LETTER TO THE EDITOR: First degree AV block due to carbon monoxide or cyanide poisoning. Which of them?

I read with interest the case presented by Salih et al. published in your journal [1]. They presented a case of carbon monoxide (CO) poisoning with the first degree atrioventricular (AV) block for the first time. The victim was involved in a fire at home and rescued at the scene by the firemen. At presentation to the emergency department, he had the signs of inhalational injury and encephalopathy. Carboxyhemoglobin (COHb) level was 8.7% and hyperbaric oxygen therapy was performed. It seems that a major missed point of concern about this case is concomitant cyanide (CN) poisoning. As you know, several reports have shown that patients admitted to hospital due to fire accidents may have also been exposed to CN [2].