14. ECG - Identifying Some Basic Disturbances of Rhythm

Question 1

What is bradycardia and tachycardia?

Answer 1

Bradycardia - heart rate < 60

Tachycardia - heart rate > 100

Question 2

What are the supraventricular arrhythmias?

Answer 2

• Atrial fibrillation
• Atrial flutter
• Atrio-ventricular nodal re-entrant tachycardia (AVNRT)

Question 3

What are the ventricular arrhythmias?

Answer 3

• Ventricular fibrillation

* Ventricular tachycardia

Question 4

Which of the 2 types of arrhythmias are the most dangerous?

Answer 4

• Ventricular arrhythmias

* Atria are not as essential to sustain life, ventricles are

Question 5

What happens on the ECG if you have problems with coronary arteries (give an example)?

Answer 5

• S-T segment can shift up or down

* Myocardial Infarction results in S-T segment elevation

Question 6

What happens with people born with long QT syndrome?

Answer 6

Predisposed to arrhythmias and sudden cardiac death

Question 7

What is the standard sweep speed of an ECG?

Answer 7

25mm/s

Question 8

What are the normal values of the following:
• P wave
• PR interval
• Q wave
• QRS complex
• QT interval
• ST segment
• T wave

Answer 8

• P wave - < 0.11s; < 2.5mm (Lead II)
• PR interval - 0.12 - 0.20s
• Q wave - < 0.04s; < 25% of total QRS complex amplitude
• QRS complex - <0.12s; < 25mm (V6)
• QT interval - 0.38 - 0.42s
• ST segment - should be isoelectric
• T wave - may be inverted in Lead III, aVR, V1 & V2 without being abnormal

Question 9

What does a prolonged PR interval indicate?

Answer 9

Abnormal conduction in the ventricles

Question 10

What could a large amplitude in the QRS complex indicate?

Answer 10

Ventricular hypertrophy

Question 11

What changes on the ECG during Myocardial Ischaemia?

Answer 11

ST segment

Question 12

What is Sinus Tachycardia?

Answer 12

• Abnormally fast resting heart rate (100-200 bpm)
• Comes from the sinus node
• Normal form of waves
• Often physiological (response)
• Very common

Question 13

What is Atrial Fibrillation?

Answer 13

• Irregular beat
• Pattern of the (irregular) beat is irregular
• Normal QRS complex
• Inconsistent duration between QRS complexes
• No P waves (due to no synchronous atrial contraction)
• Wobbling baseline due to myocardium contracting at different times
• Atria - 350-650 bpm
• Ventricles - 100-180 bpm

Question 14

What is Atrial Flutter?

Answer 14

• Saw-tooth appearance of P wave with no isoelectric line - constant atrial activity
• This constant activity distinguishes it from atrial fibrillation
• Some of the atrial depolarisation is conducted down to the ventricles (around every 3rd atrial beat)
• This shows the AV node is still doing is job - protecting the ventricles from beating too fast (atrioventricular block)
• Normal QRS
• ST segment and T wave would look normal, but they are buried under the waves of atrial depolarisation
• Atria - 250-350 bpm
• Ventricles - 150 bpm (2:1 atrioventricular block)
• Regular ventricular rhythm

Question 15

What is Supraventricular Tachycardia (SVT)? (2 types)

Answer 15

• Atrioventricular Nodal Reentrant Tachycardia (AVNRT)
- depolarisation is rotating within the AV node
- simultaneous depolarisation of the atria and ventricles
- lots of (regular) QRS complexes
- no clear P waves - buried within QRS complexes
- re-entrant circuit within the AV node
- adenosine responsive (medication can block the AV node)
• Atrioventricular Reentrant Tachycardia (AVRT) - circuit within the atrium and ventricle
- re-entrant circuit through accessory pathways

Question 16

What is Pre-excitation Syndrome?

Answer 16

• AV node usually makes sure that only rates below 200 bpm get to the ventricles
• Some people born with an accessory pathway (congenital connection)
• Atrial conduction can’t be controlled
• No isoelectric PR segment and it’s abnormally short (<0.12s)
• Delta wave - slurred QRS upstroke due to activation via accessory pathway, rapid upstroke in the second segment due to activation via the normal route

Question 17

What is Wolff-Parkinson-White Syndrome?

Answer 17

• Accessory pathway leading to ventricular pre-excitation
• Short PR interval
• Delta wave
• Predisposes to AVRT - conduction comes down one way and back up the other making a loop
• 1/3 conduct antegradely (WPW) - downwards
• 2/3 conduct retrogradely (concealed pathways) - upwards

Question 18

What is the treatment for Wolff-Parkinson-White Syndrome?

Answer 18

Radio frequency ablation to burn away the accessory pathway

Question 19

What is a 1st Degree AV Nodal Block?

Answer 19

• Type of Bradyarrhythmia
• Long PR (by around 2x) due to long pause between atria and ventricles contracting
• Still 1 P wave associated with 1 QRS complex
• Largely asymptomatic

Question 20

What is a 2nd Degree AV Nodal Block (2 types)?

Answer 20

• Type of Bradyarrhythmia
• Some beats do not get conducted from the atria to the ventricles
• Some P waves are no followed by QRS complexes
• Mobitz Type 1 (Wenckebach)
- gradual prolongation of the PR interval culminating in a single dropped beat
- PR interval gradually gets longer until the AV node can’t cope and blocks conduction - mixed QRS complex
• Mobitz Type 2
- dropped beats but no pattern of gradual prolongation of the PR interval
- fixed PR intervals, then a dropped beat
- 2:1 = every other P wave isn’t followed by a QRS complex
- probably symptomatic and treatment involves fixing a pacemaker

Question 21

What is a 3rd Degree AV Nodal Block?

Answer 21

• Type of Bradyarrhythmia
• AV node doesn’t function
• No conduction from the atria to the ventricles
• Ventricles start firing on their own
• P waves and QRS complexes are completely dissociated
• May occur at regular intervals but fire independently of each other
• AV dissociation on ECG signifies a complete heart block

Question 22

What do Bundle Branch Blocks result in?

Answer 22

• If the block is in the right bundle branch, conduction only goes down the left and spreads slowly across the myocardium (from left side to right side)
• Depolarisation has to spread slowly from the left side to the right side
• QRS complex widens (> 0.12s) (bunny ears often seen with first smaller than second)
• QRS morphology changes (depending on ECG (chest) lead and if it is a right or left bundle branch block)
(• QRS complex is the time taken for all ventricular myocytes to be depolarised)

Question 23

How do you distinguish between a Right and Left Bundle Branch Block?

Answer 23

• Left - wide QRS complex with unique shape in leads overlying the right ventricle
- V1 = W
- V6 = M (bunny ears)
• Right - wide QRS complex with unique shape in leads overlying the left ventricle
- V1 = M (bunny ears)
- V2 = W

Question 24

What is Ventricular Tachyarrhythmia?

Answer 24

• Fatal
• Rapid, regular, broad QRS complex pattern
• Rapidness can cause light headedness or passing out
• Can become ventricular fibrillation if left for long

Question 25

What is Ventricular Fibrillation?

Answer 25

* Broad, irregular QRS complexes * No pattern * Defibrillator needed to try and fix the irregular contraction * High heart rate