ECG

Question 1

what happens in an ECG

Answer 1

track the electrical impulse as it travels across the heart using electrodes on the chest surface

Question 2

how do the impulses appear on the graph

Answer 2

an impulse traveling towards the electrode results in a positive deflection
an impulse travelling away results in a negative deflection

Question 3

electrode placement

Answer 3

standard ecg has 12 leads
6 on the chest called V1-6
4 limb electrodes - right arm (red), left arm (yellow), left leg (green) and right leg (black)

Question 4

chest electrode placements

Answer 4

v1 - 4th intercostal space, right sternal angle
v2 - 4th intercostal space, left sternal angle
v3 halfway between v2 and v4
v4 over the apex ( 5th ICS, mid clavicular line)
v5 - same level as v4 but on the anterior axillary line
v6 - at the same level as v4+5 but on the mid axillary line
incorrect placement can affect the ECG readings
placing them at these specific locations provides useful information across the heart
these leads look at the transverse plane

Question 5

placement of limb leads

Answer 5

look at the coronal plane
bipolar leads - 1,2,3
unipolar leads - aVL, aVR, aVF

Question 6

what does limb leads 1-3 look at

Answer 6

lead 1 - signals travelling from right arm to left are
lead 2 - signals from right arm to left leg
lead 3 - left arm to right leg

Question 7

what do leads aVL, aVF and aVR look at

Answer 7

aVL - heart to left shoulder
aVF - heart to feet
aVR - heart to right shoulder

Question 8

what are the most important leads to look at in a 12 lead ECG

Answer 8

limb lead 2 is normally long so you can determine the rhythm

Question 9

using leads 1,2 and 3 to calculate deviation

Answer 9

if leads 1 and 2 are positive then axis is normal
if leads 2 and 3 are negative then patient has left axis deviation
if lead 1 is positive and lead three is positive then patient has right axis deviation

Question 10

first thing to do when reading an ECG

Answer 10

check for calibration
check for reference pulse (rectangular wave on left hand of paper) normal calibration the wave should be 10mm tall, this is equal to 1mV
paper speed should be 25mm/s

Question 11

describe the 3 waves produced during cardiac cycle

Answer 11

p wave - caused by atrial depolarisation
QRS complex - caused by ventricular depolarisation
t wave - ventricular repolarisation

Question 12

describe the QRS complex

Answer 12

Q wave - first downward deflection
r wave - first upward deflection
s wave - downward deflection after first upward deflection

Question 13

describe the intervals

Answer 13

pr interval - time impulse takes to conduct through bundle of His (0.12-0.2s)
qrs duration - time taken for ventricular depolarisation (<0.12s)
st segment - start of ventricular repolarisation (<0.44s m, <0.46s f)

Question 14

what do the intervals tell us

Answer 14

st elevation - MI, pericarditis, repolarisation abnormalities
st depression - ischaemia, left ventricular strain
prolonged pr interval - conductive tissue disorder
shortened pr interval - impulse is bypassing the AV node (wolff-parkinson-white syndrome)
qrs duration - can show right bundle block or left bundle block

Question 15

what is left ventricular hypertrophy

Answer 15

too much muscle in the left ventricles
represented by abnormally tall r waves in v5 or v6 and deep s wave in v1

Question 16

what is right bundle branch block in v1

Answer 16

no change in initial impulse (small r wave)
impulse depolarises LV by itself (s wave)
RV depolarised late by impulse through muscle (r’ wave)
rsr’ patter (m shape on ecg trace)

Question 17

left bundle branch block in v1

Answer 17

initial deflection altered since it travels left to right now (q wave has negative deflection)
RV depolarises unopposed (may produce small r wave)
travels across septum to depolarise LV (deep s wave)
appears as a w on trace
if patient has lbbb then st segments are uninterpretable

Question 18

how to calculate heart rate from an ECG

Answer 18

if cardiac rhythm is regular count the number of squares between r waves
rate = 300/number of large squares between r waves
if rhythm is irregular - use rhythm strip at the bottom of 12-lead ecg
this is a 10sec recording of the heart, therefore rate = number of QRS complexes x 6

Question 19

what is bradyarrhythmia

Answer 19

any abnormality of cardiac rhythm resulting in a slow heart rate (<60bpm)
could be caused by heart block or slow AF

Question 20

what is tachyarrhythmia

Answer 20

any abnormality of cardiac rhythm resulting in a fast heart rate (>100bpm)
could be due to SVT, uncontrolled AF/flutter or VT

Question 21

what is 1st degree av block

Answer 21

regular rhythm
pr interval of more than 0.2s and is constant
usually does not require treatment
causes - ischaemic heart disease, conduction system disease, can be seen in healthy kids or athletes

Question 22

what is 2nd degree av block (mobitz 1)

Answer 22

irregular rhythm
pr interval continues to lengthen until a qrs complex is missing (non-conducted sinus beat)
pr interval is not constant
rhythm is usually benign unless associated with underlying pathology (MI)

Question 23

what is 2nd degree av block (mobitz 2)

Answer 23

irregular rhythm
qrs complexes may be wide (>.12s)
non-conducted sinus impulses appear at irregular intervals
rhythm is somewhat dangerous as the block is lower in the conduction system
may cause syncope or may deteriorate into complete heart block
its appearance in the setting of an acute MI identifies a high risk patient
treatment - pacemaker
causes - IHD, fibrosis of the conduction system

Question 24

what is 3rd degree av block

Answer 24

complete heart block
atria and ventricles beat independent of each other (av dissociation)
qrs complexes have their own rhythm, p waves have their own rhythm
may be caused by inferior MI, and its presence worsens the prognosis
may cause syncopal symptoms or angina, especially if ventricular rate is low
treatment - pacemaker

Question 25

what is narrow complex tachycardia

Answer 25

qrs duration of <.12s
uncontrolled atrial fibrillation of flutter
atrial tachycardia
atrioventricular nodal reentry tachycardia
atrioventricular reentrant

Question 26

what is broad complex tachycardia

Answer 26

qrs duration >.12s
ventricular tachycardia
ventricular fibrillation