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MD3001 > ECG Interpretation > Flashcards

ECG Interpretation Flashcards

1
Q

What are the steps in looking at an ECG ?

A
  1. Identity, Standardisation
  2. Rate
  3. Rhythm
  4. P Wave
  5. P–R Interval
  6. QRS Complex
  7. QT Interval
  8. ST Segment
  9. T Wave
  10. Axis
  11. Other Abnormal Components
  12. Formulate an Interpretation
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2
Q

Explain what you look for when looking at identity and standardization of an ECG.

A

 First confirm patient’s name and age and ECG’s date

 Standardisation

  • Make sure that 1cm = 1mV and
  • Paper speed 25mm/sec
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3
Q

Explain what you look for when looking at Rate of an ECG.

A

 Calculation:

  • Divide 300 by the number of big squares per R – R interval (i.e. by number of 0.20 s segments per R-R interval)
  • Calculate this in the second lead
  • Normal rate 60-100 b.p.m (Bradycardia <60 and Tachycardia >100)
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4
Q

What is the scale that is usually used for an ECG per small square or big square ?

A

A small square = 0.04 s (40 ms)

A large squares = 0.2 s (200 ms)

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5
Q

Define R-R interval.

A

Intervals between successive heartbeats

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6
Q

Explain what you look for when looking at Rhythm of an ECG.

A

 Are the normal P waves present (<0.25mV, and upright in II III and AVF)?
 Are the QRS complex narrow-normal <120 ms (0.12s) or wide >120 ms (0.12s)?
 Relationship between P waves and QRS complexes. (One P wave followed by one QRS complex)
 Is the rhythm regular or irregular (arrhythmia)?

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7
Q

How can you ensure whether the rhythm is regular or irregular ?

A

 Mark position of 3 successive R waves

 Slide the mark forward and check that intervals are equal

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8
Q

Define sinus rhythm.

A 
"normal cardiac rhythm proceeding from the sinoatrial node"
Hence, 
Normal P waves
Normal QRS complexes
One P wave followed by one QRS complex
Regular rhythm
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9
Q

What are possible abnormalities if the rhythm is found to be irregular (arrhythmia).

A

1) Atrial Fibrillation (=”atrial contractions are rapid and random”): No discernible P waves and irregular QRS complexes
2) Atrial Flutter (=” atrial contractions are rapid but regular”): More than 1 P wave per QRS complex (ventricular activation may in the meantime be completely regular)
3) Junctional (Nodal) Tachycardia (=”Tachycardia resulting from a focus in the atrioventricular node”): Normal QRS complexes but absent P wave
4) Ventricular Tachycardia (=”Tachycardia originating in a ventricle”): Broad QRS complexes, T waves possibly difficult to identify. (> 120 ms)

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10
Q

What event within the heart does the P-Wave represent ?

A

Atrial Depolarisation

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11
Q

Explain what you look for when looking at the P-wave of an ECG.

A

 <0.25mV, and upright in II III and AVF

 Normally precedes each QRS complex

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12
Q

Give examples of abnormal P waves.

A

Absent P-wave due to:
 Atrial fibrillation
 Nodal (junctional) rhythm

P-Mitrale: Bifid P wave, signifying left atrial hypertrophy

P-Pulmonale: Peaked P wave (more than 0.25 mV height), signifying right atrial hypertrophy

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13
Q

What is the P-R interval ?

A

The time between atrial and ventricular depolarisation.

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14
Q

Explain what you look for when looking at the P-R interval of an ECG.

A

Measure from the beginning of P to the beginning of Q wave, normal range 120-200 ms (0.12-0.2 s).

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15
Q

Identify possible abnormalities in the P-R interval, explaining why each might occur.

A

Prolonged P-R interval >200 ms (0.2 s) implies delayed AV conduction (= Heart Block)

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16
Q

What event in the heart does the QRS complex represent ?

A

Ventricular Depolarisation (also hides atria repolarisation)

17
Q

Explain what you look for when looking at the QRS complex of an ECG.

A
  • Measure from the beginning of Q to the end of S wave.
    Normal Duration <120 ms (0.12 s)
    Normal Q wave <40 ms (0.04 s) and <2mm depth
18
Q

Identify possible abnormalities in the QRS complex, explaining why each might occur.

A

If >120ms (0.12 s):
-ventricular conduction defects (L or R bundle branch block)

Low voltage (<5 mm):

  • Hypothyroidism
  • Chronic Obstructive Airways Disease (COAD)
  • Myocarditis
  • Pericarditis and Pericardial effusion

Left ventricular hypertrophy:
-R wave in V5 >25mm or
sum of the S wave in V1 and R wave in V5 or V6 >35mm (=Sokolow-Lyon index)

Right ventricular hypertrophy:

  • Dominant R wave in V1 (> 7mm tall)
  • Deep S wave in V6 (> 7mm deep)
  • T wave inversion in V1-V3 or V4
Significant Q wave: 
- >40ms (0.04 s) 
- Depth >2 mm
Present couple of hours/days after acute
MI
If present in lead III consider PE.
19
Q

What is the Q-T interval ?

A

“the period from onset of depolarisation to completion of repolarisation of the ventricular myocardium”

20
Q

Explain what you look for when looking at the QT Interval of an ECG.

A
  • Measure from start QRS to end of T wave (varies with rate)

-Calculate QTc interval (“adjusts the QT interval correctly for heart rate extremes”)
QTc= QT/√RR
Normal is 380-420 ms (0.38-0.42 sec)

21
Q

Identify possible abnormalities in the QT interval, explaining why each might occur.

A

Prolonged QT Interval:

  • Acute Myocardial Ischaemia
  • Myocarditis
  • Bradycardia
  • Head Injury
  • Hypothermia
  • U&E Imbalance (K+ Ca2+ Mg2+ )
  • Congenital
  • Drugs (Quinidine, Antihistamines, Macrolides, Amiodarone, Phenothiazines)
22
Q

What is the ST segment ?

A

Time from the end of ventricular

depolarisation to the start of ventricular repolarisation

23
Q

Explain what you look for when looking at the ST Interval of an ECG.

A

Usually isoelectric

24
Q

Identify possible abnormalities in the ST interval, explaining why each might occur.

A

Elevation > 2mm in two adjacent chest leads
OR
Elevation > 1mm in two adjacent limb leads
=Myocardial Infarction

ST depression upon exercice
=Myocardial Ischemia

25
Q

What is the T wave ?

A

Ventricular Repolarisation

26
Q

Explain what you look for when looking at the T wave of an ECG.

A

Normally inverted in VR and V1 and in V2 in young

27
Q

Identify possible abnormalities in the T wave, explaining why each might occur.

A

T wave inverted in I, II and V4 -V6
=Ischaemia /Infarction

T wave inversion and ST segment sloping depression
=Digitalis Effect (due to Digoxin)

28
Q

Explain what you look for when looking at the Axis of an ECG.

A

Sum of all ventricular forces during ventricular depolarisation (expect leads I II and III to be predominantly positive )
Normally, between -30° and +90°.

29
Q

Identify possible abnormalities in the Axis of the heart, explaining why each might occur.

A

Left Axis Deviation (-30 to -90°)

  • Negative QRS deflections in leads II and III
  • Could signify LV hypertrophy, MI

Right Axis Deviation (+90° to +180°)

  • Negative QRS deflection in lead I
  • Could signify RV hypertrophy, PE, MI
30
Q

Describe the ECG changes which take place in an MI.

A 
During an Acute MI, the ECG evolves
through 3 stages:
- T wave peaking followed by T wave inversion
- ST segment elevation
-Appearance of new Q waves
31
Q

Which leads will we see changes in for an infarction of which area of the heart ?

A

Anterior Infarction:
-Any of precordial leads (V1 through V6)

Lateral Infarction:
-Leads I, AVL, V5 and V6

Inferior Infarction:
-Leads II, III, and AVF

Posterior Infarction:
-Reciprocal changes in lead V1 (ST- segment depression, tall R wave)

32
Q

What changes would you expect to see in an anterior infarction ?

A
  • Sinus rhythm
  • Q waves in leads V2-V4
  • Inverted T waves in leads V4-V6
33
Q

What changes would you expect to see in an anterolateral infarction ?

A
  • Sinus rhythm
  • Q waves in leads I, II, AVL, V3-V5
  • Raised ST segments in leads V2-V6
34
Q

What changes would you expect to see in an inferior infarction ?

A
  • Sinus rhythm
  • Q waves in leads III and AVF
  • Depressed (ischemic) ST segment in leads AVL and V6
35
Q

What changes would you expect to see on an ECG in a pulmonary embolism (PE) ?

A
  • Large S wave in lead I
  • Deep Q wave in lead III
  • Inverted T wave in lead III
36
Q

Identify metabolic abnormalities for which you could see differences on the ECG (name the differences).

A
  • Hyperkalaemia:
    Tall, tented T wave, widened QRS

Hypokalaemia:
Small T waves, prominent U waves (successor of T wave)

Hypercalcaemia:
Short QT interval

Hypocalcaemia:
Long QT interval, small T waves

MD3001 (75 decks)

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