ECG Flashcards by Neysa Patel

What is the normal duration of the P wave?

80ms

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What is the normal duration of the QRS complex and the QRS interval?

80-120ms

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What is the normal duration of the T wave?

160ms

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What is the normal duration of the PR segment?

50-120ms

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What is the normal duration of the ST segment?

80-120ms

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What is the normal duration of the PR interval?

120-200ms

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What is the normal duration of the ST interval?

320ms

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What is the normal duration of the QT interval?

350-450ms

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How is an interval measured on an ECG?

From the start of a wave to the end of the last letter

e.g. QT interval from start of Q to end of T

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How is a segment measured on an ECG?

From the end of the wave to the start of the next

e.g. ST segment from end of S to start of T

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What does the gradient on an ECG represent?

Velocity of the action potential

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What does the width of a wave on an ECG represent?

Duration of the event

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What does the P wave represent?

SAN myocytes depolarise causing atrial depolarisation

Wave moves across from right to left ventricle via internodal fibres slightly towards the cathode

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What does the PR segment represent?

Depolarisation of the AVN

Isoelectric to delay impulse and allow ventricular filling

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What does the Q wave represent?

@Start of Q wave - bundle of His rapidly conducts wave of depolarisation down septum
rest of Q wave - septum depolarises away from cathode

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What does the R wave represent?

Ventricular depolarisaton due to Purkinje fibres that carry wave UP towards the cathode

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What does the S wave represent?

Purkinje fibres carry wave up myocardium for late ventricular depolarisation, moving away from the cathode

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What does the ST segment represent?

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Depolarised ventricles produce isoelectric ECG

What does the T wave represent?

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Ventricular repolarisation moving towards the cathode

How are ECG recordings obtained?

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3 bipolar leads that measure potential difference between the limbs
I RA to LA  - to +
II RA to LL 
III LA to LL
3 augmented limb leads 
aVF
aVL
aVR
6 chest leads

How are augmented limb leads formed?

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Comparison of a single +ve electrode with a combination of the other two
aVR RA-(LA+LF)
aVL LA-(LF+RA)
aVF LF-(RA+LA)

Where are the 6 chest leads placed?

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V1 - right 4th intercostal space, parasternal
V2 - left 4th intercostal space, parasternal
V3 - Left midway between V2 and V4
V4 - Left 5th intercostal space @ midclavicular line
V5 - Same horizontal level as V4 but along anterior axillary line
V6 - same horizontal level as V4, but along mid axillary line

What is the systematic approach to reading and analysing an ECG, and the expected readings for a normal ECG?

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1) Ensure it is correct recording
2) Check signal and quality of leads
3) Voltage and paper speed
4) Patient background
THEN
1) Rate and rhythm (regular R-R intervals, 60/rr interval between 60 and 100)
2)P wave and PR interval (80ms, 120-200ms)
3) QRS duration (80-100ms)
4) QRS axis (between 30° and 120°)
5) ST segment (80-120ms, not isoelectric)
6) QT interval (420ms)
7) T wave (160ms)
DOUBLE CHECK EVERYTHING

What is Einhoven’s triangle?

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Imaginary triangle formed by the bipolar limb leads
Used to measure movement of electrical activity away from the heart
Augmented leads measure the potential difference from centre of triangle out to each corner of triangle (LL RA LA)
Chest leads act as cathodes

What are the lead axes angles?

``` Centre of Einhoven's triangle is centre ∴ Lead I 0° Lead II 60° Lead III 120° aVL -30° aVF 90° aVR -150° ```

How can the cardiac axis be calculated and what does it show?

The mean electrical axis of the heart during ventricular depolarisation Helps us recognise when a patient has a deviation of the cardiac axis 1) Calculate net QRS deflection for lead I and for aVF 2)Mark these on the respective axes 3)intercept perpendicular lines to get the cardiac axis vector 4) calculate cardiac axis w tan

What is the normal direction of the cardiac axis?

between 0° and 90°

What value of cardiac axis would be classed as left axis deviation and what could this be caused by?

``` Axis lies between -90° and 0° Left ventricular hypertrophy Left bundle branch block Hyperkalemia Inferior myocardial infarction Conditions that elevate diaphragm e.g. COPD, pregnancy, ascites, abdominal tumours ```

What value of cardiac axis would be classed as right axis deviation and what could this be caused by?

Axis lies between +90° and 180° Right bundle branch block Right ventricular hypertrophy Lateral wall myocardial infarction

What value of cardiac axis would be classed as the indeterminant region and what could this be caused by?

Axis lies between -90° and -180° Very rare most commonly caused by leads wrong way round

What is normal sinus rhythm?

each P followed by QRS wave regular rate and normal HR otherwise unremarkable

How can sinus bradycardia be recognised and what can it be caused by?

Each P wave followed by QRS wave regular rate, SLOW HR Can be healthy, caused by medication or vagal stimulation

How can sinus tachycardia be recognised and what could it be caused by?

Each P wave followed by a QRS wave Regular rate, FAST HR Often is a physiological response

How can sinus arrhythmia be recognised?

Each P wave followed by a QRS wave Rate IRREGULAR, normal -ish HR R-R interval varies with breathing cycle

How can atrial fibrillation be recognised?

Oscillating baseline - atria contracting asynchronously | Rhythm can be irregular and slow rate

How can atrial flutter be recognised?

Regular saw tooth pattern in baseline of II,III, aVF Atrial to ventricular beats at a 2:1 ratio or higher (Saw tooth not always visible in all leads)

How can 1st degree heart block be recognised and what could it be caused by?

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

How can 2nd degree heart block Mobitz I (Wenckebach) be recognised and what could it be caused by?

Gradual prolongation of the PR interval until beat skipped Most P waves followed by QRS, some not Regularly irregular Caused by diseased AV node

How can 2nd degree heart block Mobitz II be recognised?

Regular P waves, only some followed by QRS No PR prolongation like in Mobitz I Regularly irregular Can rapidly deteriorate into 3rd degree heart block

How can 3rd degree heart block be recognised?

P waves regular, QRS regular, but no relationship P waves can be hidden by bigger vectors Truly non-sinus rhythm

How can ventricular tachycardia be recognised?

P waves hidden - dissociated atrial rhythm Rate regular and fast High risk of deteriorating into fibrillation Shockable rhythm

How can ventricular fibrillation be recognised?

Irregular HR 250bpm and above Heart unable to generate an output Cardiac arrest Shockable rhythm

How can ST elevation be recognised and what can it be caused by?

P waves visible and always followed by QRS Rhythm regular, rate normal ST segment elevated >2mm above isoelectric line Caused by infarction (tissue death due to hypoperfusion)

How can ST depression be recognised and what can it be caused by?

P waves visible and always followed by QRS Regular rhythm, normal rate ST segment depressed >2mm below isoelectric line Caused by myocardial ischaemia (coronary insufficiency)