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Physiology > 4- Cardiac Physiology > Flashcards

4- Cardiac Physiology Flashcards

1
Q

Where does the heartbeat originate from?

A

Cardiac pacemaker cells that generate spontaneous action potentials

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2
Q

Discuss the differences between pacemaker cells and non pacemaker cells

A

Pacemaker cells
No resting potential
Spontaneous depolarization and repolarization

Non pacemaker cells
True resting potential
Prolonged depolarization

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3
Q

What is membrane potential determined by?

A

Ion concentration gradients
Ion conductances
Electrogenic pumps

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4
Q

How do the opening and closing of ion channels alter the membrane potential

A

In resting potential
K+ channels opens (Na+, Ca2+ closed)
Hyperpolarized cell

In action potential
Na+, Ca2+ channels open (K+ closed )
Depolarized cell

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5
Q

Discuss pacemaker action potential

A

Phase 4- pacemaker potential
Phase 0- depolarization
Phase 3- repolarization

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6
Q

What are the intrinsic rate of firing for the nodes?

A

SA node: 60-100/min
AV node & bundle of His: 40-60/min
Purkinje fibers: 30-40/min

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7
Q

Discuss parasympathetic activation

A

Parasympathetic (vagal) activation decreases nodal rate (negative chronotropy)
Muscarinic (M2) receptors

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8
Q

Discuss sympathetic activation

A

Sympathetic activation increases nodal rate (positive chronotropy)
Beta-1 adrenergic receptors

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9
Q

What are the vagal, intrinsic and sympathetic rates?

A

Vagal 50/min
Intrinsic rate 100-110/min
Sympathetic 200/min

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10
Q

How is pacemaker activity influenced by hormones?

A

Hyperthyroidism increases heart rate
Hypothyroidism decreases heart rate
Catecholamines increase heart rate

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11
Q

How is pacemaker activity influenced by ions?

A

An increase in K+ decreases heart rate (K+ channels open)
A decrease in K+ increases heart rate
Nodal ischemia/hypoxia decreases heart rate

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12
Q

What are the heart rate ranges?

A

During resting
Tachycardia >100/min
Bradycardia <60/min

Maximal
220/min -age of patient ~15minutes
Decreases with age, measured during stress test

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13
Q

Discuss non pacemaker action potentials

A 
Phase 4- resting potential 
Phase 0- rapid depolarization 
Phase 1- increase gK+ &amp; decrease gNa+
Phase 2- increase gCa2+
Phase 3- increase gK+
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14
Q

Which element of the cardiac electrical pathway is the fastest conductor?

A

Purkinje fibers

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15
Q

Which element of the cardiac electrical pathway is the slowest conductor?

A

AV node

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16
Q

What is the term related to the speed of conduction in a nerve fiber?

A

Dromotropy

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17
Q

Where are possible sites of conduction blocks?

A

AV blocks: AV node, Bundle of His

Bundle branch blocks: Left bundle branch, Right bundle branch

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18
Q

Which AV block is associated with ventricular bradycardia, 2 or 3 ventricular depolarization & some atrial potential that has failed to be conducted into ventricles?

A

2nd degree AV block

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19
Q

Which AV block is associated with ventricular bradycardia and complete dissociation between atrial & ventricular depolarizations and contractions?

A

3rd degree AV block

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20
Q

Which AV block is associated with delayed conduction through AV node but the presence of a sinus rhythm?

A

1st degree AV block

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21
Q

Why don’t Purkinje fibers normally take over?

A

Every time an action potential comes through, the clock is reset

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22
Q

Ectopic foci generate action potentials that don’t follow normal conduction pathways, what effect does this have?

A

Ventricles take longer to depolarize

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23
Q

What does the ECG measure?

A

Potential differences between + and - electrodes that are generated by electrical currents emanating from the heart during global depolarization and repolarization

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24
Q

The ST segment corresponds to which electrical event in the heart?

A

Isoelectric depolarized state of the ventricles

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25
Q

Heart rate is based on which electrocardiogram tracing interval?

A

RR interval

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26
Q

The P wave corresponds to which electrical event in the heart?

A

Atrial depolarization

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27
Q

The PR intervals corresponds to which electrical event in the heart?

A

Atrial depolarization, AV nodd delay, bundle of His and branches

28
Q

The QRS complex corresponds to which electrical event in the heart?

A

Ventricular depolarization

29
Q

What is usually the cause of a widened QRS complex?

A

A premature ventricular complex

30
Q

The QT interval corresponds to which electrical event in the heart?

A

Ventricular action potential duration

31
Q

The T wave corresponds to which electrical event in the heart?

A

Ventricular repolarization

32
Q

In resting conditions when the membrane potential is around -90 mV, which channel is most likely open in a cardiac myocyte?

A

Potassium channels

33
Q

What is the primary current responsible for phase 0 of a nodal cell action potential?

A

I Ca (L)

34
Q

Which mechanism does the sympathetic nervous system use to increase the heart rate?

A

Positive chronotropy, norepinephrine releases from presynaptic yterminal and binds to Beta 1 adrenergic receptors to speed up heart rate. Increase in rate of phase 4 depolarization.

35
Q

Which element of the cardiac electrical pathway is the primary pacemaker?

A

The SA node

36
Q

Non pacemaker cells are usually found in which cardiac elements?

A

Ventricular myocytes

37
Q

What is the usual resting membrane potential for ventricular myocytes?

A

-90 mV

38
Q

Which phase is the depolarization phase of the action potential

A

Phase 0

39
Q

The SA node normally beats in between?

A

60-100 bpm

40
Q

Acetylcholine binds to which muscarinic receptors on the SA node?

A

M2 receptors

41
Q

Norepinephrine binds to which adrenergic receptors to speed up the heart?

A

Beta 1 adrenergic receptors

42
Q

The conductance of which ion results in phase 2 characteristics in a ventricular myocyte action potential?

A

Calcium

43
Q

Which cell junctions connect heart cells together?

A

Gap junctions

44
Q

Based on the concentration gradient of sodium, potassium and calcium in cardiac myocytes, what occurs to the process of depolarization?

A

Sodium and calcium move into the cell

45
Q

Which phase occurs if there is a signal through the gap junctions that travels through and stimulates fast sodium channels?

A

Phase 0

46
Q

The small downward deflection in the QRS complex of the ECG is most likely related to which electrical event?

A

Septal depolarization

47
Q

A depolarization traveling toward a negative electrode will give what ECG change?

A

Negative (downward) deflection

48
Q

The normal period of PR interval is between?

A

0.12 and 0.2 seconds

49
Q

In which phase of the cardiac cycle does the a-wave occur in left atrial pressure

A

Phase 1-2

50
Q

During transmural ischemia what changes are seen on an ECG?

A

Normal P wave, ST segment elevation, normal T wave

51
Q

Which phases of the cardiac cycle are seen during both systole and diastole?

A

Active relaxation

52
Q

Ventricular volume curve drops sharply during which stage of the cardiac cycle?

A

Ejection

53
Q

Which location has the absolute lowest diastolic pressure in a normal healthy individual?

A

Right ventricle

54
Q

Which heart sound is associated with early diastolic filling and could be an indicator of pathology

A

S3

55
Q

Atrial systole accounts for up to what percentage of ventricular filling during exercise conditions?

A

40%

56
Q

Stroke volume is calculated by?

A

End diastolic volume-End systolic volume

57
Q

Atrio-ventricular valve open during which stage of the cardiac cycle?

A

Ventricular filling

58
Q

What contributes to 2nd heart sound?

A

Closure of aortic and pulmonary valves

59
Q

What contributes to 1st heart sound dying systole?

A

Closure of AV valves

60
Q

Cardiac output is calculated through which formula?

A

Stroke volume x heart rate

61
Q

Which parameter increases ventricular preload?

A

Increased atrial inotropy

62
Q

Velocity of myocardial contraction depends on which factor?

A

Ease of valvular opening

63
Q

A decrease in inotropy does what to stroke volume of all other cardiac variables are held constant?

A

Decrease stroke volume

64
Q

Which cardiac change will increase stroke volume?

A

Increased preload

65
Q

Greater atrial contraction occurs in which physiological condition?

A

Increase in venous return

66
Q

Which parameter decreases ventricular preload?

A

Decreased atrial inotropy

Physiology (8 decks)

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