In a 66‑year‑old patient presenting with dizziness and an electrocardiogram showing left‑axis deviation, what is the clinical significance of the left‑axis deviation and how should the dizziness be evaluated?

Left Axis Deviation in a 66-Year-Old with Dizziness

In this 66-year-old patient, the left axis deviation most likely represents left anterior fascicular block or age-related conduction changes, but the dizziness is unlikely to be directly caused by the ECG finding and requires a separate systematic evaluation focused on vestibular, cardiovascular, and neurological etiologies.

Clinical Significance of Left Axis Deviation

Definition and Interpretation

• Left axis deviation is defined as a mean frontal plane QRS axis between -30° and -90°, with moderate LAD at -30° to -45° and marked LAD at -45° to -90° 1, 2.
• At age 66, moderate LAD (-30° to -45°) often reflects normal aging rather than pathology, as the QRS axis progressively shifts leftward with advancing age even in the absence of structural heart disease 2.

Most Common Pathological Cause: Left Anterior Fascicular Block

Left anterior fascicular block (LAFB) is the most common pathological cause of LAD, accounting for approximately 40% of cases, and is especially likely when the axis deviation is marked (-45° to -90°) 2, 3.

To diagnose LAFB, verify these specific criteria 1, 2:

• Frontal plane axis between -45° and -90°
• qR pattern in lead aVL
• R-peak time in lead aVL ≥ 45 ms
• QRS duration < 120 ms (excludes bundle branch block)

Other Structural Causes to Consider

• Left ventricular hypertrophy: LAD may accompany LVH but should be regarded as a supporting, not diagnostic, criterion for hypertrophy 2.
• Prior inferior myocardial infarction: Accounts for approximately one-sixth of LAD cases due to loss of inferior forces 3.
• Congenital heart defects: Complete atrioventricular septal defect causes LAD through altered conduction system location, though this is unlikely in a 66-year-old without prior diagnosis 1, 2.

Evaluation of Dizziness

Critical Point: LAD Does Not Cause Dizziness

The left axis deviation itself is not a cause of dizziness in this patient 4, 5. The two findings require parallel but separate evaluation pathways.

Structured Approach Using Timing and Triggers

Use the timing and triggers diagnostic approach to categorize the dizziness 5:

1. Acute vestibular syndrome (continuous dizziness lasting days):

   • Differentiate vestibular neuritis from posterior circulation stroke using bedside physical examination 5
   • Look for nystagmus pattern, head impulse test, and test of skew 5

2. Spontaneous episodic vestibular syndrome (recurrent episodes without triggers):

   • Associated symptoms help differentiate vestibular migraine from transient ischemic attack 5
   • Consider cardiovascular causes including arrhythmias and orthostatic hypotension 4, 6

3. Triggered episodic vestibular syndrome (position-dependent):

   • Perform Dix-Hallpike and supine roll test to differentiate benign paroxysmal positional vertigo from posterior fossa structural lesions 5

Age-Specific Considerations

• In patients over 65, dizziness has been experienced by at least one-third of the population and may have multiple concurrent causes 4.
• Cardiovascular diseases are important contributors to dizziness in this age group and must be systematically excluded 4, 6.
• Medication review is essential, as polypharmacy commonly contributes to dizziness in older adults 6.

Recommended Diagnostic Workup

For the Left Axis Deviation

Obtain an echocardiogram to evaluate for structural heart disease, particularly left ventricular hypertrophy, regional wall motion abnormalities from prior infarction, and valvular disease 2, 7.

• Echocardiography is the primary imaging modality and superior to ECG for detecting structural changes 2, 8.
• Measure LV wall thickness, calculate LV mass indexed to body surface area, and assess for regional wall motion abnormalities 7.
• Evaluate for left atrial enlargement, which frequently accompanies LVH and increases arrhythmia risk 8.

For the Dizziness

Perform a targeted physical examination based on the timing and trigger pattern 5:

• Cardiovascular assessment: Orthostatic vital signs, cardiac auscultation for murmurs or arrhythmias, carotid examination 4.
• Vestibular examination: Dix-Hallpike maneuver, head impulse test, assessment of nystagmus 5.
• Neurological examination: Cranial nerves, cerebellar function, gait assessment 4.

Consider additional testing based on clinical suspicion 4:

• Electronystagmography and audiometry if peripheral vestibular disorder suspected
• Brain MRI if central nervous system disorder suspected (infratentorial ischemia, multiple sclerosis, cerebellar atrophy)
• Prolonged ECG monitoring if arrhythmia suspected, particularly given the association between LVH and supraventricular arrhythmias 8

Common Pitfalls to Avoid

• Do not assume the LAD is causing the dizziness: These are likely unrelated findings requiring separate evaluation 4, 5.
• Do not rely on dizziness "quality" (vertigo vs. presyncope) to guide diagnosis: This traditional approach is inconsistent with current best evidence and does not distinguish benign from dangerous causes 5.
• Do not overlook multiple concurrent causes: In older adults, dizziness may result from more than one etiology simultaneously 6.
• Do not diagnose LAFB based on LAD alone: Additional specific ECG criteria must be met 2.
• Do not use R-wave amplitudes in leads I and aVL to assess for LVH when LAFB is present: LAFB alters voltage patterns and makes these measurements unreliable 2.