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Physiology > [2] Lecture 8:Heart rhythmicity/Norm ECG > Flashcards

[2] Lecture 8:Heart rhythmicity/Norm ECG Flashcards

1
Q

Conduction system of the heart

A

Sinus(SA) node-intermodal pathways-Atrioventricular node- AV bundle- bundle branches [l/r]

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2
Q

Describe the delay in heart’s electrical system:

A

AV node receives impulse from SA after .03 s.
Signal is delayed in AV for .09 s.
Signal is delayed in penetrating bundles for .04 s.
=.16 delay from initial SA signal to ventricular contraction

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3
Q

Why the delay from SA to AV?

A

Takes .03 s to get signal through atrial fibers that are directly connected to SA.

D/t small size of cells, low amplitude of AP, and slow rate of depolarization during excitation the signal is delayed .09 s.

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4
Q

What’s main cause of slow conduction along the electrical pathway of heart?

A

Slow conduction is d/t diminished # gap junction in pathway resulting in the resistance to conduction

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5
Q

Resting membrane potential and threshold of SA node

A

Resting: -55 to -60 mV
Threshold: -40mV

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6
Q

What is open @ -55 to -60 mV in SA node

A

Slow sodium-calcium channels-making membrane more positive.

Atrial nodal AP is slower

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7
Q

What happens @ -40 mV?

A

Sodium-calcium channels become activated

Inactivated again in 100-150 msec

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8
Q

What happens to SA node @ approx. 0 mV?

A

Repolarization by means of large potassium channels open [after Na-Ca channels close]

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9
Q

Differ ventricular and SA node resting potential

A

SA=-55 to -60 mV

Ventricular=-85 to -90 mV

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10
Q

Difference btw sinus rhythm and ectopic focus

A

AP originating in SA node=sinus

Generated anywhere else is ectopic

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11
Q

Vagus nerve and parasympathetic effects on HR:

A

Acetylcholine involves muscarinic receptors…decreases rate of rhythm of SA d.t decreased excitable AV junctional fibers.

This is done by increasing permeability of potassium ions in fiber membranes. Hyper polarization.

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12
Q

Vagus nerve and sympathetic effects on HR:

A

Noepinephrine stimulates beta-1 adrenergic receptors, increases depolarization rate.

May increase permeability of NA+/Ca++in fiber membranes.

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13
Q

Positive chronotropic effect

A

Increases depolarization rate

Hyperpolarization: - chronogenic effect

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14
Q

What do the P, QRS, and T waves represent on typical ECG?

A

P- atrial depolarization [contraction]

QRS-ventricular depolarization [contraction]

T- ventricular repolarization

  • can’t see atrial repolarization; it’s behind QRS complex.
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15
Q

Difference between ECG recording and transmembrane potential recording

A

ECG measures extracellular potential; not the same as transmembrane potential: only concerned w/ what is happening across membrane interface.

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16
Q

When there is current flow between regions of the heart what doe the ECG look like

A

Deflection from 0. Current flows between different membrane potentials. Monophasic potential of ventricular muscle

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17
Q

What potential is recorded when ventricle is completely polarized or depolarized?

A

No potential.

It is only when the muscle is partially polarized/ depolarized does current flow from one part of the ventricle to another.

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18
Q

PR interval

A

0.16 s

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19
Q

QT interval

A

0.35 s

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20
Q

Beginning of atria contraction

Phase 0 of AP through atrial muscle

A

P wave

21
Q

Beginning of the ventricle contraction

Phase 0 of the AP’s through the atrial muscle

A

QRS complex

22
Q

Repolarization of ventricles occurs after end of

Represents phase 3 of repolarization of ventricle

A

T wave

23
Q
  • terminal= R arm
    + terminal= L arm
    Looks at heart from R to L
A

Limb lead I

24
Q
  • terminal=R arm
    + terminal=L leg
    Looks at heart from R to L
A

Limb lead II

25
Q
  • terminal=L arm
    + terminal=R arm
    Looks at heart from upper L to lower L
A

Limb lead III

26
Q

2 arms and left leg form spices of triangle

A

Einthoven’s triangle

27
Q

If the electrical potentials of any 2 of the 3 bipolar limb ECG leads are known at any given instant, the third can be determined by summing the first 2

A

Einthoven’s law

28
Q

Normal current flow in the ventricle:

A

Negative to positive in the direction from the base of the heart to apex.

= base (-) and apex (+)

29
Q

All limb leads record: (-/+)

A

Positive

30
Q

An arrow that points in the direction of the electrical potential generated by the current flow, with the arrowhead in the + direction.

A

Vector

31
Q

Axis for Lead I

A

0 degrees

32
Q

Axis Lead II

A

60 degrees

33
Q

Axis lead III

A

120 degrees

34
Q

Summated vector of the generated potential at a particular instant

A

Instantaneous mean vector

35
Q

Horizontal and extends towards a persons L side; this direction = 0 degrees

A

Reference vector; lead I

36
Q

What is the mean electrical axis of the heart

A

About +59 degrees in relation to the zero reference point

37
Q

Limb leads and T, P, atrial T wave are all:

A

Positive

38
Q

How is the mean electrical axis measured

A
  • to +
    Base to apex

Vector addition leads I and III

39
Q

abnormal Conditions that cause axis deviation:

A
  • Change of heart position in chest
  • One sided ventricular hypertrophy
  • BBB
  • Fluid in pericardium
  • pulmonary emphysema
40
Q

Most common cause of increased voltage ECG [>4mV]

A

Hypertrophy of ventricle

41
Q

Causes for decreased voltage ECG:

A

Cardiac myopathies

Conditions surrounding heart

42
Q

Norm QRS duration

A

0.06-0.08

43
Q

Conditions that may cause bizarre complexes:

A
  • destruction of cardiac muscle and replacement by scar tissue
  • multiple small local blocks in the conduction impulses at many points in the purkinje system.
44
Q

What causes prolongation of QRS:

A

Hypertrophy or dilation of either ventricle

45
Q

Reference point for analyzing current of injury

A

J point

46
Q

Different cardiac abnormalities cause part of the heart to remain partially or totally depolarized all the time. This goes through both pathologically and normally polarized areas

A

Currents of injury

47
Q

Abnormalities causing current of injury:

A

1: ischemia-most common
2: infectious process
3: mechanical trauma

48
Q

What is the effect of current of injury?

A

Abnormal negative current flows from infarcts area and spreads toward the rest of the ventricles

49
Q

Where dopes J point occur?

A

Very end of the QRS wave-this is the point where all parts of the ventricle [injured/healthy] depolarize….ex: ST elevation!!

Physiology (10 decks)

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