What is the recommended approach to recognize, classify, and manage atrioventricular (AV) block that occurs intraoperatively under anesthesia?

Intraoperative Management of Atrioventricular Block During Anesthesia

For patients with pre-existing first-degree AV block or bifascicular block, prophylactic temporary pacing is not routinely required for non-cardiac surgery, but transcutaneous pacing pads should be immediately available in the operating room, and any progression to higher-grade block during anesthesia mandates immediate pacing intervention. 1

Pre-Anesthetic Risk Stratification

Low-Risk Patients (No Special Precautions Required)

• Isolated first-degree AV block with PR interval < 300 ms in asymptomatic patients requires only standard ASA monitoring (continuous ECG, pulse oximetry, blood pressure) without prophylactic pacing equipment. 1
• These patients do not require pre-operative cardiology consultation or temporary pacemaker placement before elective surgery. 1

High-Risk Patients (Enhanced Monitoring Required)

• First-degree AV block combined with bifascicular block (RBBB + left anterior or posterior fascicular block) warrants transcutaneous pacing pads in the operating room, though routine prophylactic temporary pacing is not indicated. 1
• Patients with neuromuscular diseases (myotonic dystrophy, Kearns-Sayre syndrome, Emery-Dreifuss muscular dystrophy, peroneal muscular atrophy) require pre-operative cardiology consultation because of unpredictable risk of sudden progression to high-grade block. 1
• Second-degree 2:1 AV block—even when asymptomatic—should prompt prophylactic temporary pacemaker placement before elective surgery, as progression to complete heart block during anesthesia is common. 2
• PR interval ≥ 300 ms requires closer intraoperative monitoring, although progression to complete heart block remains uncommon when no other conduction abnormalities are present. 1

Intraoperative Recognition of AV Block

Electrocardiographic Classification

• First-degree AV block is defined as PR interval > 200 ms with 1:1 AV conduction. 3
• Second-degree AV block type I (Wenckebach) shows progressive PR prolongation before a blocked P wave; type II shows constant PR intervals before the blocked P wave. 3
• 2:1 AV block is classified separately and cannot be definitively categorized as type I or type II without additional monitoring. 3
• High-grade AV block is defined as multiple consecutive blocked P waves without complete AV dissociation. 3
• Third-degree (complete) AV block shows complete dissociation between P waves and QRS complexes with no conducted beats. 3

Anatomic Localization by QRS Morphology

• Narrow QRS escape rhythm (< 120 ms) suggests AV nodal or high His-bundle block with escape rates typically 40–60 bpm; these blocks are more likely to respond to atropine. 4
• Wide QRS escape rhythm (≥ 120 ms) indicates infranodal (His-Purkinje) block with escape rates 20–40 bpm; these blocks are unresponsive to atropine and carry higher risk of asystole. 4
• Type I second-degree AV block with narrow QRS is usually at the AV node level; with wide QRS it may be within or below the His bundle. 3
• Type II second-degree AV block is usually within or below the His bundle and most often presents with bundle branch block. 3

Immediate Intraoperative Management Algorithm

Step 1: Hemodynamic Assessment

• Immediately assess for signs of poor perfusion: altered mental status, hypotension (systolic BP < 80–90 mmHg), acute heart failure, chest pain, or shock. 5
• Symptomatic bradycardia—manifested by heart-failure symptoms, syncope, or ventricular arrhythmias—at any heart rate mandates immediate intervention. 5

Step 2: Pharmacologic Management (AV-Nodal Block Only)

Atropine Administration

• For narrow-QRS escape rhythms (AV-nodal level block), administer atropine 0.5–1.0 mg IV bolus, repeatable every 3–5 minutes up to a maximum total dose of 3 mg. 5
• Doses < 0.5 mg may paradoxically worsen bradycardia via central vagal stimulation and must be avoided. 5
• Atropine is completely ineffective for wide-QRS escape rhythms (infranodal block) and must not delay pacing. 5

Alternative Pharmacologic Agents

• β-adrenergic agonists (isoproterenol, dopamine, dobutamine, epinephrine) may be considered when atropine fails in AV-nodal block and coronary ischemia is unlikely, but only as a bridge to pacing. 5
• Intravenous aminophylline may be considered for AV block occurring in the setting of acute inferior myocardial infarction. 5
• Dopamine infusion (2–20 µg/kg/min) can maintain systolic blood pressure > 90 mmHg in refractory hypotension but must never replace pacing as primary therapy. 5

Step 3: Pacing Strategies

Transcutaneous Pacing (First-Line for Unstable Patients)

• Initiate transcutaneous pacing immediately for hemodynamically unstable patients or those with wide-QRS escape rhythms, without awaiting atropine response. 5
• Do not postpone transcutaneous pacing to administer atropine in hemodynamically unstable patients. 5

Transesophageal Pacing

• Transesophageal ventricular pacing is an effective alternative when transcutaneous pacing fails or is not tolerated, particularly in the prone or lateral decubitus position. 6

Temporary Transvenous Pacing

• Temporary transvenous pacing is appropriate for patients who remain symptomatic or unstable after medical measures, serving as a bridge to permanent pacemaker implantation. 5
• For anticipated prolonged temporary pacing, an externalized permanent active-fixation lead is preferred over standard passive-fixation temporary leads. 5

Anesthetic Considerations

Anesthetic Agents and AV Conduction

• Volatile anesthetics (sevoflurane, isoflurane) can depress AV nodal conduction and may unmask or worsen pre-existing conduction abnormalities. 6, 2
• Excess vagal activity during anesthesia—from laryngoscopy, surgical manipulation, or opioid administration—can precipitate complete AV block in patients with pre-existing first-degree block. 7
• Intraoperative hypothermia may transiently worsen AV conduction but is reversible and does not require permanent pacing. 1

Medication Management

• Continue β-blockers and other AV-nodal-blocking agents perioperatively when indicated for comorbid conditions (coronary artery disease, heart failure); withholding is not required solely for isolated first-degree AV block. 1

Etiology Assessment During Anesthesia

Reversible Causes to Exclude

• Systematically rule out acute myocardial infarction, drug toxicity (β-blockers, calcium-channel blockers, digoxin), electrolyte disturbances (hyperkalemia, hypomagnesemia), and excessive vagal stimulation before attributing block to structural disease. 3, 5
• Infectious causes (Lyme carditis, bacterial endocarditis with perivalvular abscess) and infiltrative diseases (sarcoidosis, amyloidosis) should be considered in the appropriate clinical context. 3
• Inferior wall myocardial infarction commonly causes transient AV block that may be vagally mediated and responsive to atropine or aminophylline. 5

Structural and Degenerative Causes

• Degenerative causes (Lev's and Lenegre's diseases) are most common in clinical practice and are associated with increased age, chronic hypertension, and diabetes mellitus. 3
• Iatrogenic causes from cardiac surgery (especially valve surgery), TAVR, or catheter ablation are usually clear from the clinical circumstances. 3

Postoperative Management

Observation Period

• A mandatory observation period is required after anesthesia-induced AV block before deciding on permanent pacing, because the block may be transient. 5
• Temporary pacing capability should not be discontinued until sustained resolution of the conduction disturbance has been confirmed for at least 24 hours. 5

Indications for Permanent Pacemaker (Class I)

• Permanent pacemaker implantation is indicated for third-degree AV block at any anatomic level with symptomatic bradycardia, including heart failure symptoms or ventricular arrhythmias presumed due to AV block. 5
• Asymptomatic third-degree AV block in awake patients with high-risk features (documented asystole ≥ 3.0 seconds, escape rate < 40 bpm, or escape rhythm below the AV node) requires permanent pacemaker implantation. 5
• Persistent second-degree Mobitz type II, high-grade AV block, or third-degree AV block after the observation period warrants permanent pacemaker placement. 5

When Permanent Pacing Is NOT Indicated

• Permanent pacemaker implantation should be avoided when AV block resolves completely after treatment of reversible causes. 5
• Asymptomatic vagally mediated AV block does not require permanent pacing. 5

Critical Pitfalls to Avoid

• Do not assume first-degree AV block is benign in asymptomatic patients; continuous monitoring reveals that approximately 40% may have intermittent higher-grade block. 1
• Do not delay necessary surgery solely for isolated first-degree AV block; there is no evidence that prophylactic pacemaker implantation improves perioperative outcomes in asymptomatic patients. 1
• Do not mistake isolated first-degree AV block for higher-grade block; exercise-induced progression to second-degree block suggests underlying His-Purkinje disease and warrants permanent pacing before elective surgery. 1
• Do not use atropine for wide-QRS escape rhythms; it is ineffective and wastes critical time. 5
• Do not rely on atropine for infranodal blocks; its effect is limited to AV-nodal conduction. 5
• In the setting of acute anterior-wall myocardial infarction, atropine may exacerbate ischemia and is contraindicated for infranodal block. 1
• Do not assume third-degree AV block is benign based on age alone; definitive evaluation and treatment are required irrespective of patient age. 5

Special Populations

Neuromuscular Disease

• Patients with myotonic muscular dystrophy, Kearns-Sayre syndrome, Erb's dystrophy, or peroneal muscular atrophy may experience sudden progression to high-grade AV block even when only first-degree AV block is present; prophylactic permanent pacing may be considered (Class IIb). 1

Cardiac Surgery

• In cardiac surgery (valve replacement, coronary bypass), first-degree AV block does not influence operative decision-making or the need for additional pacing strategies beyond standard epicardial wire placement. 1
• Development of AV block after cardiac surgery may necessitate temporary pacing, but pre-existing first-degree AV block does not predict this complication. 1