CVS 7 (ECG) Flashcards
Name the tissue which electrically connects the atria, allowing an action potential to travel from the SAN to the left atria:
Bachmann’s Bundle
Which surface of the heart tissue repolarises first?
Epicardial surface
How many electrodes are attached for a standard 12-lead ECG?
10 electrodes
How many leads are used for a standard ECG?
12 leads
Which limb lead looks from the apex of the heart to the right atria? Where are the electrodes placed?
Lead II
Right arm
Left leg
Why does depolarisation appear as a positive deflection from the baseline of an ECG?
Depolarisation moves towards positive electrode = positive deflection
Depolarisation moving away from an electrode would appear as what kind of deflection in an ECG?
Negative deflection
Repolarisation moving away from an electrode would appear as what kind of deflection in an ECG?
Positive deflection
What are the chest leads used in an ECG?
V1-6 (medial to lateral)
What does the P wave show?
Atrial depolarisation
What does the QRS complex show?
Ventricular depolarisation
What point of the ECG shows atrial repolarisation?
Lost in QRS complex
What does the T wave show?
Ventricular repolarisation
List some possible confounders for an incorrect ECG:
- Lead misplacement
- Sweat
- Hair
- Muscle contraction
- Interference
What is the name given to the normal rhythm of the heart?
Sinus rhythm
What is meant by ‘sinus rhythm’?
The normal rhythm of the heart
Why does atrial depolaristaion produce a much smaller deflection in an ECG compared to ventricular depolarisation?
Atria have much less muscle compared to the ventricles, so less electrical activity needed to depolarise the muscle.
If electrical activity started at the AVN instead of the SAN, how would the P wave appear in an ECG?
Negative deflection (rather than positive deflection), as depolarisation moving away from electrode.
The muscle in the interventricular septum depolarises in which direction?
From left to right
What part of an ECG should be used to assess heart rhythm?
Rhythm strip
Which lead is used for the rhythm strip of an ECG?
Lead II
What is the constant speed an ECG runs at?
25 mm/s
How many large squares of an ECG corresponds to 1 sec?
5 large squares = 1 sec
How many large squares of an ECG corresponds to 1 min?
300 large squares = 1 min
How can you calculate heart rate from an ECG with a regular rhythm?
HR = 300 / number of large squares between 2 QRS complexes
How can you calculate heart rate from an ECG with an irregular rhythm?
Count number of QRS complexes in 6 sec (30 large squares) and x 10
How do you measure the RR interval?
What is the normal range of an RR interval?
Measure between peaks of R waves
0.6-1.2 secs
If the RR interval is decreased below the normal range, what can you tell about the heart rate?
Heart rate is increased above normal - tachycardic
How do you measure the QRS interval?
What is the normal length?
From start of Q wave to end of S wave
< 3 small boxes, or 0.12 secs
Wide QRS waves indicate that the ventricular depolarisations are not going through the normal purkinje system. List some causes of this:
- Left or Right bundle branch block
- Hyperkalaemia
- Na+-channel blockade
- Pacemaker
How do you measure the PR interval?
What is the normal length?
From start of P wave to start to Q wave
Between 3-5 small boxes, or 0.12 - 0.2 secs
What is indicated by a short PR interval?
Either:
- Atria have been depolarised from area close to AV node
- Abnormally fast conduction from atria to ventricles
What is the diagnosis if PR interval > 5 small squares, but normal P wave and QRS complex?
1st degree heart block
How do you measure the ST segment?
From the end of S wave to start of T wave
Elevated ST segment indicates:
- Acute MI
- Pericarditis
Depressed ST segment indicates:
- Ischaemia
How do you measure the QT interval?
From start of Q wave to end of T wave
List some causes of Long QT syndrome:
Medication - diuretics, anti-arrhythmics, cholesterol-lowerers etc
Hypokalaemia - excessive vomiting/diarrhoea, EDs, thyroid dysfunction
Torsades de pointes is a complication of which heart syndrome?
Long QT syndrome
How does Torsades de pointes lead to sudden syncope?
- Ventricular tachycardia
- Decreased CO
- Decreased blood to brain
- Sudden syncope
How can you diagnose atrial fibrillation from an ECG trace?
- Absent P waves
- Irregularly irregular QRS complexes
Name the 4 types of heart block:
- 1st degree
- Mobitz type 1 2nd degree
- Mobitz type 2 2nd degree
- Complete AV 3rd degree
Which type of heart block is characterised by progressive lengthening of the PR interval (leading to loss of a QRS complex)?
Mobitz type 1 2nd degree
Which type of heart block is characterised by a sudden dropped QRS complex (normal PR interval)?
Mobitz type 2 2nd degree
What type of heart block is characterised by the lack of relationship between the P waves and QRS complexes?
Complete AV 3rd degree
