ISSN 2398-2950      

Heart: dysrhythmia

ffelis

Synonym(s): Arrhythmia, Heart block, Ectopic beat


Introduction

  • Definition: abnormalities of rate and rhythm of the heartbeat.
  • Cause: primary cardiac disease - muscular or conduction abnormalities; systemic disease; trauma.
  • Signs: many are asymptomatic; syncope, sudden death, congestive heart failure.
  • Diagnosis: auscultation; electrocardiography (ECG).
  • Treatment: anti-arrhythmic drugs depending on type of arrhythmia; correction of metabolic factors.
  • Prognosis: depends on cause and response to therapy.
    Follow the diagnostic trees for Common Cardiac Arrhythmias Common cardiac arrhythmias and Bradyarrhythmia & Tachyarrhythmia Bradyarrhythmia & Tachyarrhythmia.

Pathogenesis

Predisposing factors

General

  • Toxemia Shock: septic.
  • Hypoxia.
  • Myocardial wall abnormality.
  • Drugs.
  • Neurological abnormality, ie 'brain-heart syndrome'.
  • Systemic/metabolic diseases.
  • Cardiomyopathies.

Specific

Bradycardia

AV block in cats is always abnormal and needs investigation.

Tachycardia

  • Hyperthyroidism Hyperthyroidism.
  • Myocardial disease.
  • Drugs:
    • Atropine (parasympatholytics).
    • Anti-arrhythmics.
    • Anesthetic agents.
    • Cardiac glycoside toxicity (can   →   VPCs).
  • Electrolyte imbalance:
  • Hypomagnesemia.
  • Acidosis.
  • Nervousness/adrenaline.
  • Fever.
  • Pain.

Pathophysiology

  • Conduction abnormalities or development of ectopic foci   →   trigger dysrhythmias.
  • Depolarization of pacemaker cells in sino-atrial node (dictates intrinsic heart rate):
    • Increased by sympathetic stimulation (excitement, fear and pain).
    • Decreased by parasympathetic stimulation.
    • Altered by drugs, hormone levels, electrolytes.
    • Reflected by damage to conduction tissues   →   AV or branch bundle block.
  • Ectopia:
    • Myocardial disease (myocarditis, fibrosis or hypoxia), electrolyte imbalances, endotoxins or toxins released from reperfusion injury or sympathetic stimulation   →   ectopic foci.
  • Extracellular potassium affects heart rate:
    • Hypokalemia   →   faster depolarization.
    • Hyperkalemia   →   reduces resting membrane potential   →   slows conduction velocity and heart rate.
  • Intracellular calcium ion concentration affects the Na+/Ca++ exchange pump.
  • Abnormal automaticity refers to site of depolarization in non-pacemaker tissue.
  • Re-entry refers to second depolarization when part of impulse is delayed by passage through diseased tissue (due to hypoxia or fibrosis).
  • After-potentials are oscillations in resting membrane potential following repolarization which may reach threshold potential and trigger an impulse.
  • After-potentials are enhanced by adrenergic stimulation, digitalis toxicity and increased intracellular calcium.

Timecourse

  • Depends on cause.

Diagnosis

This article is available in full to registered subscribers

Sign up now to obtain ten tokens to view any ten Vetlexicon articles, images, sounds or videos, or Login

Treatment

This article is available in full to registered subscribers

Sign up now to obtain ten tokens to view any ten Vetlexicon articles, images, sounds or videos, or Login

Outcomes

This article is available in full to registered subscribers

Sign up now to obtain ten tokens to view any ten Vetlexicon articles, images, sounds or videos, or Login

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Rials S J, Wu Y, Ford N et al (1995) Effect of left ventricular hypertrophy and its regression on ventricular electrophysiology and vulnerability to inducible arrhythmia in the feline heart. Circulation 91 (2), 426-430 PubMed.
  • Kowey P R, O'Brien R, Wu Y et al (1992) Effect of gallopamil on electrophysiologic abnormalities and ventricular arrhythmias associated with ventricular hypertrophy in the feline heart. Am Heart J 124 (4), 898-905 PubMed.
  • Boyden P A, Tilley L P, Albala A et al (1984) Mechanisms for atrial arrhythmias associated with cardiomyopathy - a study of feline hearts with primary myocardial disease. Circulation 69 (5), 1036-1047 PubMed.

Related Images

RELATED ARTICLES

Acepromazine maleate

Acid base imbalance

Analgesia: overview

Anemia: overview

Atenolol

Atrial fibrillation

Atropine

Blood biochemistry: creatinine

Blood biochemistry: potassium

Blood biochemistry: total calcium

Blood biochemistry: urea

Calcium gluconate

Cardiac sounds: overview

Cimetidine

Diaphragm: hernia

Diazepam

Digoxin

Diltiazem

ECG: overview

ECG: principles of interpretation

Endocarditis

Esmolol

Feline dysautonomia

Fluid therapy: for electrolyte abnormality

Glucose

Glycopyrronium

Heart: aortic stenosis

Heart: atrial premature complexes

Heart: atrial septal defect

Heart: congestive heart failure

Heart: dilated cardiomyopathy (DCM)

Heart: disease - clinical investigation

Heart: hypertrophic cardiomyopathy (HCM)

Heart: pathophysiology of CHF

Heart: restrictive cardiomyopathy (RCM)

Heart: ventricular premature contraction

Heat stroke

Hematology: band neutrophil

Hypercalcemia: overview

Hyperkalemia

Hypertension

Hyperthyroidism

Hypoadrenocorticism

Hypoglycemia

Hypokalemia

Hypothermia

Insulin

Kidney: acute renal failure

Kidney: chronic kidney disease

Kidney: ischemia

Lidocaine

Mexiletine

Myasthenia gravis

Nasal oxygen administration

Pericardial disease

Poisoning: overview

Procainamide

Propranolol

Radiography: thorax

Sedation or sedative protocol

Shock: septic

Sodium bicarbonate

Sotalol

Spleen: trauma

Splenectomy

Standard reasons for failure in a treatment

Syncope

Thorax: trauma

Thyroid: T4 assay

Ultrasonography: heart

Ventricular fibrillation

Ventricular tachycardia

Xylazine

Can’t find what you’re looking for?

We have an ever growing content library on Vetlexicon so if you ever find we haven't covered something that you need please fill in the form below and let us know!