# AI instructs placement of V1 and V2 ECG leads in the 2nd intercostal space instead of the 4th, leading to misdiagnosis of anterior MI

- **ID:** `medical/ecg-lead-placement-wrong`
- **Domain:** medical
- **Category:** data_error
- **Error Code:** `AHA-2019-ECG`
- **Verification:** ai_generated
- **Fix Rate:** 88%

## Root Cause

Standard 12-lead ECG placement requires V1 (red) in the 4th intercostal space at the right sternal border, and V2 (yellow) in the 4th intercostal space at the left sternal border. Placing them in the 2nd intercostal space (a common layperson error) produces a QS pattern in V1-V2 that mimics anterior myocardial infarction (poor R-wave progression), leading to unnecessary catheterization or missed true inferior/lateral MI.

## Workarounds

1. **Correct placement: Palpate the sternal angle (angle of Louis) to find the 2nd intercostal space. Count down two more intercostal spaces to the 4th. Place V1 (red) at the 4th intercostal space, right sternal border. Place V2 (yellow) at the 4th intercostal space, left sternal border. For women, place leads under the breast tissue, not on top. Verify by checking that the R wave amplitude in V1 is small (<3 mm) and increases progressively to V5-V6.** (95% success)
   ```
   Correct placement: Palpate the sternal angle (angle of Louis) to find the 2nd intercostal space. Count down two more intercostal spaces to the 4th. Place V1 (red) at the 4th intercostal space, right sternal border. Place V2 (yellow) at the 4th intercostal space, left sternal border. For women, place leads under the breast tissue, not on top. Verify by checking that the R wave amplitude in V1 is small (<3 mm) and increases progressively to V5-V6.
   ```
2. **If a patient has a pectus excavatum or chest deformity, use a 15-lead ECG or right-sided leads to avoid misplacement. Document any anatomical variations.** (85% success)
   ```
   If a patient has a pectus excavatum or chest deformity, use a 15-lead ECG or right-sided leads to avoid misplacement. Document any anatomical variations.
   ```

## Dead Ends

- **Assuming that any intercostal space is acceptable as long as leads are symmetric** — The 4th intercostal space is anatomically specific; the 2nd space produces a different electrical axis relative to the heart, altering QRS morphology and ST segments significantly. (80% fail)
- **Telling staff to 'palpate the angle of Louis' but not specifying to count down two more interspaces** — The angle of Louis (sternal angle) marks the 2nd intercostal space. Many mistakenly place leads there, counting that as the starting point for V1 instead of counting 2 more spaces down. (70% fail)
- **Suggesting that ECG machines automatically correct for lead placement errors** — ECG machines interpret the electrical signal as received; they cannot detect or correct for incorrect lead placement. The algorithm assumes standard placement. (90% fail)