What is the workup and management for PR depression observed during an exercise (EXE) stress test?

PR Depression on Exercise Stress Testing: Workup and Differentials

PR depression observed during exercise stress testing is a normal physiological response due to increased sympathetic tone and vagal withdrawal, and does not require specific workup unless accompanied by other concerning findings.

Normal PR Segment Changes During Exercise

• During exercise, the PR segment normally shortens and slopes downward in the inferior leads 1
• This downward slope is attributed to atrial repolarization (the Ta wave) 1
• The PR interval can shorten by as much as 0.10-0.11 seconds during exercise as heart rate increases 1
• These changes are considered normal physiological responses, particularly in young, healthy individuals 1

Mechanism of PR Depression

• PR depression during exercise is caused by:
  • Increased sympathetic tone
  • Vagal withdrawal
  • Atrial repolarization (Ta wave) that persists into early ventricular repolarization 1
• The decreasing slope of the PR segment can sometimes cause apparent ST-segment depression when the negative Ta wave extends into the early ventricular repolarization period 1

When to Consider Further Workup

Further evaluation is warranted only when PR depression is accompanied by:

1. Concerning symptoms:

   • Moderate-to-severe angina 1
   • Central nervous system symptoms (ataxia, dizziness, near-syncope) 1
   • Signs of poor perfusion (cyanosis or pallor) 1

2. Concerning ECG findings:

   • Horizontal or downsloping ST depression ≥1 mm at 60-80 ms after the J point 1
   • ST segment elevation >1.0 mm in leads without preexisting Q waves 1
   • Development of arrhythmias or conduction blocks 1

3. Hemodynamic abnormalities:

   • Drop in systolic blood pressure >10 mm Hg despite increasing workload 1

Differential Diagnosis When PR Depression is Accompanied by Other Findings

1. Myocardial ischemia:

   • Primary concern when PR depression is accompanied by typical ST-segment depression
   • Standard criteria: horizontal or downsloping ST depression ≥1 mm at 60-80 ms after the J point 1

2. Intraventricular conduction disorders:

   • Rate-dependent intraventricular blocks may develop during exercise 1
   • Can precede the appearance of chronic blocks that develop later at rest 1

3. Pericarditis:

   • Can cause PR depression at rest that may worsen with exercise
   • Usually accompanied by ST elevation in multiple leads

4. Pre-excitation syndromes (e.g., Wolff-Parkinson-White):

   • May show PR depression with delta waves
   • Delta waves can disappear during exercise in approximately 20% of patients 2

Recommended Workup Algorithm

If PR depression is observed during exercise stress testing:

1. If isolated PR depression with no other concerning findings:

   • No further workup needed - this is a normal physiological response 1

2. If PR depression with concerning findings:

   • Evaluate for structural heart disease with echocardiography
   • Consider myocardial perfusion imaging (SPECT or PET) to assess for ischemia
   • Consider 24-hour ambulatory ECG monitoring if arrhythmias are suspected

3. If PR depression with first-degree AV block (PR interval ≥0.3 seconds):

   • Exercise stress test to assess PR interval shortening with exercise
   • 24-hour ambulatory monitoring
   • Echocardiogram to rule out structural heart disease 1
   • Electrophysiology studies rarely necessary but may be considered in selected cases 1

Important Caveats

• PR depression can sometimes mimic ST depression, leading to false-positive interpretations of ischemia 1
• The ST level should be measured relative to the end of the PR segment (P-Q junction) rather than the isoelectric baseline 1
• In patients with depression or anxiety, exercise performance may be affected, potentially influencing the reliability of ECG findings 3
• Upsloping ST depression (which may be confused with PR depression) is generally not predictive of myocardial ischemia in general populations 1, 4

Reporting Recommendations

When documenting PR depression on exercise stress testing:

• Note that it is a normal physiological finding
• Document other relevant ECG changes separately
• Specify if any concerning symptoms occurred during the test
• Include details about exercise capacity and hemodynamic response
• Provide a clear conclusion about the overall significance of the findings 1