The Electrocardiogram (ECG) Flashcards

1
Q

What do standard limb leads measure?

A

They record the spread of depolarisation in one limb with respect to another

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2
Q

What are the standard limb leads?

A

From:
Right Arm -> Left Arm (SSL1)
Right arm -> Left Leg (SSL2)
Left Arm -> Left Leg (SSL3)

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3
Q

Which standard limb lead gives us the classes P wave, QRS, T wave pattern?

A

SSL2
The right arm -> Left Leg as its in line with the main vector of depolarisation down the interventricular septum.

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4
Q

How does the spread of depolaristion appear on an ECG?

A

Approaching depolarisation causes an upward blip

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5
Q

In SSL2 which cardiac events correspond to the P Wave, QRS Complex and T Wave?

A

P Wave - Atrial Depolarisation
QRS - Ventricles depolarising
T Wave - Ventricles Repolarising.

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6
Q

Why are there 3 parts to the QRS complex?

A

Different parts of the ventricles depolarise at slightly different times.
First, Interventricular Septum depolarises from left to right
Second, Bulk of ventricle depolarises from endocardial to epicardial surface
Thirds, Upper part of interventricular septum depolarises.

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7
Q

Why is the R wave bigger than the Q & S?

A

Because when the bulk of the ventricle depolarises from the endocardial to epicardial surface the mean vector of depolarisation is in line with the SLL2 recording.

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8
Q

What is the PR interval?

A

Start of P wave to start of QRS complex
Its the time from the start of atrial depolarisation to the start of ventricular depolarisation, mainly transmission in the AV node.

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9
Q

How long does the PR interval last?

A

0.1-0.2 seconds.

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10
Q

How long does the QRS complex last?

A

Around 0.08 seconds

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11
Q

What is the QT interval?

A

Time from the start of the QRS complex to the end of the T wave.
Essentially the time the ventricle spends depolarised.

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12
Q

How long is the QT interval?

A

It varies with HR.
The standard is 0.42 seconds at 60 BPM.

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13
Q

Since the T wave is a repolarisation why isn’t it negative on the ECG?

A

Because it actually runs in the opposite direction to the depolarisation (away from the recording electrode), causing it to flip.
This is because the AP is longer in the endocardial than epicardial cells.

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14
Q

What do augmented limb leads record?

A

The wave of depolarisation from one SSL to the third limb.

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15
Q

What are the 3 augmented limb leads?

A

aVR - Midpoint of Left Arm/Left Leg -> Right Arm
aVL - Midpoint of Right Arm/Left Leg -> Left Arm
aVF - Straight down from arms line to left leg.

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16
Q

What do precordial (Chest) leads do?

A

Measure the same events as the limb leads but in the transverse plane as opposed to the vertical.

17
Q

What are the precordial leads?

A

Theres 6.
V1 is -ve and V6 is +ve, the flip occurs around V3/V4

18
Q

How many perspectives do we have from which to observe cardiac events?

A

12:
3 - SSL
3 - Augmented limb leads
6 - Precordial Leads

19
Q

What is the rhythm strip?

A

A 10 second recording from SSL2

20
Q

What do we use the rhythm strip for?

A

Calculating HR
Checking for presence of P waves
Checking regularity of QRS complexes
Checking for appropriate length of the PR interval, QRS complex and QT interval.

21
Q

What does STEMI/NSTEMI stand for?

A

(Non) ST elevated myocardial infarction.
(ST as in end of QRS complex to T wave)