ECG Rhythm Disturbance Flashcards
Bradyarrhythmia origins
- SA node
- AV node
How to know if a bradyarrhythmia is from a sinus node?
- Decreased rate of P waves or absent P waves
How to know if a bradyarrhythmia is from AV node?
- Slow/absent conduction through the AV nodes
- P waves without QRS
Characteristics of sinus bradycardia or bradyarrhythmia
- Normal P wave for every QRS but P and QRS occur at a slow rate
- Normal PR interval
- Normal QRS
- QRS may be variably spaced if sinus arrhythmia
Treatment for sinus bradycardia
- Generally a response to other systemic issues
- High vagal tone (disease of GIT, pulmonary organ, brain, or eyes)
- Anesthesia/sedation
- Medications
- ID and address underlying cause
- In situations such as anesthesia complications, atropine may be given
Sick sinus syndrome
- Abnormal rhythm disturbance in older small breed dogs (schnauzer, dachshund, west highland white terrier, cocker spaniel)
Characteristics of sick sinus syndrome
- Sinus bradycardia
- Sinus arrest (pause without P or QRS)
- AV block
- Supraventricular tachycardia (especially after a long pause)
- See the example
What can happen during sinus arrest?
- Collapse due to absence of cardiac contraction
- Usually 6 second break is enough
AV node disease characteristics
- Normal or elevated P wave rate
- Decreased rate of conduction from P to QRS (long PR interval)
- Complete block of conduction through the AV node (AV block)
How many different types of AV block are there?
- Three types
First degree AV block characteristics
- Usually high vagal tone
- Normal HR
- Prolonged PR interval
- Most often a PHYSIOLOGIC process
- No symptoms
Second degree AV block characteristics
- P wave without a QRS
- Intermittent failure of conduction through the AV node
- Normal to slow HR
- Often irregular
- Symptoms are variable
- Normal in the horse
- Seen in dogs with high vagal tone or AV node disease
How do you differentiate vagal tone vs AV node disease with second degree AV block?
- Atropine
- Block resolves if vagally mediated
Third degree AV block characteristics
- Ps and QRSs are regular but not related
- Ventricular (QRS) activity is from escape foci in AV node or ventricle (wide/bizarre)
- Slow HR
- Often regular beats
- Symptoms are weakness, exercise intolerance, collapse
- Cause is AV node disease
- 99% of the time is pathologic; structural problem
Treatment of third degree or complete AV block
- Requires pacemaker implantation
- Generally not responsive to medical treatment
- Can be insignificant in very geriatric cats if they aren’t symptomatic
Which diseases can you use a pacemaker for?
- Sick sinus syndrome and complete AV block
Pacemaker overview
$3000-5000
- Lifespan of a generator is ~7 years
- Prognosis is good if no other major diseases
What are the three types of tachycardia?
- Sinus (normal)
- Supraventricular
- Ventricular
Characteristics of sinus tachycardia
QRS shape
Regularity
Onset
P wave
QRS shape: Normal
Regularity: Regular
Onset: Gradual
P wave: Normal
Characteristics of supraventricular tachycardia
QRS shape
Regularity
Onset
P wave
QRS shape: normal
Regularity: Irregular (often)
Onset: Abrupt
P wave: Abnormal
Characteristics of ventricular tachycardia
QRS shape
Regularity
Onset
P wave
QRS shape: Wide/bizarre
Regularity: Regular (often)
Onset: Abrupt
P wave: Not associated
Sinus tachycardia definition
- Increased heart rate that originates in the sinus node
Causes of sinus tach
- Response to systemic issues (pain, excitement, hypotension)
Treatment of sinus tach
- Address the primary cause
Supraventricular tach definition
- 3+ supraventricular beats in a row
- Abrupt and irregular, starts suddenly, ends suddenly
- QRS is the same
- P wave may be abnormal
Causes of supraventricular tachycardia
- Atrial enlargement*** (most common)
- Enlarged hilar lymph nodes
- Thoracic masses
- Pulmonary inflammation
- Electrolyte disturbances
- Horses can have SV tachycardia without structural heart disease
Atrial fibrillation characteristics
- Type of SV tachycardia
- Rapid heart rate
- Irregularly irregular R-R intervals
- No obvious P waves
- +/- f waves
Causes of atrial fibrillation in small animals
- Most commonly observed with severe atrial enlargement
- Dilated cardiomyopathy
- Chronic valvular disease
- Other causes possible (as for SVT)
- Fairly uncommon in cats
Treatment of canine supraventricular tachycardia and atrial fibrillation
- Goal to decrease HR to normal range by decreasing ventricular response rate of conduction through the AV node
- Do NOT expect a return to normal rhythm, especially in atrial fibrillation
- Consider one of the following:
1. ) Calcium channel blocker (Diltiazem, negative chronotrope)
- ) Digoxin (negative chronotrope; positive inotrope)
- ) Beta blockers (Atenolol, sotalol)
- ) Combinations (digoxin + diltiazem)
Equine atrial fibrillation
- QRS is normally negative
- Sawtooth jaggedy baseline with a negative QRS
- Irregularly irregular and faster than normal rate
Equine (lone) atrial fibrillation
- Lone = no evidence of structural heart disease and successful treatment often converts rhythm to normal sinus rhythm
- Atrial fibrillation can have a negative impact on horses, so they should be treated
Atrial fibrillation treatments for horses (yes this is SA med….)
- Quinidine (+ Digoxin) or amiodarone
- Treat as soon as possible after fibrillation begins to increase likelihood of good response
- relapses are common
Bovine atrial fibrillation causes
- Most often associated with 1° GI disease
Treatment for bovine Afib
- Treatment may not be indicated - once primary disease is addressed, arrhythmia usually resolves
Ventricular tachycardia definition
- 3 or more ventricular premature beats (VPC) in a row
- Sustained
- Paroxysmal (means intermittent)
Things to consider when treating ventricular tachycardia
- Sudden death can result from Vtach
- Antiarrhythmics decrease risk of VT but sudden death avoidance not guaranteed
- Many anti-arrhythmics are pro-arrhythmic and can make arrhythmia worse or better
- Make sure you have indications to treat
8 indications to treat Vtach****
- Paroxysms or sustained Ventricular tachycardia >140-160 BPM
- > 20 VPCs per minute
- Multiform VPCs
- Arrhythmias with myocardial failure present
- Breeds at risk for sudden death (boxers/Dobermans)
- Clinical signs of hypotension
- VPCs close to the T wave of the preceding complex (R on T phenomenon
- Critically ill patients
Emergency treatment for Ventricular Tachycardia
- IV lidocaine bolus
- If response is noted can switch to a CRI
- Side effects of lidocaine are CNS (seizures), vomiting
- Caution in cats
Chronic therapy for ventricular tachycardia (oral medications)
- Mexilitine (like lidocaine)
- Sotalol (beta blocker/class 3)
- Atenolol (beta-blocker)
- Other options available but less common
Ventricular fibrillation definition
- Disorganized ventricular activity, end result of Vtach
- No pulses generated, leads to death
- Only effective treatment is electrical defibrillation
- Anti-arrhythmics are not effective
