ECG Review Flashcards
what is the beginning of the ST segments called
J point sometimes
Name the steps in the ECG protocol
- What is heart rate? (look at RR intervals)
- What is heart rhythm? : (Is rate regular or irregular? )
- Can you see a P wave? Is there one P wave before each QRS complex? Is the P wave of normal duration?
- Is the PR interval of normal duration ?
- Is the QRS complex of normal duration?
- Is the ST interval elevated or depressed? Is the QT interval normal? Is the T wave inverted?
how do you work out the heart rate
- Count the number of R waves in 30 oarge grid sqautes and multiply by 10
- 1 sqaure = 0.04ms
how do you work out the rhythm
- Determined by the interval between the RR waves
- Check if all the RR intervals are the same
what does it indicate if there is variable RR intervals
- Variable RR intervals indicate some kind of heart block
what lead is P wave always positive in sinus rhythm
- P wave is always positive in lead II during sinus rhythm
describe how long the p wave should be
- P wave should be not more than about 2 small squares long (0.08s or 80ms)
- 80-120ms
what changes to an ECG are shown if the atria becomes enlarged
- If an Atria becomes enlarged its contribution to the P wave will be enhanced,
- enlargement of the left and right atria causes typical P wave changes in lead II and lead VI
what does the PR interval tell us
- Tells us about the time it takes for the conduction from the atria through the AV node to the ventricles
how long should the PR interval be
120-200 ms (three to five small squares).
if a PR interval is over 200ms what does it mean
- A PR interval of over 200 ms usually indicates a form of heart block, usually due to slow conduction through the AV node.
- Prolongation can also be associated with hypokalemia, acute rheumatic fever, or carditis.
What is the QRS complex
- The QRS complex is measured from the start of Q wave to finish of S wave ( Q wave often absent in normal ECG)
what does the QRS complex show
- Contraction starts in the apex – this is the upstroke of the R wave
- Down stroke of the R wave is when the contraction reaches the start of the ventrciles
what is QRS complex an indication of
- The QRS complex or interval is an indicator of the synchronisation of the contraction of the ventricular muscle
what does a long QRS complex indicate
- A long QRS duration indicates that ventricular depolarization is slow, or that part of the ventricular muscle is not contracting normally
how long is the QRS complex supposed to be
- it should be less than 120ms in duration (3 small sqaures)
what does a flat ST segment indicate
- it indicates that all the ventricles are contracting together
what is the ST measured to
measured from the start of the Q wave to finish of the Wave
- measured to the end of the T wave
what does the QT/ST interval depend on
QT interval depends on heart rate
what is the heart rate adjusted QT interval called
- the corrected QT interval - (QTc interval)
what is a long QTc interval indiciative of
- a long QTc interval indicates an increased risk of ventricular arrhythmias
what depolarises first the endocardial or epicardial layer
- The inner (endocardial) layer of ventricular muscle which includes the papillary muscle depolarises first . (This pulls the AV valves closed).
- The outer (epicardial) layer of muscle depolarises slightly later
when the endocardial muscle contracts what does it pull close
- it pulls the AV valves closed
what is the T wave due to
T wave is due to the timing of the repolarisation of different parts of the ventricles
what can cause an inverted T wave
- The inner (endocardial) layer of ventricular muscle is more susceptible to the effects of ischaemia; this reduces the duration of the endocardial action potential
- If the outer (epicardial ) muscle layer has a normal duration we can get an inverted T wave as the endocardial AP is now shorter than the epicardial
what are inverted T waves associated with
- Inverted T waves can be benign in children but in adults they are often associated with..
- coronary artery disease
- pulmonary damage such as pulmonary embolism
what is the definition of sinus bradycardia
- A heart rate less than 60 beats per minute
describe sinus bradycardia
- rhythm
- QRS duration
- P wave
- PR interval
Rhythm - Regular QRS Duration - Normal P Wave - Visible before each QRS complex P Wave – normal duration P-R Interval - Normal duration
what is sinus bradycardia seen
- it is usually benign and often seen in patients on beta blockers
- may be due to increased vagal tone from drug abuse
- hypoglycaemia
- brain injury
- athletes
define sinus tachycardia
high More than 100 beats per minute
describe sinus tachycardia
- rhythm
- QRS duration
- P wave
- PR interval
- Rhythm - Regular
- QRS Duration - Normal
- P Wave - Visible before each QRS complex
- P Wave – normal duration
- P-R Interval - Normal
what does sinus tachycardia originate form
- it originates from the SA node
what are the causes of sinus tachycardia
- stress, fright, illness, exercise
- not abnormal if it is triggered to response of illness or injury
- but I their is no apparent trigger than medication may be required to suppress the rhythm
describe ventricular tachycardia
- rate
- rhythm
- QRS duration
- P wave
- Rate - 180-190 Beats per minute
- Rhythm - Regular
- QRS Duration - Prolonged
- P Wave - Not visible
What does ventricular tachycardia result from
- Results from abnormal tissues in the ventricles generating a rapid and irregular heart rhythm and patient is at risk of cardiac output
what is the difference between ventricular tachycardia and ventricular fibrillation
- Ventricular tachycardia is not the same as ventricular fibrillation in VT the rhythm and amplitude of the QRS complex is regular it is just faster than normal
describe ventricular fibrillation
- rate
- rhythm
- QRS duration
- P wave
- Rhythm - Irregular
- Rate - 300+, disorganised
- QRS Duration - Not recognisable
- P Wave - Not seen
what causes ventricular fibrillation
Disorganised electrical signals cause the ventricles to quiver instead of contract in a rhythmic fashion
when does ventricular fibrillation occur
- This condition may occur during or after a myocardial infarct.
- Due to the asynchronous contraction there is little or no cardiac output.
- IMMEDIATE TREATEMTN BY DEFIBRILLATION IS VITAL
describe the features of first degree heart block
- PR interval is a fixed constant duration greater than 200ms
- The rate is regular
- Condition rarely causes any problems by itself and often trained atheletes can be seen to have it
describe the features of second degree heartblock type 1 wekebach
- PR interval gets progressively longer until the P wave is not followed by a QRS
- After this the system resets and repeats
describe the features of second degree heart block type 2
- P wave is regular but AV node randomly fails to respond to some atrial impulses
- Ventricular rate is irregularly irregular
- Do an angiogram see if there is a blockage
describe the features of third degree heart block
- P waves present but unsynchronised with QRS complex. The ventricles generate their own signal from a focus somewhere within the ventricle.
- These ventricular ‘escape’ beats are usually slow, so marked bradycardia present
- There is no relationship between PR and QRS complex
what causes Atrial fibrillation
- In AF many separate sites within the atria, not just the SAN, are generating electrical impulses, leading to irregular conduction of impulses to the ventricles
what symptoms is Atrial fibrillation associated with
It may cause no symptoms, but it is often associated with…
- palpitations
- fainting
- chest pain
- congestive heart failure
who is Atrial fibrillation common in
the elderly
describe Atrial fibrillation
- rate
- rhythm
- QRS duration
- P wave
- PR interval
- Rate - usually 100-160 beats per minute but slower if on medication
- Rhythm - Irregularly irregular
- QRS Duration - Usually normal
- P Wave - Not distinguishable
- P-R Interval - Not measurable
why can you get tachycardia with atrial fibrillation
- Can also get tachycardia associated with this, this reduces the stroke volume
- It is a consequence of the poor cardiac output caused by the atrial fibrillation
describe what causes atrial flutter
- Re-excitation of electrical impulses in the atria cause a high frequency bombardment of AV node (~300 bpm) leading to a high but regular heart rhythm
describe atrial flutter
- rate
- rhythm
- QRS duration
- P wave
- PR interval
- Rate - Around 110 beats per minute
- Rhythm - Regular
- QRS Duration - Usually normal
- P Wave - Replaced with multiple F (flutter) waves,
- P Wave rate - 300 beats per minute
- P-R Interval - Not measurable
describe the difference between atrial flutter and atrial fibrillation
Atrial fibribllation
- A ‘firework display’ of separate atrial pacemakers going off like a bunch of rockets
Atrial flutter
- One atrial pacemaker generating a re-entrant or circus excitation going round and round at a fast rate
what causes junctional rhythm
- In junctional rhythm there is damage to the sinoatrial node or a block in the conduction pathway in the atria
- When this happens, the atrioventricular node takes over as the pacemaker
what are the features of junctional rhythm
- bradycardia
- normal QRS complex
- P wave will normally be absent or inverted
describe junctional rhythm
- rate
- rhythm
- QRS duration
- P wave
- PR interval
- Rate - 40-60 Beats per minute
- Rhythm - Regular
- QRS Duration - Normal
- P Wave - Ratio 1:1 if visible. Inverted in lead II
- P Wave rate - Same as QRS rate
- P-R Interval - Variable
describe supraventricular tachycardia
- rate
- rhythm
- QRS duration
- P wave
- PR interval
- Rate - 140-220 beats per minute
- Rhythm - Regular
- QRS Duration - Usually normal
- P Wave - Absent or buried in preceding T wave
- P-R Interval –Depends on site of supraventricular pacemaker
what causes supra ventricular tachycardia
There is a high frequency of impulses generated at or near the AV node (which override those from the SA node) .
- The effect is very similar to atrial flutter:SVT can occur in all age groups
name the most common type of regular supra ventricular tachycardia
- AV nodal reentrant tachycardia (AVNRT)
when does - AV nodal reentrant tachycardia (AVNRT) occur
- AVNRT occurs when a re-entry circuit forms within or just next to the atrioventricular node
- This means that the atrial impulses instead of dying away after activating the AV node go around ‘in a circle’ and then activate the AV node again after a short delay.
what is the main symptoms of AVNRT
palpitations
- It is more common in women than men (approximately 75% of cases occur in females due to oestrogen hormone
describe bundle branch block
- rate
- rhythm
- QRS duration
- P wave
- PR interval
- Rate - Normal
- Rhythm – Regular
- QRS Duration - Prolonged
- P Wave -normal
- P Wave rate - Normal and same as QRS rate
- P-R Interval – Normal
what causes bundle branch block
- Abnormal conduction through the bundle branches will cause a depolarization delay through the ventricular muscle, the ventricles wont contract at the same time, this delay shows as a widening of the QRS complex
- . Right Bundle Branch Block (RBBB) indicates problems in the right side of the heart.
- Whereas Left Bundle Branch Block (LBBB) is an indication of heart disease.
what does the ST segment represents
ST segment represents the time when all ventricular tissue is fully depolarised
what should the duration of the ST segments be
80-120ms (same as QRS complex)
what can a depression of ST segments mean
- Depression ST segements can indicate coronary ischaemia or hypokalaemia
what is a STEMI
- STEMI – ST Elevation associated with an MI
- STEMI is a form of MI where the ST interval is elevated above normal
what does a person need to qualify as having a STEMI
For a person to qualify as having a STEMI, the ECG must show new ST elevation in two or more adjacent ECG leads.
describe a STEMI
- rate
- rhythm
- QRS duration
- P wave
- PR interval
- Rate - 80 Beats per minute
- Rhythm - Regular
- QRS Duration - Normal
- P Wave - Normal
What is an NSTEMI
Some people have an MI without ST elevation. This is called NSTEMI.
- It is usually a less serious form where there is cardiac ischaemia but not necessarily regions of cardiac muscle death
