ECG Equipment and Monitoring Flashcards
how is the heart rate controlled?
2 branches of the autonomic NVS -
sympathetic and parasympathetic branches
how is the heart rate accelerated?
sympathetic nervous system releases hormones to accelerate heart rate
what is released by the sympathetic nervous system to accelerate heart rate?
catecholamines - adrenaline and noradrenaline
how is the heart rate decelerated?
parasympathetic nervous system releases acetylcholine to slow heart rate
what are the 2 types of cardiac cells?
electrical cells
myocardial cells
what is the function of the electrical cells
spontaneously generate electrical impulses and respond to impulses
transmit an electrical pulse from one cell to the next
how are electrical cells distributed?
in an orderly fashion
which type of cells make up the conduction system of the heart?
electrical cells
where are the myocardial cells found?
make up the walls of the atrium and ventricles of the heart
which type of cells make up the atrial and ventricular walls?
myocardial cells
what cardiac functions are the myocardial cells responsible for?
contraction and ability to stretch
which cells make the heart able to contract and stretch?
myocardial cells
what is required for cardiac muscle cells to contract?
an electrical stimulus
what state are the cardiac cells at rest?
polarised (relaxed)
when happens to the cardiac cells when there is an electrical stimulus?
cells start to depolarise
what allows the heart time to refill ready for the next stimulation and contraction?
heart must repolarise and return to its resting potential between beats
which parts of the heart are involved in contraction?
SA node
AV node
Bundle of His
Purkinje fibres
what is the SA node?
a small area of modified cardiac cells (specialised fibres)
where is the SA node located?
right atrium wall
which cells act as the pacemaker for the heart?
cells making up the SA node
how does autonomic tone affect heart rate?
sympathetic increases rate
parasympathetic decreases rate
what is the AV node?
specialised group of cardiac muscle cells
where is the AV node located?
top if the interventricular septum
how quickly does the electrical impulse from the SA node pass through the AV node?
passes through AV slower than SA
why is the electrical impulse through the ANV node slower than the SA node?
is it deliberately slow, so that ventricular contraction will be correctly coordinated following atrial contraction
(allows atria time to fully contract before the ventricles do)
what is the Bundle of His?
specialised bundle of nerve tissue fibres
why is the bundle of His necessary?
myocardium of the atrium walls is not in electrical continuity with myocardium of the ventricular walls
how does conduction pass through the AV ring?
through the Bundle of His
what does the AV ring connect?
the atria to the ventricles
where is the bundle of His located?
a narrow pathway which runs down the interventricular septum
how does the bundle of His divide?
divides in the interventricular septum into left and right bundle branches - these branches then spread into the right and left ventricles
what happens to the left bundle branch of the bundle of His?
divides further into anterior and posterior fascicles
what are the Purkinje fibres?
a network of specialised neurones, which are organised in very fine branches
what does the bundle of His go on to connect with?
the Purkinje fibres
where are the Purkinje fibres located?
spread out through the myocardium of the right and left ventricles
where does the wave of ventricular contraction begin?
in the myocardium at the apex of the heart (bottom of ventricles)
what is the stage where the ventricles contract called?
ventricular systole
what happens after the heart cells repolarise?
the SA node fires another impulse and the cycle begins again
what is electrocardiography?
a continuous measurement of the changing potential differences in the electrical activity of the heart
what does an ECG machine detect?
the depolarisation wave travelling across the heart
how does the ECG machine records the depolarisation wave?
as deflection
-ive deflections = downwards
+ive deflections = upwards
when are ECGs used?
diagnostic - arrhythmias
triage
anaesthesia
monitoring patients with known arrhythmias
newly identified pulse deficits
during CPR
metabolic or electrolyte abnormalities
blood transfusions
which type of surgery heavily relies on ECG for monitoring?
during pericardiocentesis and central line catheter placement (arrhythmias can arise during procedure)
what are the 2 types of commonly used ECG electrodes?
crocodile clips - directly onto patients skin with spirit
ECG pads - onto paws with tape/thorax
what are the general considerations for obtaining a good ECG trace?
patient in right lateral recumbency
remove sources of interference e.g. mobiles
why might a paper trace ECG recording machine be used?
has high diagnostic value
why might a patient be attached to a Holter monitor?
for monitoring over a longer period - patient can go home and any abnormal activity reviewed at recheck
what is telemetry?
monitoring patients with ECG from a distance
what is the advantage of telemetry?
less machines attached directly to patient
what should you consider when troubleshooting an ECG?
check setting on machine, batteries, charge
are leads still attached and on correct legs
minimise patient movement as interferes with trace, ideally have in right lateral recumbency
panting/purring can also affect trace
check contact of crocodile clips to skin, reapply spirit
change pads if dry/dislodged/not sticking well
clip fur for better contact
what does the P wave represent?
atrial depolarisation
why is the P wave small compared to the QRS wave?
muscle mass of atria is relatively small, therefore electrical changes associated with the depolarisation are also small
what does the P-R interval represent?
the time between atrial depolarisation and ventricular depolarisation
how is the P-R interval measured?
as the onset of the P wave to the onset of the R wave
what is indicated by a normal P-R interval?
the electrical impulse is travelling between the atria and ventricles correctly
what is indicated by the Q wave?
depolarisation of the ventricular septum
which part of the ventricles is the first to depolarise?
ventricular septum
why is the Q wave shown as a downward deflection on an ECG trace?
travels in a direction away from the positive electrode
what does the R wave indicate?
depolarisation of the majority of the ventricular myocardium
why is the R wave so large?
the ventricular myocardium is a large mass of muscle tissue - creates a large positive deflection
what does the S wave respresent?
final depolarisation of a small mass of tissue at the base of the heart
what does the QRS complex represent?
depolarisation (activation) of the ventricles, followed by ventricular muscle contraction
where do we see baseline ECG trace?
the P-R segment and the S-T segment
what is the s-T segment?
the interval between ventricular depolarisation and ventricular repolarisation
what does the T wave represent?
repolarisation of the ventricles - marks the beginning of ventricular relaxation
why does the T wave occur?
there is a potential difference across the myocardium here, until is completely repolarised - usually results in a small positive deflection from the baseline
why can the T wave vary?
repolarisation of the myocardium can be random in cats and dogs - can be positive, negative or both
what are our main considerations when interpreting an ECG?
heart rate
presence/absence of expected waves
presence/absence of arrhythmias
what is a bradyarrhythmia?
slow arrythmia
what is a tachyarrhythmia?
fast arrhythmia
what do we need to consider in terms of arrhythmia source?
sinus arrhythmia vs ventricular arrhythmia vs supraventricular arrhythmia
what type of issues can cause arrhythmias?
abnormalities in rate, electrical impulse conduction and abnormalities associated with ectopia
what are the types of sinus rhythms?
normal sinus rhythm
sinus arrhythmia
what are the types of bradyarrhythmias?
sinus bradycardia
sick sinus syndrome
AV blocks
escape beats
hyperkalaemia
what are the types of tachyarrhythmias?
sinus tachycardia
supraventricular tachycardia
atrial fibrillation
ectopic beats
accelerated idioventricular rhythm
ventricular tachycardia
R-on-T phenomenon
what are the cardiac arrest rhythms?
ventricular fibrillation
pulseless ventricular tachycardia
pulseless electrical activity
asystole
what is sinus rhythm?
normal rhythm
what does an ECG trace look like for sinus rhythm>?
P wave, QRS complex and T wave present
P wave present for every QRS complex
all complexes identical
what does sinus rhythm sound like on auscultation?
regular heart sounds
where does the electrical impulse originate from in sinus arrhythmia?
SA node
what does sinus arrhythmia look like on ECG?
normal P wave for every QRS wave
what is sinus arrhythmia?
commonly a regular variation in HR, which co-insides with respiration (respiratory sinus arrhythmia)
what is sinus arrhythmia associated with?
an increase in parasympathetic activity (vagal tone) on the SA node
what heart rhythm can be seen due to increased parasympathetic activity on the SA node?
sinus arrhythmia
do cats dispay sinus arrhythmia?
rarely
what type of rhythm is sinus arrhythmia?
regularly irregular
what causes sinus bradycardia?
SA node impulse and corresponding depolarisation occurs slower than normal
what does sinus bradycardia look like on ECG?
P wave for every QRS wave
what happens to the heart rate in sinus bradycardia?
heart rate may be inappropriately slow for age/breed/species
pulse for every heart beat
what type of rhythm is sinus bradycardia?
regularly regular
what are the broad causes of sinus bradycardia?
normal in some breeds
can be due to issue with SA node
often secondary to another disease process which increases vagal tone
what are the other causes of sinus bradycardia?
hyperadrenocorticism and associated electrolyte abnormalities
BOAS
raised ICP
vaso-vagal reaction (nerve stimulation)
hypocalcaemia/hypothermia/hypoglycaemia
hypothyroidism
how is sinus bradycardia treated?
dictated by underlying cause - depends if patient has clinical signs of arrhythmia
temporary management via an anticholinergic to increase HR
positive inotrope if anticholinergic unsuccessful
what is sick sinus syndrome?
problem with SA node function - failure to discharge electrical impulse
how does sick sinus syndrome present?
severe bradycardia occurs due to decreased SA node input (<30bpm)
periods of asystole can be present for several seconds without escape beats (sinus arrest)
which animals are affected by sick sinus syndrome?
older animals (6-10 years)
WHWT, cocker spaniels, cairn terriers and miniature schnauzers
rare in cats
what type of condition is sick sinus syndrome?
degenerative condition
how is sick sinus syndrome treated?
responds poorly to medical management
requires pacemaker
what are the potential risks of pacemaker placement?
infection
lead dislodgement
failure to place correctly
venous thrombosis
what are the nursing considerations after pacemaker placement?
no walking for 48 hours post-placement
harness walks only
care with neck restraint
no jugular samples
what is heart block?
problem with the electrical conduction system of the heart
how does AV block occur?
electrical impulses from the SA node are delayed, or completely blocked, going through the AV node - electrical signals may not reach the ventricles
what causes AV block?
can be due to a disease process or drug-related effect at the AV node
which blocks affect the AV node?
AV bock or AV nodal block
which blocks affect the left or right bundle branches?
bundle branch blocks
what is first degree AV block?
delayed conduction through the AV node
what does first degree AV block look like on ECG?
normal P wave and QRS complex
longer interval between the P wave and corresponding QRS complex (prolonged P-R interval)
how does second degree AV block differ from first degree?
longer conduction delay, some beats dropped
what does second degree AV block look like on ECG?
some P waves will not have a corresponding QRS
QRS complexes are normal in morphology
how do the QRS complexes in AV block have a normal shape?
there is conduction through the AV node
what are the 2 types of second degree AV block?
mobitz type I
mobitz type II
what happens in mobitz type I?
P-QRS gap becomes longer and longer, then there is a P wave without a corresponding QRS complex
once QRS complex missed, snaps back to normal
what is mobitz type I also known as?
wenkebach
what happens in mobitz type II?
P-QRS complex normal (P-R interval same each time)
occasionalP with with no corresponding QRS complex
what is 3rd degree AV block?
complete lack of conduction through the AV node
what does 3rd degree AV block look like on ECG?
multiple P waves without QRS complexes
P waves occur faster, sometimes followed by a tall QRS-T complex
why do ventricular ‘escape beats’ occur in 3rd degree AV block?
they are ectopic beats which act as a rescue for the heart, permitting a heart beat
animal would die without them
how do ventricular escape beats occur?
an electrical impulse occurs from random cardiac cells, before cardiac standstill occurs
what do ventricular escape beats look like?
wide and bizarre, with an absent P wave
what is the heart rate during AV block?
rate of ventricular escape beats is typically 20-40bpm
what are the clinical signs of AV block?
if severe block is present, signs of decreased cardiac output e.g. lethargy, syncope, collapse
how can AV block be treated?
management of underlying condition e.g. hypoadrenocorticism
vagolytic drugs e.g. atropine, glyocpyrrulate
severe 2nd and 3rd degree blocks require pacemaker implantation
what is hyperkalaemia?
increased serum potassium levels
what is the normal range for serum potassium?
3.5-5.0 mmol/l
what effect does increased potassium have on heart function?
severity of arrhythmia progresses as K+ increases
what type of arrhythmia does hyperkalaemia typically induce?
bradyarrhythmias
how do arrhythmias due to hyperkalaemia present on ECG?
reduced/absent P waves
spiked T waves
shortened QT interval
prolonged QRS complex
how does severe hyperkalaemia affect the heart?
progresses to atrial standstill, sine wave pattern, ventricular fibrillation and eventual asystole
what are some of the causes if hyperkalaemia?
urethral obstruction e.g. blocked bladder
AKI e.g. toxin
hypoadrenocorticism e.g. Addisonian crisis
arrhythmias due to hyperkalaemia be treated?
calcium gluconate bolus
neutral insulin infusion
dextrose infusion
how can a calcium gluconate bolus treat arrhythmias due to hyperkalaemia?
reduces risk of ventricular fibrillation and protects cardiac myocytes from effect of elevated K+
(doesn’t actually reduce K+ levels)
how can a neutral insulin infusion help treat hyperkalaemia?
causes movement of potassium into cells
how can a dextrose infusion help treat hyperkalaemia?
cells uptake glucose, intracellular shift of K+ into cells prevents hypoglycaemia due to insulin infusion
what happens in sinus tachycardia?
SA node generates an impulse and depolarisation at a rate faster than normal
what does sinus tachycardia look like on ECG?
normal sinus rhythm, with normal P-QRS-T complexes
what type of rhythm is sinus tachycardia?
regularly regular rhythm
can pulses still be felt in sinus tachycardia?
pule should be present for every heartbeat, with very fast rates pulses may become weaker
when does sinus tachycardia occur?
can be normal e.g. after exercise
occurs with pain, stress, hypovolaemia, anaemia
where do supraventricular tachyarrhythmias originate?
atrial in origin (occurs in atrium)
where do supraventricular tachyarrhythmias occur?
occur at a point other than the SA node, then conduct via the AV node to the ventricles
what does a supraventricular arrhythmia typically look like on ECG?
QRS complexes relatively normal in appearance
often taller and narrower than normal
where do ventricular arrhythmias originate?
ventricular in origin
what happens in ventricular arrhythmias?
normal conduction pathway is not followed
how do ventricular arrhythmias appear on ECG?
QRS complexes appear wide and bizarre
how can we tell if a cardiac impulse has arisen from an ectopic location?
if the P-QRS-T complex looks different to normal
if a P-QRS-T complex in a trace looks abnormal, what does this mean?
the impulse has arisen from an ectopic location
what does ectopic mean?
out of place (electrical impulse did not originate from the SA node)
when do ectopic beats occur?
prematurely
why do ectopic beats look abnormal?
they interrupt the normal rhythm, before the SA node is ready to initiate another impulse
where do ectopic beats originate?
can originate from the atria or ventricles
how are ectopic beats classified?
by their point of origin
what an atrial premature complex?
an ectopic beat that is atrial in origin
what is an ectopic beat that is atrial in origin called?
atrial premature complex
what is an ectopic beat that is junctional in origin called?
junctional premature complex
what is a junctional premature complex?
an ectopic beat that is junctional in origin
what is an ectopic beat that is ventricular in origin called?
ventricular premature complex
what is a ventricular premature complex?
an ectopic beat which is ventricular in origin
give an example of some arrhythmias which have ectopic beats
supraventricular tachycardia
escape beats (e.g. 3rd degree AV block)
what is a supraventricular arrhythmia?
an abnormal electrical impulse which occurs at an ectopic site in the atria (not the SA node)
what does a supraventricular arrhythmia look like on ECG?
often an abnormal P wave (as it is not initiated by the SA node) followed by a QRS complex
what type of rhythm is a superventricular arrhythmia?
often irregularly irregular
what are the alternative terms for a superventricular arrhythmia?
atrial premature complex (APC)
premature atrial contraction (PAC)
atrial premature beat (APB)
how many APCs are considered supraventricular tachycardia?
three or more APCs in a row
what is the heart rate during supraventricular tachycardia?
rapid - can be 170-350bpm
what does supraventricular tachycardia look like on ECG?
QRS complexes are almost like normal, however they are narrower and more upright
may or may not be an associated P wave
what type of rhythm is supraventricular tachycardia?
regularly irregular
what are the clinical signs associated with supraventricular tachycardia?
slow SVT = often no signs
fast SVT (>250bpm) = weakness/collapse, poor pulse quality, poor peripheral perfusion, pale MMs, prolonged CRT
why do clinical signs of supraventricular tachycardia occur?
due to inadequate diastolic filling
what causes supraventricular tachycardia?
usually associated with underlying cardiac disease e.g. DCM
sometimes associated with systemic disease e.g. toxicity, hypovolaemia, electrolyte imbalance, ischaemia
how can supraventricular tachycardia be treated?
treatment of any underlying causes
beta-blockers
calcium channel blockers
what type of arrhythmia is atrial fibrillation?
supraventricular tachyarrhythmia
what is atrial fibrillation?
characterised by rapid and irregular contractions of the atria (‘quivering’)
which species gets atrial fibrillation more commonly?
relatively common in dogs, rare in cats
what might we find on examination of a patient in atrial fibrillation?
pulse deficits common
irregular pulse (ventricles may contract before they have filled sufficiently)
rapid HR (>200bpm), irregular beating with no obvious pattern
what does atrial fibrillation look like on ECG?
fibrillating baseline
QRS complex tall and narrow
no visible P waves
why is there no visible P waves with atrial fibrillation?
impulse not from the SA node
what type of rhythm is atrial fibrillation?
irregularly irregular
how can atrial fibrillation be treated?
calcium channel blockers
beta-blockers
digoxin
amiodarone
what are the goals of atrial fibrillation treatment?
decrease heart rate and increase cardiac output
what is a junctional premature complex?
ectopic beats that arise from an area within the atrioventricular junction, therefore ventricles are usually activated normally
what is the atrioventricular junction?
region of the AV node
what do junction premature complexes look like on ECG?
QRS complexes are premature, with morphology very similar to sinus complexes but narrower
usually without a preceding P wave, but this may be hidden, abnormal or premature
what are junctional premature complexed also called?
premature junctional complex
junctional premature beat
where does the impulse come from in ventricular arrhythmias?
abnormal electrical impulse starts at an ectopic site below the AV node
what acts as the pacemaker in ventricular arrhythmias?
another area in the ventricles
what do complexes look like in ventricular arrhythmias?
wide and bizarre as normal electrical pathway is not followed
what cause ventricular arrhythmias?
underlying primary cardiac disease
as a complication due to another condition e.g. GDV, pyometra, splenectomy, pancreatitis, anaemia
what is a ventricular premature complex?
an ectopic beat that occurs prior to normal SA node depolarisation
where do VPCs start?
an unusual location in the ventricles
what do VPCs look like on ECG?
no preceding P wave (except by coincidence)
wide and bizarre QRS complex
how do VPCs affect pulses?
pulse quality may feel weak with certain beats
pulse deficits present
what can ventricular premature complexes also be called?
premature ventricular contractions
what does AIVR stand for?
accelerated idioventricular rhythm
what is AIVR?
3 or more VPCs together
what is the heart rate during AIVR?
not very elevated - 140-180bpm
does AIVR affect cardiac function significantly?
generally considered benign rhythm at lower rates, unlikely to be causing decreased cardiac output, haemodynamic compromise or hypotension
what is the treatment for AIVR?
treatment not usually required
when is AIVR sometimes seen?
in patient recovering from abdominal surgery
what can AIVR develop into?
ventricular tachycardia
what is the difference between AIVR and ventricular tachycardia?
traces look similar but AIVR is at a slower HR (140-180bpm)
how are VPCs identified as V-tach?
3 or more VPCs occurring in a row with heart rate >180bpm
what does V-tach look like on ECG?
QRS complexes wide and bizarre, with absent P waves and large T waves
what clinical findings would you expect to see in a patient with V-tach?
pulses weak, rapid and irregular, with pulse deficits
hypotension/collapse due to reduced cardiac output
signs of haemodynamic compromise
what signs of haemodynamic compromise might be seen in a patient with V-tach?
altered mentation
signs of hypoperfusion (pale mm’s prolonged CRT, hypothermia, weak/absent peripheral pulses)
what are some of the causes of V-tach?
primary cardiac disease e.g. DCM/HCM
significant abdominal pathology e.g. GDV
inflammation/inflammatory mediators e.g. septic abdomen, trauma
severe anaemia
abnormal autonomic activity e.g. pain
electrolyte disturbances
drug toxicities e.g. caffeine, cocaine
neoplasia e.g. haemangiosarcoma
what are the consequences of sustained V-tach?
decreased systemic tissue perfusion (cardiogenic shock)
decreased cardiac perfusion
development of myocardial failure
development of malignant arrhythmia (v-fib)
sudden death
what is the aim of treatment for V-tach?
convert to sinus rhythm and low HR down to allow better cardiac output and peripheral perfusion
what does treatment for V-tach depend on?
degree of haemodynamic compromise and underlying cause
which patients in V-tach are more likely to require immediate drug intervention?
patients with underlying heart disease - risk of cardiac arrest
what is V-tach called if there is no associated pulse?
pulseless ventricular tachycardia (PVT)
which drug is the most commonly used for treating V-tach?
lidocaine - sodium channel blocker
how is lidocaine given for treatment of V-tach?
boluses then CRI
which other drugs might be used in management of V-tach?
beta-blockers
amiodarone
procainamide
magnesium
how does the R-on-T phenomenon occur?
VPC is so premature, it is superimposed on the T wave of the preceding complex - can be a sinus beat or ectopic beat
why is R-on-T phenomenon potentially very serious?
the end of the T wave is a ‘vulnerable period’
anything abnormal during this period can preclude the occurrence of V-tach and V-fib
what happens to the ventricles during R-on-T phenomenon?
ventricles have not had time to completely repolarise from the previous contraction before they are depolarised again
what is the aim of using a defibrillator?
to reset the electrical state of the heart, thereby converting from a shockable arrhythmia to normal sinus rhythm
why do we need to take car with which rhythms we defibrillate?
shockable rhythms seen less frequently - defibrillating a non-shockable rhythm can be detrimental to survival
what are the shockable rhythms?
ventricular fibrillation
pulseless ventricular tachycardia
what are the non-shockable rhythms?
asystole
pulseless electrical activity (PEA)
what is ventricular fibrillation?
no effective ventricular contractions (all chaotic)
how serious is V-fib?
pre-terminal condition - results in patient death unless instantly recognised and treated
what does v-fib look like on ECG?
rapid, irregular, wavy baseline with no recognisable normal complexes
what are the 2 types of v-fib?
fine or coarse
how will a patient in v-fib present?
collapsed - no cardiac output, therefore no palpable pulses
what is the treatment for v-fib?
immediately start CPR
v-fib is a shockable rhythm - defib required
what is PEA?
electrical impulses within the heart, but no corresponding myocardial contractions
what does PEA look like on ECG?
may show slow, normal or fast HR
often normal P-QRS-T complex, which may become increasingly wide and bizarre
what will be found upon clinical exam of a patient with PEA?
no audible heart beats, no palpable pulses, no cardiac output
what is the treatment for PEA?
CPR, adrenaline, atropine
only defibrillate if converts to a shockable rhythm
what is the most common arrest arrhythmia in dogs and cats?
asystole
what does asystole look like on ECG?
straight, flat-line ECG
no complexes
what does asystole mean?
patient in CPA - no cardiac movement, no pulses or cardiac output
what is the treatment for asystole?
start CPR immediately
non-shockable rhythm
