From the Guidelines
Atropine is the first-line medication for symptomatic bradycardia due to AV heart block, particularly for first-degree and Mobitz type I (Wenckebach) second-degree AV blocks, with a recommended dose of 0.5-1 mg IV, which can be repeated every 3-5 minutes up to a maximum total dose of 3 mg, as stated in the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1.
The effect of atropine on atrioventricular (AV) heart block is to increase heart rate and improve AV nodal conduction by blocking parasympathetic (vagal) influences on the heart. However, atropine is generally ineffective for infranodal blocks, including Mobitz type II second-degree AV block and third-degree (complete) AV block, especially with wide QRS complexes, as these blocks occur below the AV node where vagal innervation has minimal influence.
Some key points to consider when using atropine for AV heart block include:
- The recommended dosage is 0.5-1 mg IV, which can be repeated every 3-5 minutes up to a maximum total dose of 3 mg 1.
- Atropine should be used cautiously in patients with acute coronary syndromes as increased heart rate may worsen myocardial ischemia.
- Side effects of atropine include dry mouth, blurred vision, urinary retention, confusion (especially in elderly patients), and paradoxical bradycardia at very low doses (less than 0.5 mg).
- Temporary pacing is usually required for infranodal blocks, including Mobitz type II second-degree AV block and third-degree (complete) AV block, especially with wide QRS complexes.
It's worth noting that the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1 provides the most recent and highest quality evidence for the use of atropine in AV heart block, and should be consulted for further guidance.
From the FDA Drug Label
Atropine also may lessen the degree of partial heart block when vagal activity is an etiologic factor In some patients with complete heart block, the idioventricular rate may be accelerated by atropine; in others, the rate is stabilized. Occasionally a large dose may cause atrioventricular (A-V) block and nodal rhythm.
The effect of Atropine on Atrioventricular (AV) heart block is that it may lessen the degree of partial heart block when vagal activity is the cause. However, in some cases, large doses may cause atrioventricular (A-V) block and nodal rhythm. In patients with complete heart block, atropine may accelerate the idioventricular rate or stabilize it. 2
From the Research
Effect of Atropine on Atrioventricular (AV) Heart Block
- Atropine can have both beneficial and adverse effects on patients with AV heart block, as seen in studies 3, 4, 5, 6, 7.
- In some cases, atropine can improve atrioventricular conduction in patients with AV block, particularly those with inferior myocardial infarction 5, 7.
- However, atropine can also worsen bradycardia in patients with AV block, especially those with infranodal blocks, as reported in a case study 3.
- The response to atropine can vary depending on the location and type of AV block, with some patients experiencing adverse effects such as ventricular tachycardia or fibrillation 5, 7.
- Studies have shown that approximately 50% of patients with hemodynamically unstable bradycardia or AV block respond to atropine therapy, with some achieving normal sinus rhythm 4, 6.
Factors Influencing the Effect of Atropine on AV Heart Block
- The dose and administration of atropine can impact its effectiveness and safety in patients with AV heart block, with higher doses increasing the risk of adverse effects 5, 7.
- The presence of underlying conditions such as acute myocardial infarction can influence the response to atropine, with some patients experiencing improved outcomes and others experiencing adverse effects 4, 6.
- The location and type of AV block can also impact the effectiveness of atropine, with some blocks responding better to treatment than others 3, 5, 7.