Discussion:
The yew tree is a common, native poisonous evergreen with bright red-berries that could be appealing to young children (1). If searching through graveyards and harvesting the tree is unappealing, the seeds can be purchased easily online, as happened in this case. Once ingested (and particularly if chewed during ingestion) the taxine alkaloids are absorbed where their main action is on cardiac myocytes, where they primarily antagonise the Ca2+ channels causing heart block and eventually cardiac arrest (2). It is estimated that 1g of yew leaves contain 5mg of taxines, and the lethal dose can be as low as 3.0mg/kg in humans (2).
Previous case studies on Yew Tree poisoning in adults generally outline lethal cardiotoxicity, and provide pessimistic reading whilst awaiting the arrival of a similar patient in the emergency department. With no prior experience in treating taxine alkaloid toxicity, and with a relatively junior on-call night staff in a district general hospital, this case had a more positive outcome. Guidance from Toxbase (6) previously published case reports and the experience of a cardiothoracic nurse working on the critical care outreach team overnight were pertinent to this outcome.
The decision to use Dobutamine (a B1-agonist) and Isoprenaline (a non-selective beta agonist) over Atropine (an antimuscarinic alkaloid) and Adrenaline (a non-selective alpha and beta agonist) meant the drug administered were more cardio-specific than what may otherwise be used and the aforementioned hypotension as a result of the non-specific actions of adrenaline was not noted. However with hindsight, and having received no ill effects on switching to an adrenaline infusion in the ICU, we would have a lower threshold for using adrenaline in future similar cases. External, and then later internal, pacing allowed for a reduction in doses of both medications (and the total cessation of Isoprenaline).
Without the pacing the underlying rhythm was asystole. Several previous case studies have described successful outcomes after prolonged cardiac arrests, and a review of 43 cases of Yew Tree poisoning found CPR was required in 26 (60%) of cases (4). With this in mind, it may be beneficial to have a Lucas or similar device available, if possible, to save on staff resources, shall the patient deteriorate to cardiac arrest. Replacing the fast patches the paramedics apply with hospital parches may also be a consideration, as though they may be compatible with hospital defibrillators you are not always able to pace through the patches paramedics use.
The accidentally triggered emesis on the ICU admission covid-19 throat swab may also have helped in this case. This episode occurred about 9 hours post ingestion of the seeds, and the regurgitation of whole and partially digested seeds in the vomit may well have reduced subsequent plasma levels of the taxine alkaloids and prevented any further deterioration over the following days. Toxbase does suggest initiating vomiting or using activated charcoal, but it was not deemed appropriate in the initial management due to the fluctuating GCS and possible aspiration risk. In future, earlier consideration of gastric emptying could be considered.
Poisoning from Yew Tree seeds may become more prevalent, due to the easy access to the toxic substance from online shops. We were lucky our patient informed us of what he took, allowing the team to prepare for his arrival adequately. Many patients who attempt suicide through ingestion of substances may not share this information, and so supportive therapy and treating symptoms may be the best option. In this case, there was no direct antidote and so supportive therapy was also all that was available. A successful outcome was obtained without the need for ECMO by following the valuable guidelines of Toxbase, verbal conversations with UK NPIS and the experience of the multi-disciplinary acute care team. Whilst this case was managed successfully in a district general hospital we would still recommend early discussion with UK NPIS and the local ECMO centre, as early transfer to a more appropriate centre may be required.