Early release, published at www.cmaj.ca on February 8, 2016. Subject to revision. CMAJ Practice CME Cases Two cases of cardiac glycoside poisoning from accidental foxglove ingestion Renée M. Janssen MD MSc, Mattias Berg MD, Daniel H. Ovakim MD MSc 67-year-old Chinese woman presented showed no substantial coronary artery disease, Competing interests: None to the emergency department with a and transthoracic echocardiography showed nor- declared. A three-day history of nausea and vomit- mal biventricular structure and function. This article has been peer ing, palpitations and chest discomfort. Her On day 3, the patient’s husband, age 66, pre- reviewed. symptoms had started suddenly a few hours after sented to the same emergency department with The authors have obtained eating lunch, beginning with generalized weak- similar symptoms. He had a medical history of patient consent. ness and fatigue; she had noticed that her pulse dyslipidemia and was taking no prescription Correspondence to: Renée was slow and irregular. A few hours later, chest medications. Laboratory investigations showed Janssen, renee.janssen@ pressure developed along with abdominal cramp- normal electrolyte levels (potassium 4.3 mmol/L, alumni.ubc.ca ing associated with nausea and vomiting, which magnesium 1.10 mmol/L), renal function and CMAJ 2016. DOI:10.1503 persisted. complete blood count. Serial troponin levels were /cmaj.150676 The patient’s medical history included hy- not elevated. An ECG showed sinus bradycardia pertension, dyslipidemia, Meniere disease and with nonspecific ST-segment changes and lateral asthma. She was not taking prescription medica- T-wave inversion; there was no previous ECG tions; supplements included vitamin B12, glucos- for comparison. In the emergency department, amine and Chinese herbs (prepared licorice, dried the husband was noted to have episodes of brady- rehmannia root, cinnamon twig, Ophiopogon cardia, with a heart rate in the 30s. Both patients japonicus, ejiao, hemp seed, jujube and ginger). reported visual disturbances, described as flash- Her vital signs were notable for bradycardia ing lights and yellow/red halos around objects. (53 beats/min); other findings on physical exami- On further questioning, the wife revealed they nation were normal. had consumed a bitter-tasting leafy green plant Results of initial laboratory investigations, in- on the day her symptoms began. Her husband cluding electrolyte levels, renal function, liver had picked the leaves from their vegetable gar- biochemistry and synthetic function, were normal. den, believing them to be kale. Given the con- Her serum potassium level was 4.1 (normal 3.5– stellation of symptoms in both patients following 5.0) mmol/L and magnesium level 0.96 (normal this meal, a toxic ingestion seemed likely. 0.70–1.10) mmol/L. Complete blood count re- Serum digoxin levels, normally undetectable, vealed a slightly elevated leukocyte count (14.0 × were 0.3 nmol/L in the wife and 0.4 nmol/L in the 109/L). Serial troponin levels were not elevated. husband. The family brought in plant specimens A chest radiograph was normal. An electrocardio- from their garden (Figure 2), which were later gram (ECG) showed sinus rhythm with first- confirmed to be foxglove (Digitalis purpurea). degree atrioventricular block and sinus pauses of one to two seconds. The patient was admitted to Key points the cardiac intensive care unit for monitoring. • Cardiac glycoside toxicity is primarily a clinical diagnosis and should be Over the next four days, recurrent dysrhyth- suspected in patients presenting with nausea, vomiting, hyperkalemia mias developed, including third-degree atrioven- and unexplained cardiac arrhythmias. tricular block with accelerated junctional rhythm, • The local poison control centre should be contacted in all suspected or sinus bradycardia, frequent premature ventricular confirmed cases of cardiac glycoside toxicity. contractions, nonspecific ST-segment changes • In poisonings from nonpharmaceutical cardiac glycosides, quantitative and T-wave inversion in the lateral leads. On day serum digoxin levels do not correlate with measurements of these toxins and cannot be used to calculate the dose of digoxin-specific antibody 4, a 30-second episode of monomorphic ventricu- fragments (digoxin-Fab). lar tachycardia occurred (Figure 1) that prompted • Serum digoxin levels should not be measured following administration consideration for insertion of an implantable of digoxin-Fab owing to interference with the immunoassay. cardioverter-defibrillator. Coronary angiography ©2016 8872147 Canada Inc. or its licensors CMAJ 1 Practice Once the diagnosis of cardiac glycoside tox- dreds of cardiac glycosides have been isolated icity was confirmed and the provincial poison from plants across 12 botanical families, includ- control centre was consulted, both patients were ing members of the Digitalis genus (foxglove), given digoxin-Fab. The husband initially re- Cascabela thevetia (yellow oleander) and Con- ceived 5 vials, and his wife, whose symptoms vallaria majalis (lily of the valley). The cardiac were more severe, received 10 vials. Both pa- glycosides of medical importance are extracted tients experienced considerable improvement in from D. purpurea and D. lanata, yielding digi- symptoms within an hour after receiving the anti- toxin and digoxin, respectively. dote. Over the course of the next several days, Foxglove (Figure 3) is native to Europe and they were each administered a total of 12 vials. widely naturalized to temperate climes in North Both patients experienced complete resolution of America, including Canada. Accidental ingestion their symptoms and were discharged home. of foxglove is uncommon because of its distinctive flowers and bitter taste. However, the plant does Discussion not flower in its first year, and the rosette of basal leaves of the juvenile plant has been mistaken for Foxglove (including D. purpurea and Digi- borage1 or comfrey.2 In British Columbia, the talis lanata) is one of many plants containing two cases we have described here constitute the cardiac glycosides that exert potent inotropic and only cases of symptomatic cardiac glycoside poi- electrochemical effects on cardiac tissue. Hun- soning from plant ingestion requiring antidote Figure 1: Electrocardiogram (ECG) strips from lead II (A through D) and leads II and V1 (E), showing the progression of ECG changes in a 67-year-old woman during her hospital admission, before administration of digoxin immune antibody fragments. (A) Admission ECG shows sinus rhythm with first-degree atrioventricular block (PR interval 210 ms) and sinus pauses. (B) ECG later on day 1 shows sinus bra- dycardia (heart rate 45 beats/min); PR interval has returned to normal (166 ms). (C) ECG on day 2 shows accelerated junctional rhythm with P waves and atrioventricular dissociation (complete heart block). (D) ECG on day 3 shows sinus bradycardia with non specific ST-segment changes and ST-segment depression. (E) ECG from telemetry strip on day 4 of admission shows monomorphic ventricular tachycardia, which lasted for about 30 seconds and was self-limited. 2 CMAJ Practice treatment since 2012. Toxicity from pharmaceuti- Pharmaceutical cardiac glycoside toxicity cal digoxin use is much more common, with 184 Cardiac glycosides, such as digoxin, have long cases receiving antidotal treatment in the prov- been used to improve inotropy in patients with ince from 2012 to 2014 (Dr. Debra Kent, BC congestive heart failure, and to slow ventricular Drug and Poison Information Centre: personal rates in patients with atrial fibrillation or flutter. communication, 2015). Although the therapeutic range for digoxin is 0.64–1.28 nmol/L, cardiotoxicity has been re- Manifestations of toxicity ported in patients maintained within this range, Cardiac glycosides exert their effects on myo- particularly those receiving long-term treatment. cardial tissue by inhibiting the sodium–potas- Serum digoxin levels, and the risk of subsequent sium–adenosinetriphophatase (Na–K–ATPase) toxicity, are highly susceptible to changes in re- enzyme, leading to increased intracellular so- nal function, serum potassium levels (hypokale- dium and calcium concentrations; this effect is mia), concurrent use of medications that interfere responsible for both the desired positive inotro- with digoxin excretion (e.g., amiodarone and pic effects and the undesirable arrhythmias. Car- non-dihydropyridine calcium-channel blockers) diac glycosides are also believed to exert effects and genetic polymorphisms that impair the activ- on the autonomic nervous system, causing sup- ity of P-glycoprotein.6 Digoxin toxicity should be pression of sympathetic activation and increased suspected and treated in patients who present vagal tone. with consistent clinical features regardless of The cardiac manifestations of cardiac glyco- their serum digoxin level (Box 2). side toxicity result from increased automaticity with concomitant conduction block. Although Diagnosis almost any arrhythmia may result, paroxysmal Cardiac glycoside toxicity is primarily a clinical di- atrial tachycardia with block, accelerated junc- agnosis. Serum digoxin levels should be obtained tional rhythm and bidirectional ventricular to confirm the diagnosis and to guide anti dote tachycardia are highly suggestive of cardiac gly- administration (in the context of pharmaceutical coside toxicity.3 Death typically results from digoxin poisoning).8 Although there is cross- refractory ventricular fibrillation or asystole.