Category:Altered Supraventricular Impulse Formations

1. Supraventricular Tachycardia

Small Animal: Common

Large Animal: Uncommon

a. Paroxysmal Atrial Tachycardia (PAT)=regular rapid atrial contractions arising from atrial tissue outside the SA node

b. Atrioventricular Junctional Tachycardia (AJT)=regular rapid atrial contractions arising from AV nodal tissue

c. Supraventricular Tachycardia a term used to include both PAT and AJT. Rapid premature beats occuring somewhere above the ventricles.

Causes

Result from pathological conditions in the cardiac atria, hypoxia, stress, digitalis toxicity, systemic hypertension etc.

ECG Appearance: Rapid heart rate, abnormal P wave (inverted) which can be preceded, be superimposed, or follow QRS complexes

Treatment

Small Animals

• Treat underlying cause

• Vagal manoeuvres (e.g. carotid sinus or ocular massage)

• Drug Treatment:

-If + for congestive heart failure treat with digoxin and other heart failure drugs

-If - for congestive heart failure treat with diltiazem, propranolol, or adenosine

• Avoid digoxin if a reentry mechanism is suspect in causing the supraventricular tachycardia

• Pacing methods

Large Animals

• Treat underlying cause

• Box rest with heart rate and rhythm monitoring

• If + for heart failure, give digoxin

• Vagal manoeuvres (e.g. carotid sinus or ocular massage)

• Quinidine sulfate

2. Supraventricular Premature Complexes

Small Animal: Common

Large Animal: Uncommon, but more common then ventricular premature complexes

a. Atrial Premature Complexes (APC)=As the name suggests, an APC is an abnormal ectopic premature beat occurring in the atrial tissue outside the SA node and above the AV node.

b. Junctional Premature Complexes (JPC)=As the name suggests, a JPC is an abnormal ectopic premature beat occurring in the AV nodal region.

Causes

APCs and JPCs can arise as the result of pathological conditions in the cardiac atria, or electrolyte and acid-base disturbances.

ECG Appearance: Premature ectopic P wave +/-; Premature QRS complex

Treatment

Small Animals

• Treat underlying cause

• Treat with antiarrhythmic drugs if clinical signs remain

Antiarrhythmic drugs: e.g digoxin, diltiazem

Large Animals

• Treat underlying cause

• Box rest with heart rate and rhythm monitoring

• If + for heart failure, give digoxin

• Vagal manoeuvres (e.g. carotid sinus or ocular massage)

• Quinidine sulfate

3. Atrial Fibrillation & Atrial Flutter

Dog: common

Cat: uncommon

Horse: common; male>female; Standardbreds and Draft horses are most affected

Cattle: common; especially dairy cattle

Atrial Fibrillation: Occurs when many ectopic waves of depolarisation spread throughout the atria. While the atria fail to contract some of the disorganized depolarization waves are conducted through the AV node reaching the ventricles. As a result the ventricles have a rapid, irregular rate.

Atrial Flutter: A rare unstable arrhythmia consisting of rapid atrial rate and abnormal atrial depolarization. Atrial flutter is an arrhythmia that cycles between atrial fibrillation and sinus rhythm.

Causes

Atrial pathology, pathology of other systems, electrolyte imbalances, drug interactions

ECG Appearance: lack of P waves (atrial fibrillation); small f waves (atrial flutter)

Treatment

Treat all underlying conditions

Dog & Cat: digoxin +/- diltiazem or +/- propranolol; quinidine or diltiazem (used in animals without cardiac failure or enlargement)

Horse: quinidine sulfate or treat congestive heart failure (furosemide, digoxin etc.)

Cattle: quinidine sulfate; Digoxin (given first if tachycardic)