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Anatomy & Physiology 208 > EKGs and the Cardiac Cycle > Flashcards

EKGs and the Cardiac Cycle Flashcards

1
Q

Action Potentials of Contractile Heart Cells

A
  • Most of the heart is made of contractile cells
  • contractile cells are responsible for the heart’s pumping function
  • like skeletal muscle, depolarization precedes contraction
  • unlike skeletal muscle, action potentials in cardiac muscle cells have a characteristic hump/plateau
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2
Q

non contractile cells

A

pacemaker cells

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3
Q

3 steps of cardiac action potential

A
  1. depolarization
  2. voltage change opens Ca2+ channels, influx of extracellular Ca2+
  3. repolarization
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4
Q

depolarization

A

opens fast sodium (na+) channels, extracellular Na+ enters
- rising phase of action potential (-90mV to +30mV)
- influx of Na+ will stop quickly

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5
Q

voltage change opens ca2+ channels, influx of extracellular ca2+

A
  • ca2+ influx prolongs depolarization - the plateau
  • cells will contract as long as ca2+ is entering
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6
Q

repolarization

A

results from inactivated ca2+ channels; the opening of potassium (k+) channels - an efflux of K+
- resting potential (-70mV) is restored
- ca2+ is either pumped out of the cell or into the sarcoplasmic reticulum

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7
Q

function of the plateau

A
  • both the action potential and the contraction phase are longer in cardiac muscle than skeletal muscle
  • sustained contraction ensures efficient ejection of blood from the ventricles
  • longer absolute refractory period avoids tetany
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8
Q

electrocardiography

A

detects the electrical currents generated in and transmitted through the body

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9
Q

ECG/EKG

A

graphic recording of the heart’s activity
- composite of all action potentials generated by nodal and contractile cells
- typically has 3 distinguishable waves or deflections

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10
Q

P wave

A

EKG wave
- lasts 0.08 seconds
- results from movement of the depolarization wave from SA to AV node
- the atria contract 0.1s after the P wave begins

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11
Q

QRS complex

A

EKG
- lasts 0.08s
- results from ventricular depolarization

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12
Q

T wave

A

EKG
- lasts 0.16s
- results from ventricular repolarization

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13
Q

atrial repolarization

A

occurred during ventricular depolarization - the resultant wave was obscured by the qrs complex

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14
Q

intverval

A

duration of time that includes 1 segment and 1+ wave

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15
Q

segment

A

a region between 2 waves

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16
Q

P-R interval

A

0.16s - the beginning of atrial depolarization to the beginning of ventricular depolarization

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17
Q

S-T segment

A
  • action potentials of ventricular myocytes are in plateau, the entire ventricular myocardium is depolarized
  • an elevated or depressed ST segment can indicate cardiac ischemia
18
Q

depolarization and repolarization

A

always precede mechanical events of the heart

19
Q

Intrinsic conduction with EKG

A
  1. Atrial Depolarization
    - Completed by SA Node, causes P Wave
  2. Atrial Depolarization Complete
    - Impulse delayed at AV Node
  3. Ventricular Depolarization
    - Begins at apex, causes QRS complex
    - Atrial repolarization occurs, but is obscured
  4. Ventricular Depolarization Complete
  5. Ventricular Repolarization
    - Begins at apex, causes T Wave
  6. Ventricular Repolarization Complete
20
Q

cardiac cycle

A

mechanical events of the heart

21
Q

systole

A

contraction
- blood is forced out of the hearts chambers

22
Q

diastole

A

relaxation
- blood refills the heart’s chambers

23
Q

1 cardiac cycle

A

all events associated with blood flow through the heart in 1 complete beat
(atrial systole + atrial diastole + ventricular systole + ventricular diastole)

24
Q

steps of the cardiac cyclel

A
  1. ventricular filling
  2. isovolumetric contraction
  3. ventricular ejection
  4. isovolumetric relaxation
25
Q

ventricular filling

A
  • pressure is low, blood flows from atria to ventricles
  • av valves open, sl valves are closed
  • responsible for 80% of ventricular filling
  • following atrial depolarization (p wave), atrial systole occurs, and blood is compressed into the ventricles
  • EDV
  • atrial diastole and the start of ventricular depolarization
26
Q

End diastolic volume (edv)

A

the maximum volume of blood that the ventricles will contain in the cardiac cycle

27
Q

isovulmetric contraction

A
  • atria relax, the ventricles start contracting, pressure in the ventricles rises
  • AS valves close
  • for a moment, the ventricles are closed chambers with a constant blood volume
  • pressure continues to rise until it exceeds rhe pressure in the great vessels
  • sl valves open
28
Q

ventricular ejection

A
  • blood moves from the ventricles to the great vessels (pulmonary trunk vs aorta)
  • pressure in the aorta is typically 120mmHg
29
Q

isovolumetric relaxation

A
  • follow the t wave, the ventricles relax
  • ESV
  • ventricular pressure drops, blood slides from the great vessels back towards the ventricles - sl valves close
  • ventricles are again closed chambers
  • dicrotic notch
30
Q

End systolic volume (ESV)

A

the un-ejected blood remaining in the ventricular chambers

31
Q

dicrotic notch

A

a brief rise in aortic pressure caused by blood rebounding off the newly closed aortic valve

32
Q

restarting the cardiac cycle

A
  • flow of blood through the heart is governed by pressure changes - blood always follows down a pressure gradient (high-low)
  • while the ventricles are contraction in systole, the atria are in diastole
  • when the pressure in the filling atria exceeds the pressure in the. ventricles, the av valves open, and the ventricular filling begins again
33
Q

1 cardiac cycle

A

0.8s
- atrial systole = .1s, ventricular systole = .3s, quiescent period = .4s

34
Q

pulmonary circulation

A

low pressure circuit - pressure in the pulmonary arteries = ~24/10 mmHg

35
Q

systemic circulation

A

higher pressure circuit - pressure in the aorta + ~120/80 mmHg
- despite difference in pressure, both sides of the heart eject the same volume of blood with each beat

36
Q

heart sounds

A
  • 2 sounds can be hear with each heart beat “lub-dup”
  • sounds heard are the sounds of the valves closing
  • the pause between sounds is the quiescent period
37
Q

1st sound

A

av valves closing
- start of ventricular systole
- longer, louder sound

38
Q

2nd sound

A

sl valves closing
- start of ventricular diastole
- shorter, sharper sound

39
Q

valve closure

A

typically, the mitral valve closes slightly before the tricuspid valve, and the aortic valve closes slightly before the pulmonary valve

40
Q

murmur

A

an abnormal heart sound secondary to turbulent blood flow
- more common in children and elderley people; thin-walled hearts allow more vibration
- can be indicative of a valve problem - insufficient or incompetent valves allowing regurgitation or backflow

41
Q

stenotic valves

A

fail to open all the way - the narrowed opening restricts blood flow, and a high-pitched sound (or click) can be hear

Anatomy & Physiology 208 (39 decks)

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