ECG review Flashcards
How is heart rate on an ECG determined?
Look at the RR intervals
How long should a p wave last?
no more than 0.08 seconds
What is the normal duration of a PR interval? What could a prolonged interval indicate?
0.12-0.2 seconds
Prolonged = heart block
What is the normal duration of a QRS complex?
- 06-0.1 seconds
- usually <0.12 seconds
What is the normal duration of a QT interval? What could a prolonged interval indicate?
=0.4 seconds (for a HR ~70bpm)
Prolonged = ventricular arrhythmia
What are the different classes for anti-arrhythmic drugs?
Class I: Na+ channel blockers
Class II: Beta blockers
Class III: K+ channel blockers
Class IV: Ca2+ channel blockers
Give examples of Na+ channel blockers/Class I anti-arrhythmics?
- Quinidine
- Procainamide
- Lidocaine
- Phenytoin
- Flecainide
- Propafenone
Give examples of beta blockers/Class II anti-arrhythmics?
Metoprolol
Propanolol
Give examples of K+ channel blockers/Class III anti-arrhythmics?
Amiodarone
Sotalol
Give examples of Ca2+ channel blockers/Class IV anti-arrhythmics?
Verapamil
Diltiazem
Describe a normal sinus rhythm.
4-5 R waves (in 15 squares)
Regular RR intervals
Everything of normal duration
Describe how sinus bradycardia would appear on ECG. When does sinus bradycardia usually occur?
Less than 60 bpm - ~3 R waves in 15 squares Occurs: - in athletic people - drug abusers - hypoglycaemia - brain injury
Describe how sinus tachycardia would appear on ECG. When does sinus tachycardia usually occur?
More than 100 bpm - ~6 R waves in 15 squares Occurs: - stress - fright - illness - exercise
Describe how ventricular tachycardia would appear on ECG. When does ventricular tachycardia usually occur?
Rate is high (180-190bpm) QRS is prolonged No P wave Occurs: - abnormal tissues in ventricles - poor CO = cardiac arrest
(looks like little fishing sticking their heads out of water)
Describe how ventricular fibrillation would appear on ECG. When does ventricular fibrillation usually occur?
Irregular rhythm rate ~300 bpm Occurs: - previous heart attacks - myocardial damage
How does first degree heart block appear on an ECG? When does this usually occur?
PR interval has fixed duration of >200 ms
Rate is regular
Occurs:
- trained athletes
What is the difference between type 1 and type 2 second degree heart block? When does this usually occur?
Type 1: PR interval progressively longer
- resets once QRS complex doesn’t follow P
Type 2: ECG irregularly irregular
An expected QRS complex is missed
Occurs:
- underlying heart condition (CHD)
How does third degree heart block appear on an ECG?
P waves before or after QRS
Bradycardia is present
How does atrial fibrillation appear on an ECG?
Rate: 100-160 bpm
Rhythm: irregularly irregular
P waves: not visible
PR: immeasurable
How does atrial flutter appear on an ECG?
Rate: ~110 bpm
Rhythm: regular
P wave: replaced by multiple flutter (F) waves –> rate is ~300 bpm
How does junctional rhythm appear on an ECG? What is junctional rhythm?
Bradycardia
Rate: 40-60 bpm
P wave: Normally absent, but if visible in 1:1 ratio with QRS complex
PR: variable
Junctional rhythm = block in conduction pathway to atria (damage to SA node)
How does supra ventricular tachycardia appear on an ECG? What is the most common type of supra ventricular tachycardia?
Rate: 140-220 bpm
P wave: absent/obscured by T wave
Most common type = AV node re-entrant tachycardia
- QRS is regular but narrow (<0.12s)
- no distinct P wave or retrograde P wave
How does bundle branch block appear on an ECG?
Widening of QRS complex
May see notched/double R wave
Everything else is normal
What can cause ST segment depression
Coronary ischaemia or hypokalaemia
How does depressed ST segment appear on an ECG?
must have new ST elevation in 2 or more adjacent ECG leads
Rate: ~80 bpm
Everything else normal
Is a significantly visible Q wave pathological or physiological?
Pathological
Q wave is usually not seen or is not usually significant
If it is enlarged this is a sign of damage to inter ventricular septum
–> may be due to previous AMI/combined with STEMI
Apart form heart block, what else can a prolonged PR interval be associated with?
- hypokalaemia
- acute rheumatic fever
- carditis
What is indicated by a long QRS duration?
ventricular muscle not contracting normally –> taking longer to depolarise
(normal = synchronisation of the contraction of the ventricular muscle)
In terms of QRS complex and T wave, when is an ECG signal seen?
When there is a difference in the depolarisation of the endocardial and epicardial layers of ventricular muscle
- endocardial depolarises first
- epicardial depolarises slightly later - action potential is also shorter
- -> when it repolarises the T wave appears
Which layer of ventricular muscle is more susceptible to the effects of ischaemia - endocardial or epicardial? What is the impact of this?
Endocardial
–> reduces the duration of the endocardial action potential (shorter than epicardial) giving an inverted T wave
