ECG Flashcards
What does the P wave on an ECG represent?
Atrial depolarisation. Duration is less than 0.12s.
What does the QRS complex on an ECG represent?
Ventricular depolarisation. Duration is 0.08-0.1s.
What does the T wave on an ECG represent?
Ventricular repolarisation.
What might an elevated ST segment be associated with?
MI
ECG: where would you place lead 1?
Right arm (-ve) to left arm (+ve).
ECG: where would you place lead 2?
Right arm (-ve) to left leg (+ve).
ECG: where would you place lead 3?
Left arm (-ve) to left leg (+ve).
Eindhovens triangle
An imaginary formation of the 3 limb leads in a triangle shape.
ECG: where would you place lead aVR?
Left arm and left leg (-ve) to right arm (+ve).
ECG: where would you place lead aVF?
Right arm and left arm (-ve) to left leg (+ve).
ECG: where would you place lead aVL?
Right arm and left leg (-ve) to left arm (+ve).
ECG chest leads: In which intercostal space would you place V1 and V2? (Precordial leads)
The 4th intercostal space. V1 is right of the sternum and V2 in left.
ECG chest leads: In which intercostal space would you place V3-V6. (Precordial leads)
The 5th intercostal space. V3 is left of the sternum, V4 is in the mid-clavicular line, V5 is left of V4 and V6 is under the left arm.
What is an ECG?
Representation of electrical events at cardiac cycle
What can an ECG identify?
Arrhythmias
Myocardial ischemia and infarction
Pericarditis
Chamber hypertrophy
Drug toxicity
SA node
Dominant pacemaker with an intrinsic rate of 60-100 bpm
AV node
Back up pacemaker with an intrinsic rate of 40- 60 bpm
Allows for delay
Ventricular cells
Back up pacemaker with an intrinsic rate of 20-45 bpm
If electrical impulse travels towards electrodes what does it produce?
Upright positive deflection
What is the flow of impulse condition?
SA node > AV node > Bundle of His > bundle branches > Purkinje fibres
PR interval
Atrial depolarisation + delay in AV junction
Delay allows time for atria to contract before ventricles
Normal ECG
Look at slide 23 of Normal ECG’s
Horizontally on an ECG what is one small box worth?
0.04s
Horizontally on an ECG what is one large box worth?
0.2s
Vertically on an ECG what is one large box worth?
0.5mV
What does an ECG measure?
Measuring the difference in electrical points between 2 points
What is a bipolar lead?
2 Different points on the body
What are unipolar leads?
One point on the body and a virtual reference point with zero electrical potential, located in the center of heart
How many leads done the standard ECG have?
3 standard limb leads
3 augmented limb leads
6 precordial leads
What are the augmented unipolar limb leads?
AVR, AVL, AVF
Where is V7, V8, V9 placed and why?
On the back inferior to scapula
For left vetricle as LV is mostly posterior
Which leads show the lateral electrical signals of the heart?
I, aVL, V5, V6
Which leads show the electrical signals of the inferior surface of the heart?
II, III, aVF
Which leads show the electrical signals of the anterior surface of the heart?
V3, V4
Which leads show the electrical signals of the septum of the heart?
V1, V2
Features of P wave:
Always positive in lead I and II
Always negative in a lead aVR
< 3 small sqaures in duration
< 2.5 small squares in amplitude
commonly biphasic in lead V1
Best seen in leads II
3 small squares wide and tall
What can you see on the ECG for right atrial enlargement?
Tall (>2.5mm) pointed P waves (P pulmonale)
Left atrial enlargement
M shaped P wave in limb leads
What indicates P Pulmonale?
Peaked P wave taller than 2.5mm in the limb leads indicates P pulmonale
What is the PR interval
Consists of atrial depolarisation and conduction from atria to ventricles
Normally 120-200 ms
Prolonged in disorders of AV node and specialised conducting tissue
Shorter in younger patients or in pre-excitation (Wolf-Parkinson-White)
What is a short PR interval indicative of?
Wolff parkinson white syndrome
Accessory pathway allows early activation of the ventricle
Broad QRS complex typical of WPW - BYPASSES Atrial node
What is a long PR interval indicative of?
First degree heart block
Which leads can non-pathological Q waves be found?
I, III, aVL, V5 and V6
Features of QRS complexes?
R wave in lead V6 smaller than V5
Depth of S wave should not exceed 30mm
Size of complexes related to myocardial mass
Predominantly negative S wave in V1, transitioning to positive R wave by V6
Normal frontal axis -30 to +90 (positive in leads I, II)
What is a pathological Q wave defined by?
2mm deep and 1mm wide
25% amplitude of the subsequent R wave
Indications of left ventricular hypertrophy
S wave in V1 and R in V5 or V6 > 35mm
R wave of 11 to 13 mm or more in lead aVL
Features of ST segment
Flat (isoelectric)
Elevation or depression of ST segment by 1mm or more
Normally isoelectric
Can be elevated in early repolarisation, myocardial infarction, pericarditis/myocarditis,
What is the “J” junction?
Point between QRS and ST segment
T wave features?
Asymmetrical
Must be atleast 1/8 but less than 2/3 of R wave
Amps rarely exceed 10mm
Follows direction of QRS deflection
Height of T wave normally less than QRS
Abnormal T waves look like what?
Symmetrical, tall, peaked, biphasic or inverted
What is QT interval
Total duration of ventricular depolarisation and repolarisation
Decreases when HR increases
HR 70bpm - QT <0.40s
0.35s to 0.40s
QT can be corrected to be shorter or faster
U wave
Related to after depolarisations which follow repolarisation
Small, round, symmetrical and positive in lead II with amplitude <2mm
Direction same as T wave
More prominet at slow HRs
2 rules of determing HR
rule of 300/1500
10 second rule
Rule of 300
Count number of big boxes between 2 QRS complexes and divide this into 300 (smaller boxes with 1500)
for regular rhythms
10 second rule
ECGs record 10 seconds of rhythms per page
Count number of beats present on ECG
X6
For irregular rhythms
QRS axis represents?
Overall direction of hearts electrical activity
Abnormalities of QRS axis hint at what?
Ventricular enlargement
Conduction blocks
Normal QRS axis (Look at intro to ECG powerpoint for this shit)
-30 degrees to -90
Left axis deviation in QRS
-30* to -90*
Right axis deviation (RAD)
+90 to +180
What is the conducting system of the heart?
1.The SAN generates an electrical impulse.
2.This generates a wave of contraction in the atria.
3.Impulse reaches AVN.
4.There is a brief delay to ensure the atria have fully emptied.
5.The impulse then rapidly spreads down the Bundle of His and Purkinje fibres.
6.The purkinje fibres then trigger coordinated ventricular contraction.
What is the amplitude of deflection based on?
related to mass of myocardium
Bigger mass of myocardium gives bigger deflection
What is the width of the deflection reflecting?
reflects speed of conduction
When do we get a positive deflection?
Positive deflection is towards the lead/vector
After this look arrhythmia lecture please for the flashcards
Whats one large square worth?
200 ms
Two squares (400ms) =
Three squares (600ms) =
Four squares (800ms) =
Five squares (1000ms) =
150bpm
100bpm
75 bpm
60bpm
Where are the limb leads and what part of the heart do they look at?
Limb leads on left
Look at frontal plane
Limb leads frontal plane
Slide 13
Where is most of the heart?
2/3 on the left side of the chest
1/3 on the right side of chest
What is the normal QRS axis?
-30 to +90 degrees
What does Left axis deviation -30 to -90 degrees show?
Left anterior fascicular block
Left bundle branch block
Left ventricular hypertrophy
What does Right axis deviation 90 to 180 degrees show?
Left posterior fascicular block
Right heart hypertrophy/strain
What can a low amplitude of P wave show?
Atrial fibrosis, obesity, hyperkalaemia
What can high amplitude of p wave show?
Right atrial enlargement
What does a bifid p wave show?
Left atrial enlargement
Alternative pacemaker foci for p wave?
Focal atrial tacycardias
‘wandering pacemaker’
What can a broad QRS show?
Ventricular conduction delay / bundle branch block
Pre-excitation
What do small QRS complexes show?
Obese patient
Pericardial effusion
Infiltrative cardiac disease
More myocardium than expected
What can tall QRS complexes show?
Left ventricular hypertrophy
(S wave in V1 and R wave in V5/V6 >35mm)
Thin patient
What can Excessively rapid or slow repolarisation show?
can be arrhythmogenic
“Long QT” or “Short QT” syndromes
Congenital, drugs, electrolyte disturbances
Where are T waves usually inverted?
T waves usually inverted in aVR, can be inverted in III
T wave changes (inversion) show what?
Ischaemia/infarction
Myocardial strain (hypertrophy)
Myocardial disease (cardiomyopathy)
What are (ventricular) tachycardia caused by?
Atrial fibrillation, Atrial Flutter
Supraventricular tachycardia
Ventricular tachycardia
Ventricular fibrillation
Supraventricular rhythms
Slide 38
What does an ECG show for ventricular tachycardia?
QRS comples lot broader – his purkinje system not being used for ventricular depolarisation
What does bradycardia cause?
Conduction tissue fibrosis
Ischaemia
Inflammation/infiltrative disease
Drugs
What is bradycardia caused by?
Sinus node disease
AV node / distal conduction problems
First degree heart block
If pr interval is longer than 200ms but 1 p wave for each QRS is first degree AV block
2nd degree heart block
P no QRS P QRS P no QRS second degree AV block
3rd degree heart block
Complete heart block – no relationship between P wave and QRS – ventricles and atria are doing independent activity – 3rd degree
What is mobitz type 1?
PR interval gradually increases until AV node fails completely and no QRS wave anymore
Starts again - PR gradually lengthens
What is mobitz type 2?
Sudden unpredictable loss of AV conduction and loss of QRS-
Due to loss of conduction in Bundle of His and Purkinje fibres
PR interval contant but every nth QR constant is missing
Characteristics of Left branch bundle block
V1 wave - looks like a W
V6 wave - looks like M
RV activated first in front of LV instead of simulatenously
Remember wiLLiam
Characteristics of RIGHT branch bundle block
V1 wave - looks like a M
V6 wave - looks like W
LV activated first in front of RV instead of simulatenously
Remember maRRow
ECG for ischaemia:
T wave flattening inversion
ST segment depression
ECG for infarction:
ST segment elevation
Q waves – old infarction
What leads show the RCA territory?
inferior leads
What leads show the anterior surface of heart?
anterior leads
What leads show the circumflex territory?
lateral leads
ECG hyperkalaemia?
Tall T waves, flattening of P waves, broadening of QRS… eventually ‘sine wave pattern’
ECG Hypokalaemia?
Flattening of T wave, QT prolongation
ECG hypercalcaemia?
QT shortening
ECG hypocalcaemia?
QT prolongation
What do you see in atrial fibrillation ECG?
irregular ventricular response
Atrial flutter ECG?
saw tooth waves
Pericarditis ECG?
Global ST elevation with saddle shape appearance – suggestive of pericarditis
PR depression which is only really seen in pericarditis
What do ectopic beats look like?
2 sinus beats and a beat that comes early – eg of broad appearance when ventricles doesn’t activate by his- purkinje system
Features of ectopic beats?
Very Common
Non sustained beats arising from ectopic regions of atria or ventricles
Generally benign
How can you help with ectopic beats?
Most patients will gain symptomatic relief from reassurance/betablockers
What can high burden VE and AE cause?
High burden VE can cause heart failure
High burden AE can progress to AF
Who do you refer for ectopic beats?
High burden ectopy (>5%, though risk prob not increased till >20%)
Refractory to BB
Structural heart disease
Syncope
Whats the commonest sustained arrhythmia?
Atrial fibrillation (AF)
Features of AF?
Paroxysmal (self terminating) OR
Persistent (continues without intervention)
Rapid chaotic firing causes
-Loss of atrial mechanical contraction
-Irregular often rapid ventricular response
What is the medical treatments for AF?
Treat underlying cause:
Alcohol, Thyroid disease, Hypertension, Valve disease, Heart failure, Obesity, Excessive exercise, Infection etc.
Rate control (accept AF):
Beta blockers
Calcium channel blockers
(Digoxin)
Restore sinus rhythm acutely:
Electrical cardioversion (acutely / after anticoagulation)
Pharmacological cardioversion (flecainide / amiodarone)
How can we maintain sinus rhythm?
Flecainide
Dronedarone
Sotalol
Amiodarone
What can AF do?
Lack of mechanical contraction in atrium can lead to clot in ventricles which can travel to the brain leading to stroke
What can AF do?
Lack of mechanical contraction in atrium can lead to clot in ventricles which can travel to the brain leading to stroke
Direct Xa inhibitors?
Stops conversion of prothrombin to thrombin
Rivaroxaban
Apixaban
Edoxaban
Direct thrombin inhibitor?
Dabigatran
What do you do for someone with Supraventricular tachycardia?
Advice on valsalva manoeuvres
Can try beta blocker/CCB
Who to refer:
Frequent / sustained episodes
Needed adenosine for termination
Abnormal ECG (pre-excitation)
What are accessory pathways?
Congenital remnant muscle strands between atrium and ventricle
What can accessory pathways cause on ECGs?
Can be manifest (pre-excitation on ECG)
Or concealed (ECG normal, only conduct retrogradely and only detected at EP study)
Ventricular tachycardia ECG
Broad QRS complex
Concordance here
NO1 feature is the fact that P wave is independent to QRS complex
P wave rate is slower than the ventricular wave
What is an electrical storm?
3 or more sustained episodes of VT or VF, or appropriate ICD shocks during a 24-hour period
High risk / poor prognosis
Manage on CCU/ITU
What is an electrical storm?
3 or more sustained episodes of VT or VF, or appropriate ICD shocks during a 24-hour period
High risk / poor prognosis
Manage on CCU/ITU
What is the treatment for electrical storm?
Correct any provoking factors e.g. electrolyte (K/Mg), ischaemia, infection, heart failure
Beta blockers, sedation
Amiodarone +/- lignocaine
Overdrive pacing
General anaesthesia / Neuraxial blockade
Catheter ablation
Narrow complex tachycardias?
SVT
AF/flutter
Broad comples tachycardias?
VT
SVT with BBB/preexcitation
Sinus node disease and bifascicular block ECG
PR interval is prolonged
