From the Guidelines
For ST segment monitoring, leads II, V1, and V5 are generally considered the best options. Lead II is excellent for detecting inferior wall ischemia, while V1 is optimal for right ventricular and posterior wall changes. Lead V5 provides good visualization of anterior and lateral wall ischemia. When continuous monitoring is needed, a three-lead system using these leads provides coverage of approximately 90% of potential ischemic areas. If more comprehensive monitoring is required, a five-lead system adding leads III and V3 increases detection sensitivity to about 95% 1.
The selection of appropriate leads is based on the coronary anatomy and the specific area of myocardium at risk. The ST segment represents ventricular repolarization, and changes in this segment can indicate myocardial ischemia, injury, or infarction. Different leads view the heart from different angles, so using multiple leads increases the likelihood of detecting ST segment abnormalities regardless of which area of the heart is affected. In clinical practice, the choice of leads may also depend on the patient's specific cardiac history and the suspected area of compromise.
Some key points to consider when selecting leads for ST segment monitoring include:
- Lead II is useful for detecting inferior wall ischemia
- Lead V1 is useful for detecting right ventricular and posterior wall changes
- Lead V5 is useful for detecting anterior and lateral wall ischemia
- A three-lead system using leads II, V1, and V5 provides coverage of approximately 90% of potential ischemic areas
- A five-lead system adding leads III and V3 increases detection sensitivity to about 95% 1.
It's also important to note that the joint task force of the AHA and the American College of Cardiology recommends recording right-sided chest leads VR and V4R in all patients presenting with ECG evidence of acute inferior wall ischemia/infarction 1.
From the Research
ECG Leads for ST Segment Monitoring
The choice of ECG leads for ST segment monitoring is crucial for detecting myocardial ischemia. According to the studies, the following leads are recommended:
- V1 and V6 are valuable for arrhythmia monitoring, but are seldom sensitive in detecting ischemia 2
- Leads III and aVF are the most valuable limb leads for detecting ischemia due to abrupt artery closure, and are more sensitive than lead II 2
- The best combinations of leads for ST monitoring are: V1 + aVF, V1 + III, V6 + III, and V6 + aVF 2
- V4 is more sensitive and appropriate than V5 for detecting prolonged postoperative ischemia and infarction 3
- Combining two precordial leads, such as V3 + V5 or V4 + V5, increases the sensitivity for detecting ischemia and infarction 3
Recommendations for ST Segment Monitoring
The studies suggest the following recommendations for ST segment monitoring:
- 12-lead ST monitoring is recommended for patients with acute coronary syndromes 4
- Continuous ST-segment monitoring can identify transient episodes of myocardial ischemia, even when asymptomatic 5
- ST episodes detected by continuous ST-segment monitoring are associated with worse 1-year outcome 6
- The presence of ST episodes adds independent prognostic information to the TIMI and PURSUIT risk scores, but not to the GRACE risk score 6