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PHYSIOLOGY II > WEEK VI (ECG) > Flashcards

WEEK VI (ECG) Flashcards

1
Q

What are the main structures of the conduction of the heart?

A
  • Sino-atrial node
  • Atrio-ventricular node
  • Fibrous atrio-ventricular septum
  • Bundle of His
  • Pukinje Fibres
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2
Q

_____ node is the dominant pacemaker of the heart; other pacemakers exist but are slower

A

SA (Sino-atrial node)

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3
Q

What happens when the SA node fails?

A

The other nodes take over but with decreased beats per minute

SA NODE = 60-100 bpm
AV NODE = 40-60 bpm
HIS = 25-40 bpm
BUNDLE BRANCHES = 25-40 bpm
PURKINJE FIBERS = 25-40 bpm

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4
Q

Why has the AV node got the slowest conduction velocity?

A

So that the ventricle has time to fill

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5
Q

What has the fastest conduction velocity?

A

PURKINJE FIBERS

Purkinje > Atria > Ventricle > AV node

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6
Q

What is an ECG?

A

A representation of the electrical activity of the heart muscle as it changes with time. It is the sum of electrical activity that is amplified and recorded.

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7
Q

What is the Iso Electrical Line?

A

It represents the resting potential of the heart and electrical events of the cardiac cycle will be represented by deflections away from this line

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8
Q

What are important things to remember about recording the ECG?

A
  • VERTICAL LINES measure AMPLITUDE/VOLTAGE
  • Each small box represents 0.1 mV & each large block (5 small boxes) is 0.5 mV
  • HORIZONTAL LINES measure TIME
  • Each small box is 0.04 secs & each large block (5 small boxes) is 0.2 secs
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9
Q

Describe the ECG

A

P WAVE = atrial depolarisation
QRS complex = ventricular depolarisation
T WAVE = ventricular repolarisation

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10
Q

What happens during the P wave?

A
  • ATRIAL DEPOLARISATION = the wave of electrical depolarisation is conducted through the cardiac muscle of both atria
  • ATRIAL CONTRACTION= depolarising wave causes contraction of atria pushing blood into ventricles
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11
Q

What happens during the PR interval?

A

The wave of depolarisation reaches the atria-ventricular node which DEPOLARISES and DONDUCTS but SLOWS the wave

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12
Q

What happens during the QRS complex?

A
  • The coordinated, synchronised depolarisation causes both ventricles to contract
  • The AV node conducts the depolarisation to the Bundle of His
  • Wave of depolarisation quickly moves through the specialised conducting tissue
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13
Q

What happens during the T wave?

A

The ventricles repolarise, returning to resting potential

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14
Q

What are the positions of the electrodes for limb leads?

A
  • Right wrist = aVR
  • Left wrist = aVL
  • Left leg = aVF
  • Right leg (earth/neutral)
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15
Q

What is the relationship between limb and chest leads?

A
  • Chest leads look at the heart across the HORIZONTAL PLANE
  • Limb leads look at the heart in a VERTICAL PLANE
  • Leads aVR, aVL and aVF look from three separate directions
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16
Q

Leads I, II and III are summation of ________________ between limb leads

A

Potential differences

17
Q

Describe Lead 1

A
  • -VE terminal is connected the RIGHT arm and +VE terminal to the LEFT arm
  • LA = electrical voltages of the heart transmitted to LEFT ARM & RA = electrical voltages of the heart transmitted to RIGHT ARM
  • LA - RA = Lead 1 (potential difference)
  • Travels horizontally
18
Q

When does Lead 1 show a positive wave and when does it show a negative wave?

A

Lead 1 shows a POSITIVE WAVE when impulses moves TOWARDS the LEFT ARM and a NEGATIVE WAVE when impulses moves AWAY from the LEFT ARM

19
Q

Describe Lead 2

A
  • -VE terminal is connected to RIGHT ARM and +VE terminal to the LEFT LEG
  • When right arm is -ve with respect to left leg, ECG records positively
  • Points downward diagonally
  • Lower pole (LL) is +ve and upper pole (RA) is -ve
  • Lead II = LL - RA
20
Q

Describe Lead 3

A
  • -VE terminal connected to LEFT ARM and +VE terminal connected to LEFT LEG
  • When left arm is -ve with respect to left leg -> ECG records positively
  • Points downward diagonally
  • Lower pole (LL) is +ve and upper pole (LA) is -ve
  • Lead III = LL - LA
21
Q

What does Einthoven’s law state?

A

If the electrical potentials of any two of the three bipolar limb electrocardiographic leads are known at any given instant, the third one can be determined mathematically by simply summing the first two.

22
Q

Which leads show the Inferior view of the heart?

A

II, III & aVF

23
Q

Which leads show the Lateral view of the heart?

A

I, aVL, aVR, V5 & V6

24
Q

Which leads show the Anterior view of the heart?

A

V3 & V4

25
Q

Which leads show the Septal view of the heart?

A

V1 & V2

26
Q

What do the waves in ECGs represent?

A

Repolarisation/Depolarisation

27
Q

What do positive deflections above the Iso Electrical line mean?

A

The electricity is flowing towards that lead

28
Q

What do negative deflections below the Iso Electrical line mean?

A

The electricity is flowing away from that lead

29
Q

What are the characteristics of a normal P wave?

A
  • Atrial depolarisation initiated by the SA node
  • width <3 small squares (0.12s) and height <2.5mm
  • Upward in leads I & II and inverted in lead aVR
  • P wave after the QRS complex or inverted P wave indicates its origin from other source
30
Q

How can abnormal P waves present?

A
  • Peaked (taller than 2.5mm)
  • Blobbed or notched
  • Biphasic (both +ve and -ve parts broad)
  • Inverted
  • Buried in QRS complex
  • Retrograde
31
Q

In the ________ complex, the impulse is slightly delayed at the AV node before entering the ventricles through the common AV bundle

A

QRS

32
Q

What does the J point represent?

A

The end of the QRS complex and the beginning of the ST segment

33
Q

What are the characteristics of a Normal T wave?

A
  • Repolarisation of ventricles
  • Same direction as preceding QRS complex
  • Height <5mm in limb I precordial leads
  • Smooth contours
  • May be tall in athletes
34
Q

What are the characteristics of the Normal U wave?

A
  • Repolarisation of Purkinje fibers and/or the ventricular septum
  • <1/3 T wave amplitude in same lead
  • Same direction is the same as T wave direction in that lead
  • More prominent at slow heart rates and best seen in the right precordial leads
35
Q

What is the normal PR interval?

A

Normally lasts 0.12 and 0.20 seconds (3-5 squares on ECG paper)

[Measured from the beginning of the P wave to the first deflection of the QRS complex]

36
Q

What is the normal QRS interval?

A

Normally lasts between 0.08 and 0.12 seconds (3 small squares on ECG paper)

[Measured from the first deflection of QRS complex to end of QRS complex at isoelectric line]

PHYSIOLOGY II (15 decks)

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