What is the significance of a borderline electrocardiogram (ECG) and how should it be managed?

Borderline ECG: Clinical Significance and Management

A borderline ECG represents findings that in isolation likely do not indicate pathologic cardiovascular disease, but require clinical correlation and may warrant further investigation when multiple borderline findings coexist or when accompanied by symptoms, family history, or other risk factors. 1

Definition of Borderline ECG Findings

Borderline ECG abnormalities are distinct from normal physiologic variants and clearly abnormal findings. The most commonly recognized borderline findings include: 1

• Left axis deviation (-30° to -90°) - more common in women in their 50s due to age-related leftward axis shift 2
• Right axis deviation (>120°) 1
• Left atrial enlargement - P wave duration >120 ms with negative portion ≥1 mm depth and ≥40 ms duration in V1 1
• Right atrial enlargement - P wave ≥2.5 mm in leads II, III, or aVF 1
• Complete right bundle branch block - rSR' pattern in V1 with QRS ≥120 ms 1

Clinical Significance and Risk Stratification

When Borderline Findings Are Likely Benign

Isolated borderline findings in asymptomatic patients without family history typically do not require extensive workup. 1, 2 Specifically:

• Single borderline finding + normal physical exam + no symptoms + no family history of cardiac disease or sudden death = reassurance and routine follow-up only 2
• In athletic populations, isolated borderline findings represent physiologic adaptation to training rather than pathology 1

When Further Evaluation Is Warranted

Additional investigation becomes necessary when: 1

• Two or more borderline ECG findings are present simultaneously - this combination warrants echocardiography at minimum 1
• Any symptoms are present including chest pain, dyspnea, palpitations, syncope, or dizziness 1
• Family history of premature cardiac disease or sudden cardiac death exists 1, 2
• Associated clearly abnormal ECG findings such as pathologic Q waves, ST depression ≥0.5 mm, or T-wave inversion ≥1 mm 1

Diagnostic Approach

Initial Assessment

Every borderline ECG requires: 1

• Comparison with previous ECGs - critical for determining if findings are new or longstanding 1
• Clinical correlation - integrate patient age, sex, symptoms, cardiovascular risk factors, and family history 1
• Verification of proper technique - confirm correct lead placement and exclude technical artifacts 1, 3
• Physician over-reading - computer interpretations of borderline findings require verification by qualified physician 1

Specific Evaluation for Multiple Borderline Findings

When ≥2 borderline findings coexist, the recommended workup includes: 1

• Echocardiography - first-line imaging to exclude structural heart disease 1
• Consider cardiovascular magnetic resonance (CMR) if echocardiography is inconclusive or suggests cardiomyopathy 1
• Exercise ECG testing may be appropriate to assess for exercise-induced arrhythmias or ischemia 1

Management Strategy

For Isolated Borderline Findings

The appropriate management pathway is: 2

• Reassurance that isolated borderline findings likely represent normal variants or age-related changes 2
• Blood pressure optimization - ensure hypertension is well-controlled 2
• Routine follow-up - repeat ECG only if symptoms develop or new cardiac risk factors emerge 2
• No restriction from activities in asymptomatic individuals 1

For Multiple Borderline Findings or High-Risk Features

A more intensive approach is required: 1

• Cardiology referral for comprehensive evaluation 1
• Echocardiography as initial structural assessment 1
• Serial ECG monitoring if initial workup is negative but clinical suspicion remains 1
• Consider temporary activity restriction in athletes until evaluation is complete 1

Common Pitfalls and Caveats

Technical Errors Mimicking Borderline Findings

Lead misplacement is a frequent cause of apparent ECG abnormalities: 1, 3

• Superior placement of V1-V2 can create artifactual poor R-wave progression and axis deviations 3
• Lead transposition can simulate conduction abnormalities 3
• Variability in lead placement as small as 2 cm can cause diagnostic errors 3

Population-Specific Considerations

Interpretation must account for patient demographics: 1

• Athletes - isolated voltage criteria for hypertrophy or axis deviations are common physiologic adaptations 1
• Adolescents <16 years - anterior T-wave changes may represent normal juvenile pattern 1
• Black athletes - ST elevation with T-wave inversion in V1-V4 is a normal variant 1
• Older adults - age-related leftward axis shift is expected 2

When "Borderline" May Actually Be Pathologic

Certain borderline patterns require heightened vigilance: 1, 4

• Borderline Brugada pattern - may require sodium channel blocker challenge to unmask diagnostic findings 1, 4
• Borderline QT prolongation - repeat ECG on separate day and consider family screening if QTc approaches 470 ms (males) or 480 ms (females) 1
• Progressive changes - borderline findings that worsen on serial ECGs warrant investigation even if still "borderline" 1

Documentation and Follow-up

Proper documentation is essential: 1

• Specify which borderline findings are present rather than using vague terminology 1
• Document clinical context including symptoms, risk factors, and family history 1
• Establish follow-up plan - clarify whether repeat ECG is needed and under what circumstances 2
• Communicate with patient about significance (or lack thereof) to prevent unnecessary anxiety 2