ECG

Question 1

Describe the standard calibration settings of an 12 lead ECG

Answer 1

X - axis is time: 25 mm = 1 second

• each small squae is 40 ms
• each large square is 0.2 s

Y-axis is voltage: 10 mm = 1 mV

Question 2

How can a deep breath change the ECG

Answer 2

It can change the orientation of the T wave in leads III and aVF but has little effect in the rest of the ECG

Question 3

What usually implies incorrect lead placement rather than pathology

Answer 3

North West axis

Question 4

What is the normal PR interval

Answer 4

0.12 to 0.2 seconds

Question 5

What is the normal duration of the QRS complex

Answer 5

0.06 to 0.1 seconds

Question 6

What is the normal QT interval

Answer 6

< 0.44 seconds

Question 7

Describe the electrical vector measured by each of the vertical leads

Answer 7

Lead 1: 0 degrees
Lead 2: + 60 degrees
Lead 3: + 120 degrees
aVF: + 90 degrees
aVL: - 30 degrees
aVR: - 150 degrees

Question 8

Which index is the most commonly used for assessment of Left Ventricular Hypertrophy

Answer 8

Sokolow-Lyon index

- S wave voltage in V1 plus R wave voltage in V5 or V6, whichever is the larger, greater than or equal to 35 mm.

Question 9

Which is a more common cause of Left Axis Deviation: Left ventricular hypertrophy or left anterior hemiblock?

Answer 9

Left anterior hemiblock

Question 10

What is left anterior hemiblock and state the ECG criteria

Answer 10

= Left anterior fascicular block (LAFB)

Electrical impulses are conducted to the left ventricle via the left posterior fascicle, which inserts into the left infero-septal wall of the left ventricle along its endocardial surface.

Initial electrical vector –> down and right followed by up and left to the left ventricle
Therefore: delay !

ECG CRITERIA:

QRS > 110ms
Prolonged R wave peak time >45ms in aVL

Increased QRS voltage in the limb leads
Left axis deviation (-45 to -90 degrees)
qR in I and aVL
rS in II, III, aVF

In LAFB, the QRS voltage in lead aVL may meet voltage criteria for LVH (R wave height > 11 mm), but there will be no LV strain pattern.

Question 11

What is Left Ventricular Strain pattern

Answer 11

ST segment depression and T wave inversion in the left-sided leads

Question 12

What are the criteria for diagnosing LVH

Answer 12

Voltage criteria must be accompanied by non-voltage criteria to be considered diagnostic of LVH.

VOLTAGE CRITERIA

• S (V1) + R (V5 or V6) > 35 mm
• R in aVL > 11 mm

NON-VOLTAGE CRITERIA

• Left ventricular strain pattern
• Increased R wave peak time in V5 or V6

Question 13

What are the additional changes seen in patients with LVH

Answer 13

Left atrial enlargement
Left axis deviation
ST elevation in the right precordial leads V1-3 (“discordant” to the deep S waves).

Question 14

What are the ECG criteria for left atrial enlargement

Answer 14

P-mitrale:

Lead II

• Bifid p wave > 40 ms between the peaks
• Total p wave duration> 110 ms

V1
- Biphasic p wave with terminal negative portion> 40 ms duration OR > 1 mm deep

Question 15

What are the ECG criteria for right atrial enlargement

Answer 15

P-pulmonale

Lead II
- p wave amplitude > 2.5 mm

V1
- p wave amplitude > 1.5 mm

Question 16

What are the ECG criteria for right ventricular hypertrophy

Answer 16

RAD (> +110 degrees)

V1
- R wave > 7mm tall or R/S ratio > 1

V5/V6
- S wave > 7mm deep or R/S ration < 1

QRS duration> 120 ms

Associated

• Right atrial enlargement
• RV strain ( ST depression/T-wave inversion V1 - 4 and inferior leads)

Question 17

What are the ECG criteria for RBBB

Answer 17

Broad QRS > 120 ms
RSR’ pattern in V1-3 (‘M-shaped’ QRS complex)
Wide, slurred S wave in the lateral leads (I, aVL, V5-6)

Associated Features
ST depression and T wave inversion in the right precordial leads (V1-3)

Question 18

Is Right Axis Deviation always abnormal

Answer 18

A minor degree of right axis deviation is not uncommon in tall thin subjects in whom the heart lies more vertically

Question 19

What is a normal q wave?

Answer 19

Small Q waves are normal in most leads
Deeper Q waves (>2 mm) may be seen in leads III and aVR as a normal variant
Under normal circumstances, Q waves are not seen in the right-sided leads (V1-3)

Question 20

What is a pathological q wave

Answer 20

> 40 ms (1 mm) wide
2 mm deep
25% of depth of QRS complex
Seen in leads V1-3

Question 21

What is aVR used for

Answer 21

If aVR QRS complex is upright the limb leads have been placed incorrectly

Question 22

What is Wellen’s syndrome

Answer 22

Wellen’s syndrome is a pattern of deeply inverted or biphasic T waves in V2-3, which is highly specific for a critical stenosis of the left anterior descending artery (LAD).

• Patients may be pain free by the time the ECG is taken and have normally or minimally elevated cardiac enzymes; however, they are at extremely high risk for extensive anterior wall MI within the next few days to weeks.

Due to the critical LAD stenosis, these patients usually require invasive therapy; do poorly with medical management; and may suffer MI or cardiac arrest if inappropriately stress tested

Question 23

How long should elective surgery be delayed in the instance of an MI prior to surgery

Answer 23

At least 3 months

Question 24

What physiological effect does potassium have on the heart

Answer 24

Progressively worsening hyperkalaemia leads to suppression of impulse generation by the SA node and reduced conduction by the AV node and His-Purkinje system, resulting in bradycardia and conduction blocks and ultimately cardiac arrest.

(Increased EC K+ mean lower gradient for K+ efflux during repolarization)

K > 5.5 –> repolarization abN = peaked t waves

K > 6.5 –> Paralysis of atria: Wide/flat/absent p wave

K > 7.0 –> Conduction abN and bradycardia: QRS wide + AV block with junctional/ventricular escape rhythms BBB/Fascicular blocks/Sinus brady/Slow AF –> Sine wave is a pre-terminal rhythm.

K > 9.0 –> Asystole/VF/PEA with bizarre wide complex rhythm

Question 25

What is the difference between hyperacute t waves and peaked t waves in hyperkalaemia

Answer 25

Hyperkalaemia –> tall, narrow, symmetrical

Hyperacute –> broad and asymmetrically peaked

Question 26

causes of Mobitz type I AV block include:

Answer 26

Increased vagal tone (as in athletes)
Acute myocardial infarction (especially inferior infarction)
Myocarditis
Drugs such as beta-blockers, calcium channel blockers, digoxin and amiodarone

Question 27

How do you distinguish SVT from sinus tachycardia?

Answer 27

An SVT is not affected by deep inspiration as the sinus node is not active during SVT. If the patient cannot comply with your request to take a deep breath, just watch the monitor for a few minutes. The rate of SVT changes very little, by 1 or 2 bpm. Sinus tachycardia varies a lot more than that.

Question 28

How is WPW relevant to the anaesthetist?

Answer 28

These patients may develop paroxysmal tachyarrhythmias during anaesthesia. Patients who give a history suggestive of frequent arrhythmias should be investigated by a cardiologist and put on appropriate treatment prior to elective surgery.

Question 29

In what % of the population is RBBB a normal variant

Answer 29

10 to 15%

Question 30

What causes LBBB

Answer 30

Always pathological (unlike RBBB)

• IHD
• HPT
• Dilated CMO
• Isolated conduction system disease

Question 31

Why is it important that definitive treatment is concluded in patients with Mobitz type 2 and complete heart block prior to surgery

Answer 31

Perioperative hypoxia/electrolyte imbalance/hypotension/ischaemia can lead to temporary worsening of existing atrioventricular block