Electrocardiography and Rhythm Disorders Flashcards
What can ECGs show?
- the electrical activity of the heart
- clinical abnormalities
- structural abnormalities
- perfusion abnormalities
What are the advantages of using an ECG?
- cheap
- easy
- reproducible
- quick
What is a vector?
a quantity with both a magnitude and a direction
What does the isoelectric line represent?
no net change in voltage (the vector is perpendicular to the lead)
What does the steepness of the line show?
the velocity of the action potential
What does the width of the wave represent?
the duration of the action potential
What does the p wave represent?
the electrical signal for atrial contraction given by the SA node
What does the QRS complex indicate?
The electrical signal that stimulates contraction of the ventricles (ventricular systole)
What does the T wave indicate?
The electrical signal that signifies relaxation of the ventricles
What part of the heart does the P wave represent?
the atria
what does the SA node do?
Contains auto-rhythmic myocytes that electrically signal for atrial depolarisation
What does the AV node do?
- Slow signal conduction
- Allows for ventricular filling
-AVN depolarisation - Protective
What part of an ECG represents the action of the AVN?
the PR segment
Why is there no deflections shown during the conduction by the Bundle of His?
Rapid, Insulated conduction that is perpendicular to the direction of the lead (therefore doesn’t show on the trace)
What is responsible for Q?
Bundle branches cause septal depolarisation
- left side is slightly less insulated, therefore the signal escapes against Lead II direction.
What causes an R wave?
Purkinje fibres causing ventricular depolarisation
What causes an S wave?
Late depolarisation of Purkinje fibres of ventricle
What causes the T wave?
Ventricular repolarisation
What is the rule of Ls?
Lead I - Right Arm> Left Arm (one L)
Lead II - Right Arm> Left Leg (two Ls)
Lead III - Left Arm> Left Leg (three Ls)
What is the rule of reading ?
Drawn as a triangle, read from Left to Right, and then Top to Bottom
the first electrode of each bipolar pair you reach is the –ve electrode
where is V1 placed?
- Right of sternum
- 4th intercostal space
Where is V2 placed?
- Left of the sternum
- 4th intercostal space
Where is V3 placed?
- Left
- halfway between V2 and V4
Where is V4 placed?
- Left mid-clavicular line
- 5th intercostal space
Where is V5 placed ?
- Left anterior axillary line
- 5th intercostal space
Where is V6 placed?
- Left mid axillary line
- 5th intercostal space
Can you shock during asystole?
No
What are the characteristics of sinus rhythm?
- every P wave is followed by a QRS complex
- regular rate (even R-R intervals)
- normal HR (60-100bpm)
What causes a sinus arrhythmia and what are its characteristics?
- stress
- exercise
- stimualtants
- rate is irregular (variable R-R intervals)
- R-R intervals vary with breathing cycle
What are the characteristics of atrial fibrillation?
- oscillating baseline (atria contracting asynchronously)
- turbulent blood flow increases clot risk
- slow rate
- irregularly irregular PR intervals
What are the characteristics of atrial flutter?
- regular, saw tooth pattern in baseline
- saw tooth is not always visible
What are the characteristics of a first degree heart block?
- prolonged PR interval caused by slower AV conduction
- regular rhythm
What are the characteristics of second degree heart block (Mobitz I/Wenckebach)?
- gradual prolongation of the PR interval until a beat is skipped
- most P waves are followed by QRS complexes, some are not
- regularly irregular rhythm - diseased AV nodes
What are the characteristics of second degree heart block (Mobitz II)?
- regular P waves, only
- skipped QRS complex
- regularly irregular rhythm
- can rapidly deteriorate into 3rd degree heart block
What are the characteristics of third degree (complete) heart block?
- regular P waves, regular QRS complexs - BUT no relationship
- no sinus rhythm
when does something have a non-sinus rhythm?
when the electrical stimulation of the heart isn’t initiated by the SA node
What are the characteristics of ventricular tachycardia?
- P waves hidden - dissociated atrial rhythm
- rate is regular and fast (100-200bpm)
- shockable rhythm
- high risk of deteriorating into fibrillation
What are the characteristics of ventricular fibrillation?
- HR is irregular and >250bpm
- heart is unable to generate output
- shockable rhythm
What are the characteristics of an ST elevation?
- visible P waves followed by a QRS complex (1:1)
- regular rate and rhythm
- ST segment is elevated >2mm above the isoelectric line
- caused by infarction
What are the characteristics of an ST depression?
- visible P waves followed by a QRS complex (1:1)
- regular rhythm and normal rate
- depressed >2mm below the isoelectric line
- caused by myocardial ischemia
What can cause ST elevation?
infarction (tissue death due to hypoperfusion) - STEMI
What causes Mobitz-1 type second degree heart block?
a diseased AV node
What is first degree heart block indicative of?
benign, progressive disease of aging
Where does atrial flutter tend to be seen?
leads II, III, and aVF
What can be a complication associated with atrial fibrillation?
turbulent blood flow pattern increases the risk of clots
What is the impact of atrial fibrillation on cardiac output?
minimal, as atria are not essential to the cardiac cycle
What tends to cause sinus tachycardia?
often a physiological response, secondary to another factor
What can cause sinus bradycardia?
- can be normal/healthy
- medication
- vagal stimulation
What are the steps of reading an ECG?
- rate and rhythm
- P wave and PR interval
- QRS duration
- QRS axis
- ST segment
What is every small box on an ECG worth (s)?
0.04 seconds
What is every small box on an ECG worth (mV)?
0.1mV
What are the lateral leads?
I, aVL, V5, V6
What are the inferior leads?
II, III, aVF
What are the septal leads?
V1, V2
What are the anterior leads?
V3, V4
What is the normal length of an R-R interval?
0.6-1.2 seconds
What is the normal length of a P wave?
80ms
What is the normal length of a P-R interval?
120-200ms
What is the normal length of a QRS complex?
<120ms
What is the normal length of a Q-T interval?
420ms
What is the normal length of a T wave?
160ms
How do you calculate cardiac axis?
- calculate the net deflection of the QRS complex of II and aVL (parallel leads)
- SoH CaH ToA to find the angle
- 60 - angle found =
What is the PR interval?
start of P wave to the start of the QRS complex
When is a change in the PR interval problematic?
> 0.2 seconds (one big box)
What is a prolonged QRS complex?
> 0.12seconds
What is the relationship between the QT interval and heart rate?
as heart rate increases, QT interval shortens
What are these?
Electrodes, connect to person
What are these?
Cables, attach the person to the machine
What are these?
Leads, represent electrical activity
What do upward deflections represent?
Movement towards the positive electrode
What do downward deflections represent?
Movement towards the negative electrode
How are cardiac vectors represented?
by an arrow in the net direction of movement, whose size reflects the magnitude
Which heart block is the most benign?
- first degree
-progressive disease of aging
What do the 12 leads show?
The 12 views of the heart
Which leads are on the coronal plane?
3 limb leads and 3 augumented vector leads
Which leads are on the axial plane?
6 chest leads
How many electrodes are needed for a 12 lead ECG?
10
What do the lateral leads correspond to?
Left circumflex artery
What do the inferior leads correspond with?
Right coronary artery
What do the anterior and septal leads correspond with?
Left anterior descending artery
How do you calculate the rate on an ECG?
300/number of large squares between R-R intervals
How can the rhythm be described on an ECG?
- sinus or non-sinus
- regular, regularly irregular, irregularly irregular
What is the cardiac axis?
The net effect of all generated action potentials
What is a normal cardiac axis?
-30 to +90 degrees
