Introduction

• Can be serious life-threatening dysrhythmia, often incidental non-life-threatening arrhythmia.
• Cause: usually myocardial irritation due to primary cardiac or systemic disease.
• Signs: weakness, collapse and death.
• Diagnosis: electrocardiography.
• Treatment: treat underlying disease, antidysrhythmic agents.
• Prognosis: guarded for some, good for others.

Pathogenesis

Etiology

• Myocarditis Heart: myocarditis.
• Endocarditis Endocarditis: bacterial.
• Congestive heart failure Heart: congestive heart failure.
• Myocardial ischemia or hypoxia, eg hypertrophic myocardium secondary to aortic stenosis Heart: aortic stenosis.
• Inherited, eg German Shepherd dog, Boxer.

• Electrolyte abnormalities, eg hyperkalemia or hypokalemia Hypokalemia.
• Trauma.
• Systemic disease:
  • Splenic disease.
  • Pyometra Pyometra.
  • Gastrointestinal disease.
  • Renal failure Kidney: chronic kidney disease (CKD).
  • Phaeochromocytoma Pheochromocytoma.
• Hypothermia.
• Drug therapy (digoxin Digoxin ).
• Autonomic stimulation.

Predisposing factors

• Underlying heart failure with poor cardiac output resulting in myocardial hypoxia (especially Dobermanns).

Specific

• Acid/base imbalance Acid base imbalance.
• Hypoxia.
• Catecholamine release.

Pathophysiology

• Spontaneous depolarization of ventricular myocardial cells.
• More than 3 ventricular premature complexes (VPCs) in a row Ventricular premature contraction.
• May progress to ventricular fibrillation in some cases.

• Severe shock or autonomic stimulation → myocardial ischemia and myocyte damage.
• Myocardial disease or damage → changes in resting potential, sodium and calcium currents across cell membranes → arrhythmogenesis.
• This effect may be enhanced by other factors, eg hypoxemia.
• Ectopic depolarization occurs in ventricular myocardial cells outside the normal impulse generating nodes and below the atrioventricular junction.
• Ventricles are incompletely filled by the time of the ectopic discharge and contraction of myocardium follows abnormal sequence → reduced cardiac output on ectopic beat.
• Hypotension and myocardial ischemia may → syncope, seizures or progression of arrhythmia to ventricular fibrillation → death.

Timecourse

• Often incidental finding in VT 2° to extracardiac pathology, eg trauma
• Severity of signs ensures early diagnosis.

Diagnosis

Treatment

Outcomes