What is the recommended management for a 27-year-old male with dizziness and lightheadedness, first-degree atrioventricular (AV) block, and bradycardia, without chest pain, and a very active lifestyle?

Management of First-Degree AV Block with Symptomatic Bradycardia in a Young Active Adult

In this 27-year-old active male with dizziness, lightheadedness, first-degree AV block, and bradycardia, ambulatory ECG monitoring is the most appropriate next step to establish correlation between symptoms and rhythm abnormalities, followed by exercise testing to assess for progression of AV block or inadequate heart rate response during activity. 1

Initial Assessment and Risk Stratification

Determine Symptom-Rhythm Correlation

• Ambulatory electrocardiographic monitoring (24-48 hour Holter or event monitor) is reasonable (Class IIa) to establish whether symptoms correlate with the first-degree AV block or if higher-grade block is occurring intermittently. 1
• This is critical because first-degree AV block can be a marker for more severe intermittent conduction disease—one study found that 40.5% of patients with first-degree AV block progressed to higher-grade block requiring pacemaker implantation. 2

Assess for Reversible Causes

• Review all medications, particularly beta-blockers, non-dihydropyridine calcium channel blockers, digoxin, and antiarrhythmic drugs that can cause AV block. 3
• Check electrolytes (potassium, magnesium) as abnormalities can contribute to conduction delays. 3
• Consider infectious causes (Lyme disease) or infiltrative diseases (sarcoidosis, amyloidosis) if clinically indicated. 3

Exercise Testing for Active Patients

Why Exercise Testing Matters in This Case

• An exercise treadmill test is reasonable (Class IIa) for patients with exertional symptoms who have first-degree AV block at rest to determine whether permanent pacing may be beneficial. 1
• In a young, active patient, the PR interval should normally shorten during exercise; failure to do so or progression to higher-grade block during exercise (not due to ischemia) indicates His-Purkinje disease with poor prognosis and warrants pacing. 3
• Exercise testing can also reveal inadequate chronotropic response (inability to increase heart rate appropriately with activity), which could explain dizziness and lightheadedness in an active individual. 4

Determine PR Interval Severity

PR Interval <300 ms (Likely in This Case)

• Asymptomatic first-degree AV block with PR <300 ms requires no specific treatment, and permanent pacemaker implantation is not indicated. 4, 3
• However, this patient is symptomatic, so further evaluation is warranted to determine if symptoms are truly attributable to the AV block. 1

PR Interval ≥300 ms (If Present)

• Marked first-degree AV block (PR ≥300 ms) can produce symptoms similar to pacemaker syndrome, including fatigue, exercise intolerance, dizziness, and lightheadedness due to inadequate timing of atrial and ventricular contractions. 4, 3, 5
• Permanent pacemaker implantation is reasonable (Class IIa) for symptomatic patients with PR >300 ms causing hemodynamic compromise or pacemaker syndrome-like symptoms. 4, 3

Management Algorithm

If Ambulatory Monitoring Shows:

Higher-Grade Block (Second-Degree Mobitz II, High-Grade, or Third-Degree)

• Permanent pacing is recommended (Class I) regardless of symptoms if acquired second-degree Mobitz type II, high-grade, or third-degree AV block is documented and not attributable to reversible causes. 1

Symptomatic Bradycardia Correlating with First-Degree AV Block

• If PR ≥300 ms and symptoms clearly correlate: Consider permanent pacemaker (Class IIa). 4, 3
• If PR <300 ms but exercise testing shows progression or inadequate chronotropic response: Consider permanent pacemaker. 3

No Correlation Between Symptoms and Rhythm

• Investigate alternative causes of dizziness and lightheadedness (orthostatic hypotension, vestibular disorders, psychiatric causes). 6
• Continue observation with periodic ECG monitoring for progression. 4

Important Caveats and Pitfalls

Do NOT Pace Asymptomatic First-Degree AV Block

• Permanent pacemaker implantation should not be performed for asymptomatic first-degree AV block, as there is little evidence that pacing improves survival in isolated first-degree AV block. 4, 3

Avoid Atropine Unless Acute Symptomatic Bradycardia

• Atropine (0.5 mg IV) may be considered for acute symptomatic bradycardia at the AV node level, but doses <0.5 mg can paradoxically slow heart rate further. 3, 7
• Atropine is not appropriate for chronic management and should only be used in acute settings. 7

Monitor for Progression

• First-degree AV block, especially with coexisting bundle branch block or bifascicular block, should be monitored closely for progression to higher-grade block. 4
• Consider cardiology referral if PR >300 ms, coexisting bundle branch block, structural heart disease, or evidence of progression on monitoring. 4

Special Consideration for Athletes

• Athletes with asymptomatic first-degree AV block can participate in all competitive sports unless excluded by underlying structural heart disease. 4
• However, this patient is symptomatic, so clearance for competitive sports should be deferred until symptom etiology is clarified. 4

When to Refer to Cardiology

Refer to cardiology if any of the following are present:

• Symptoms of fatigue, dizziness, or exercise intolerance correlating with first-degree AV block 4
• PR interval >300 ms 4
• Coexisting bundle branch block or bifascicular block 4
• Evidence of structural heart disease on examination or echocardiography 4
• Progression to higher-grade block on ambulatory monitoring 4

Prognosis

• Most cases of isolated first-degree AV block have excellent prognosis when asymptomatic. 4
• However, symptomatic first-degree AV block, especially with PR ≥300 ms, may benefit from pacing to improve quality of life. 4, 3, 5
• Educate the patient about symptoms that might indicate progression to higher-grade block (sudden worsening of dizziness, syncope, severe fatigue). 4