Chapter 13 - Guyton

Question 1

Tachycardia

Answer 1

defined as heart rate >100bpm; caused by increased body temperature, stimulation of the heart by sympathetic nerves, or toxic conditions of the heart

Question 2

Bradycardia

Answer 2

defined as parasympathetic on heart

Question 3

What is carotid sinus syndrome?

Answer 3

patients with this have pressure receptors (baroreceptors) in the carotid sinus region of the carotid artery walls that are excessively sensitive, even mild external pressure on the neck elicits a strong baroreceptor reflex, causing intense vagal acetylcholine effects on the heart, including extreme bradycardia

Question 4

SA Block

Answer 4

impulse from the sinus node is blocked before it enters the atrial muscle, ventricles pick up a new rhythm (AV node) so that the rate of the ventricular QRS-T complex is slowed but not otherwise altered

Question 5

Bundle of His

Answer 5

means by which impulses ordinarily can pass from the atria into the ventricles

Question 6

AV Block

Answer 6

ischemia (coronary insufficiency), compression (scar tissue or calcified portions of heart), inflammation (myocarditis), extreme stimulation by vagus nerves (carotid sinus syndrome)

Question 7

First Degree (Incomplete) AV Block

Answer 7

PR interval > 0.20 sec, delay of conduction from
the atria to the ventricles but not actual blockage of conduction (could be caused by some heart diseases such as acute rheumatic heart disease)

Question 8

Second Degree AV Block

Answer 8

PR interval increased to 0.25 - 0.45 sec, sometimes the action potential is not strong enough to pass through the bundle so will see dropped beats

Question 9

Third Degree (Complete) AV Block

Answer 9

complete block of the signal from the atria to ventricles occur and ventricles establish their own rhythm originating in the A-V node or A-V bundle, P waves become dissociated from the
QRS-T complexes (separate rates for atria and ventricles)

Question 10

Stokes-Adams Syndrome - Ventricular Escape

Answer 10

in some patients with A-V block, the total block comes and goes; each time A-V conduction ceases, the ventricles often do not start their own beating until after a delay of 5 to 30 seconds (overdrive suppression); some part of the Purkinje system beyond the block begins discharging rhythmically at a rate of 15 to 40 times per minute and acting as the pacemaker of the ventricles (ventricular escape)

Question 11

Why would a person with Stokes-Adams syndrome faint?

Answer 11

Because the brain cannot remain active for more than 4 to 7 seconds without blood supply, most patients faint a few seconds after complete block occurs because the heart does not pump any blood for 5 to 30 seconds, until the ventricles “escape.”

Question 12

Incomplete Intraventricular Block—Electrical Alternans

Answer 12

blocked impulse conduction in the peripheral ventricular Purkinje system; partial intraventricular block every other heartbeat

Question 13

What is a premature contraction?

Answer 13

also known as ectopic beat or extrasystole, most premature contractions result from ectopic foci in the heart, which emit abnormal impulses at odd times during the cardiac rhythm

Question 14

Premature Atrial Contractions

Answer 14

P-R interval is shortened, indicating that the ectopic origin of the beat is in the atria near the A-V node. Also, the interval between the premature contraction and the next succeeding contraction is slightly prolonged (compensatory pause); these are not as serious and can occur in athletes, smoking, lack of sleep, too much coffee, alcoholism

Question 15

What is pulse deficit?

Answer 15

pulse wave passing to the peripheral arteries after a premature contraction may be so weak that it cannot be felt in the radial artery (decreased stroke volume)

Question 16

AV Node or Bundle Premature Contractions

Answer 16

P wave is superimposed onto the QRS-T complex because the cardiac impulse traveled backward into the atria at the same time that it traveled forward into the ventricles (this condition is usually not as serious like premature atrial contractions)

Question 17

Premature Ventricular Contractions (PVCs) result in what on the electrocardiogram?

Answer 17

QRS complex is usually considerably prolonged, QRS complex has a high voltage (uneven depolarization of ventricles), T wave has an electrical potential polarity exactly opposite to that of the QRS complex (slow conduction of the impulse)

Question 18

Paroxysmal Tachycardia

Answer 18

Some abnormalities in different portions of the heart, including the atria, Purkinje system, or ventricles, can occasionally cause rapid rhythmical discharge of impulses that spread in all directions throughout the heart (can be stopped by vagal reflex).

Question 19

Atrial Paroxysmal Tachycardia

Answer 19

inverted P wave is seen before each QRS-T complex, and this P wave is partially superimposed onto the normal T wave of the preceding beat; this indicates that the origin of this paroxysmal tachycardia is in the atrium

Question 20

AV Nodal Paroxysmal Tachycardia

Answer 20

usually causes almost normal QRS-T complexes but totally missing or obscured P waves

Question 21

Supraventricular Tachycardias

Answer 21

atrial or AV nodal paroxysmal tachycardia, usually
occurs in young, otherwise healthy people, and they generally grow out of the predisposition to tachycardia after adolescence

Question 22

Ventricular Paroxysmal Tachycardia

Answer 22

usually a serious condition, usually does not occur unless considerable ischemic damage is present in the ventricles, frequently initiates the lethal
condition of ventricular fibrillation

Question 23

Ventricular Fibrillation

Answer 23

results from cardiac impulses stimulating
first one portion of the ventricular muscle, then another portion, and eventually feeding back onto itself to re-excite the same ventricular muscle repeatedly (usually fatal within minutes)

Question 24

Causes of ventricular fibrillation?

Answer 24

sudden electrical shock of the heart, or ischemia of

the heart muscle, of its specialized conducting system, or both

Question 25

What could cause circus movement (re-entry of impulse into muscle that has already been excited)?

Answer 25

pathway is too long (dilated hearts), velocity of conduction becomes decreased (blockage of Purkinje, ischemia, high potassium), refractory period of muscle becomes shortened (drugs such as epinephrine)

Question 26

If electroshock can cause ventricular fibrillation, how does it cause defibrillation?

Answer 26

Although a moderate alternating-current voltage
applied directly to the ventricles almost invariably
throws the ventricles into fibrillation, a strong high voltage alternating electrical current passed through the ventricles for a fraction of a second can stop fibrillation by throwing all the ventricular muscle into refractoriness simultaneously.

Question 27

Atrial Fibrillation

Answer 27

same as ventricular fibrillation except in atria, frequent cause is atrial enlargement resulting from heart valve lesions that prevent the atria from emptying adequately into the ventricles, or from ventricular failure with excess damming of blood in the atria (no P waves, will cause a fast, irregular heartbeat but person can live and efficiency of ventricles is only reduced 20-30%).

Question 28

Atrial Flutter

Answer 28

circus movement in the atria, rapid rate usually 25-300 bpm, signals reach the A-V node too rapidly for all of them to be passed into the ventricles, refractory periods of the A-V node and A-V bundle are too long to pass more than a fraction of the atrial signals. Therefore, there are usually two to three beats of the atria for every single beat of the ventricles (P waves without QRS complexes).

Question 29

Cardiac Arrest

Answer 29

buh-bye! hypoxia can prevent the muscle fibers and conductive fibers from maintaining normal electrolyte concentration differentials across their membranes, and their excitability may be so affected that the automatic rhythmicity disappears