ECG Theory Flashcards
How can ECG rate be calculated
two ways:
- number of QRS complexes on the rhythm strip x 6
- 300/ number of large squares between QRS complexes
how many seconds is
- one small square
- one large square
one small square = 0.04s
one large square = 0.2s
how do you assess rhythm of ECG
look for P waves followed by QRS complexes
which rhythm has no P waves and is irregularly irregular
Atrial fibrillation
how do you assess the axis of the ECG
Imagine lead 1 = left hand and AvF = right hand - raise hand if lead is +ve - if both +ve then normal axis
what kind of axis deviation is there if lead 1 +ve and AvF -ve
left axis deviation
what kind of axis deviation is there if lead 1 -ve and AvF +ve
right axis deviation
what does P wave represent
atrial depolarisation
normal duration of P wave
0.08 - 0.1s
what does QRS complex represent
ventricular depolarisation
normal duration of QRS complex
< 0.1 s
what does PR interval represent
AV nodal delay
normal duration of PR interval
0.12-0.2 s
causes of a prolonged PR interval
ischaemic heart disease
hypokalaemia
digoxin toxicity
lyme disease
what does T wave represent
ventricular repolarisation
what causes peaked T waves
hyperkalaemia
(flattened T waves in hypokalaemia)
what leads is it abnormal for T waves to be inverted?
what are some of the causes?
Leads I, II, V4-V6
- Ischaemia, digoxin toxicity, PE, ventricular hypertrophy
where do the ventricles contract
ST segment - systole
where do the ventricles relax
TP segment - diastole
what condition causes widespread saddle shaped ST elevation
pericarditis
drugs that can cause long QT
macrolides
amiodarone
tricyclic antidepressants e.g. amitryptilline
SSRI - citalopram
(also metabolic disturbances: hypokalaemia, hypocalcaemia)
drugs that can cause short QT
digoxin
beta-blockers
phenytoin
when are U waves seen
hypokalaemia
(occur after T waves)
causes of J waves
hypothermia
hypercalcaemia
easy way to differentiate between right + left bundle branch block
QRS has to be broad in bundle branch block
- QRS will point down in V1 in a LBBB
- QRS will point up in V1 in a RBBB
anterior MI affects which leads?
which vessel is affected?
Anterior = V2-V5
- Left anterior descending
anteroseptal MI affects which leads?
which vessel is affected?
anteroseptal = V1-V3
- Left anterior descending
anterolateral MI affects which leads?
what vessel is affected?
Anterolateral = I, AvL, V4-V6
- left circumflex
inferior MI affects which leads?
what vessel is affected?
inferior = II, III, AvF
- right coronary
normal QT length in
- males
- females
males = < 430 ms
females = < 450 ms
