ECGs and Conduction

Question 0

What are the main generalised symptoms of heart block ?

Answer 0

SOB
Palpitations (caused by irregular heart beat)
Fainting
Can result in bradycardia

Question 1

What is heart block?

Answer 1

A type of arrhythmia (a problem with rate or rhythm) whereby the electrical signals from the SA node to the AV node are disrupted / slowed

Question 2

What is 1st degree heart block?

Answer 2

A split second delay in time taken for electrical impulse to pass from SA node to AV node

Question 3

What is 2nd degree heart block?

Answer 3

Intermittent complete failure of excitation passing through the AV node or bundle of His (2/3 types of 2nd degree heart block)

Question 4

What is Mobitz Type 2 heart block?

Answer 4

Most beats conducted with a constant PR interval but occasionally a P wave (atrial depolarisation/contraction) is not flowed by a QRS wave (ventricular depolarisation/contraction)

Question 5

What happens in Mobitz Type 1 “Wenkebach” heart block?

Answer 5

Progressive lengthening of PR interval (delay between atrial and ventricular contraction) until failure of conduction (P wave NOT followed by QRS) then a conducted beat with short PR interval

Question 6

What is 2:1 type 2nd degree heart block?

Answer 6

Where you get alternate conducted followed by non-conducted atrial beats. Twice as many P waves as there are QRS (some P waves will present hidden within T waves, showing as distorted T wave on ECG)

Question 7

What can both Mobitz Type 2 and 2:1 lead to if not treated?

Answer 7

Complete (3rd degree) heart block

Question 8

What is 3rd degree heart block?

Answer 8

Where atrial contraction is normal but NO beats are conducted to the ventricles

Question 9

How do the ventricles contract with 3rd degree heart block?

Answer 9

Via a slow “escape mechanism”

Question 10

What is the “escape mechanism” which occurs in 3rd degree (complete) heart block?

Answer 10

Where other sites in the heart (further down the conduction pathway) initiate depolarisation where SA node fails to or where there is a blockage in the depolarisation pathway.

Question 11

What average depolarisation frequencies do foci in the atrial muscle or around the region of the AV node have (atrial / AV escape rhythm)?

Answer 11

50 per minute (resulting in bradycardia)

Question 12

What average depolarisation frequency does a ventricular focus (ventricular escape rhythm) have and when would this focus take over?

Answer 12

30 per minute (very bradycardic).

Occurs when there is a failure of conduction through Bundle of His

Question 13

Give an example of when acute complete heart block might be experienced.

Answer 13

During a myocardial infarction (MI)

Question 14

Give an example of why chronic complete heart block might be experienced.

Answer 14

Due to fibrosis around the Bundle of His

Question 15

Widening of the QRS complex is indicative of what?

Answer 15

A Bundle Branch Block

Question 16

In what direction does the intraventricular septum normally depolarise?

Answer 16

Left to right

The left ventricle has a greater muscle mass and so exerts more influence on the ECG

Question 17

An UPWARD deflection on an ECG signifies what?

Answer 17

That the electrical impulse / excitation is spreading TOWARDs that particular lead

Question 18

A DOWNWARD deflection on an ECG signifies what?

Answer 18

Excitation / electrical impulse moving AWAY from that particular lead

Question 19

What is a normal PR interval?

Answer 19

0.12 - 0.2 seconds (3-5 small squares on ECG paper)

Question 20

What is the PR interval?

Answer 20

Time taken for excitation to spread from SA node, through AV node, down Bundle of His and through ventricles

Question 21

What does the QRS complex illustrate?

Answer 21

How long excitation takes to spread through the ventricles

Question 22

What is a normal QRS duration?

Answer 22

0.12 seconds (3 small squares)

Question 23

What is the correct calibration of an ECG?

Answer 23

1mV; should move stylus 1cm (2 large squares) vertically

Question 24

What length of time does one large square denote?

Answer 24

200 milliseconds / 0.2 seconds

Question 25

What length of time does one small square denote?

Answer 25

40 milliseconds

Question 26

What length of time do 3 small squares denote?

Answer 26

0.12 seconds

Question 27

When calibrated properly what does a tall P wave indicate?

Answer 27

Atrial hypertrophy

Question 28

When calibrated properly what does a tall R wave indicate in left ventricular leads?

Answer 28

Ventricular hypertrophy

Question 29

What do 5 large squares represent?

Answer 29

1 second

Question 30

Why ECG changes are typical of pericarditis?

Answer 30

Widespread ST elevation (throughout limb and precordial leads)
(May also get a Troponin rise)

Question 31

What are the treatment options for a patient in AF?

Answer 31

Cardioversion (Direct Current synchronised shock)
Pharmacological (Flecainide, Amiodarone - rhythm control; Beta-Blockers, calcium channel blockers or digoxin - rate control)

Question 32

What major ECG change is seen in AF?

Answer 32

No defined P waves as no synchronised contraction

Question 33

What is the characteristic change seen on an ECG in Atrial Flutter?

Answer 33

‘Saw-toothed’ appearance

Usually due to re-entry circuit in the right atrium

Question 34

What ECG changes are typical of Left Atrial Hypertrophy?

Answer 34

Bifid P waves

Question 35

Give some causes of LAH

Answer 35

HTN, aortic stenosis, mitral regurgitation

Though mitral stenosis in association with LVH is prob more common

Question 36

What ECG features are seen with a Junctional Escape Rhythm?

Answer 36

Narrow complex QRS
SA node rate 60-100bpm
AV node rate 40-60bpm
Ventricular rate 20-40bpm

Question 37

What ECG changes are typical of Wolff-Parkinson-White syndrome?

Answer 37

Very short PR interval
Broad complex QRS with “Delta wave” (slurred upstroke to QRS)
(Accessory pathway)

Question 38

What ECG changes are typical is RBBB?

Answer 38

“MaRRoW” or “MaRRooN” (latter perhaps more accurate)
V1 - “M” (rSR)
V6 - “W” or “N” (qRs)
Wide QRS complexes

Question 39

What ECG changes are typical is LBBB?

Answer 39

"WiLLiaM" or "ViLLhelM" (latter better)
V1 - "V" (rS - dominant S wave)
V6 - "M" (double peaked R)
Absence of Q waves in lateral leads
Wide QRS complexes

Question 40

What ECG changes are typical of LVH?

Answer 40

Increased S wave in V1-V3 (downward deflection)
Increased R wave in V4-V6 (upward deflection)
Left axis deviation
(Causes aortic stenosis, HTN, mitral or aortic regurgitation)

Question 41

What ECG changes are typical of hyperkalaemia?

Answer 41

Peaked T waves
Prolonged PR though P waves may be absent
Bizarre QRS complexes which merge with P and T waves each side

Question 42

Which leads do you compare to assess for left or right axis deviation?

Answer 42

Leads I and II

Leads aVL and aVF

Question 43

Give two causes for left axis deviation and three causes for right axis deviation?

Answer 43

Left - LVH and LBBB

Right- RVH, PE and COPD

Question 44

Which two arrest rhythms are shockable and which are not?

Answer 44

Shockable - VF and pulseless VT

Non-Shockable - PEA and Asystole (IV adrenaline every 3-5mins)

Question 45

List 3 things a Long QT rhythm can lead to

Answer 45

Palpitations
Fainting
Sudden Death due to VF
(Implantable cardioverter used to treat)