What does an abnormal lead V6 (ventricular sixth lead) signify in an electrocardiogram (ECG)?

Significance of Lead V6 in Electrocardiogram (ECG)

Lead V6 is a lateral precordial lead that primarily views the lateral wall of the left ventricle, and abnormalities in this lead can indicate lateral wall ischemia, injury, or infarction.

Anatomical Positioning and What V6 Captures

• Lead V6 is positioned at the midaxillary line at the same horizontal level as V4 and V5 (fifth intercostal space)
• It provides a lateral view of the heart, specifically the lateral wall of the left ventricle
• V6 is considered anatomically contiguous with leads I and aVL in viewing the lateral cardiac region 1

Normal Findings in V6

• Normal QRS complex in V6 typically shows a dominant R wave
• Normal ST segment is isoelectric (at baseline)
• T waves are normally upright in V6
• In normal situations, lead I is generally similar to V6 with respect to the morphology of the P wave and QRS direction 1

Abnormal Findings in V6 and Their Significance

ST-Segment Abnormalities

• ST-segment elevation ≥1 mm (0.1 mV): Indicates lateral wall myocardial injury or infarction 1
• ST-segment depression ≥0.5 mm (0.05 mV): May indicate:
  • Lateral wall subendocardial ischemia
  • Reciprocal changes from inferior or posterior wall infarction
  • Non-ischemic causes (e.g., left ventricular hypertrophy, digoxin effect)

T-Wave Abnormalities

• T-wave inversion ≥1 mm in depth: Considered abnormal and may indicate:
  • Lateral wall ischemia
  • Cardiomyopathy
  • Post-infarction changes
  • Requires further evaluation when present with other leads 1

Q-Wave Abnormalities

• Pathological Q waves: Q/R ratio ≥0.25 or ≥40 ms in duration in V6 and other contiguous leads suggests previous lateral wall myocardial infarction 1

Clinical Implications and Evaluation

1. Lateral Wall Ischemia/Infarction:

   • ST-segment elevation in V6 along with leads I and aVL suggests lateral wall STEMI
   • Requires immediate reperfusion therapy if active symptoms are present 2

2. Cardiomyopathy Assessment:

   • T-wave inversion in lateral leads including V6 may be an early sign of cardiomyopathy
   • Particularly significant when found in athletes over age 16 1, 3

3. Lead Placement Errors:

   • V6 is often mispositioned too high on the lateral chest wall, which can alter ECG interpretation 4
   • Proper placement is essential for accurate diagnosis

4. Comparison with Other Leads:

   • V6 should be interpreted in conjunction with other lateral leads (I, aVL, V5)
   • Discordance between lead I and V6 may indicate lead reversal or dextrocardia 1

Common Pitfalls and Caveats

1. Lead Misplacement:

   • V6 is frequently placed too high on the chest wall, altering ECG morphology
   • Proper placement at the fifth intercostal space in the midaxillary line is crucial 4

2. Lead Reversal:

   • Can cause false ECG patterns mimicking pathology
   • Suspected when there's unexpected discordance between lead I and V6 1, 5

3. Isolated Interpretation:

   • Never interpret V6 changes in isolation
   • Always consider in context with other leads, especially V5, I, and aVL

4. Normal Variants:

   • Early repolarization can cause ST elevation in V6 that is benign
   • Distinguished by concave upward ST elevation with prominent T waves 1

Algorithm for Evaluating Abnormal V6 Findings

1. ST-segment elevation in V6:

   • If ≥1 mm with chest pain: Consider lateral wall STEMI
   • If accompanied by ST elevation in I and aVL: Confirms lateral wall involvement
   • If accompanied by concave ST elevation and tall T waves: Consider early repolarization

2. ST-segment depression in V6:

   • If accompanied by ST elevation in V1-V3: Consider posterior wall infarction 6
   • If accompanied by ST depression in other lateral leads: Consider subendocardial ischemia
   • If accompanied by tall R waves and strain pattern: Consider LVH

3. T-wave inversion in V6:

   • If deep and accompanied by T inversion in other lateral leads: Evaluate for cardiomyopathy
   • If new compared to previous ECG: Consider acute coronary syndrome
   • If persistent: Consider structural heart disease

By understanding the significance of lead V6 and interpreting its findings in context with other leads, clinicians can more accurately diagnose cardiac conditions that affect the lateral wall of the left ventricle.