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?
- Slows signal conduction
- Allows for ventricular filling
- 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
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
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
- 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)?
regularly irregular rhythm
What are the characteristics of second degree heart block (Mobitz II)?
- 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