Ventricular fibrillation

Introduction

• Cause: can occur as electrophysiological complication of other "malignant" (ie prefibrillatory) ventricular arrhythmia such as very fast and sustained ventricular tachycardia (VT    ) in the presence of severe organic myocardial disease (eg hypertrophic cardiomyopathy).
  • In severe heart failure, when diastolic function is poor, intraventricular diastolic filling pressure is high, and myocardial hypoxia is present, VT can be a precursor to VF.
• Untreated ventricular fibrillation    →   hemodynamic cardiac arrest and death.
• May be induced by lengthy or deep-planed general anesthesia (eg when lengthy and severe myocardial hypoxia present) or at onset of anesthesia induction, either in severely diseased patients or (rarely) in healthy animals.
• Respiratory arrest and ventilatory failure can lead to VF.
• Diagnosis : electrocardiography. Chaotic/random, irregular, low-amplitude oscillations or undulations at a rate ranging between 150 and 300, or even >400 cycles/minute, with no distinct P waves (despite continuation of organized atrial electrical and mechanical activity), QRS complexes or T waves.
• Undulations either coarse (and relatively more amenable for cardioversion) or fine (less amenable for cardioversion).
• Many malignant ventricular arrhythmias that electrocardiographically and hemodynamically appear to be asystole (see Differential Diagnosis) are, in fact, fine VF. Therefore, open-chest heart massage and direct observation of myocardial activity may be warranted early with this arrhythmia.
• Treatment : direct current (DC) electrical countershock (defibrillation) only effective therapy.
• Prognosis : in the severely diseased, poor to grave, often even if promptly and successfully treated.
• More favorable if defibrillation performed immediately in otherwise normal animal with chemical etiology, eg drug toxicity:
  • Anesthetic overdose such as halothane or barbiturates.
  • Drug-drug interaction.

Diagnosis

Clinical signs

• Cardiopulmonary arrest with acute unconsciousness, often either in patients that were previously asymptomatic despite severe myocardial disease, or following severe morbidity in patients with extracardiac disease or with terminal congestive heart failure    .
• Pulseless peripheral arteries.
• Absence of auscultable heart sounds     .
• Absence of palpable cardiac apex beat.
• Apnea.
  Apnea can occur with a normally beating heart, but normal respiration cannot last during cardiac arrest or VF.
• Cyanosis if ventricular fibrillation occurring for a few minutes or more.
• Centrally fixed, dilated pupils.
• Capillary refill time (CRT) not sensitive nor specific tool for diagnosing VF or cardiac arrest. Can remain within normal limits for as long as 30 minutes following cardiac arrest.

Diagnosis

Differential diagnosis

• Other "malignant" ventricular dysrhythmic conditions that may lead to circulatory arrest.
• One of the relatively more treatable of these "arrest arrhythmias" is VF and immediate defibrillation is the treatment of choice.

Sequelae

Prognosis

• Prognosis for long-term survival in such cases is poor even if cardiorespiratory function is temporarily regained.

Sources

Publications

Refereed papers

• Recent references from PubMed.

Other sources of information

• Crowe D T, Fox P R, Devey J J & Spreng D (1999)Cardiopulmonary and cerebral resuscitation.In:Textbook of Canine and Feline Cardiology. Principals and Clinical Practice. 2nd Edn. Eds: P R Fox, D Sisson D and N S Moise. WB Saunders Co, Philadelphia. pp 427-445.
• Kittleson M D (1998)Diagnosis and treatment of arrhythmias (dysrhythmias).In:Small Animal Cardiovascular Medicine. Eds: M D Kittleson and R D Kienle. Mosby Inc, St Louis. pp 449-494.
• Labato M A (1995)Cardiopulmonary arrest and resuscitation.In:Textbook of Veterinary Internal Medicine. Diseases of the Dog and Cat.1 , Eds: S J Ettinger and E C Feldman. WB Saunders Co, Philadelphia. pp.71-79.
• The Merck Veterinary Manual, Eighth Edition, Published by Merck & Co Inc, Whitehouse Station, NJ, USA. In cooperation with MERIAL LIMITED, a Merck and Aventis Company:http://www.merckvetmanual.com/(All rights reserved).