Dysrhythmias SDL Flashcards

1
Q

What is the correct way to interpret an ECG?

A
  • 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?
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2
Q

What is a NORMAL SINUS RHYTHM (N.S.R.).?

A
  • 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).

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3
Q

What does a normal sinus rhythm look like?

A
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4
Q

What is a sinus SINUS ARRHYTHMIA.?

A
  • 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

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5
Q

What does a sinus arrhythmia look like?

A
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6
Q

What are SINUS ARRHYTHMIA - ASSOCIATED CONDITIONS?

A

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.
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7
Q

SINUS ARRHYTHMIA - TREATMENT?

A

None

UNLESS profound bradycardia and clinical signs associated

See bradydysrhythmias.

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8
Q

Discuss a wandering pace maker?

A

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

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9
Q

What are Bradydysrhythmias?

A

–Variations on sinus arrhythmia – not usually clinically significant

Sinus arrest, 2nd/3rd degree AV block – usually are clinically significant

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10
Q

What are Tachydysrhythmias?

A

–Supraventricular – arise in or above AVN, USUALLY narrow and upright in lead II

–Ventricular – arise from ventricles – wide and bizarre in lead II

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11
Q

What does sinus bradycardia look like?

A
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12
Q

Discuss Prolonged sinus pause bradydysrhythmias?

A

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
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13
Q

What is sinus arrest?

A

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
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14
Q

Look at this sinus arrest?

A
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15
Q

Discuss Persistent atrial standstill Bradydysrhythmias?

A

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
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16
Q

Discuss Sick-sinus syndrome (sinus node dysfunction)?

A

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
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17
Q

Discuss First degree AV block?

Bradydysrhythmias - heart block

A

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

18
Q

Discuss second degree AV block?

Bradydysrhythmias - heart block

A

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
19
Q

Look at this second degree AV block?

20
Q

Discuss complete (third degree) AV block?

Bradydysrhythmias - heart block

A

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
21
Q

List clinically significant bradydysrhythmias?

A
  • High grade 2nd degree AV block
  • 3rd degree AV block
  • Sinus arrest
  • Sick sinus syndrome
  • Atrial standstill
22
Q

Clinical signs of Bradydysrhythmias?

A
  • weakness
  • lethargy
  • syncope
  • sudden death - rare
23
Q

MUST rule out primary causes of Bradydysrhythmias whic are?

A

MUST rule out primary causes

  • cardiomyopathy
  • digitalis/drug toxicity/effect
  • AV node fibrosis
  • endocarditis
  • electrolyte imbalance
24
Q

Think about this for bradydysrhythmias?

A
  • Is it vagal?
  • Usually prolonged sinus pause/block
  • Abolished by atropine/exercise
  • Rarely produce clinical signs
  • Rule out if exercise intolerant/collapsing
25
What is this?
Sinus pause/block Exaggerated sinus arrhythmia ?
26
What is the treatment for bradydysrhythmias?
Treatment * Primary cause – especially electrolyte disorders * Pacemaker implantation * Parasympatholytic drugs (e.g. atropine) – rules out “sinus” rhythms
27
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
28
Discuss SUPRAVENTRICULAR TACHYDYSRHYTHMIAS?
Dysrhythmias Rate \> Normal Origin in or above the AVN Atrial or Junctional – narrow complex
29
30
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
31
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
32
SupraV tachycardia can be?
33
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
34
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
35
36
Discuss VENTRICULAR PREMATURE COMPLEXES (VPCs).?
* A.k.a. ventricular ectopics - not always premature * Wide bizarre complexes interrupt normal rhythm
37
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
38
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).
39
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
40
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
41
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