Arrhythmias

• Conduction Nodes

  • Sinoatrial node
  • 1st of the conduction nodes to start signal
  • Has automaticity (spontaneous signaling)
  • Lateral wall right atrium
• Conduction Nodes

  • Atrioventricular node
  • 2nd of the conduction nodes
  • On atrial septum on right atrial side
• Conduction Nodes

  • Bundle of His-Purkinje fiber system
  • Last of the conduction nodes
  • Node aspect in ventricular septum and fibers extend into apex of heart
• Parts of ECG Wave

  • P wave- depolarization of atrial muscle
  • Followed by return to baseline (isoelectric line)
  • Traverses AV node which doesn’t generate enough voltage to show up on ECG
• Parts of ECG Wave

  • QRS complex- activation of His-Purkinje system and ventricular muscle contraction
  • Depolarization of ventricles
  • Repolarization of atria happens same time as ventricular depolarization
• Parts of ECG Wave

  • T wave- ventricular repolarization
• ECG Intervals

  • P-R interval
  • Measured from beginning of P wave to beginning of QRS complex
  • Shows time required for the wave of excitation to travel fromSA node to ramifications of His-Purkinje system
• ECG Intervals

  • QRS duration
  • Spread of impulses throughout ventricles
  • Measure of intraventricular conduction time
• ECG Intervals

  • Q-T interval
  • Measured from beginning of Q to end of T wave
  • Measures approximate duration of ventricular systole and ventricular refractory period
• Sinus Rhythms

  • This is a normal ECG in our cats and dogs
  • Altered normals include: sinus bradycardia, tachycardia, and sinus arrhythmia
• Abnormal Impulse Formation

  • Atrial abnormalities○ Atrial fibrillation○ Atrial premature complex (APC)
• Abnormal Impulse Formation

  • Ventricular abnormalities○ Ventricular fibrillation○ Ventricular premature complex (VPC)○ Ventricular tachycardia
• Abnormal Impulse Conduction

  • AV block (3 types)
  • Type I
  • Type II
  • Mobitz I and II
  • Sick Sinus Rhythm
• Atrial Fibrillation

  • Associated with a lack of P waves, irregular, and an irregular ventricular rate
  • QRS complexes are normal to slightly different
• Atrial Fibrillation

  • Rate in the untreated atrial fibrillation animal is very rapid and is associated with a marked pulse deficit clinically
  • Can be due to other heart issues
• Atrial Fibrillation

  • Can develop during surgery after giving opioids or as a result of GI, respiratory, or neurologic diseases that elevate parasympathetic tone
• Atrial Fibrillation Risk factors

  • More common in male dogs
• Atrial Fibrillation Clinical signs

  • Lethargy
  • Weakness
  • Exercise intolerance
  • Syncope (loss of consciousness due to low blood pressure)
• Atrial Fibrillation Clinical signs

  • Coughing
  • Dyspnea
  • Ascites
  • Anorexia
• Atrial Fibrillation physical exam

  • Rapid heart rate and an irregular heart rhythm
  • Irregularity of rhythm may not be easily heard when the heart rate is extremely fast
• Atrial Fibrillation physical exam

  • A murmur, typically systolic, may be auscultated in dogs with underlying cardiac disease
  • Character of the murmur is inconsistent from beat to beat and depends on heart rate
• Atrial Fibrillation physical exam

  • Pulse quality may be normal to decreased with an irregular rhythm +/- pulse deficits
• Atrial Fibrillation diagnostics

  • Gold standard is ECG
  • Normal cycling of AV node through active and refractory states prevents some of electrical impulses from passing through to the ventricles → irregular ventricular rate
• Atrial Fibrillation diagnostics

  • 24hr Holter vest
  • Works like a constant ECG → stored for 24hrs and evaluated by a cardiologist
  • Provides a better overall estimate of heart rate in the clinical setting and home environment
• Atrial Fibrillation diagnostics

  • Echo, CBC/chem, BP check, and thoracic rads are other tests that can be done to rule out underlying causes
• Atrial Fibrillation treatment

  • Can also include heart failure medications depending on severity of heart disease (talked about those on Tuesday)
• Atrial Fibrillation treatment

  • Mainly treat in dogs showing hemodynamic issues
  • Procainamide 1st choice if not sure if atrial or ventricular
• Atrial Premature Complex (APC)

  • Generally occur secondary to structural heart diseases such as enlargement and stretch of the atria
  • Young dogs with APCs is usually due to accessory pathways that for communication between atria and ventricles outside of AV node
  • Can be the result of extra-cardiac illnesses such as electrolyte abnormalities, anemia, endocrine disease (such as thyroid disease) or trauma
• Atrial Premature Complex (APC)

  • Characterized by premature P waves/P waves that differ from normal in both size and or configuration
• Atrial Premature Complex (APC) risk factors

  • High sympathetic tone or administration of sympathomimetics
  • More common in males
  • No breed dispositions
• Atrial Premature Complex (APC) Clinical signs

  • Atrial dilation
  • Atrial myocardial disease
  • Electrolyte and metabolic disturbances
  • Hypoxia, anemia
  • Fever
• Atrial Premature Complex (APC) clinical signs

  • Usually no complaints
  • Labored breathing
  • Exercise intolerance
  • Weakness
  • Collapse
  • Drug administration
  • Previous episodes of atrial fibrillation
• Atrial Premature Complex (APC) physical exam

  • An irregular cardiac rhythm on auscultation
  • Intensity of the 1st sound is usually normal or decreased
• Atrial Premature Complex (APC) physical exam

  • Can produce a soft atrial sound or may not be heard on auscultation at all
  • If not showing signs of CHF, NSF on physical exam otherwise
• Atrial Premature Complex (APC) Diagnostics

  • ECG
  • ○ Best way to definitively diagnose the arrhythmia
• Atrial Premature Complex (APC) diagnostics

  • 24hr Holter test
  • May help evaluate the extent of the arrhythmia in a calmer environment
• Atrial Premature Complex (APC) diagnostics

  • Should do an echocardiogram, T4 level,thoracic rads, and CBC/chem to rule outpotential underlying causes
• Atrial Premature Complex (APC) treatment

  • If arrhythmia persists, can consider anti-arrhythmic medications
  • beta blockers
  • Sotalol- 1-3.5mg/kg PO BID
  • Atenolol- 0.25-1.5mg/kg PO BID; 6.25mg/cat PO BID
  • Carvedilol- starting dose of 0.31mg/kg PO BID and target dose of 1.11mg/kg PO BID
• Atrial Premature Complex (APC) treatment

  • Need to treat underlying cause first
  • Ca2+ channel blockers
  • Diltiazem- start at 1mg/kg PO TID and increase to max 3mg/kg PO TID if needed
• Ventricular Fibrillation

  • Terminal rhythm with nonexistent heart sounds, pulses, and blood pressure
  • Basically cardiac arrest
  • Can be secondary to ventricular tachycardia (like seen in ARVC), being too deep under anesthesia, or respiratory arrest/ventilator failure