What is the most likely cause of loss of consciousness in a patient with Mobitz type II (second-degree atrioventricular block) - beta blocker, hypothermia, or hypoglycemia?

From the Guidelines

The most likely cause of loss of consciousness in a patient with Mobitz type II (second-degree atrioventricular block) is hypoglycemia. This is because Mobitz type II second-degree atrioventricular (AV) block can lead to sudden and unpredictable complete heart block, resulting in a significant decrease in cardiac output and potentially causing loss of consciousness 1. Hypoglycemia can further exacerbate this condition by increasing the heart rate and potentially worsening the block, whereas beta blockers may actually be used to control the heart rate in some cases, and hypothermia is less directly related to the loss of consciousness in this specific context.

Key Points

• Mobitz type II second-degree AV block is associated with a higher risk of sudden and unpredictable complete heart block, which can lead to loss of consciousness 1.
• Hypoglycemia can worsen the condition by increasing the heart rate and potentially worsening the block 1.
• Beta blockers may be used to control the heart rate in some cases, and are not the most likely cause of loss of consciousness in this context.
• Hypothermia is less directly related to the loss of consciousness in this specific context.

Clinical Implications

In patients with Mobitz type II second-degree AV block, it is essential to monitor for signs of hypoglycemia and to manage the condition promptly to prevent loss of consciousness. Additionally, the use of beta blockers should be carefully considered, and hypothermia should be ruled out as a potential cause of loss of consciousness. Overall, the management of Mobitz type II second-degree AV block requires careful evaluation and treatment to prevent complications such as loss of consciousness 1.

From the Research

Causes of Loss of Consciousness in Mobitz Type II

The most likely cause of loss of consciousness in a patient with Mobitz type II (second-degree atrioventricular block) can be attributed to several factors.

• Beta blockers: There is no direct evidence in the provided studies to suggest that beta blockers are the most likely cause of loss of consciousness in patients with Mobitz type II.
• Hypothermia: None of the studies provided mention hypothermia as a cause of loss of consciousness in patients with Mobitz type II.
• Hypoglycemia: Similarly, hypoglycemia is not mentioned as a cause of loss of consciousness in patients with Mobitz type II in the provided studies.

Alternative Causes

However, the studies suggest that Mobitz type II second-degree atrioventricular block can lead to complete heart block and Stokes-Adams arrest, which can cause loss of consciousness 2.

• Vagovagal reflex triggered by stimulation of the oral cavity can also cause AV block, leading to loss of consciousness 3.
• Additionally, pembrolizumab-induced Mobitz type 2 second-degree atrioventricular block can progress to symptomatic complete heart block, requiring emergent placement of a temporary transvenous pacemaker and potentially leading to loss of consciousness 4.

Diagnostic Considerations

It is essential to distinguish second-degree atrioventricular block from other causes of pauses, such as nonconducted premature atrial contractions and atrial tachycardia with block 2.

• The Ottawa Electrocardiographic Criteria can help identify patients at risk for cardiac outcomes within 30 days, including those with second-degree Mobitz type 2 or third-degree atrioventricular block 5.
• A thorough evaluation of the cause of syncope is warranted in all patients, and a deliberate approach based on initial risk stratification is more likely to reap the dual rewards of a correct diagnosis and initiation of effective treatment in a cost-effective manner 6.