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

- **ID:** `medical/ecg-lead-placement-v1-v2-4th-ics`
- **Domain:** medical
- **Category:** runtime_error
- **Error Code:** `ECG_V1_V2_2ND_ICS`
- **Verification:** ai_generated
- **Fix Rate:** 93%

## Root Cause

V1 and V2 must be placed in the 4th intercostal space (ICS) at the right and left sternal borders, respectively. Placement in the 2nd ICS shifts the QRS axis, producing false ST elevation that mimics anterior STEMI.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| ECG-machine:GE-MAC-5500-2024 | active | — | — |
| ECG-machine:Philips-IntelliVue-MP70-2023 | active | — | — |

## Workarounds

1. **Use the angle of Louis (sternal angle) as a landmark for the 2nd intercostal space. Palpate the space below the clavicle: the first palpable space is the 2nd ICS. Count down two more spaces to reach the 4th ICS. Place V1 at the right sternal border in the 4th ICS, V2 at the left sternal border in the 4th ICS. Document the intercostal space used on the ECG report.** (95% success)
   ```
   Use the angle of Louis (sternal angle) as a landmark for the 2nd intercostal space. Palpate the space below the clavicle: the first palpable space is the 2nd ICS. Count down two more spaces to reach the 4th ICS. Place V1 at the right sternal border in the 4th ICS, V2 at the left sternal border in the 4th ICS. Document the intercostal space used on the ECG report.
   ```
2. **If the patient is female, place V1 and V2 electrodes on the sternum, not on breast tissue. Lift breast tissue if necessary to access the 4th ICS. Use a skin marker to mark the 4th ICS before placing electrodes.** (90% success)
   ```
   If the patient is female, place V1 and V2 electrodes on the sternum, not on breast tissue. Lift breast tissue if necessary to access the 4th ICS. Use a skin marker to mark the 4th ICS before placing electrodes.
   ```
3. **Use a 15-lead ECG (adding V4R, V8, V9) if there is any doubt about lead placement or if the patient has a history of previous MI. This helps differentiate true anterior ischemia from lead placement artifact.** (88% success)
   ```
   Use a 15-lead ECG (adding V4R, V8, V9) if there is any doubt about lead placement or if the patient has a history of previous MI. This helps differentiate true anterior ischemia from lead placement artifact.
   ```

## Dead Ends

- **Assuming that the 2nd intercostal space is correct because it is easier to palpate (just below the clavicle)** — The 2nd ICS is commonly mistaken for the 4th ICS because the angle of Louis (sternal angle) marks the 2nd ICS, not the 4th. Proper technique requires counting down two more spaces to the 4th ICS. (80% fail)
- **Believing that small variations in lead placement do not significantly affect ECG interpretation** — Even a 1-2 intercostal space difference can produce up to 0.2 mV of ST elevation in V2, which meets STEMI criteria in many guidelines, leading to unnecessary catheterization lab activation. (70% fail)
- **Using a 'one-size-fits-all' approach: placing V1 and V2 at the same level as V3-V6** — V3-V6 are placed at the 5th ICS along the left chest; placing V1-V2 at that level is too low and may miss right ventricular involvement. (60% fail)