Cardiotoxic Plants
Basic Information 
Synonym(s)
• Oleander poisoning (Nerium oleander)
• Summer pheasant’s eye poisoning (Adonis aestivalis)
• Grayanotoxin intoxication (Azalea spp., Rhododendron spp; see “Rhododendron Toxicosis” in this section.)
• Yew poisoning (Taxus spp; see “Taxus Toxicosis” in this section.)
• Avocado poisoning (Persea spp.)
• Cardiac glycoside intoxication (N. oleander, Digitalis spp., Asclepias spp.)
Epidemiology
Risk Factors
• Fresh cardiotoxic plants have low palatability. Animals are more likely to ingest dried cardiotoxic plant material.
• Plant trimmings present the most common source for oleander and yew poisoning.
• Contamination of hay or hay cubes with cardiotoxic plants is a great risk.
• The Guatemalan race of avocados and the Fuerte hybrid are reportedly toxic. The Mexican race has low toxicity.
Geography and Seasonality
• Oleander exposure is a year-round risk. Oleander poisoning is common in horses, especially in California, Arizona, and Texas. Ingestion of dried oleander clippings often causes poisoning.
• Summer pheasant’s eye has been limited to some northern California counties.
• Grayanotoxin-containing plants have the highest toxin concentrations in the leaves.
• Ingestion of yew clippings is the most common cause for poisonings with Taxus spp. All species of Taxus, including T. baccata (English yew), T. cuspidata (Japanese yew), and T. brevifolia (Pacific or Western yew), are considered toxic.
• Avocado is extensively cultivated in California and Florida but can also be found as an ornamental in the Gulf Coast areas. Avocado leaves are especially toxic.
• Some cardiotoxic plants are most abundant in the spring and summer, depending on the location
Clinical Presentation
Disease Forms/Subtypes
• Acute cardiotoxicity subsequent to exposure to cardiotoxic plants.
• Acute death from ingestion of oleander, yew, summer pheasant’s eye, avocado, or azaleas. Animals are often found dead.
• Cardiac changes include bradyarrhythmias, tachyarrhythmias, atrioventricular (AV) blocks, ectopic beats, and gallop rhythms.
Physical Exam Findings
• Oleander: Irregular fast pulse with tachycardia, ventricular arrhythmias, or gallop rhythms; anorexia and colic; occasionally diarrhea
• Summer pheasant’s eye: Gastrointestinal (GI) stasis, feed refusal, dyspnea, and cardiac arrhythmias
• Grayanotoxins: Depression, salivation, abdominal pain, possibly diarrhea; in severe cases: recumbency, seizures, tachycardia, tachypnea, and pyrexia
• Yew: Incoordination, nervousness, difficulty in breathing, bradycardia, diarrhea, and convulsions. Sudden death is often all that is seen.
• Avocado: Subcutaneous edema of the head and chest, submandibular edema, respiratory dyspnea, and cardiac arrhythmias
Etiology and Pathophysiology
• Oleander contains cardiotoxic glycosides, such as oleandrin. Cardiac glycosides inhibit Na+/K+ ATPase, which leads to increased intracellular Ca2+ concentrations and a subsequent positive inotropic effect. In addition, direct effects on the sympathetic nervous system are seen.
• Summer pheasant’s eye contains cardiotoxic glycosides.
• Grayanotoxins, found in azaleas and rhododendrons, are diterpenes that bind to sodium channels in excitable cell membranes (skeletal and myocardial muscle, nerves, and central nervous system). Excitable cells are maintained in a state of depolarization. Additionally, increased intracellular sodium results in an exchange with extracellular calcium, which affects the control of transmitter release.
• Yews contain taxine alkaloids (such as taxine A and B) that are inotropic and change AV conduction. Yews also contain ephedrine, nitriles, and irritant oils that are likely to be responsible for colic and diarrhea.
• Avocado contains persin, but the exact mechanism of toxic action is not known.
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