Electrocardiography and Rhythm Disorders Flashcards
What can ECGs show?
the electrical activity of the heart
What are the advantages of using an ECG?
- cheap
- reproducible
- quick
What is a vector?
a force with both a magnitude and a direction
What does the isoelectric line represent?
no net change in voltage (of that the vector is perpendicular to the lead)
What does the steepness of the line show?
the speed of the action potential/electric conduction
What does the width of the wave represent?
the duration of the action potential
What does the p wave represent?
the signal for atrial contraction given by the SA node
What does the QRS complex indicate?
septal depolarisation, ventricular depolarisation and late ventricular depolarisation
What does the T wave indicate?
ventricular repolarisation
What part of the heart does the P wave represent?
the atria
what does the SA node do?
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 - RA > LA (one L)
Lead II - RA > LL (two Ls)
Lead III - LA > LL (three Ls)
What is the rule of reading ?
Read from Left to Right, and then Top to Bottom
The first time you come across a lead, it is negative
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
- 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
What are the 3 augmented vector lead?
- 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?
- stress
- exercise
- stimualtants
What are the characteristics of atrial fibrillation?
- oscillating baseline due to asynchronous atrial contraction
- irregular rhythm, slow rate
What are the characteristics of atrial flutter?
- regular, saw tooth pattern in baseline
- atrial:ventricular contraction at 3:1,2:1 ratio or higher
What are the characteristics of a first degree heart block?
- prolonged PR segment/interval caused by slower AV conduction
- regular rhythm (1:1, P waves:QRS complexes)
What are the characteristics of second degree heart block (Mobitz I / Wenckebach)?
- gradual prolongation of the PR interval until a beat is skipped (missing QRS complex)
- most P waves are followed by QRS complexes, some are not
- regularly irregular
What are the characteristics of second degree heart block (Mobitz II)?
- regular P waves, only some are followed by a QRS complex
- no PR elongation
- regularly irregular (success:failure, 2:1)
- can rapidly deteriorate into 3rd degree heart block