ECG and Dysrhythmias in Small Animals Flashcards
what is the P wave
atrial depolarization
what occurs during the P wave (5)
- SA node cells in RA spontaneously depolarize –> depolarizes adjacent RA cells
- wave of depolarization moves towards the left
- cells in left atrium are at rest and a dipole is created –> positive end is closer to the positive electrode so get a upward trace
- when all RA and LA are depolarized the trace returns to base line
- next delay is the wave of depolarization passing through the atrioventricular node to the ventricles
what is the Q wave
early ventricular depolarization
what occurs in the Q wave
- wave of depolarization passes down the interventricular septum
- wave of depolarization spreads from left to right creating a dipole
- negative end of the dipole is closer to the + electrode so it creates a negative deflection on the ECG trave
what is the R wave
ventricular depolarization
what occurs in the R wave (4)
- endocardium depolarizes before the epicardium
- dipole is created which is very large since the number of cardiomyocytes within the left ventricle are numerous
- the positive end of the dipole is closer to the + electrode so it creates an upward deflection on ECG trace
- a dipole is created towards the left since the ventricular apex is directed towards the left and the left ventricle is much larger than the right and dominates
what is the S wave
late ventricular depolarization
what occurs in the S wave (3)
- the wave of depolarization finishes spreading from the endocardium to the epicardium of both ventricles
- the ECG returns to baseline and can sometimes go negative
- the negative end of the dipole is closer to the + electrode –> downward deflection in trace
what is the T wave
ventricular repolarization
what occurs in the T wave (3)
- the epicardium is the last to depolarize but the first to repolarize
- epicardial cells are now positive on the extracellular surface and create a dipole with the endocardial cells which are still depolarized
- positive end of the dipole is closer to the + electrode –> upward deflection in ECG occurs
what is the PR interval
PR: time between atrial depolarization and ventricular depolarization
what is the QT interval
length of time between the ventricles remain depolarized
what is the QRS complex interval
time take for the ventricular depolarization to occur once the wave of depolarization has passed through the AVN from the atria
what is the PP interval
time between atrial depolarizations
what is the RR interval
time between ventricular depolarizations
what are the uses of the ECG (4)
- diagnosis of arrhythmias noted on clincal exam
- rule in/out arrythmias in animals with a history of collapse
- provide info regarding chamber enlargement
- information on certain electrolyte disturbances (K+)
how are ECGs analyzed (8)
- heart rate (slow/normal/fast)
- heart rhythm (regular/irregular/chaotic)
- P:QRS ratio (1:1)
- relationship of P to Q-P-Q interval
- P and QRS complex variation
- normal complex measurement
- QT interval, ST segment & T waves
- assess the significance of any arrhythmias detected
how is the heart rate measured
count Y beats in 6s
Y x 10 = beats/min
with 25 mm/s paper speed (need to know)
what can you look for when assessing the rhythm (4)
- early beats
- delays
- fibrillation
- ectopic beats
what do you look at when looking at P:QRS ratio and relationship (3)
- check distance between P wave and the QRS complex. Is it too long?
- is there a P wave before the QRS
- is there a P wave without QRS
what is wandering pacemaker
P wave variation: tall wave and short wave
what are QRS complex variations
- venticular ectopies either from left ventricle or right ventricle
what occurs during an abnormal ventricular activation pattern from the left ventricle
sometimes called a right bundle branch block pattern QRS complex
electrical signal spreads through in an abnormal direction –> spread cranially –> negative QRS
wide bizarre QRS
what is an abnormal ventricular activation pattern from the right ventricle
sometimes called a left bundle branch block pattern QRS complex.
electrical activity travels from the right ventricle and travels from cranial to caudal which creates a positive QRS
what are the differences between premature and escape beats
what are P wave changes (3)
- absent: atrial standstill
- wide P waves: left atrial dilation
- tall P waves: right atrial dilation
what change is shown here
atrial standstill
absent P wave
what is shown here
wide P waves
left artial dilation
what abnormality is shown here
tall P waves
right atrial dilation
what are common QRS changes (4)
- tall R: left ventricular enlargement
- deep S: right ventricular enlargement
- small complexes: pleural effusion, obesity
- small variable height complexes: pericardial effusion
what is shown here
tall R left ventricular enlargement (also T wave is large)
what change is shown here
deep S
right ventricular enlargement
what is shown here
small complexes
pleural effusion, obesity
what is shown here
small variable height complexes
pericardial effusions
what could be causes of a prolonged QT interval (4)
- hypocalcemia
- hypokalemia
- hypothermia
- drugs (sotalol)
what are causes of shortened QT intervals (3)
- hypercalcemia
- hyperkalemia
- drugs (digoxin)
what does a prolonged QT cause
excessive intracellular calcium and possibly a rapid, fatal ventricular tachycardia called Torsade de Pointes
what does ST segment depression indicate
hypoxia
what is shown here
ST segment depression
what does ST segment coving indicate
left ventricular enlargement
what is shown here
ST segment coving
left ventricular enlargement
when are arrhythmias treated (3)
- causing signs in their own right (syncope)
- potentially life-threatening (ventricular tachycardia)
- no underlying immediately treatable cause
what are the classifications of rhythms (3)
- normal
- bradyarrhythmias
- tachyarrhythmias
what are normal rhythms (2)
- sinus rhythm
- sinus arrythmia (normal for dogs)
what rhythm is shown here
sinus rhythm
what rhythm is shown here
sinus arrhythmia
what are bradyarrhythmias (8)
- sinus arrest
- sick sinus syndrome
- sinus bradycardia
- atrial standstill
- primary AV block
- second degree AV block: mobitz type 1
- second degree AV block: mobitz type 2
- 3rd degree/complete AV block
what are the causes of a sinus arrest (2)
- medication: sedatives, beta blockers, calcium channel blockers, digoxin
- diseases: high vagal tone, atrial disease, hypothyroidism
what is sinus arrest
complete sessation SA node activity
normal beats but there is a pause –> followed by a ventricular ectopic beat which would be an escape because it follows a pause
what are arrhythmia is shown
sinus arrest
how do you treat sinus arrhythmias
address underlying problem
what breed might sinus arrest be normal for
brachycephalic
what can sinus arrest be accentuated by
general anesthesia
what rhythm is shown here
sick sinus syndrome
sinus tachycardia?
what breeds have a hereditary component to sick sinus syndrome
mini schnauzer
west highland white terrier
what diseases cause sick sinus tachycardia
idiopathic
may also have spells of tachycardia
how is sick sinus syndrome treated (3)
- pacemaker
- sympathomimetics: theophylline, propentofylline, terbutaline
- parasympathomimetics: propantheline
what is sinus bradycardia
sinus rhythm –> but very slow <60 in dogs, <100-120 in cats
beats of normal sinus origin and conduction, often regular
when can sinus bradycardia be normal (3)
- excessive vagal tone
- athletic animals
- normal rhythm under GA if not too slow if BP is acceptable
what are the causes of sinus bradycardia (3)
- medication: sedatives (ACP), drugs used to treat tachyarhythmias
- disease: hypothyroidism, increased intracranial pressure, dysautonomia, eletrolyte imbalances
- metabolic: hypothermia
how is sinus bradycardia treated
address the underlying problem
what is shown here
sinus bradycardia
what is atrial standstill
no P wave, regular QRS, followed by large spikey T waves
what rhythm is shown
atrial standstill
no P wave, regular QRS followed by large spikey T waves
what are the causes of atrial standstill (2)
- persistent: idiopathic, presumed atrial cardiomyopathy, muscular dystrophies, treated by pacing but prognosis is poor
- temporary: hyperkalemia (hypoadrenocorticism, oliguric renal failure)
how is atrial standstill treated
address underlying problem
what is first degree AV block
P wave then a delay before QRS complex
when is a first degree AV block normal
can be normal in dogs with slow heart rates esp during sleep
what can cause a first degree AV block (2)
- drugs: sedatives, tachyarrhythmia drugs
- disease: high vagal tone, fibrosis of AV node
what is a second degree AV block mobitz type 1
occasional P wave occurs without QRS-T complex
what rhythm is shown here
first degree AV block
delay after P wave
when can 2nd degree AV block mobitz type 1 be normal
in dogs with high vagal tone or alseep
normal in horses
what are the causes of 2nd degree AV block mobitz type 1 (2)
- diseases causing high vagal tone
- regular cycle of (several) dropped beats is more likely to be associated with progressive myocardial disease and may progres to 3rd degree AV block
how are 2nd degree AV block mobitz type 1 treated
address the underlying problem if possible but not usually symptomatic
what is the atropine response test
record ECG
give atropine s/c 0.04 mg/kg
approx 30 min later record a second ECG
if the arrythmia is gone –> then it is vagal in origin (HR usually >150)
what is a 2nd degree AV block mobitz type 2
Don’t see progressive lengthening of the PR interval and there is much more frequent dropping of beats and more frequent isolated P waves often in a an irregular (alternating between conductive and dropped beats)
what does a 2nd degree AV block mobitz type 2 indicate
significant and indicates AV node disease
what are the causes of 2nd degree AV block mobitz type 2
- diseases: AV node fibrosis, infiltration
how is 2nd degree AV block mobitz type 2 treated
pace if symptomatic often progresses to 3rd degree block
what rhythm is shown here
2nd degree AV block mobitz type 2
what is a 3rd degree/complete AV block
P waves and QRS-T complexes are completely dissocaited
normal P waves occur but the ventricles are activated at a slower rate from a junctional or ventricular focus –> escape beats look bizarre
what is the arrhythmia shown here
3rd degree/complete AV block
P waves and QRS-T complexes are completely dissociated
what are the causes of 3rd degree/complete AV block
- diseases: AV node fibrosis, AV node infiltration, lyme disease
what is the treatment of 3rd degree/complete AV block (3)
- pacemaker
- sypathomimetics: theophylline, propentofylline, terbutaline
- parasympatholytics: propantheline
what can a 3rd degree/complete AV block represent
serious myocardial disease or toxemia or conduction system degeneration but often myocardial function is otherwise preserved
what arryhthmia is shown here
3rd degree/complete AV block with no escape beats
what are the tachycarrythmias (7)
- sinus tachycardia
- supraventricular premature beat
- atrial fibrillation
- supraventricular/atrial tachycardia
- ventricular premature complex (VCP)
- ventricular tachycardia
- rapid ventricular tachycardia
what is sinus tachycardia
normal P-QRS-T complexes of SA node origin but at a higher than normal rate, regular rhythm
can be normal finding in nervous or excitable dogs (even up to 280-300)
what are the causes of sinus tachycardia
- medication: drugs used to treat bradycardia
- disease: anemia, pain, pyrexia, resp distress or in response to hypovolemia, shock, dehydration, septicemia, decreased CO, hyperthyroidism, hypertension under GA or due to cardiac failure
how is the sinus tachycardia treated
address underlying problem but not usually treated
what arrhythmia is this
sinus tachycardia
what is supraventricular premature beat
ectopic beat from the myocardium
can’t see P wave and if its there its abnormal in conformation
QRS-T complex is normal
what arryhthmia is shown
supraventricular premature beat
what causes supraventricular premature beats
- disease: atrial fibrillation, atrial fibrosis, systemic diseases such as pyrexia, neoplastic diseases
how is supraventricular premature beat treated
address underlying problem, but not treated specifically
what is atrial fibrillation
absent P waves which are replaced by fibrillation waves
QRS-T complexes are normal in conformation but are rapid and erratic (chaotic) rhythm
what are the causes of atrial fibrillation
- disease: atrial dilation, atrial infiltration, atrial fibrosis, occult dilated cardiomyopathy/lone atrial fibrillation
- larger dogs, uncommon in cats
what is the most common treated atrial arrhythmia in dogs
atrial fibrillation
how is atrial fibrillation treated
slow down ventricular rate, slow conduction through AV node
- digoxin
- usually with diltiazem
- (atenolol)
what is supraventricular/atrial tachycardia
bursts of atrial ectopic beats
what are the causes of supraventricular/atrial tachycardia
- congenital: by-pass tract (Wolf-Parkinson-White syndrome) –> bridging the atrial to the ventricular myocardium and bypassing the AV node and allowing rapid circuit of impulses going down the AV node and going back up the bypass tract
- disease: atrial dilation, atrial infiltration, atrial fibrosis, systemic disease
what is the treatment of supraventricular/atrial tachycardia (4)
- digoxin
- diltiazem
- atenolol
- sotalol ablation of by-pass tract
what is shown here
atrial fibrillation
what is shown here
supraventricular/atrial tachycardia
what is ventricular premature complex (VCP)
no P wave present (except by coincidence)
QRS-T complex is premature and prolonged duration and bizarre in shape often with a large, slurred S-T segment and T wave
what is paroxysmal ventricular tachycardia
ventricular premature complexes can occur as single or pairs or as rapid bursts
what is shown here
ventricular premature complexes (VCP)
what are the causes of ventricular premature complex (3)
- disease: ventricular myocardial dilation, inflammation, infiltration, fibrosis
- systemic disease: anemia, septicemia, splenic mass, gastric dilation, pyometra
- metabolic: electrolyte imbalance (hypokalemia)
how is ventricular premature complex treated
address underlying problem, but not treated specifically
what is ventricular tachycardia
runs of ectopic beats
can cause syncope and is life threatening
what is shown here
ventricular tachycardia
what are the causes of ventricular tachycardia
- disease: ventricular myocardial dilation, inflammation, infiltration, fibrosis
- systemic disease: anemia, septicemia, splenic mass (if rate in dogs is between 60 & 160/min, called accelerated idioventricular rhythm and NOT usually treated)
how is ventricular tachycardia
if runs >180/min, symptomatic, multiform R-on-T
lidocaine, magnesium, mexilitine, sotalol, amoidarone
what is shown here
rapid ventricular tachycardia
what are the causes of ventricular tachycardia
ventricular myocardial dilation
inflammation
infiltration
fibrosis
trauma
hypoxia
what is ventricular escape beat
ventricular ectopic following a pause are called escape beats
rescue beat: look for underlying cause of bradycardia
what is shown here
ventricular escape beat
