ECG Flashcards
What are the first things to check on every ECG? (Before looking at the ECG recording itself)
Patient details
Date/ time of ECG
Calibration
How to check the calibration of an ECG?
In most patients, the ECG is recorded at a paper-speed of 25 mm = 1 second with a voltage calibration of 10 mm = 1 mV.
The calibration marker is displayed at the beginning of each ECG
Y axis = Voltage; 10mm = 1mV
X axis = Time; 1 large sq = 5 small squares = 0.20 secs = 5 x 40 msecs
What is a normal PR interval?
<0.20 seconds = 1 large or 5 small squares
What is a normal QT interval?
<0.44 seconds = 12 small squares
What is the QTc?
QT interval corrected for heart rate.
QTc = QT interval in seconds/ Square root of RR interval in seconds
What is the normal QRS duration?
<0.10 seconds
What does the axis of an ECG show? (Specifically the vertical axis)
The vertical axis gives a measure of the relative myocardial mass of the two ventricles and is abnormal in various disease states.
What leads are used to determine the axis of an ECG?
Lead I measures the electrical vector of the heart at 0 degrees
Lead II is the +60 vector
Lead III is the +120 vector
How do you calculate the axis deflection in each lead? (i.e. the formula)
(Height of R wave) - (Height of Q wave) - (Height of S wave)
What is the normal axis of an ECG?
Between -30 and +90 degrees
What are the causes of Right axis deviation?
RBBB
RVH (e.g. COPD, PE, ASD, Pulmonary Stenosis)
Normal variant in young
What are the causes of left axis deviation?
Inferior MI Left anterior hemiblock LBBB Cardiomyopathy Pregnancy (mechanical displacement)
What are the criteria for LVH?
(S wave voltage in V1) + (R wave voltage in V5 or V6 whichever is largest) = >=35mm
You might also see T wave inversion in leads V3-V6
What would be seen on an ECG in an inferior MI?
1mm ST elevation in two of leads II, III, aVF
What would be seen on an ECG in a posterior MI?
ST depression in leads V1 and V2 with prominence of the R wave in these leads, often associated with concurrent inferior infarction.
What would be seen on an ECG in hyperkalaemia?
Peak T waves Prolonged QRS (>0.12 seconds) Prolonged QT interval (>0.44 seconds)
What would be seen on an ECG in digoxin use (not toxicity)?
Digoxin has an effect on the ECG: Slurring and inversion of the ST segments in the lateral leads, V4, V5 and V6
What would be seen on an ECG in olanzapine overdose?
Prolonged QT interval
In a normal ECG, which leads is the R wave NOT dominant in?
aVR, V1 and V2
In a normal ECG, which leads have a dominant S wave?
V1 and V2
In a normal ECG, in which leads can a Q wave be a normal variant?
V1 and/or lead III
Which leads represent the territory supplied by the LAD?
V1 to V3
This is the anterior wall of the heart
Which leads represent the territory supplied by the circumflex artery?
I, aVL, V5 and V6
This is the lateral wall of the heart
Which leads represent the territory supplied by the RCA?
II, III and aVF
This is the inferior wall of the heart
Which leads represent the septum?
V3 to V5
What is the purpose of lead aVR?
The sole use of aVR is to determine whether the limb leads are on correctly.
The QRS complex must be negative.
How do you calculate the HR?
Rate = 300/ Number of large squares between R wavesor
or
Rate = 60/RR interval in seconds
or
Take 4 beats, count the number of large squares, then - (300/ number of large sqares) x4
What abnormalities are seen in RBBB?
QRS duration >120 msecs
Tall R wave in V1
S wave in V6
What abnormalities are seen in LBBB?
QRS duration >120 msecs
Q waves across anteroseptal leads
T wave inversion in lateral leads
What are the ECG features of 1st degree heart block?
Prolonged PR interval
What are the ECG features of Mobitz type I AV block (Wenckebach AV block)?
Progressive prolongation of the PR interval culminating in a non-conducted P wave
What are the causes of Mobitz type I AV block (Wenckebach AV block)?
Increased vagal tone (athletes)
Acute MI
Myocarditis
Beta blockers, CCBs, digoxin, amiodarone
How do you distinguish SVT from sinus tachycardia?
By asking the patient to take a deep breath in and out. A sinus tachycardia first slows a little and then speeds up, natural sinus arrhythmia with deep inspiration.
An SVT is not affected by deep inspiration as the sinus node is not active during SVT.
What does a delta wave signify?
Wolf-Parkinson-White syndrome.
If the QRS morphology in a broad complex tachycardia is identical to that in the patient’s normal sinus rhythm ECG - what is the rhythm?
Supraventricular tachycardia (SVT) with aberrant conduction
Pacemaker Code
I Chamber paced 0 A V D II Chamber sensed 0 A V D III Response 0 T I D IV Rate modulation 0 R V Anti arryrhythmia function 0 P S D
What are the types of cardiomyopathy?
Dilated: Severe dilatation without heart valve abnormalities.
Hypertrophic: Enlarged heart with asymetric hypertrophy
Restrictive: Development of scar tissue causing incomplete ventricular filling
Arrhythmogenic: RV tissue death and scarring
Causes of Dilated Cardiomyopathy
Genetic: Duchennes Infection: Post myocarditis Autoimmune: RA, SLE, MG, GPA Toxic: Alcohol, cocaine, amphetamines, anabolic steroids, amyloidosis Drugs: SACT, lithium Endocrine: DM, thyroid dysfunction Peripartum
What are the causes of hypertrophic cardiomyopathy?
Genetic
Storage diseases
Neuromuscular
What are the causes of restrictive cardiomyopathy?
Idiopathic
Infiltrative: amyloidosis, sarcoidosis
Storage disease: iron overload
Endomyocardial: Carcinoid, XRT, SACT
What is Bazett’s formula
QTc = QT / √RR
