ECGs (Yr3) Flashcards
how is electrical activity conducted across the atria?
cell to cell
what causes the P wave?
atrial depolarisation
what causes the P-R interval?
wave of depolarisation reaching the AV node and being slowed down
what causes the QRS complex?
ventricular depolarisation
what causes the T wave?
ventricular repolarisation
what is the amplitude of a wave of depolarisation associated with?
size of the atria/ventricles
where are the ECG leads attached to?
red - right fore
yellow - left fore
green - left hind
black - right hind
what is the best lead to assess the heart? and why?
lead II as it runs roughly parallel to heart position (from right fore to left hind)
what does normal narrow QRS complexes mean if an animal has an arrhythmia?
supraventrcular origin
what does wide bizarre QRS complexes mean?
ventricular origin or there is a conduction disturbance within the purkinje fibres so conduction is cell to cell
what is the normal HR for a dog?
70-160bpm
(<220 for pups)
what is the normal HR for cats?
160-240bpm
in terms of chambers, what does a prolonged P wave mean?
left atrial enlargement (P mitrale)
in terms of chambers, what does a tall P wave mean?
right atrial enlargement
in terms of chambers, what does a tall R wave mean?
left ventricular enlargement
in terms of chambers, what does a prolonged QRS complex means?
ventricular enlargement/hypertrophy
what is sinus arrhythmia?
normal heart rhythm indicating high vagal tone in dogs
R-R increases with expiration and decreases with inspiration
what is sinus arrest?
no electrical activity for a period of time exceeding two normal R-R intervals (can be due to high vagal tone)
what is first degree AV block?
normal ratio of P:QRS but the P-R interval is longer than it should be (could be due to drugs, disease or high vagal tone)
what is second degree AV block?
some P waves are not followed by QRS complexes
what is mobitz one second degree AV block?
P-R interval slowly increases until QRS is dropped
some non-conducting P-waves present and varying P-R interval (it is normal and reflects high vagal tone)
what is mobitz two second degree AV block?
random non-conducting P waves
what is third degree AV block?
P waves and QRS complexes have no relationship to each other
are third degree AV blocks always associated with disease?
yes, always associated with disease of the conduction system
what is a feature seen with third degree AV block, that is responsible for “rescuing” the heart?
ventricular escape complexes
how do the T waves and QRS complexes appear with third degree AV block?
wide/bizarre QRS
oppositely directed T waves
what is atrial fibrillation associated with?
dilated or stretched atria meaning normal cell to cell conduction is lost
how do the T waves, P waves and QRS complexes appear in cases of atrial fibrillation?
T waves and QRS complexes are normal
no P waves (usually get fibrillation)
what causes a supraventricular premature complex?
ectopic focus in the atria or AV junction depolarises the atria prematurely causing a normal looking premature complex
what is it called when there is a run of supraventricular premature complexes?
paroxysmal supraventricular tachycardia
what is the hallmark feature of a ventricular ectopic complexes?
wide and bizarre QRS
oppositely directed T waves
what is ventricular bigeminy?
alternating sinus complexes (normal P, QRS, T) with ventricular premature complexes (wide bizarre QRS, opposite T waves)
what is the outcome for animals in ventricular fibrillation?
usually terminal event
how does hyperkalaemia affect ECGs?
bradycardia
no discernible P waves
normal QRS complex
tall spikes T waves (negative, positive or biphasic)
