| Axis | Normal | Abnormal | | --- | --- | --- | | Electrical axis | -30° to +90° | Outside this range |

| Waveform | Normal | Abnormal | | --- | --- | --- | | P-wave | ≤ 0.25 mV, < 120 ms | > 0.25 mV, > 120 ms | | QRS complex | < 120 ms | ≥ 120 ms | | T-wave | Upright in leads I, II, V4-V6 | Inverted in leads I, II, V4-V6 | | ST-segment | ≤ 1 mm depression | > 1 mm depression |

Here's a concise cheat sheet to help you with 12-lead ECG interpretation:

| Interval | Normal | Abnormal | | --- | --- | --- | | PR interval | 120-200 ms | < 120 ms or > 200 ms | | QT interval | < 440 ms (men), < 460 ms (women) | > 440 ms (men), > 460 ms (women) | | QRS interval | < 120 ms | ≥ 120 ms |

A 12-lead electrocardiogram (ECG) is a medical test that measures the electrical activity of the heart from 12 different angles. It's a crucial diagnostic tool for cardiologists and healthcare professionals to assess heart function and detect potential cardiac conditions.

Interpreting 12-lead ECGs requires a systematic approach and practice. This overview provides a foundation for understanding the basics of 12-lead ECG interpretation. Use the cheat sheet and online resources to reinforce your knowledge and improve your skills.