Flashcards in Identifying some basic disturbances of rhythm Deck (51):
what is a vector
a quantity that has both magnitude and direction
why can't we see the atrial repolarisation as we can see the ventricular repolarisation?
QRS is hiding it. Time wise it will happen in the QRS.
What heart rate is considered bradycardia and tachycardia?
Bradycardia = < 60 bpm
Tachycardia = > 100 bpm
What is the difference between segments and intervals?
Segments are isoelectric regions between two waveforms.
1. PR segment
- pause between atrial and ventricular depolarisation
2. ST segment
- is isoelectric
- any changes in potential during this segment could indicate myocardial infarction or ischaemia
Interval is the time between the start of one wave and the start of the next.
What is the sweep speed of ECG?
What does a 1mm box represent?
How wide is a small square and a large square and what time interval does that represent?
X-axis: 1mm box = 0.04s.
Y-axis: 1mm = 0.1mV
Small Square = 0.04 s (1 mm)
Large Square = 0.2 s (5 mm)
What's the duration and amplitude of a normal P wave?
Duration = < 0.11 s
Amplitude = < 2.5 mm
What is the duration of a normal PR interval?
0.12 - 0.20 s
- If prolonged could show abnormal conduction in the ventricles
What is the duration and amplitude of a normal QRS complex?
Duration = < 0.12 s (<120ms)
Amplitude = < 25 mm
What is the normal range for the cardiac axis?
-30 to + 90
What is the duration and amplitude of a normal Q wave?
Duration = < 0.04 s
Amplitude = < 25% of the total QRS complex
What is the duration of a normal QT interval?
What does a QRS complex with a large amplitude indicate?
what does prolonged PR interval indicate?
Abnormal conduction in the ventricles
what should the ST segment look like?
The ST segment should be isoelectric so any changes in potential during the ST segment could suggest myocardial ischaemia or infarction.
What are the ECG features of sinus tachycardia and what is this?
-It is an abnormally fast resting heart rate.
-Sinus tachycardia comes from the sinus node.
-form of the waves is normal but the rate is fast.
-Abnormally fast resting heart rate
-Atrial and Ventricular Rate = 100- 200 bpm
What are the ECG features of atrial fibrillation and what is this? Include atrial rate and ventricular rate in your answer.
The beat is irregular and the pattern of the irregular heart beat is also irregular.
The duration between the QRS complexes is inconsistent.
ABSENT P WAVES (may get an oscillating baseline)
Irregular ventricular rhythm (duration between QRS varies)
Could be high or normal ventricular rate
QRS complexes are normal
Atrial Rate = 350-600 bpm
Ventricular rate = 100-180 bpm
What is the sinus rhythm (normal)?
- Each p wave is followed by QRS complex (1:1)
- Rate is regular (even R-R intervals) and normal (83 bpm)
- Otherwise unremarkable
What is sinus bradycardia?
- Each P-wave is followed by a QRS wave (1:1)
- Rate is regular (even R-R intervals) and slow (56 bpm)
- Can be healthy, caused by medication or vagal stimulation
What is sinus tachycardia?
- A sinus trachycardia is a fast resting heart rate, originates at the sinus node (pacemaker)
- Each P-wave is followed by a QRS wave (1:1) so no loss of conduction
- Wave form is normal, PR interval is normal
- Rate is regular (even R-R intervals) and fast (107 bpm)
- Atrial and Ventricular Rate = 200 bpm
Usually you can't get a healthy tachycardia
Often a physiological response (i.e. over reactive adrenal gland, hyperactive sympathetic nervous system. )
Loss of blood
What is a sinus arrhythmia?
Each P-wave is followed by a QRS wave
Rate is irregular (variable R-R intervals) and normal-ish (65-100 bpm), heart rate changes depending on where you look on the trace.
R-R interval varies with breathing cycle
R-R interval is one cardiac cycle.
What is atrial fibrillation?
-Oscillating baseline --atria contracting asynchronously, (no isoelectric line)
Rhythm can be irregular and rate may be slow
Turbulent flow pattern increases clot risk
Atria not essential for cardiac cycle
- An AF is a rhythm composed of randomly contracting atria
- The beat is irregular and the pattern of the beat is irregular leading to -> irregular-irregular
- No p wave - wave only occurs when atria contract simultaneously and synchronised
- QRS = normal and no ventricular abnormality
- Variable heart rate and atrial heart rate may be very high while ventricular heart rate is normal
- Atrial rate: 350-600bpm (irregular)
- Ventricular rate: 100-180bpm (normal)
What is atrial flutter?
-Regular saw-toothed pattern in baseline.
-Pattern is regular.
-Ratio is also regular.
-Saw-tooth not always visible in all leads
-No isoelectric line - shows constant atrial activity
-Regular ventricular rhythm
- Nearly every third beat of the atrium conduct down to the ventricles as AV node blocks some depolarising wave from conducting
- Atrial to ventricular beats at a 2:1 ratio, 3:1 ratio or higher (4:1 is common)
- QRS, ST segment and T wave normal
- Atrial rate = 250-350 bpm.
- Ventricular rate = 150 bpm.
What is 1st degree heart block?
- Prolonged PR segment/interval caused by slower AV conduction
- Regular rhythm (1:1 ratio of P waves to QRS complexes)
- Most benign heart block, but a progressive disease of aging
- The effects are fairly asymptomatic as cardiac output isn't really affected.
- Could be caused by disease to the AV node.
What is 2nd degree heart block (Mobitz Type 1)?
- In 2nd degree, SOME beats of the atria do NOT conduct to the ventricles
- Gradual prolongation of the PR interval until beat skipped
- Most p-waves followed by QRS but some P waves are not
- Regularly irregular; caused by diseased AV node
- Also called Wenckebach
- In Mobitz Type 1 - There is a gradual prolongation of the PR interval culminating in a no-contraction (a missed QRS complex).
What is 2nd degree heart block (Mobitz Type 2)?
- Similar to type 1 but there is NO gradual prolongation, just random dropped heartbeats.
- Every other P wave isn't followed by a QRS complex.
-P-waves are regular, but only some are followed by QRS
- Regularly irregular (successes to failures e.g. 2:1)
- This will most likely be symptomatic and treated by implantation of a pacemaker.
- Can rapidly deteriorate into third degree heart block
Each cardiac cycle is different.
What is 3rd degree heart block?
- P-waves are regular, QRS are regular but no relationship
- P waves can be hidden within bigger vectors
- Non-sinus rhythm - back-up pacemaker in action
- AV node is not functioning --> no conduction.
- The ventricles fire on their own as a back-up mechanism.
- P wave and QRS complexes completely dissociated
P waves regular but faster
QRS waves are regular but slower
What is a ventricular tachycardia?
- This has a broad QRS and can be deadly.
- Characterises as a rapid, regular, broad QRS complex pattern.
- P-waves hidden - dissociated atrial rhythm
- Rate is regular and fast (100-200bpm)
- At high risk of deteriorating into fibrillation (cardiac arrest)
- Shockable rhythm - defibrillators widely used
-Do still talk.
-Faster than they can fill
-different heart rate when looking at P wave and QRS complexes.
What is ventricular fibrillation?
- Broad, irregular QRS complexes that are void of any pattern.
- Irregular in terms of amplitude and rhythm.
- As the QRS is irregular à problem in ventricles.
- Heart rate irregular and 250bpm and above
- Heart unable to generate an output
- Shockable rhythm - defibrillators widely used
-Do not tend to talk.
-At high risk of deteriorating into fibrillation (cardiac arrest
What is ST elevation?
P waves visible and always followed by QRS
Rhythm is regular and rate is normal (85 bpm
ST-segment is elevated >2mm above the isoelectric line
Caused by infarction (tissue death caused by hypoperfusion
How is atrial fibrillation different to atrial flutter?
Atrial flutter has a regular ventricular rhythm
What are the three types of atrioventricular nodal block and how do they vary?
Broad QRS complexes that are VOID OF ANY PATTERN
1st degree = prolonged PR interval
2nd degree (Mobitz type 1 and type 2) = some conduction gets there but it's slow
3rd degree = complete heart block
What is an ECG feature of grade 1 AVN block?
Prolonged PR interval
What is the difference between Mobitz type 1 and Mobitz type 2 atrioventricular nodal block?
2nd degree block = some of the beats from the atria do NOT reach the ventricles
Mobitz type I = gradual prolongation of the PR interval culminating in a dropped beat
Mobitz type II = fixed PR interval and then a dropped beat (you do NOT see gradually prolonging of the PR interval)
What is the ECG feature of 3rd degree atrioventricular nodal block?
There is NO conduction from atria to ventricles
ECG shows COMPLETE DISSOCIATION between QRS complexes and P waves
Ventricles fire on their own as a protective mechanism
What is the main ECG feature of bundle branch blocks?
QRS complex WIDENS
It takes longer to depolarise the ventricles
What are the ECG features of ventricular tachyarrhythmia?
Rapid, regular, broad QRS complex pattern
What are the ECG features of ventricular fibrillation?
Broad QRS complexes that are VOID OF ANY PATTERN
What are the 3 broad types of abnormalities that can be detected on an ECG?
Conduction abnormalities: if something that isn't passing through part of the cardiac muscle, or part ha is supposed to be insulated isn't, ECG can spot it.
Structural abnormalities: if cardiac axis is in the normal range, then can assume the impulse is going in the normal direction.
But if you have more muscle in the base, then you get axis deviation.
Left: left axis deviation
Perfusion abnormality; narrowing or blockage of coronary artery, causing ischaemia of the cells.
what is cardiac axis?
is the net direction of depolarisation.
Normal range: from -30 to -90.
What are the layers of the heart?
Endocardium: blood facing part of the heart
Myocardium: big muscular part
Epicardium: on the outside
What is the systematic approach of looking at ECG?
1. Look at rate and rhythm.
2. P-wave and PR interval:how long does it take the wave of excitation to get through the atrial myocardium.
3. QRS duration: compare to the 120 ms it should be
4. Calculate the QRS axis using tan-1
5. ST segment, this is the bit of the isoelectric line between the S ave and the T wave, looking for its height
6. QT interval
How to work out heart rate?
Do 300 divide by the number of big squares in one cardiac cycle, do not get confused with small squares that you can also get.
R-R interval divide by 60.
How to tell if the ECG is right/left axis deviated not a rule of thumb?
1. Look at lead I
2. Look at lead II
3. Lead I is positive- QRS pointing upwards
4. Lead II is negative- QRS pointing downwards
5. Therefore we can say that they are leaving the middle of the paper, SO left axis deviation.
Right axis deviation:
Lead I was negative
Lead II positive
returning to the paper .
What is the clinical relevance of an ECG?
- Cheap, reliable and fast way to access heart function
- Can evaluate conduction system and structure
What are examples of sub-ventricular arrhythmias?
Sinus rhythms - normal (sinus), fast (tachy-), slow (brady-) or linked with breathing (sinus arrhythmia)
Atrial fibrillation - oscillating baseline, high risk of clots managed with oral anticoagulation
Atrial flutter - sawtooth pattern often occurring in a 2:1 or 3:1 ratio of P to QRS
What are examples of junctional arrhythmias?
First degree block - PR interval longer than normal, due to slower conduction
Second degree block (I) - PR interval gradually widens until a beat is missed
Second degree block (II) - P waves are regular, but some beats not conducted (e.g. 2:1 is two beats conducted then one missed)
Third degree block - atria and ventricles beat asynchronously - HR at non-sinus rhythm
What are examples of ventricular arrhythmias?
Ventricular tachycardia - very fast ventricular rate, can rapidly progress and needs defibrillation
Ventricular fibrillation - cardiac arrest; asynchronous ventricular contract, no output, needs defibrillation
ST elevation and depression - >2 mm deviation up or down indicates infarction or ischaemia, respectively
What systematic method should be used when performing the analysis of an ECG waveform?
1. Identify and confirm the correct recording (e.g. name/DOB)
2. Identify the leads
3. Check the calibration and speed of the paper
- Standard speed is 25mm/s
- 10mm vertical deflection is 1mV of potential measured
4. Identify the rate and rhythm
- Determine the regularity of the rhythm
e.g. regular rhythm but fast (tachycardia) or slow (bradycardia)
e.g. irregular - determine type of irregularity
- Determine cardiac rhythm
e.g. sinus rhythm (normal cardiac rhythm)
5. Look at the QRS axis. This can tell you:
- Orientation in the chest - horizontal in obese patients, otherwise vertical.
- Thickness of ventricular muscle - Left-shifted axis in left ventricular hypertrophy and right-shifted axis in right ventricular hypertrophy.
- Abnormalities in direction of depolarisation - Disease in conduction pathways.
6. Look at the p-wave (atrial depolarisation)
- Determine amplitude and duration
- E.g. long p wave, often with two peaks suggest left atrial enlargement
7. Look at the PR interval - Time from atrial --> ventricular depolarisation.
- Time from atrial depolarisation to ventricular depolarisation.
- e.g. long PR interval but still with QRS following p wave could be first-degree heart block due to delayed conduction through AV node.
8. Look at QRS complex
- Determine amplitude of QRS complex
- High amplitude predicts left ventricular hypertrophy
9. Determine QRS axis
10. Determine position of ST segment
- e.g. if ST segment lies below isoelectric line, patient could have ST depression
11. Calculate QT interval
- Length of time between onset of Q wave and end of T wave reduces as heart rate increases.
- e.g. Interval can be increased by certain drugs
12. Look at T wave
- Amplitude and duration of T wave and whether it is upright or inverted.
- e.g. Inverted T wave is a sign of a previous MI
What is a heart block (AV Nodal Block) and its types?
- A problem with the conduction system which results in delayed conduction through the heart landing to Bradu-arrythmias and heart block
1. 1st degree - prolonged PR interval
2. 2nd degree - conduction gets through but it is slow
- Mobitz Type I - Wenckeback
- Mobitz Type 2
3. 3rd degree - complete heart block, no conduction to ventricles