ECG introduction Flashcards Preview

Cardio and Resp Week 3 > ECG introduction > Flashcards

Flashcards in ECG introduction Deck (29)
Loading flashcards...

Define ECG

It is the summation of all of the action potentials of the heart. 


Label the regions of the cardiac conduction pathway 


Does the SA depolarisation show up on an ECG?



What is happening in the "P" region of the ECG? 

  • Atrial Depolarisation
  • The first "deflecton" on the ECG 
  • Typically small, low amplitude


What is happening at the highlighted pont of the ECG?

Delay of signal at the AV node 

GIves times for Atria to contract, and for ventricles to fill


What is happening at "Q"?

  • conduction through the bundle branches of the ventricles 


What is happening at QRS?

Ventricular depolarisation

Should be nice and narrow 


What is represented by the box on this ecg?

Plateau phase of repolarisation - this is the ST Segment 


What is happening at this stage of the ECG?

Rapid repolarisation of ventricles 


Unipolar and bipolar leads are both used in ECG. List which leads these are, and what the difference is


  • Measuring electrical activity at a single point


  • Measuring electrical activity between two points

Unipolar leads: 

  • aVR, aVL, aVF, V1-6 

Bipolar lewads: 

  • Limbs 1, 2 and 3


What is an ECG lead?

  • Electrical vector - the angle and direction of the electrical impulse of the heart - basically an imaginary line between 2 electrodes 
  • Not the wire attached to the patient 


How many electrodes are attached to a patient for ECG? List where they are attached 


List the 12 ECG leads and what they all measure 

Chest leads

V1 – Septal view of heart

V2 – Septal view of heart

V3 – Anterior view of heart

V4 – Anterior view of heart

V5 – Lateral view of heart

V6 – Lateral view of heart


Other leads

Lead I – Lateral view (RA-LA)

Lead II – Inferior view (RA-LL)

Lead III – Inferior view (LA-LL)

aVR – Lateral view (LA+LL – RA)

aVL – Lateral view (RA+LL – LA)

aVF – Inferior view (RA+LA – LL )


Limb leads are providing the coronal view of the heart 

Chest leads are providing the transverse view of the heart 


Study electrode placement 

Note how limb electrodes can be put ALL distally or ALL proximally. Neither is better than the other 


Thinking about bipolarlimb  leads, where positions are measuring between which anatomical points? Note how the positive electrode relies on the negative electrode as a reference point 


The unipolar limb leads essentially measure an average of what the bipolar limb leads are measuring. 


Different leads are providing different views of the heart 

V1 - V4 = Anterior 

Inferior = 2,3 and VF

Lateral = 1, AVL, V5, V6


In MI, abnormality can be related to the coronary artery involved. For example, left anterior descending blockage is likely to show up as abnormality in the Anterior ECG. 


A singal moving towards a lead will give a positive signal, anyhing moving away will give negative signal. 


What is meant by the QRS? 

This is very simply a way of generalising the direction of the depolarisation of the heart. Best way is to look at QRS wave and see if there is any deviation. 


Systemic approach for an ECG

  1. Ask for clinical context of the patient 
  2. Check, data, time and Patient detaisl 
  3. Assess technical quality (paper speed - 25mm/s, gain - 10mV/mm) , are there any weird artifacts?
  4. Identify P/QRS/T wave - i.e. can you find them, are they in the right order? - use the rhythm strip which is typically the three readings at the bottom of an ECG
  5. Measure the heart rate, although generally measured by machine) 
  6. Check the ECG intervals (usually machine is accurate) 
  7. Determine the QRS axis by looking at the limb leads 
  8. Look at P/QRS/T morphology - basically look at the 12 leads  individualls


Do not rely on automatic interpretation

Looking at Old ECGs is very helpful 


Determining heart rate - there are two main ways. What are they? 

  • count the number of large squares between each QRS complex - divide 300 by that number 
  • Alternatively, count the number of QRS complexes across ECG and multiply by 6 


ECG intervals are an important factor when diagnosing an ECG. Give typical values in ms for PR interval, QRS and QT interval and  describe what these ECG phases are

PR interval (delay at AV node) < 1 large square, <200ms

QRS (ventricular  < 3 small squares, <120ms. Duration of QRS complex is very important, tells you whether the signal used the ventricular conduction systen. Anything higher suggests it did not. Broad QRS is really bad

QT interval (ventricular depolarisation AND repolarisation) < 11 small squares, <440ms 



mm of Big and small squares on ECG? 

Large = 200ms 

Small = 40ms 


In degrees, what is a typical QRS axis? How do we check this is OK?

-30 to + 90 degrees

  • Check limb leads 1 and 2 first - if the QRS is predominantly positive, then you're porbably fine 


Left Axis deviation in QRS - when lead one is predominantly normal, but 2 and aVF is MAINLY NEGATIVE. aVL is also completely positive. 

degrees is typically - 30 to -90 


Right axis deviation. This is when lead 1 is almost completely negative, avG is also very positive

Typically 90-180 degrees


Extreme axis deivation is when shit has hit the fan. Very broad QRS complex, negative QRS in lead 1,2 and 3. aVR has positive QRS, which is absolutely never should. 

Degrees is +180 to -90


  • Normal P wave is upright in leads looking at the heart from below - if it is negative in the inferior leads then this is bad - NOT SINUS RHYTHM 
  • ST segment should be flatish 
  • The normal T wave has the some polarity as the QRS 


Define bundle branch block. The only leads you need to look at are V1 and v6. There will be a broad QRS

Either the left or right bundle branch is not transmitting properly, meaning the ventricles contract out of SYNC. 

LV and RV will be out of SYNC.