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Guyton - unit questions EW > Unit III (9-13)- The Heart > Flashcards

Unit III (9-13)- The Heart Flashcards

1
Q

Parasympathetic innervation of the heart is provided by what nerves

A

Vagus nerve

Pre-ganglionic fibers of of the recurrent laryngeal n.

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2
Q

Sympathetic innervation of the heart is provided by what nerves

A

Cardiac nerves that originate from the cervicothoracic/middle and 1st few thoracic ganglion

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3
Q

What mechanical event is represented by a P-wave?

A

Atrial depolarization

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4
Q

What mechanical event is represented by a QRS complex?

A

Ventricular depolarization

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5
Q

What mechanical event is represented by a T wave?

A

Ventricular repolarization

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6
Q

What mechanical event is represented by a QT interval?

A

Ventricular contraction and relaxation

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7
Q

What mechanical event is represented by a PR interval?

A

Atrial contraction and relaxation

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8
Q

What does S1 sound represent?

A

Lub - Closure of mitral and tricuspid valves

Usually occurs at the end of QRS complex

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9
Q

What does S2 sound represent?

A

Dub - Closure of semilunar valves

Usually occurs at the end of T wave

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10
Q

What does S3 sound represent?

A

Early ventricular filling

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11
Q

What does S4 sound represent?

A

Atrial contraction

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12
Q

At what stage of the cardiac cycle do gallop sounds occur?

A

Diastole

low frequency in dogs; higher frequency in cats

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13
Q

What pathology is usually associated with S3 sounds?

A

DCM

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14
Q

What pathology is usually associated with S4 sounds?

A

HCM

pushing blood into a stiff non compliant ventricle

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15
Q

What do systolic clicks represent?

A

Primary AV valve prolapse

(usually higher amplitude, just as loud or louder than S1 and S2) would occur between S1 and S2

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16
Q

What do split sounds represent?

A

Delay between closure and opening of valves
S1 - Mitral and tricuspid valves
S2 - semilunar valves

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17
Q

ECG paper speed of 25mm/sec

1 small box = ___

A

0.04 seconds

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18
Q

ECG paper speed of 50mm/sec

1 small box = ___

A

0.02 seconds

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19
Q

ECG paper speed of 25mm/sec

30 big boxes x ____ = beats per pen

A

10

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20
Q

ECG paper speed of 50mm/sec

30 big boxes x ____ = beats per pen

A

20

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21
Q

What are the ECG characteristics of sinus block? sinus arrest?

A

Abrupt pause in rhythm
Block - 2x longer than the previous R-R interval
Arrest - more than 2x longer than previous R-R interval

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22
Q

What are the ECG characteristics of atrial standstill?

A

No P waves

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23
Q

What diseases are associated with atrial standstill?

A

Hyperkalemia

Atrial fibrosis - english springer spaniels, old english sheepdogs

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24
Q

What are the ECG characteristics of 1st degree AV block?

A

Prolonged P-R interval

There is a P for every QRS

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25
What are the causes of 1st degree AV block?
increased vagal tone - resting and digestion
26
What are the ECG characteristics of 2nd degree AV block Type 1?
Gradually prolonged PR interval | P without QRS complex
27
What is the cause of 2nd degree AV block Type I?
High vagal tone
28
What are the ECG characteristics of 2nd degree AV block Type 2?
Fixed P-R interval | P without a QRS
29
What are the causes of 2nd degree AV block Type 2?
AV nodal disease (myocarditis, tumors, age related fibrosis) | more likely to go into 3rd degree AV block
30
What are the ECG characteristics of 3rd degree AV block?
Complete dissociation between P and QRS complex
31
What is the mechanism behind atrial tachycardia?
increased automaticity of ectopic foci with re-entry
32
What are the ECG characteristics of atrial tachycardia?
Abnormal P wave morphology | Normal QRS complex with regular R-R interval
33
What is the mechanism behind atrial fibrillation?
Micro-reentry
34
What are the ECG characteristics of atrial fibrillation?
No P waves Irregularly irregular of R-R interval Normal QRS complex
35
What is the mechanism behind atrial flutter?
Macro-reentry
36
What are the ECG characteristics of atrial flutter?
Flutter waves - saw tooth appearance to the baseline Regular R-R interval Normal QRS complex
37
A VPC with positive deflection originates from what side?
Right
38
A VPC with negative deflection originates from what side?
Left
39
How does cardiac muscle differ from skeletal?
Cardiac muscle is a syncytium - muscle fibres separated by intercalated discs
40
What are 2 differences in action potentials in cardiac/skeletal muscle?
1 - cardiac muscle action potential caused by opening of fast sodium and slow calcium channels (vs fast sodium only) 2 - in cardiac muscle, after onset of action potential membrane potassium permeability decreases until calcium channels close Both cause plateau in action potential
41
Describe the stages of cardiac muscle action potential
0 - fast sodium channels open 1 - fast sodium channels close 2 - slow calcium channels open. K+ channels close 3 - calcium channels close, k+ channels open
42
What is a difference in excitation-contraction coupling between cardiac and skeletal muscle?
In cardiac muscle calcium diffuse into the sarcoplasm from the T tubules, as well as the sarcoplasmic reticulum
43
Where is the sinus node located?
In the right atrium
44
How much of ventricular filling is active/passive?
80% passive 20% active
45
What are the pressure changes in the atria known as?
a wave - atrial contraction c wave - ventricular contraction w wave - flow of blood from veins
46
What is preload?
End diastolic pressure
47
What is afterload?
Pressure in aorta
48
Where does the energy for cardiac contraction come from?
70-90% fat metabolism 10-30% glucose/lactate
49
What is the Bainbridge reflex?
Stretch of the right atrial wall increases HR by 40-60%
50
What are the effects of vagal stimulation on the heart?
Mostly decrease in HR, slight reduction in contractility (vagus innervates atria not ventricles)
51
What are the effects of sympathetic stimulation on the heart?
Increase in HR and contractility
52
What are the effects of excess potassium ions on the heart?
Dilated, flaccid, reduced HR High extracellular potassium decreases membrane potential - less negative, reduced intensity of action potential
53
What are the effects of excess calcium ions on the heart?
Spastic contraction - direct effect of ions to initiate contraction
54
What are the effects of deficiency of calcium ions on the heart?
Cardiac weakness
55
What is the effect of increased body temperature on the heart?
Increased HR - increased permeability of cardiac membrane
56
What are the effects of increased arterial blood pressure on cardiac output?
Minimal up to 160mmHg - cardiac output determined by venous return
57
How is the tissue of the sinus node different to other heart muscle fibre?
Resting potential -55-60mV (vs -85-90mV) Due to cell membrane being leaky to sodium and calcium At less negative resting potential fast sodium channels blocked - only slow sodium channels open
58
How does the sinus node self excite?
Sodium ions leak through membrane - funny currents Resting potential slowly rises until L-type calcium channels activate L-type channels inactivate and potassium channels open - repolarisation
59
Which parts of the heart can exhibit intrinsic rhythmical activity?
Sinus node, AV node, Purkinje fibres
60
What is the mechanism of vagal effects on the heart?
ACh increases permeability to potassium => hyperpolarisation
61
Where is the majority of energy needed for heart contraction derived from?
Oxidative metabolism of fatty acids
62
How does high atrial stretch increase heart rate?
Directly increased by 10-20% Bainbridge reflex (vagus) - increases an additional 40-60%
63
What causes respiratory sinus arrhythmia?
Spillover of signals from the medullary respiratory centre into the adjacent vasomotor centre
64
What are the possible causes of a SA block?
Myocardial ischaemia, myocarditis, medication, fitness
65
What are the possible causes of a SA block?
Ischaemia of the AV node/bundle Compression of the AV bundle with scar tissue Inflammation of the AV node/bundle Extreme vagus stimulation Degeneration of the AV conduction system Medication (digitalis, beta blockers)
66
What are the types of second degree AV block? What causes them
Mobitz type I (Wenckeback periodicity) - progressive prolongation of PR until ventricular beat dropped. Usually abnormal AV node, normally benign Mobitz type II - fixed number of non-conducted P-waves. Usually associated with issue with His-Purkinje system, may require pacing
67
What is electrical alternans and what causes it?
Partial intraventricular block every other heartbeat Tachycardia, ischaemia, myocarditis, digitalis toxicity
68
What are the causes of premature contractions?
Ischaemia Calcified plaques Toxic irritation of AV node, purkinje system or myocardium
69
What are the classical features of VPCs?
Prolonged QRS High voltage QRS T wave has opposite electrical potential polarity opposite to QRS
70
What is long QT syndrome and why are they of potential concern?
Delayed depolarisation of ventricles Increased susceptibility to torsades de pointes
71
What are the possible causes of long QT?
Congenital - mutations of Na or K channels Acquired - hypomagnesaemia, hypokalaemia, hypocalcaemia, drugs (quinidine, fluoroquinolone, erythromycin)
72
What causes ventricular tachycardia?
Usually considerable damage to ventricles Digitalis
73
How can ventricular tachycardia be treated?
Lidocaine Amiodarone
74
What is the MOA of lidocaine?
Reduced sodium permeability of cardiac muscle membrane
75
What is the MOA of amiodarone?
Prolongs action potential and refractory period in cardiac muscle Slows AV conduction
76
What factors can predispose to circus movements?
Cardiac dilation Delayed velocity of contraction - blockage of Purkinje, ischaemia, hyperkalaemia Short refractory period - epinephrine, repeated stimulation

Guyton - unit questions EW (14 decks)

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