Dysrhythmias SDL Flashcards
What is the correct way to interpret an ECG?
- What is the rate – MAX, MIN, MEAN
- Is it regular or irregular?
- If irregular - is it irregularly irregular or regularly irregular?
- Is there a P for every QRS?
- Is there a QRS for every P?
- Are the Ps and the QRSs consistently and similarly related?
- Are all the Ps alike?
- Are all the QRSs alike?
- Are the QRSs narrow and upright in leads 2/3/AVF
- Are the QRSs wide and bizarre?
What is a NORMAL SINUS RHYTHM (N.S.R.).?
- Normal impulse originates in the S.A.N.
- The S.A.N. has an inherent pacemaker rate of
- 70-160 b.p.m in the dog (upto 180 in toy breeds, 220 in puppies) 160-240 b.p.m. in the cat
- P waves are usually positive in lead II, consistent configuration
- The PR interval is usually consistent from beat to beat.
- The QRS complex is usually “normal” (unless IVCD)
- QRS is wide and bizarre if an intraventricular conduction defect
(e.g. bundle branch block)
• The rhythm may be regular or irregular (sinus arrhythmia).
What does a normal sinus rhythm look like?
What is a sinus SINUS ARRHYTHMIA.?
- As N.S.R. except greater variation in P-P interval.
- The rhythm is irregular - regularly so
- If related to the respiratory cycle -
RESPIRATORY SINUS ARRHYTHMIA
normal rhythm in the dog,abnormal in the cat
mediated by fluctuations in vagal tone
abolished by atropine
accentuated by vagal manouvres.
•”NON-RESPIRATORY” SINUS ARRYHTHMIA
What does a sinus arrhythmia look like?
What are SINUS ARRHYTHMIA - ASSOCIATED CONDITIONS?
Sinus arrhythmia may be marked in:
- Pulmonary, C.N.S., G/I conditions (secondary to high vagal tone).
- Cholinergic drug use e.g. digoxin, opiates.
- Brachycephalic individuals.
SINUS ARRHYTHMIA - TREATMENT?
None
UNLESS profound bradycardia and clinical signs associated
See bradydysrhythmias.
Discuss a wandering pace maker?
WANDERING PACEMAKER
- Often accompanies sinus arrhythmia
- THE ONLY TIME YOU WILL SEE A WP IS IN ASSOCIATION WITH RSA!
- QRS complex is normal (unless IVCD)
- The P wave configuration varies, often cyclically
- The PR interval stays within normal limits but may vary
- In extreme forms P wave changes
from positive, through isoelectric to negative
as pacemaker shifts from SAN to region of AVN
•Physiological
What are Bradydysrhythmias?
–Variations on sinus arrhythmia – not usually clinically significant
Sinus arrest, 2nd/3rd degree AV block – usually are clinically significant
What are Tachydysrhythmias?
–Supraventricular – arise in or above AVN, USUALLY narrow and upright in lead II
–Ventricular – arise from ventricles – wide and bizarre in lead II
What does sinus bradycardia look like?
Discuss Prolonged sinus pause bradydysrhythmias?
Prolonged sinus pause
- Failure of pacemaker to discharge
- Pause with no P-QRS-T complex
- Maybe a variation of sinus arrhythmia, with slightly longer pauses?
- NB normal variation - brachycephalic breeds exaggerated sinus arrythmia
- 1 complex missing (sinus block?)
- If pause is >2RR intervals, it is called prolonged sinus pause, followed by another P wave
What is sinus arrest?
INTERMITTENT long periods with no P wave - followed by escape complexes (junctional or ventricular) - may result in syncope
Causes:
- Vagal?
- Fibrosis
- Cardiomyopathy
- Drugs (esp. digitalis)
- Electrolyte, esp potassium, imbalance
Look at this sinus arrest?
Discuss Persistent atrial standstill Bradydysrhythmias?
Persistent atrial standstill
- There is an absence of P waves
- The heart rate is usually slow
- QRST - normal - junctional escape rhythm
- May progress to ventricular escape rhythm – wide and bizarre complexes
- Clinically - weakness, lethargy and syncope
- DDx - hyperkalaemia and digitalis toxicity
- Atropine no effect
- Treatment - pace if no treatable primary disease
- May be part of generalised muscular condition
Discuss Sick-sinus syndrome (sinus node dysfunction)?
Bradydysrhythmias
Sick-sinus syndrome
(sinus node dysfunction)
- A number of abnormalities of the SAN node
- Including severe sinus bradycardia and severe SA block/arrest
- Often also have episodes of supraventricular tachycardias
- “bradycardia-tachycardia syndrome”
- During sinus arrest, often failure of escape beats
- Especially some breeds - WHWT
- Atropine or exercise - no effect
- Treatment - pacemaker implantation
- Possibly + antidysrhythmic drugs for tachycardia
Discuss First degree AV block?
Bradydysrhythmias - heart block
First degree AV block
- P wave and QRS complex are normal
- P-R interval is prolonged (dog >0.13 sec., cat >0.09 sec.)
- May occur normally in animals with a slow heart rate
- May be seen in ageing animals due to AV node degenerative changes
- Does not in itself cause any clinical problems
- Treat any underlying disease e.g.
–digitalis toxicity
–other drugs (e.g. propranolol, procainamide)
–potassium imbalance
Discuss second degree AV block?
Bradydysrhythmias - heart block
Second degree AV block
- P wave not conducted through the AV node - P without QRS
- Frequency of the block may be constant i.e. 2:1, 3:1
- High grade – lots of dropped P waves – may be clinical
- Low grade occasional dropped P wave (may be an extension of sinus arrhythmia?).
- Usually idiopathic
- R/O drug use and potassium imbalance
Look at this second degree AV block?
Discuss complete (third degree) AV block?
Bradydysrhythmias - heart block
Complete (third degree) AV block
- Persistent failure of conduction through AV node
- Ventricles usually paced from ventricular focus
- wide, bizarre escape complexes
–Approximately 30-40/min (dog)
- P waves at normal/fast rate - P-P interval constant
- QRS-T at a slower rate - R-R interval constant
- Independent of each other - atrioventricular dissociation
- Ps are unrelated to QRSs
- Usually idiopathic
List clinically significant bradydysrhythmias?
- High grade 2nd degree AV block
- 3rd degree AV block
- Sinus arrest
- Sick sinus syndrome
- Atrial standstill
Clinical signs of Bradydysrhythmias?
- weakness
- lethargy
- syncope
- sudden death - rare
MUST rule out primary causes of Bradydysrhythmias whic are?
MUST rule out primary causes
- cardiomyopathy
- digitalis/drug toxicity/effect
- AV node fibrosis
- endocarditis
- electrolyte imbalance
Think about this for bradydysrhythmias?
- Is it vagal?
- Usually prolonged sinus pause/block
- Abolished by atropine/exercise
- Rarely produce clinical signs
- Rule out if exercise intolerant/collapsing
What is this?
Sinus pause/block
Exaggerated sinus arrhythmia ?
What is the treatment for bradydysrhythmias?
Treatment
- Primary cause – especially electrolyte disorders
- Pacemaker implantation
- Parasympatholytic drugs (e.g. atropine) – rules out “sinus” rhythms
Discuss tachydysrhythmias?
•Supraventricular – NARROW COMPLEX
–Unless conduction abnormality
•Ventricular – WIDE COMPLEX
–No P wave
•Causes
–Structural heart disease
–Systemic disease
–Sympathetic nervous system activation
–Drugs and toxins
Discuss SUPRAVENTRICULAR TACHYDYSRHYTHMIAS?
Dysrhythmias
Rate > Normal
Origin in or above the AVN
Atrial or Junctional – narrow complex
Discuss SUPRAVENTRICULAR PREMATURE COMPLEXES?
- Rhythm interrupted by supraventricular (narrow and upright) complex
- P wave may be different/lost in preceding T waves
Associated conditions.
Most commonly seen in patients with atrial enlargement, stretch - all forms of structural cardiac disease
Discuss SUPRAVENTRICULAR TACHYCARDIA?
- Narrow complex tachycardia at rate > normal
- May have different P waves from sinus P waves
- Common in patients with structural heart disease/heart failure
- High rates (>180) may need rate control
SupraV tachycardia can be?
Discuss atrial fibrillation?
- Heart rate may or may not be within normal limits
- Rhythm is irregularly irregular
- No isoelectric baseline
- Irregular, variable amplitude F waves may be evident
- QRS complex is usually normal
Atrial Fibrillation - associated conditions:
As for APCs, atrial tachycardia and atrial flutter.
- Common on dilated cardiomyopathy in giant breeds especially.
- May occur as 1ry dysrhythmia in some giant breeds
Discuss VENTRICULAR PREMATURE COMPLEXES (VPCs).?
- A.k.a. ventricular ectopics - not always premature
- Wide bizarre complexes interrupt normal rhythm
VENTRICULAR PREMATURE COMPLEXES (VPCs) Associated conditions:
- Maybe none in some individuals
- Structural cardiac disease - congenital and acquired
- Drugs - digitalis glycosides, anaesthetics etc
- Hypoxia
- Autonomic tone
- Systemic disease
Discuss ventricular tachycardia?
- A “run” of 3 or more VPCs
- Rhythm is usually regular during tachycardia
- Rate WNL but > intrinsic rate of the ventricles
>40 b.p.m. in the dog
>60 b.p.m. in the cat
- Accelerated idioventricular rhythm = rate of 60-100
- Ventricular tachycardia = rate of >100
- P waves may be evident, as may capture and fusion beats
- Atrio-ventricular dissociation.
May be sustained or non-sustained (paroxysmal).
Discuss Bundle branch blocks
(Intraventricular conduction defects)?
- right bundle branch block (RBBB)
- left bundle branch block (LBBB)
- left anterior fascicular block (LAFB)
Produce abnormal QRST depolarisation patterns
Discuss Right Bundle Branch Block?
- Prolonged complex (> 0.07 sec)
- Deep S in leads I, II, III and aVF; and is +ve in aVR and aVL
- MEA is to the right
- DDx right ventricular enlargement pattern
- The RBB vulnerable to damage
- Common in the dog
- No haemodynamic significance on its own
- Check for congenital or acquired heart disease, neoplasia
- Treat any underlying disease
Discuss Left Bundle Branch Block?
- Prolonged complex (>0.07 sec)
- Positive leads I, II, III and aVF; and –ve in aVR and aVL
- DDx left ventricular enlargement pattern
- Rarer – may represent severe underlying disease
- Treat any underlying disease
