What is the cause of atrioventricular (AV) block after blood transfusion?

From the Guidelines

AV block following blood transfusion is most likely caused by transfusion reactions, particularly hemolytic reactions or cytokine release, which can affect cardiac conduction, as suggested by the most recent and highest quality study 1. The exact mechanism of AV block after blood transfusion is not fully understood, but it is thought to involve inflammatory mediators, electrolyte disturbances, and direct myocardial effects.

• Key factors that contribute to the development of AV block include: + Transfusion reactions, such as hemolytic reactions or cytokine release + Electrolyte disturbances, particularly potassium and calcium + Direct myocardial effects from transfusion-related acute lung injury
• Management of AV block after blood transfusion includes: + Immediate discontinuation of the transfusion + Urgent cardiology consultation + Cardiac monitoring + Supportive care + Possibly temporary pacing depending on the severity of the block + Intravenous atropine (0.5-1 mg) for symptomatic bradycardia + Temporary transvenous pacing in severe cases + Corticosteroids, such as methylprednisolone (125 mg IV), if an immune-mediated reaction is suspected, as recommended by 2 and 3. The most recent study 1 provides guidance on the management of AV block, including the use of atropine and pacing, and highlights the importance of complete evaluation of the transfusion reaction to prevent recurrence in future transfusions.
• It is essential to note that most cases of AV block after blood transfusion are transient and resolve with appropriate management.
• However, complete evaluation of the transfusion reaction is crucial to prevent recurrence in future transfusions, as emphasized by 2, 3, and 1.

From the Research

Causes of Atrioventricular (AV) Block

• Ischemic heart disease is a common etiology of AV block, with up to 1 in 5 patients developing some type of conduction disturbance after a myocardial infarction (MI) 4
• Other causes of AV block include myocarditis, infectious endocarditis, infiltrative cardiac disease, congenital AV blocks, non-ischemic cardiomyopathy, electrolyte disturbances, and drug side effects 4
• AV block can also occur after cardiac transplantation, with atropine often resulting in complete AV block or sinus arrest in some patients 5
• Recurrent AV block can occur after ablation for atrio-ventricular nodal re-entrant tachycardia (AVNRT), with delayed complete heart block occurring weeks after the procedure 6

AV Block after Blood Transfusion

• There is no direct evidence in the provided studies to suggest that blood transfusion is a cause of AV block
• However, it is possible that underlying conditions or complications related to blood transfusion, such as myocardial infarction or electrolyte disturbances, may contribute to the development of AV block 4

Mechanisms of AV Block

• AV block can occur due to interference from junctional extrasystoles, which can produce debilitating symptoms despite an underlying normal AV node and His-Purkinje system properties 7
• Catheter ablation techniques can be used to alleviate AV block caused by a concealed ventricular nodal pathway interfering with AV conduction 7
• The use of atropine or other anticholinergic drugs can lead to paradoxical responses, including AV block or sinus arrest, in patients after heart transplantation 5