Electrocardiography Flashcards
What is the clinical relevance of the ECG?
Conduction abnormalities
Structural abnormalities
Perfusion abnormalities
What are the advantages of ECGs?
Relatively cheap and easy to undertake
Reproducible between people & centres
Quick turnaround on results/report
What is a vector?
‘a quantity that has both magnitude and direction’
What happens if the wave of excitation travels toward the negative electrode?
Downward deflections are towards the anode (-)
What happens if the wave of excitation travels toward the positive electrode?
Upward deflections are towards the cathode (+)
What does the isoelectric line represent?
represents no net change in voltage. i.e. vectors are perpendicular to the lead.
What does the steepness of the line relate to?
Steepness of line denotes the ‘velocity’ of action potential
What does the width of the line relate to?
Width of the deflection denotes the ‘duration’ of the event
What is the P wave?
The electrical signal that stimulates contraction of the atria (atrial systole)
What is the QRS complex?
The electrical signal that stimulates contraction of the ventricles (ventricular systole)
What is the T wave?
The electrical signal that signifies relaxation of the ventricles
What comprises the SAN?
Autorhythmic myocytes
Small amount of muscle that points more positive than negative
What does the action of the SAN show on an ECG?
Deflection is wide (slow)
Not very high (thin muscle)
Positive
What does the action of the AVN show on an ECG?
AVN depolarisation
Isoelectric ECG
Slow signal transduction
Protective
What does the action of the bundle branches show on an ECG?
Sharp but small downward spike
What does the action of the purkinje fibres show on an ECG?
QRS peak
and upward peak
Where do you place the leads?
Lead I (one L) Right Arm to Left Arm
Lead II (two L’s) Right Arm to Left Leg
Lead III (three L’s) Left Arm to Left Leg
What is the rule of reading for the leads?
English is read left to right and top to bottom.
Polarity does that too.
Drawn as a triangle and reading left to right and top to bottom the first electrode of each pair you reach is the anode (-ve
Where is the V1 electrode placed?
Right sternal border
In the 4th intercostal space
Where is the V2 electrode placed?
Left sternal border
In the 4th intercostal space
Where is the V3 electrode placed?
Halfway between V2 and V4
Where is the V4 electrode placed?
Mid-clavicular line
In the 5th intercostal space
Where is the V5 electrode placed?
Anterior axillary line
at the level of V4
Where is the V6 electrode placed?
Mid-axillary line
at the level of V4
What does each big square represent?
- 2s
0. 5mV
What does each little square represent?
- 04s
0. 1mV
What are the three main coronary arteris?
Left circumflex
Left anterior descending
Right coronary artery
What are normal values for R-R interval?
0.6-1.2 seconds
What is normal for the duration of the P wave?
80ms
3 small squares
What is normal for the P-R interval?
120-200ms
5 small squares
What is normal for duration of the QRS complex?
<120 ms
What is normal for duration of the T-wave?
420 ms
What is considered a normal heart rate?
60-100 bpm
What is the ECG reporting procedure?
Is it the correct recording?
Review the signal quality and leads?
Verify the voltage and paper speed?
Review the
What is the ECG reporting procedure?
Is it the correct recording?
Review the signal quality and leads?
Verify the voltage and paper speed?
Review the patient background if available
Can you defibrillate someone in asystole?
Not a shockable rhythm
What is sinus rhythm?
Each P-wave is followed by a QRS wave (1:1)
Rate is regular (even R-R intervals
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?
Each P-wave is followed by a QRS wave (1:1)
Rate is regular (even R-R intervals) and fast (107 bpm)
Often a physiological response (i.e. secondary)
What is sinus arrhythmia?
Each P-wave is followed by a QRS wave
Rate is irregular (variable R-R intervals) and normal-ish (65-100 bpm)
R-R interval varies with breathing cycle
What is atrial fibrilation?
Oscillating baseline – atria contracting asynchronously
Rhythm can be irregular and rate may be slow
Turbulent flow pattern increases clot risk
Atria not essential for cardiac cycle
What is atrial flutter?
Regular saw-tooth pattern in baseline (II, III, aVF)
Atrial to ventricular beats at a 2:1 ratio, 3:1 ratio or higher
Saw-tooth not always visible in all leads
What are the features of first degree heart block?
Prolonged ST 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 ageing
What are the two types of second degree heart block?
Mobitz I
Mobitz II
What are the features of Mobitz I?
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 a diseased AV node
Also called Wenckebach
What are the features of Mobtiz II?
P-waves are regular, but only some are followed by QRS
No P-R prolongation
Regularly irregular: successes to failures (e.g. 2:1) or random
Can rapidly deteriorate into third degree heart block
What are the features of third degree heart block?
P-waves are regular, QRS are regular, but no relationship
P waves can be hidden within bigger vectors
A truly non-sinus rhythm – back-up pacemaker in action
What are the features of ventricular tachycardia?
P-waves hidden – dissociated atrial rhythm
Rate is regular and fast (100-200 bpm)
At high risk of deteriorating into fibrillation (cardiac arrest)
Shockable rhythm – defibrillators widely available
What are the features of ventricular fibrillation?
Heart rate irregular and 250 bpm and above
Heart unable to generate an output
Shockable rhythm – defibrillators widely available
What are the features of 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)
What are the features of ST depression?
P waves visible and always followed by QRS
Rhythm is regular and rate is normal (95 bpm)
ST-segment is depressed >2mm below the isoelectric line
Caused by myocardial ischaemia (coronary insufficiency)
What does aVf stand for?
Augmented vector foot
What does aVR and aVL stand for?
Augmented vector Left/Right
How does a persons build influence their normal cardiac axis?
Shorter, stockier - normal axis will be more left axis deviate
Taller, leaner - normal axis will be more right axis deviated
What do you need to work out cardiac axis
Two leads 90 degrees apart
What does SOCRATES stand for?
Site Onset Character Radiation Associated symptoms Time course Exacerbating and Relieving factors Severity
What question might you ask when taking a pain history?
Site: Where is the pain?
Onset: When did they pain start? Was is sudden or gradual?
Character: What is the pain like? An ache? Stabbing?
Radiation: Does the move/spread/radiate anywhere?
Associations: Are there any other signs or symptoms that come with the pain?
Time course: Does the pain follow any pattern in when it presents?
Exacerbating/Relieving factors: Does anything make the pain better or worse?
Severity: How bad is the pain?
When are ECGs most useful?
When you have ECGs over time
e.g. 5 years ago
Current
What are the three classifications of chest pain?
Typical chest pain
Atypical chest pain
Non-cardiac
How do you classify chest pain?
Three questions
All three yes = typical
2 yes and 1 no = atypical
1 yes and 2 no = non-cardiac
What are the three questions you ask when classifying chest pain?
Is it retrosternal?
Is it worsened by exertion?
Is it relieved by rest or glyceryl trinitrate?
What is a CABG?
Surgically open up the chest. Take a vein from another part of the body and graft it so it reroutes the obstruction or creates a new perfusion pathway.
What is balloon angioplasty?
Balloon into leg and blow it up- leave it or erect a drug alluting stent to deliver vascodilators
What are p-wave problems?
Absent Inverted BIfid (left atrial dilation) Tall (P pulmonale, right atrial dilation) Sawtooth baseline
What can be wrong with a PR interval?
Prolonged Shortened Delta wave (shorted sloped PR interval) - WPW
What are some normal features of QRS complexes?
Should be narrow < 0.12s Not too tall Negative in V1+V2 V3+V4 transition point Tall QRS in V5+V6
What can be wrong with the QRS complex?
Widened Short Alternating size (electrical alternans) Absent (cardiac arrest) Negative even V5+V6 To big (hypertrophy)
What is the J point?
When the QRS becomes the ST segment
Should be isoelectric
What does an osborn wave mean?
Hypothermia
What is the ST segment complex?
Bit between QRS complex and T-wave
Should be isoelectric
What is a normal t-wave?
Should be positive in all leads except aVR and V1
What are t-wave problems?
Inverted t-waves
Biphasic t-waves
What is a U-wave?
Pathological
Waveform after the t-wave
Young, fit, athletic pts usually
Causes e.g. hyperthyroidism, hyper/hypokalaemia
What can go wrong with QT interval?
Shortened
Prolonged
What are the main features of AF?
Irregularly irregular rhythm
Absent p-waves
QRS complexes are narrow
Baseline is not narrow
What are the main features of atrial flutter?
Sawtooth baseline Regularly irregular rhythm Absent p waves HR of around 300 Narrow QRS complexes 2:1, 3:1 etc.
What is a supraventricular tachycardia?
Any tachy that starts above bundle of His
Look out for retrograde p waves after QRS
What are the features of 1st degree heart block?
Prolonged PR interval
Not necessarily a sign of pathology
Classically fit, young woman
What are the features of 2nd degree heart block? Aka Mobitz type I or Wenckenach phenomenon
Irregularly irregular rhythm
Progressively prolonger PR intervals
Occasional dropped QRS
Usually benign
What are the features of Mobitz type II?
PR interval is constant when QRS is present
But some p-waves are not followed by QRS
Bradycardia
Pathological: Damage to conduction system below AV node
What are the features of 3rd degree heart block?
Complete cessation of AV conduction
P waves and QRS complexes independent
QRS can be broad or narrow
What are the main features of wolff parkinson white?
Accessory pathway from atria to ventricles
Short PR intervals
Broad QRS complex with slurring of start (delta wave)
What are the ECG changes for pericarditis?
Widespread changes
What is really dangerous in WPW?
AF and flutter Nothing to slow down the aberrant pathway Can go into VF Need cardiovert Don't give AV node blocking drugs
What is ventricular fibrillation?
Incompatible with life Shockable ACLS Rapid, broad complexes Complexes start big and gets smaller Chaotic Pulseless
What is ventricular tachycardia?
Monomorphic is most common
Fast HR
Very broad, consisten ventricular complexes
Loss of other features
Sometime ocassional normal cycles - capture beat
Seen in structural heart disease e.g. prev MI
What are the main features of LBBB?
WiLLiaM or ViLheM
V1 and V6
Damage to left bundle branch
Broad QRS
Deep S wave in V1
Notched R wave in V6
Cannot interpret further - other abnormalities won’t be seen
Concerned about new onset MI
What are the main features of RBBB?
MaRRoW/ MaRiNe Broad QRS RSR' in V1 Wide downstroke slurred S wave in V6 V1-3 ST depression
What are the features of torsades de pointes?
Type of polymorphic VT
Different morphologies throughout the trace
Broad QRS complexed
Calcium abnormalities likely cause of prolonged QT
Changing amplitudes beat to beat
Twisting ‘bigger’ then ‘smaller’ appearance
What is the management for torsades?
IV Magnesium
What is the natural history of a STEMI in terms of ECG changes?
Hyperacute t-waves (mins)
ST elevation (0-12 hours)
Q-wave develops (1-12 hours)
ST elevation with T-eave inversion (2-5 days)
When should you be careful about giving nitrates?
RCA infarcts
What is suggestive of a posterior MI?
Reciprocal horizontal ST depression in V1-3
No posterior leads so we cannot see the ST elevation there
What are the ECG features of a NSTEMI?
Sub total occlusion
Widespread ST changes
and t-wave inversion
What ECG changes are seen in pericarditis?
Inflammation of pericardium
Saddle shaped ST elevation
PR depressions
Maybe tachy
What ECG changes are seen in hyperkalaemia?
Tented t-waves
Tachycardia
What diagnosis is associated with U waves?
Hypokalaemia
T-wave inversion
What is the difference between PR interval and segment?
Interval includes the p-wave
What should you tell the patient before doing an ECG?
Might need to shave
Chaperone
Stickers might be cold
How would you report an ECG?
This is a 12 lead ECG for X, DOB, date and time
Presenting complaint
The trace is calibrated at speed 25mm/sec and deflection of 1cm/1mV
Rate, rhythm, axis
Go through cardiac cycle
Abnormalities
How do you work out rate on an ECG?
Total number of complexes in 10s x 6
What are causes of left axis deviation?
Disease of conduction
e.g. WPW, Inferior MI, Hyperkalaemia
What are causes of right axis deviation?
Extra muscle bulk
e.g pulmonary HTN, PE
Normal in tall, thin adults
When do you get broad QRS complexes?
Problem in ventricles and conductions e.g. VT or VF
When do you get narrow QRS complexes?
Supra-ventricular
e.g. AF, A Flutter pr SVT
What are features of SVT?
No p-waves
Regular QRS
Fast
What is monomorphic VT?
All beats look the same
What would you see in RBBB?
rSR’ in V1
qRs in V6
What would you see in LBBB?
rS in V1
R in V^
