Full Atrioventricular Block Secondary to Acute Poisoning Mercury: A Case Report

Background: The biological behaviour and clinical significance of mercury toxicity vary according to its chemical structure. Mercury differs in its degree of toxicity and in its effects on the nervous, digestive and immune systems as well as on organs such as the lungs, kidneys, skin, eyes and heart. Human exposure occurs mainly through inhalation of elemental mercury vapours during industrial and artisanal processes such as artisanal and small-scale gold mining. Case presentation: A 52-years-old female, housewife, with a body mass index of 25.3 kg/cm², without smoking or alcohol habits or any important clinical or chronic cardiovascular history, was admitted to the emergency room due to probable accidental poisoning by butane gas. Clinical manifestations with a headache, dizziness, cough, and dyspnoea of medium to small efforts. An initial physical exploration with Glasgow scored at 15, with arrhythmic heart sounds, pulmonary fields with bilateral subcrepitant rales and right basal predominance. Electrocardiographic findings were as follows: a cardiac frequency of 50 beats per minute and atrioventricular dissociation. Laboratory parameters were: white blood cells at 15.8 × 10⁸/L; aspartate aminotransferase at 38 U/L; lactate dehydrogenase at 1288 U/L; creatine-kinase at 115 U/L; CK-MB fraction at 28 U/L; and other biochemical parameters were within the reference values. A radiographic evaluation showed flow cephalization, diffuse bilateral infiltrates with right basal predominance. In addition, the patient presented data of low secondary expenditure to third-degree atrioventricular (AV) block for which the placement of a transvenous pacemaker was decided, substantially improving the haemodynamic parameters. Subsequently, after a family interrogation, the diagnosis of mercury inhalation poisoning was established. An initial detection of mercury concentration (Hg(0)) was carried out, reporting 243.5 µg/L. In view of this new evidence, mercury chelation therapy with intravenous calcium disodium ethylenediamine tetraacetic acid (CaNa₂·EDTA) was initiated. After 8-days of hospital stay, she presented a favourable evolution with both clinical and radiological improvements, so that the mechanical ventilation progressed to extubating. Subsequently, she was referred for cardiology because of her persistent 3rd-degree atrioventricular block, deciding to place a definitive bicameral pacemaker. The patient was discharged from the hospital 14 days after admission due to clinical improvements with mercury plasma levels at 5 µmol/L and a heart rhythm from the pacemaker. Conclusions: We show evidence that acute exposure to elemental mercury can affect the heart rhythm, including a complete atrioventricular blockage.