What are the key ECG changes in a 12-lead anterior ECG suggestive of right-sided myocardial infarction?

Key ECG Changes in 12-Lead Anterior ECG Suggestive of Right-Sided Myocardial Infarction

ST-segment elevation in lead V1 greater than or equal to V3 is the most important ECG finding suggestive of right ventricular involvement in anterior myocardial infarction. 1

Primary ECG Findings

• ST-segment elevation pattern:

  • ST elevation in V1 greater than or equal to V3 (unlike typical anterior MI where ST elevation progressively increases from V1 to V3) 1, 2
  • Absence of normal progression of ST elevation from V1 to V3 3
  • ST elevation highest in lead V1 or V2 with decreasing elevation toward V5 2

• Associated findings:

  • Possible concurrent ST elevation in inferior leads (II, III, aVF) 3
  • Preserved R waves in leads V1-V5 (unlike anterior LV infarction where R waves decrease) 2
  • Absence of Q wave evolution in V1-V5 as MI progresses 2

Confirmation with Right-Sided Leads

The American Heart Association/American College of Cardiology guidelines strongly recommend recording right-sided chest leads (V3R and V4R) to confirm right ventricular involvement 4:

• ST elevation in V3R and V4R ≥ 0.1 mV is diagnostic of right ventricular involvement
• These leads must be recorded as rapidly as possible after symptom onset, as ST elevation in right-sided leads persists for a much shorter time than other ST elevations 4, 1

Pathophysiological Basis

The spatial vector of the ST-segment shift in right ventricular infarction is directed rightward and anteriorly, explaining:

1. More prominent ST elevation in V1 compared to other anterior leads
2. Possible concurrent inferior ST elevation (if proximal right coronary artery is involved)
3. Preserved R waves in anterior leads 1, 2

Clinical Significance

Identifying right ventricular involvement is crucial because:

• It significantly impacts morbidity and mortality 1
• These patients are preload-dependent and require careful fluid management 1
• Nitrates and other preload-reducing medications should be avoided 1

Angiographic Correlations

Two distinct patterns are seen in patients with combined anterior and inferior ST elevation 3:

1. Proximal right coronary artery occlusion (59% of cases)

   • More common cause
   • Associated with right ventricular and limited inferior LV infarction

2. Mid to distal left anterior descending artery occlusion (36% of cases)

   • Results in a smaller anterior infarction

Common Pitfalls

1. Delayed ECG acquisition: ST elevation in right-sided leads disappears more quickly than other ST changes, potentially leading to missed diagnosis 4, 1

2. Relying only on standard 12-lead ECG: The standard ECG has limited sensitivity for detecting right ventricular involvement; right-sided leads are essential 1, 5

3. Misinterpreting as anterior LV infarction: The pattern of ST elevation highest in V1-V2 with decreasing elevation toward V5 is opposite to typical anterior LV infarction pattern 2

4. Overlooking preserved R waves: Failure to notice that R waves are preserved in V1-V5 (unlike in anterior LV infarction) 2

Diagnostic Algorithm

1. Identify ST elevation in V1 ≥ V3 on standard 12-lead ECG
2. Check for absence of progressive increase in ST elevation from V1 to V3
3. Note if R waves are preserved in V1-V5
4. Immediately record right-sided leads V3R and V4R
5. Confirm right ventricular involvement if ST elevation ≥ 0.1 mV in V3R and V4R
6. Consider angiography to determine whether proximal RCA or mid-distal LAD is occluded

Remember that despite greater overall ST-segment elevation, patients with combined anterior and inferior ST elevation often have limited infarct size and preserved left ventricular function compared to those with isolated anterior ST elevation 3.