What are the possible causes of borderline left axis deviation on an electrocardiogram (EKG) in an otherwise healthy female in her 50s with a sinus rhythm and normal heart rate?

Borderline Left Axis Deviation in a Healthy 50-Year-Old Female

In an otherwise healthy woman in her 50s with borderline left axis deviation (LAD) on ECG and normal sinus rhythm, no specific treatment or extensive cardiac workup is required, as isolated borderline LAD has limited clinical significance and likely represents normal age-related leftward axis shift. 1

Understanding the Finding

Borderline LAD is defined as a QRS axis between 0° and -30°, which falls just outside the traditional normal range of +30° to +90° but is less concerning than moderate (-30° to -45°) or marked (-45° to -90°) LAD. 1 In your patient's demographic, this finding has particular relevance:

• Age-related changes: There is a natural tendency for the cardiac axis to shift leftward with increasing age, making borderline LAD more common and less pathologically significant in women in their 50s. 1
• Athletic populations: In athletes, LAD is classified as a "borderline" ECG finding that in isolation likely does not represent pathologic cardiovascular disease. 2, 1

Most Common Causes in This Population

Benign/Physiological Causes

• Normal aging: The gradual leftward axis shift that occurs with advancing age is the most likely explanation in an otherwise healthy individual. 1
• Body habitus: Variations in chest configuration and heart position can influence axis measurements without pathological significance. 3
• Left anterior fascicular block (LAFB): This is one of the most common causes of LAD, though typically produces more marked deviation (>-30°). 3

Pathological Causes to Consider

• Left ventricular hypertrophy (LVH): LAD may be associated with LVH, particularly from chronic hypertension, though LAD alone is not diagnostic. 1, 4
• Glucose intolerance/metabolic syndrome: Recent evidence suggests an association between LAD and impaired fasting glucose, even in younger ambulatory adults without cardiac symptoms. 5
• Structural heart disease: Including valvular disease, cardiomyopathy, or congenital defects, though these would typically present with additional ECG abnormalities or symptoms. 3

Clinical Approach

When Further Workup is NOT Needed

No additional cardiac evaluation is required when: 1

• LAD is truly isolated (no other ECG abnormalities)
• Physical examination is completely normal
• Patient is asymptomatic
• No family history of premature cardiac disease or sudden cardiac death

When Further Workup IS Indicated

Consider echocardiography and additional testing if: 1, 6

• Two or more borderline ECG findings are present (e.g., LAD plus frequent PVCs, LAD plus voltage criteria for atrial enlargement) 2, 1
• Associated ECG abnormalities including ST-T wave changes, QRS prolongation, or chamber enlargement patterns 1
• QRS axis is ≤-42° (moderate to marked LAD) 6
• Abnormal cardiac physical examination findings 6
• Symptoms such as chest pain, dyspnea, palpitations, or syncope 3
• Family history of cardiomyopathy or sudden cardiac death 2

Recommended Screening

Given the association with glucose intolerance, consider: 5

• Fasting plasma glucose or HbA1c testing, particularly if other metabolic risk factors are present
• Blood pressure assessment to exclude hypertension as a cause of early LVH 5
• Lipid profile as part of comprehensive cardiovascular risk assessment 5

Key Clinical Pitfalls

• Overdiagnosis: Avoid treating LAD as a primary diagnosis requiring intervention rather than recognizing it as an ECG finding that requires clinical correlation. 1
• Missing combinations: The presence of LAD with even one other borderline finding (such as voltage criteria for atrial enlargement or axis deviation) may warrant investigation, even though each finding alone would not. 2, 1
• Ignoring symptoms: Any cardiac symptoms in the presence of LAD should prompt thorough evaluation regardless of the degree of axis deviation. 3
• Assuming benignity in athletes: While LAD is considered borderline in athletic populations, it still warrants attention when combined with other findings or symptoms. 2

Management Summary

For your patient with isolated borderline LAD: 1

• Reassurance that this is likely a normal age-related finding
• Ensure blood pressure is well-controlled
• Screen for glucose intolerance and metabolic syndrome
• No restriction on physical activity
• Routine follow-up with repeat ECG only if symptoms develop or other risk factors emerge