Lecture 9: Cardiac arrhythmias

Question 1

Endogenously mediated tachycardia

Answer 1

Heart rate increases
Cardiac output increases
Filling time is reduced by stroke volume does not fall
Sympathetic stimulation contracts veins and increases venous return to help maintain ventricular filling

Question 2

First-degree incomplete AV block

Answer 2

Normal P-R time interval is 0.16 sec

When P-R interval increases to greater than 0.20 seconds, the patient has a first degree incomplete heart block

Question 3

Fibrillation occurs a result of

Answer 3

Circus movements

Question 4

Pathologically mediated tachycardia

Answer 4

Heart rate increases
Cardiac output decrease
Mean atrial pressure decreases and activates sympathetic nervous system, which occurs after the fact and is unable to compensate

Question 5

Spillover signals

Answer 5

Related to respiratory sinus arrhythmia
These signals alternately increase and decrease number of impulses transmitted through sympathetic and vagus nerves to the heart

Question 6

Causes of Atrial fibrillation

Answer 6

Enlargement of the atria (due to valve lesions)

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

Question 7

What causes conduction velocity to be slowed down

Answer 7

Blockage of the Purkinje system
Ischemia
High potassium levels

Question 8

Sinoatrial block characteristics

Answer 8

Sudden cessation of P waves
Resultant standstill of atria
Ventricles pick up a new rhythm, usually originating in AV node
Rate of QRS is slowed

Question 9

What can shorten the refractory period

Answer 9

Response to drugs such as epinephrine

Repepitive electrical stimulation

Question 10

Paroxysmal tachycardia

Answer 10

Heart becomes rapid in paroxysms
Paroxysm begins suddenly and last for variable amounts of time, then ends suddenly
Pacemaker of heart shifts back to sinus node

Question 11

Premature contraction causes

Answer 11

Most are result of ectopic foci:

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

Question 12

Causes of Tachycardia

Answer 12

Increased body temperature
Stimulation of heart by sympathetic nerves (due to loss of blood/state of shock)
Toxic conditions of heart (results in weakening of myocardium)

Question 13

Complete AV block

Answer 13

Ventricles establish their own signal (usually AV node)

No relation between rate of P waves and QRS-T complex

Question 14

Fibrillation

Answer 14

Twitching of individual muscle fibers in the atria or ventricles and also in recently denervated skeletal muscle fibers

Question 15

Stokes-adams syndrome

Answer 15

Periodic fainting spells due to complete AV block

Question 16

Partial intraventricular block

Answer 16

Referred to as “electrical alternans”

Term refers to an alternation in the amplitude of P waves, QRS complexes or T waves

Question 17

Causes of AV block

Answer 17

Ischemia of AV node or AV bundle fibers
Compression of AV bundle by scar tissue
Inflammation of AV node/bundle
Extreme stimulation of the heart by vagus nerves

Question 18

Second-degree incomplete AV block

Answer 18

When P-R time interval increases to 0.25–>0.45 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 19

Tachycardia

Answer 19

Fast heart rate (>100 beats/min)

Question 20

Causes of Bradycardia

Answer 20

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

Question 21

Three conditions that cause the impulse to travel around the circle (circus movements)

Answer 21

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

Question 22

What happens when pathway is too long

Answer 22

If the heart is dilated (making pathway too long) impulse takes longer to get back to starting point and the muscle is no longer in its refractory period, allowing for another depolarization

Question 23

Ventricular escape

Answer 23

Resumption of ventricular beat in complete AV block-may be due to parts of purkinje system acting as ectopic pacemaker

Question 24

Bradycardia

Answer 24

Slow heart rate (<60 beats/min)