First degree AV block due to carbon monoxide or cyanide poisoning. Which of them?

Dear Editor,

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]. It is not clear whether the authors ruled out the CN poisoning in their patient. Did the author determine the patient’s lactate level? Did their patient have metabolic acidosis? (The result of the patient’s arterial blood gas analysis was not stated in the article). Although blood cyanide concentrations are not practical in initial management, did they determine the blood concentration of CN for the confirmation or ruling out of CN poisoning? Did they determine arteriovenous oxygen saturation difference on arterial and venous blood gas analysis? [3]. With respect to the abovementioned major point, could the first degree AV block relate to the mild CN poisoning or concomitant CO and CN poisoning? It should be mentioned that cigarette smokers can have COHb levels between 3 and 15% [4]. The authors’ patient was a smoker and COHb level of 8.7% for this patient might not reflect absolute CO poisoning.