The ST segment represents the end of ventricular depolarization and the beginning of ventricular repolarization. The point where the QRS complex ends and the ST segment begins is called the J point. A normal ST segment is usually level. Ischemia causes ST depression and T-wave inversion. Injury causes ST elevation. Infarction causes ST elevation and the presence of a Q wave, indicating a previous heart attack. The document then shows diagrams of abnormal ST segments in different leads that indicate septal, anterior, and inferior ischemia or injury.

1. In Relationship to 12-Lead Electrocardiograms

2. Aorta Right Coronary Artery Left Main Artery Left Anterior Descending Circumflex Artery Copyright 2005 Lippincott Williams & Wilkins

5. ST segment represents the end of ventricular conduction or depolarization and the beginning of ventricular recovery or repolarization. The point that marks the end of the QRS complex and the beginning of the ST segment is called the “J Point.” A normal ST segment has these characteristics: Location: extends from the S wave to the beginning of the T wave. Deflection: usually isoelectric ST segment J Point

6. Impaired Circulation: ischemia, injury or infarction? Ischemia : ST depression and T-wave inversion Injury : ST elevation Infarction : ST elevation Q-wave : Indicates a previous infarction

7. Copyright 2001 American Heart Association

8. Copyright 2001 American Heart Association

9. ST Elevation in Septal Leads V1 & V2

10. Copyright 2001 American Heart Association

11. ST elevation in Anterior Leads V3 & V4

12. Copyright 2001 American Heart Association

13. Copyright 2001 American Heart Association

14. ST elevation in Inferior Leads II, III & aVF

15. Copyright 2001 American Heart Association

16. Copyright 2001 American Heart Association

17. Copyright 2001 American Heart Association

18. Copyright 2001 American Heart Association I Lateral Circumflex Artery aVR V1 Septal Left Anterior Descending Artery V4 Anterior Right Coronary Artery II Inferior Right Coronary Artery aVL Lateral Circumflex Artery V2 Septal Left Anterior Descending Artery V5 Lateral Circumflex Artery III Inferior Right Coronary Artery AVF Inferior Right Coronary Artery V3 Anterior Right Coronary Artery V6 Lateral Circumflex Artery