Introduction

• Rare.
• More common in young dogs and puppies.
• Cause: ingesting of toxic plants Poisonous plants: overview.
• Signs: arrhythmias and gastrointestinal signs.
• Diagnosis: history and signs.
• Treatment: controlling arrhythmias and activated charcoal to prevent further absorption.

Pathogenesis

Etiology

• Foxglove (Digitalis purpurea) Foxglove (Digitalis pupurea).
• Lily of the valley (Convallaria majalis) Lily of the valley (Convallaria majalis) - 3 cardiac glycosides of which convallotoxin is the most important.
• Spindle tree (Euonymus europaeus).
• Oleander (Nerium oleander) Oleander (Nerium oleander).
• Rhododendronspecies Rhododendron including azaleas - contains grayanotoxins,
• Pierisspecies - contains grayanotoxins.
• White Bryony (Bryonia dioica) White bryony (Bryonia dioica).
• Bluebell (Hyacinthoides non-scripta).
• Solomon's seal (Polygonatum multiflorum) - contains convallamarin.
• Hellebore species Stinking hellebore (Helleborus foetidus).
• Privet (Ligustrum species) Privet (Ligustrum spp) - especially in berries.
• Laburnum (Laburnum anagyroides) Laburnum anagyroides contains a quinolizidine alkaloid called cytisine which causes a reduction in intracellular potassium and hence high atrioventricular block:
  • All parts of the tree contain the toxin especially the bark and seeds.
  • Some alkaloids have actions on the heart.
• Yew (Taxus baccata) Yew (Taxus baccata) contains taxine alkaloids which cause a rapid, weak pulse.
• Monkshood, Wolf's bane (Aconitum napellus) Monk's-hood (Aconitum napellus) is initially stimulatory then depressive causing a slow irregular pulse:
  • Poisoning by monkshood can occur through ingestion with the lethal dose being about 5 g/dog, or by absorption through the skin.
• Toxic fungi Mushroom poisoning :
  • Muscarine-containing fungi can cause a perspiration, salivation and lacrimation syndrome:
• Blood pressure and heart rate are decreased.
• Ergot poisoning in the chronic form causes gangrene of the extremities due to peripheral vasoconstriction.

Pathophysiology

• Over 400 cardiac glycosides have been identified.
  • A cardiac glycoside consists of one or more monosaccharides and a glycone.
  • The sugar enhances cardiac activity by affecting lipid solubility and hence cell penetrability.
  • Hydrolysis releases the glycone which slows the heart and increases the force of contractility.
• Grayantoxocins bind to sodium channels of cell membranes resulting in activated cells maintained in a persistent state of excitation and depolarisation.
• Other toxic compounds in plants can also have effects on the heart.

Timecourse

• Signs occur within 4-12 h of ingestion and can last for 2-3 days.
• If lethal doses are absorbed, death occurs in 12-24 h.

Diagnosis

Treatment

Prevention

Outcomes