In a patient with atrial and ventricular pacing, can PR‑segment depression be reliably interpreted as a sign of acute pericarditis?

PR Depression Cannot Be Reliably Interpreted in Paced Rhythms

In a patient with both atrial and ventricular pacing, PR-segment depression cannot be reliably used as an ECG criterion for acute pericarditis because the native atrial depolarization and repolarization are obscured by pacing artifacts.

Why PR Depression Fails in Paced Rhythms

PR-segment depression occurs due to atrial injury currents during atrial repolarization (the Ta wave) in pericarditis. However, this finding requires:

• Visible native P waves to assess the PR segment
• Native atrial depolarization and repolarization to generate the characteristic depression

When both atria and ventricles are paced, the ECG shows pacing spikes instead of native P waves and QRS complexes, making it impossible to assess the PR segment in the traditional sense 1.

Diagnostic Approach in This Clinical Scenario

Since you cannot rely on PR depression, you must use the other 3 diagnostic criteria from the 2015 ESC Guidelines 1:

Diagnosis requires ≥2 of these 4 criteria:

1. Pericarditic chest pain (sharp, pleuritic, worse when supine, relieved by leaning forward) - present in ~90% 2
2. Pericardial friction rub - highly specific but present in <30% of cases 2
3. New widespread ST-elevation or PR depression on ECG - NOT interpretable in your paced patient
4. New or worsening pericardial effusion on echocardiography - present in ~60% 2

Your Practical Algorithm:

Step 1: Assess for pericarditic chest pain characteristics

• Sharp, pleuritic quality
• Positional (worse supine, better leaning forward)
• Radiates to trapezius ridge

Step 2: Perform careful auscultation for pericardial friction rub

• Listen during end-expiration with patient sitting up and leaning forward 3
• Three-component scratchy sound (highly specific when present)

Step 3: Order transthoracic echocardiography (Class I recommendation) 1

• Look for new or increased pericardial effusion
• Assess for tamponade physiology

Step 4: Check inflammatory markers 1, 2

• Elevated CRP, ESR, WBC count support the diagnosis
• Consider troponin (may be elevated if myopericarditis)

Critical Caveat About Pacemaker-Related Pericarditis

Importantly, pacemaker lead insertion itself is a recognized iatrogenic cause of pericarditis 1. The 2015 ESC Guidelines specifically list "pacemaker lead insertion" under traumatic/iatrogenic causes of delayed-onset pericardial injury syndromes 1. Consider:

• Timing: When was the pacemaker implanted?
• Recent manipulation: Any recent lead revisions or generator changes?
• Post-procedural pericarditis can occur as a delayed complication

What About ST Segments in Paced Rhythms?

Even ST-segment changes are unreliable in ventricular pacing due to:

• Abnormal ventricular depolarization patterns
• Secondary repolarization abnormalities
• Baseline ST-T wave changes inherent to paced rhythms

Bottom line: Do not attempt to interpret ST-segment or PR-segment changes for pericarditis diagnosis in patients with ventricular pacing 4.

Recommended Diagnostic Workup

Since ECG criteria are unreliable, rely heavily on:

1. Clinical presentation (chest pain characteristics)
2. Echocardiography (mandatory - Class I recommendation) 1
3. Inflammatory markers (CRP most useful for diagnosis and monitoring response) 1
4. Consider cardiac MRI if diagnosis remains uncertain - can show pericardial inflammation with late gadolinium enhancement 1, 5

The diagnosis becomes more challenging but not impossible - you simply cannot use the ECG as one of your diagnostic criteria in this specific clinical context.