Which EKG (electrocardiogram) leads are typically considered negative?

Negative ECG Leads in Standard 12-Lead ECG

In a standard 12-lead ECG, the leads that are typically considered negative are aVR, and in normal sinus rhythm, lead III and V1 may also show predominantly negative deflections 1, 2.

Understanding ECG Lead Polarity

• In the standard 12-lead ECG, there are two types of leads: bipolar and unipolar 1:

  • Bipolar leads (I, II, III) measure potential difference between a positive and negative electrode 1
  • Unipolar leads (aVR, aVL, aVF, V1-V6) measure potential at a single electrode relative to a reference point 1

• Lead aVR is consistently considered a negative lead because it faces the right superior surface of the heart, with all normal cardiac depolarizations moving away from it 2, 3

• In normal sinus rhythm, lead aVR typically shows negative P waves, QRS complexes, and T waves 2

Clinical Significance of Negative Leads

• Lead aVR, despite being historically neglected, provides valuable diagnostic information in various clinical scenarios 2, 3:

  • In coronary artery disease, ST elevation in aVR can help localize the culprit lesion 2
  • In wide QRS tachycardia, a tall R wave in aVR suggests ventricular tachycardia rather than SVT with aberrancy 2
  • In pericarditis, aVR often shows reciprocal ST depression 2

• Lead III may show negative deflections in normal individuals, but this can vary based on cardiac axis 1, 4

• V1 may show predominantly negative QRS complexes in normal hearts, but this can vary based on transition zone 1, 4

Understanding Electrode Placement and Lead Polarity

• In bipolar lead monitoring, the negative electrode placement is crucial for accurate interpretation 1:

  • Lead I: negative electrode is placed at RA (right arm) 1
  • Lead II: negative electrode is placed at RA 1
  • Lead III: negative electrode is placed at LA (left arm) 1

• For MCL1 (modified chest lead), the negative electrode is placed in the left infraclavicular fossa 1

Clinical Applications and Pitfalls

• Misplacement of electrodes can significantly alter ECG interpretation by changing lead polarity 1:

  • Transposition of left and right arm leads inverts lead I and switches leads II and III 1
  • This can falsely simulate or mask signs of ischemia 1

• In certain pathological conditions, normally positive leads may become negative:

  • In reverse typical atrial flutter, wide negative deflections in V1 are the most specific diagnostic sign 1
  • In dextrocardia, P waves may become upright in aVR 2

• The addition of inverted (negative) leads from a 24-lead ECG to the standard 12-lead ECG can increase sensitivity for diagnosis of acute transmural ischemia 5

Special Considerations

• When evaluating ECGs, it's important to recognize that normal variants exist based on age, ethnicity, and athletic status 1, 4

• Lead placement on the torso during bedside monitoring differs from standard 12-lead ECG placement, which can affect waveform morphology 1

• Proper electrode placement is essential for accurate ECG interpretation, as variations can result in altered waveforms that may be misinterpreted 1