What is the best course of management for a patient with a history of cardiovascular disease, currently presenting with complex cardiac rhythm abnormalities including third-degree atrioventricular (AV) block, first-degree AV block, second-degree AV block, premature atrial contractions (PACs), and premature ventricular contractions (PVCs), who has improved hyponatremia to a sodium level of 131 mEq/L, and is on high salt and fluid restrictions?

Management of Third-Degree AV Block with Persistent Hyponatremia

This patient requires permanent pacemaker implantation for third-degree AV block, as this is a Class I indication regardless of symptoms, and the hyponatremia at 131 mEq/L—while improved—does not explain the complete heart block and should not delay definitive cardiac management. 1

Immediate Cardiac Management Priority

Permanent pacemaker implantation is mandated for this patient based on the following Class I indications from ACC/AHA/HRS guidelines 1:

• Third-degree AV block at any anatomic level constitutes an absolute indication for permanent pacing, even in asymptomatic patients 1
• The presence of multiple degrees of AV block (first, second, and third-degree) on the same Holter indicates advanced conduction system disease with high mortality risk 1
• Junctional rhythm with third-degree block suggests infranodal disease with unreliable escape mechanisms 1, 2

Critical Decision Point: Reversibility Assessment

Before proceeding to permanent pacing, you must determine if the AV block is reversible 1:

Hyponatremia at 131 mEq/L is NOT a reversible cause warranting delay:

• While severe acute hyponatremia (<115-120 mEq/L) can rarely cause third-degree AV block, this typically resolves completely with sodium correction 3
• This patient's sodium of 131 mEq/L is only mildly low and does not explain complete heart block 3
• The presence of multiple conduction abnormalities (first, second, AND third-degree block with junctional rhythms) indicates structural conduction system disease, not a metabolic derangement 1

Electrolyte abnormalities that should be corrected before pacing include:

• Severe hyperkalemia (>6.5-7.0 mEq/L) 1
• Severe acute hyponatremia (<115 mEq/L with temporal relationship to block onset) 3
• Severe hypomagnesemia or hypercalcemia 1

Specific Pacemaker Indications Met

This patient meets multiple Class I indications for permanent pacing 1, 2:

1. Third-degree AV block at any anatomic level (absolute indication) 1
2. If the patient has any symptoms (fatigue, dyspnea, presyncope, heart failure), this is a Class I indication with Level of Evidence C 1, 2
3. If asymptomatic but with escape rate <40 bpm or asystole ≥3.0 seconds on Holter, this is Class I 1, 2
4. If cardiomegaly or LV dysfunction is present with persistent third-degree block, this is Class I 1, 2

Additional High-Risk Features Requiring Urgent Pacing

Second-degree AV block with symptomatic bradycardia is also a Class I indication 1, 4:

• The presence of both second and third-degree block indicates advanced conduction disease 1
• Mobitz Type II block (if present) requires pacing even if asymptomatic due to unpredictable progression 4

Hyponatremia Management Concurrent with Cardiac Care

Continue addressing the hyponatremia but do not delay pacemaker implantation:

• Sodium of 131 mEq/L requires investigation of the underlying cause (SIADH, heart failure, medications, etc.) 3
• The "high salt and fluid restrictions" statement is contradictory—clarify the actual management strategy 3
  • If hypovolemic hyponatremia: liberalize salt and fluids
  • If hypervolemic (heart failure): continue fluid restriction with salt restriction
  • If euvolemic (SIADH): fluid restriction with possible salt tablets

Critical pitfall to avoid: Do not attribute the third-degree AV block to mild hyponatremia and delay pacing 3. Only severe acute hyponatremia (<115 mEq/L) has been documented to cause reversible complete heart block, and even then, only in rare case reports 3.

Pacemaker Selection

Dual-chamber pacing (DDD mode) is preferred for this patient 4:

• Maintains AV synchrony and prevents pacemaker syndrome 4
• Appropriate for sinus node function (patient has sinus rhythm on Holter) 4
• Addresses both AV block and potential bradycardia from junctional rhythms 2, 4

Monitoring Before Implantation

While arranging urgent pacemaker implantation 2:

• Continuous cardiac monitoring for progression to symptomatic bradycardia or asystole 2
• Transcutaneous pacing pads should be placed prophylactically 2
• If symptomatic bradycardia or hypotension develops, initiate transcutaneous pacing immediately while preparing for transvenous temporary pacing 2
• Atropine is likely ineffective for infranodal third-degree block but may be attempted 2

Common Pitfalls to Avoid

1. Do not delay pacemaker waiting for further sodium correction when sodium is 131 mEq/L—this is not the cause of complete heart block 3
2. Do not assume the block will resolve with metabolic correction when multiple degrees of block are present 1, 5
3. Do not wait for symptoms to develop before implanting—third-degree block has high mortality and sudden death risk even when asymptomatic 1, 6
4. Do not order unnecessary antiplatelet therapy solely for pacemaker implantation in the absence of coronary indications 7