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CVS physiology > The electrocardiogram - ECG (CVS6) > Flashcards

The electrocardiogram - ECG (CVS6) Flashcards

1
Q

how does the heart generate surface potentials upon the skin

A

electrical activity within the cardiac muscle causes current flow within the heart and within surrounding tissues distant to the heart

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2
Q

what is caused by electrical activity within cardiac muscle cells

A
  • current flow within the heart
  • current flow within the surrounding tissues
  • potential differences between distant sites on the body surface measurable by electrodes placed on the skin coupled to a sensitive recording device, the electrocardiograph
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3
Q

what is an electrocardiogram

A

recording of potential differences in current flow between distant sites on the body surface measurable by electrodes placed on the skin coupled to a sensitive recording device, the electrocardiograph

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4
Q

3 standard limb leads used when recording an ECG

A
  • lead I: RA/right arm(-ve) - LA/left arm(+ve)
  • lead II:RA/right arm(-ve) - LL/left leg (+ve)
  • lead III: LA/left arm(-ve) - LL/left leg (+ve)
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5
Q

einthoven’s triangle

A

imaginary equilateral triangle with the heart at its center, formed by the axes of the three bipolar limb leads

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6
Q

why is lead II (between RA - LL) used when recording ECG

A

-lead II goes along the direction of the heart of the heart and so picks up electrical potentials better

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7
Q

why are the limb leads described as bipolar

A
  • the heart is like a big generator
  • so bipolar limb leads have a positive and negative end to them so that the maximum deflection in the voltage can be detected (depolarization moving towards the electrode gives an upward deflection)
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8
Q

why is right leg not included in ECG

A
  • right leg is the earth leg

- but you don’t need to see that area of the heart so its irrelevant

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9
Q

how does the ECG work (calum sreenans explanation)

A
  • there are no actual leads, the leads are vectors created between the two points that the pads are put on the person
  • so as the electricity passes across the heart and then back up it, it causes deflections in the voltage across different directions, and you can work out where it is from the direction the deflection on the graph goes
  • and you can work out where heart problems are occurring by which leads are affected
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10
Q

P wave on ECG

A

atrial depolarization (0.8-0.10seconds)

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11
Q

QRS complex on ECG

A

-ventricular depolarization (

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12
Q

T wave in ECG

A

ventricular repolarization (why an upward deflection?)

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13
Q

why does ventricular repolarization cause an upward deflection (T wave on ECG)

A

?

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14
Q

PR interval on ECG

A

largely due to AV node delay (0.12-0.20 seconds)

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15
Q

ST segment on ECG

A

ventricular systole

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16
Q

TP interval on ECG

A

diastole

17
Q

unipolar limb leads

A
  • The unipolar leads
  • augmented leads and their respective limb electrodes are:
  • aVR lead: right arm
  • aVL lead: left arm
  • aVF lead: left leg
  • one +ve electrode, two others linked as -ve eg. if looking at aVR, one lead will be +ve and the other 2 leads will be negative
  • > augmented limb leads are used to look at the heard in other directions/look at the heart in 3D
18
Q

aVR

A

augmented voltage right

19
Q

limb lead I

A

RA (-ve) to LA (+ve)

20
Q

limb lead II

A

RA (-ve) to LL (+ve)

21
Q

limb lead III

A

LA (-ve) - LL (+ve)

22
Q

P wave

A

atrial

23
Q

aVR

A
  • augmented voltage right

- RA (+ve) to [LA and LF] (-ve)

24
Q

aVL

A
  • augmented voltage left

- LA (+ve) to [RA and LF] (-ve)

25
Q

aVF

A
  • augmented voltage foot

- LF (+ve) to [RA and LA] (-ve)

26
Q

how to calculate heart rate from ECG

A
  • 300/number of large squares between beats

- 300/number of large squares between R-R interval

27
Q

what is the ECG rhythm strip

A
  • prolonged reading of one lead
  • usually standard limb lead II
  • allows you to detect rhythm disturbance
28
Q

why are 12 leads needed if one lead (lead II) is enough to show/monitor cardiac rhythm?

A
  • the 12 leads allow you to look at the heart from different directions
  • this allows you to:
  • > determine the axis of the heart in the thorax
  • > look for any ST segment or T wave changes in relation to specific regions of the heart (eg. in diagnosing ischaemic heart disease)
  • > look for any voltage criteria changes (eg. when diagnosing chamber hypertrophy)
29
Q

eg.’s that a normal resting ECG doesnt exclude

A
  • normal resting ECG doesnt exclude significant heart disease:
  • > myocardial infarction/heart attack may or may not cause characteristic ECG changes (eg. ST elevation)
  • > intermittent rhythm disturbance (if susbected do amulatory ECG for 24 hours or 7 days)
  • > stable angina/form of ischaemic heart disease, if suspected do exercise ECG (look for changes during/after exercise - usually absent during rest)

CVS physiology (11 decks)

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