From the Guidelines
Reciprocal changes on an electrocardiogram (ECG) are indicative of myocardial ischemia or infarction, typically presenting as ST-segment depression in leads opposite to those with ST-segment elevation, and are crucial for diagnosing acute myocardial infarction and localizing the affected coronary artery. These changes are a result of the electrical forces generated by the injured myocardium being recorded as opposite deflections when viewed from the other side of the heart 1. For instance, if there is ST elevation in the inferior leads (II, III, aVF), reciprocal ST depression may be seen in the anterior leads (I, aVL). The presence of reciprocal changes increases the specificity for acute myocardial infarction and helps differentiate it from other conditions that may mimic ST-elevation myocardial infarction (STEMI), such as early repolarization or pericarditis, which typically do not exhibit reciprocal changes 1.
Key points to consider when evaluating reciprocal changes on an ECG include:
- The magnitude and direction of ST-segment deviation, with reciprocal changes typically involving ST-segment depression in leads opposite to those with ST-segment elevation
- The leads involved, with reciprocal changes often seen in leads that face the wall opposite to the area experiencing ST-segment elevation
- The clinical context, including the patient's symptoms and medical history, as reciprocal changes are more likely to be associated with acute myocardial infarction in patients with chest pain or other symptoms suggestive of ischemia
- The comparison with prior ECG tracings, when available, to assess for changes over time and to help confirm the diagnosis of acute myocardial infarction
Recognizing reciprocal changes is essential in emergency settings, as they can help confirm a true STEMI and guide treatment decisions, including the need for urgent reperfusion therapy 1. Patients with prominent reciprocal changes often have more severe coronary artery disease and may have worse outcomes, making their identification important for risk stratification and treatment planning 1.
From the Research
Reciprocal Changes on ECG
Reciprocal changes on an electrocardiogram (ECG) refer to ST-segment depressions in leads that are opposite to the leads showing ST-segment elevations in patients with ST-elevation myocardial infarction (STEMI).
- These changes can be seen in various leads, depending on the location of the infarct, and are often referred to as "reciprocal ST-depression" 2, 3, 4, 5.
- The presence of reciprocal changes has been debated, with some studies suggesting that they represent "ischemia at a distance" via collateral circulation, while others propose that they are an electrical phenomenon, a "mirror image" of the ST-elevation 2, 5.
Clinical Significance
The clinical significance of reciprocal changes is still being researched, but some studies have found associations between these changes and:
- Larger myocardial area at risk and higher myocardial salvage in patients with STEMI 3.
- Increased frequency of angina pectoris, positive treadmill test response, or recurrent AMI in patients with reciprocal changes 4.
- No correlation with collateral circulation or predictive value for collaterals on angiography 2.
- Resolution of reciprocal changes after successful percutaneous coronary intervention (PCI) in patients without collaterals 2.
Mechanism
The mechanism of reciprocal changes is not fully understood, but it is thought to be related to:
- Electrical phenomena, such as a "mirror image" of the ST-elevation 5.
- Subendocardial ischemia from the primary coronary event 2.
- Ischemia at a distance via collateral circulation, although this is still debated 2, 5.
Prevalence and Association with Outcomes
Reciprocal changes have been found to occur in a significant proportion of patients with STEMI, and have been associated with various outcomes, including: