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Cardiology > ECGs > Flashcards

ECGs Flashcards

1
Q

what is an ECG?

A

An electrocardiogram is a representation of the electrical events of the cardiac cycle.

Each event has a distinctive waveform and the study of waveform can lead to greater insight into a patient’s cardiac pathophysiology.

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2
Q

what produces an upright positive deflection?

A

Electrical impulse that travels towards the electrode

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3
Q

what can ECGs identify?

A

-Arrhythmias
-Myocardial ischaemia and infarction
-Pericarditis
-Chamber hypertrophy
-Electrolyte disturbances (hyper/hypokalaemia)
-Drug toxicity

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4
Q

describe SAN

A

– dominant pacemaker with an intrinsic rate of 60-100bpm

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5
Q

describe AVN

A

back up pacemaker with an intrinsic rate of 40-60 bpm

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6
Q

describe ventricular cells

A

back up pacemaker with an intrinsic rate of 20-45 bpm

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7
Q

what are the three pacemakers of the heart?

A
  1. SAN
  2. AVN
  3. Ventricular cells
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8
Q

what is the standard calibration?

A

25mm/s
0.1mV/mm

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9
Q

what are the impulse conduction points in an ECG?

A
  1. SAN
  2. AVN
  3. Bundle of His
  4. Bundle branches
  5. Purkinje fibres
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10
Q

describe p waves

A

atrial depolarisation

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11
Q

describe the QRS complex

A

ventricular depolarisation

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12
Q

describe the t waves

A

ventricular repolarisation

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13
Q

describe the PR interval

A

atrial depolarisation and delay in AV junction (delay allows time for the atria to contract before the ventricles contract)

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14
Q

what do the ECG leads measure?

A

The leads measure the difference in electrical potential between two points

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15
Q

what are the two leads called?

A
  1. bipolar leads
  2. unipolar leads
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16
Q

describe bipolar leads

A

two different points on the body (positive and negative)

17
Q

describe unipolar leads

A

one point on the body and a virtual reference point with zero electrical potential, located in the centre of the heart (only require a positive electrode for monitoring)

18
Q

how many electrodes, precordial, limbs are used?

A

There are 12 leads calculated using only 10 electrodes: 6 precordial, 4 limbs (1 neutral).

19
Q

what do the chest electrodes do?

A

The 6 chest electrodes give 6 chest leads which provide information about the heart’s horizontal plane

20
Q

what do the 4 limb electrode do?

A

The 4 limb electrodes give 6 frontal leads that provide information about the heart’s vertical plane. The placement can be explained as Einthoven’s triangle.

21
Q

name the 6 leads

A

Lead I
Lead II
Lead III
Augmented vector right (aVR)
Augmented vector left (aVL)
Augmented vector foot (aVF)

22
Q

which leads are bipolar

A

Leads I, II, and III require bipolar leads

23
Q

which leads are unipolar?

A

all the augmented leads are unipolar.

24
Q

what are common p wave abnormalities?

A

Right atrial enlargement – tall >2.5mm – P pulmonale

Left atrial enlargement – notched (M-shaped) – P mitrale

25
Q

what are common QRS complex abnormalities?

A

Depth of the S wave should not excess 30mm
Pathological Q wave:
>2mm deep and >1mm wide
>25% amplitude of the subsequent R wave

26
Q

what does the QRS complex represent?

A

This represents the overall direction of the heart’s electrical activity, and abnormalities of the QRS axis hint at ventricular enlargement or conduction blocks.

27
Q

what are common ST segment abnormalities?

A

ST segment is usually flat (isoelectric), elevation or depression of ST segment by 1mm or more can be pathological.

28
Q

what are common T wave abnormalities?

A

Should be at least 1/8 but less than 2/3 of the amplitude of R
Abnormal T waves are symmetrical, tall, peaked, biphasic or inverted
T wave amplitude rarely exceeds 10mm

29
Q

what are common U wave abnormalities?

A

Small, round, symmetrical and positive in lead II, with amplitude <2mm (regular)
U wave should be same direction as T wave

30
Q

what are common QT interval abnormalities?

A

QT interval decreases when heart rate increases
Regular interval is 0.35-0.45s
Should not be more than half of the interval between adjacent R waves

31
Q

how do you calculate heart rate from a ECG?

A

Rule of 300/1500 – regular rhythms
Count the number of big/small boxes between two QRS complexes and divide this into 300/1500 for regular rhythms.

10 second rule – irregular rhythms
Count the number of beats present on the ECG and multiply by 6.

32
Q

describe the quadrant approach for the QRS axis

A
  1. QRS complex in leads I and aVF
  2. Determine if they are predominantly positive or negative
  3. The combination should place the axis into one of the 4 quadrants below

LAD = left axis deviation
RAD = right axis deviation

Cardiology (17 decks)

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