depolarization do the waves die out?

Answer 18

The heart muscle that has already contracted is in the refractory period and cannot respond to being stimulated by the existing depolarization waves

Question 19

What is fibrillation?

Answer 19

The twitching (usually slow) of individual muscle fibers in the atria or ventricles and also in recently denervated skeletal muscle fibers?

Question 20

What causes fibrillation in the heart?

Answer 20

Circus movements

Question 21

What are the three different conditions that cause the impulse to travel around the circle in circle movements?

Answer 21

pathway around the circle is too long
Length of the pathway remains constant but the velocity of the conduction slow down
The refractory period of the muscle might become greatly shortened

Question 22

What occurs when the pathway around the circle (ventricles) is too long?

Answer 22

Often because of a dilated heart, the impulse takes longer to get back to its starting point, and the muscle is no longer in its refractory period and can undergo another depolarization

Question 23

In normal conditions, by the time the impulse returns its starting point, in what state is the heart muscle in?

Answer 23

Refractory period

Question 24

Even if the length of the pathway remains normal, what is the cause of the conduction velocity of the impulse is slowing down

Answer 24

Usually occurs because of the blockage of the Purkinje system, ischemia, or high potassium levels

Question 25

How do circus movements occur when the refractory period of the muscle is shortened?

Answer 25

May occur in response to drugs such as epinephrine

May occur after repetitive electrical stimulation

Question 26

True/False
Atrial muscle fibers are linked to the ventricular muscle fibers by the cardiac fibrous skeleton, therefore ventricular and atrial fibrillation must occur together.

Answer 26

False, they are separated and may occur separate from one another

Question 27

What are the causes of atrial fibrillation?

Answer 27

Enlargement of the atria (due to valve lesions)

Inadequate emptying of the ventricles causing blood to back up into the atria