From the Guidelines
For first-degree AV block identified during a pre-operative evaluation, no specific treatment is typically required as this is generally considered a benign finding. First-degree AV block is characterized by a prolonged PR interval (>200 ms) on ECG but usually doesn't cause symptoms or hemodynamic compromise. The provided guideline evidence 1 primarily focuses on the management of atrial fibrillation and does not directly address the management of first-degree AV block in the pre-operative setting. However, the principle of managing cardiac conditions pre-operatively emphasizes the importance of assessing the patient's overall cardiac risk and ensuring that any potential issues are monitored appropriately during surgery.
Given the lack of direct evidence from the provided guideline regarding first-degree AV block, the approach should be based on general principles of perioperative cardiac care. Continue with the planned surgery without delay, but inform the anesthesiologist about the finding so they can monitor the patient appropriately during the procedure. No medication adjustments are necessary specifically for the first-degree AV block. However, a thorough cardiac evaluation may be warranted if the patient has other cardiac risk factors or symptoms. This should include a complete history, physical examination, and possibly additional cardiac testing depending on the patient's risk profile and the type of surgery planned. The benign nature of isolated first-degree AV block is due to the fact that all atrial impulses still conduct to the ventricles, just with a delay at the AV node. This delay rarely progresses to higher-degree blocks during surgery, though anesthetics that affect cardiac conduction should be used with appropriate monitoring.
Key considerations in the pre-operative evaluation of patients with first-degree AV block include:
- Assessing the patient's overall cardiac risk
- Evaluating for symptoms or signs of heart failure
- Reviewing medications that may affect cardiac conduction
- Ensuring appropriate monitoring during surgery
- Considering additional cardiac testing if indicated by the patient's risk profile or symptoms. The management approach should prioritize minimizing risks associated with the surgery and the patient's underlying cardiac condition, focusing on morbidity, mortality, and quality of life as the primary outcomes.
From the Research
Pre-Operative Exam Recommendations for First Degree AV Block
- Patients with first degree AV block should be evaluated for symptoms, as marked first degree AV block (PR ≥ 0.30 s) can produce a clinical condition similar to that of the pacemaker syndrome 2.
- A treadmill stress test may be required to assess symptoms with exercise, as patients are more likely to become symptomatic with mild or moderate exercise when the PR interval cannot adapt appropriately 2.
- The use of beta blockers and calcium channel blockers may be recommended as first line therapies for patients with first degree AV block, as they can reduce oxygen demand and improve overall clinical outcomes 3, 4.
- However, the effects of these drugs on AV nodal conduction should be considered, as slow channel blockers and beta blockers can affect AV nodal function and prolong the PR interval 5.
- In patients with normal AV nodal function, parasympathetic and sympathetic tone are balanced at rest, but in patients with abnormal AV conduction, the effect of the parasympathetic system is more marked 5.
- The current recommendations for temporary pacing for elective general anaesthesia in patients with first degree AV block should be considered, as asymptomatic first degree block can rarely progress to transient Wenckebach (type 1 second degree) block or complete atrioventricular block 6.
Management of First Degree AV Block
- Conventional dual chamber pacing may be recommended for symptomatic patients with normal left ventricular function 2.
- However, for patients with marked first degree AV block and left ventricular systolic dysfunction, a biventricular DDD device may be considered to avoid the risks associated with right ventricular pacing 2.
- Patients with suboptimally programmed pacemakers may develop functional atrial undersensing, and a relatively short postventricular atrial refractory period (PVARP) can often be used at rest with little risk of endless loop tachycardia 2.
Considerations for Cardiac Resynchronization Therapy
- First-degree AV block during cardiac resynchronization therapy (CRT) can predispose to loss of ventricular resynchronization, and patients with first-degree AV block may have a poorer outcome with CRT than patients with a normal PR interval 2.