What is the disposition for an adult patient with first-degree atrioventricular (AV) block, a PR interval of 220 milliseconds, and a recent episode of syncope?

Disposition for First-Degree AV Block with Syncope

This patient requires hospital admission with continuous cardiac monitoring and urgent cardiology consultation to evaluate for intermittent higher-degree AV block or other causes of syncope, as isolated first-degree AV block (PR 220 ms) does not explain syncope and suggests the presence of more advanced conduction disease. 1

Critical Clinical Reasoning

First-degree AV block alone does not cause syncope. The presence of syncope in a patient with first-degree AV block is a red flag that demands investigation for:

• Intermittent higher-degree AV block (Mobitz II, advanced second-degree, or complete heart block) that was not captured on the initial ECG 1
• Paroxysmal bradyarrhythmias occurring between documented rhythm strips 2
• Other causes of syncope unrelated to the first-degree block 3

Recent evidence demonstrates that first-degree AV block may be a marker for intermittent severe conduction disease: in one study using insertable cardiac monitors, 40.5% of patients with baseline first-degree AV block progressed to higher-grade block requiring pacemaker implantation, with 93.3% of these cases representing previously undetected severe bradycardia. 2

Immediate Management Algorithm

Inpatient Admission Criteria (This Patient)

• Admit to telemetry unit for continuous cardiac monitoring 3
• Place transcutaneous pacing pads at bedside given syncope with conduction abnormality 4
• Obtain urgent cardiology consultation for evaluation and potential electrophysiology study 1

Diagnostic Workup Required

Continuous cardiac monitoring to capture intermittent higher-degree block:

• Minimum 24-48 hours of telemetry monitoring 3
• Consider insertable cardiac monitor if initial monitoring non-diagnostic and syncope remains unexplained 2

Assess for reversible causes:

• Review all medications (beta-blockers, calcium channel blockers, digoxin, antiarrhythmics) 5, 3
• Check electrolytes (potassium, magnesium) 5, 3
• Consider Lyme serology if epidemiologically appropriate 5, 3
• Evaluate for acute myocardial ischemia 5

Echocardiography to assess for structural heart disease 3, 4

Exercise stress testing (once higher-degree block excluded) to evaluate for exercise-induced AV block, which indicates His-Purkinje disease with poor prognosis requiring pacing even if reversible causes are present 1, 3

Pacemaker Indications Based on Findings

Class I (Definite Indication)

• Any documented Mobitz II second-degree or higher-degree AV block, even if asymptomatic 1, 4
• Symptomatic bradycardia with documented second-degree or complete heart block 1
• Exercise-induced second- or third-degree AV block not due to ischemia 1, 3

Class IIa (Reasonable)

• First-degree AV block with PR >300 ms causing pacemaker syndrome-like symptoms or hemodynamic compromise 1, 3
• However, this patient's PR of 220 ms does not meet this threshold 3

Class III (Not Indicated)

• Isolated asymptomatic first-degree AV block with PR <300 ms 1, 3

Critical Pitfalls to Avoid

Do not discharge this patient without identifying the cause of syncope. First-degree AV block with PR 220 ms is insufficient to explain syncope, and the guidelines explicitly state there is no evidence that pacemakers improve survival in isolated first-degree AV block. 1

Do not assume the first-degree block is the culprit. The syncope likely represents:

• Intermittent Mobitz II or complete heart block occurring between rhythm strips 2
• Paroxysmal ventricular arrhythmias 1
• Non-cardiac causes of syncope 3

Beware of 2:1 AV block on monitoring, which cannot be classified as Type I or Type II from ECG alone and requires electrophysiology study or exercise testing to determine anatomic level and prognosis. 1, 5

Exercise-induced progression of AV block (not due to ischemia) indicates His-Purkinje disease with poor prognosis and mandates pacing regardless of baseline findings. 1, 3

Outpatient Disposition Criteria (Not This Patient)

Outpatient management would only be appropriate for:

• Asymptomatic first-degree AV block with PR <300 ms 3
• No history of syncope, presyncope, or unexplained falls 3
• No evidence of structural heart disease 3
• Reversible causes identified and corrected 5, 3

This patient does not meet these criteria due to the syncopal episode.