What is the interpretation of ST depression in leads V1-V4 with tall, biphasic T waves and a 4:1 high-grade Atrioventricular (AV) block on a 12-lead electrocardiogram (ECG)?

ECG Interpretation: ST Depression in V1-V4 with Tall Biphasic T Waves and High-Grade AV Block

The ST depression in V1-V4 with tall, symmetrical biphasic T waves most likely represents acute myocardial ischemia, specifically suggesting either posterior wall STEMI (with reciprocal anterior changes) or critical proximal left anterior descending artery stenosis, complicated by the presence of high-grade AV block which independently indicates serious conduction system disease. 1

Primary Ischemic Interpretation

The combination of ST depression >1 mm in multiple contiguous precordial leads (V1-V4) with tall, symmetrical T waves is highly suggestive of acute coronary syndrome and requires immediate evaluation for acute myocardial infarction. 1

Posterior Wall STEMI Consideration

• ST depression in leads V1-V4 with upright T waves may represent reciprocal changes from acute posterior wall myocardial infarction, which is a STEMI equivalent requiring immediate reperfusion therapy. 1
• The European Society of Cardiology recommends obtaining posterior leads (V7-V9) immediately, as ST elevation >0.05 mV in these leads confirms posterior STEMI and mandates the same urgent reperfusion strategy as anterior STEMI. 1
• Posterior wall infarction represents 15-21% of all myocardial infarctions and involves significant myocardium at risk, typically from circumflex or posterior descending artery occlusion. 1

Critical LAD Stenosis Pattern

• Deep symmetrical T-wave inversion (or in this case, the symmetrical biphasic morphology) in anterior chest leads is often related to significant proximal left anterior descending coronary artery stenosis, representing a high-risk acute coronary syndrome. 1
• The American College of Cardiology notes that marked symmetrical precordial T-wave changes ≥2 mm suggest acute ischemia, particularly from critical LAD stenosis, and may also occur with acute pulmonary embolism. 1

Confounding Factor: High-Grade AV Block

The presence of 4:1 high-grade AV block creates a critical confounding variable that can significantly alter ST-T wave morphology through atrial repolarization (Ta wave) effects superimposed on ventricular repolarization. 2

Ta Wave Interference

• In patients with AV block, the atrial repolarization wave (Ta wave) extends into the ST segment and can cause ST-segment deviation that mimics ischemic changes. 2
• Research demonstrates that in AV block patients with serious cardiovascular complications, the Ta wave shows significant differences in form, polarity, amplitude, and duration compared to uncomplicated AV block, and the atrial gradient becomes markedly large. 2
• The J-point depression you describe could partially represent Ta wave effects rather than pure ischemic ST depression, though this does not exclude concurrent ischemia. 2

Bradycardia-Related T Wave Changes

• Complete AV block with marked bradycardia (junctional escape rhythm) can contribute to QT prolongation and prominent bifid or altered T-wave morphology, particularly when combined with electrolyte abnormalities. 3
• The tall, biphasic T waves may reflect both ischemia and the effects of the slow ventricular rate on repolarization dynamics. 3

Immediate Diagnostic Algorithm

Despite the confounding AV block, the clinical approach must prioritize ruling out acute myocardial infarction given the high mortality risk. 1, 4

Step 1: Obtain Additional ECG Leads

• Record posterior leads V7-V9 immediately to detect ST elevation indicating posterior STEMI. 1
• Consider right-sided leads (V3R-V4R) if inferior involvement is suspected, as ST elevation >0.05 mV confirms right ventricular infarction. 1

Step 2: Serial Cardiac Biomarkers

• Measure cardiac troponin T or I immediately and repeat at appropriate intervals, as troponins are the preferred markers and more specific than CK-MB for detecting myocardial necrosis. 1, 4
• Elevated troponins in the setting of ST-segment changes should be labeled as myocardial infarction. 1

Step 3: Compare with Prior ECGs

• Comparison with previous ECG tracings is extremely valuable, particularly to determine if the AV block is new and if the ST-T changes represent acute changes versus chronic patterns from the conduction disease. 1, 4

Step 4: Obtain ECG During Symptoms

• If the patient develops chest pain or equivalent symptoms, obtain a simultaneous ECG, as transient ST-segment changes during symptoms strongly suggest ischemia and underlying severe coronary artery disease. 1, 4

Critical Management Pitfalls

Do not dismiss these ST-T changes as solely secondary to the AV block without excluding acute coronary syndrome, as this represents a potentially fatal error. 4

• The European Society of Cardiology emphasizes that ST-segment depression >1 mm in two or more contiguous leads, in the appropriate clinical context, is highly suggestive of unstable angina or acute coronary syndrome. 1
• A normal initial troponin does not exclude acute coronary syndrome; serial measurements are mandatory. 4
• The presence of high-grade AV block itself indicates serious cardiac pathology and warrants urgent evaluation regardless of the ST-T wave etiology. 5, 6

Risk Stratification

This patient falls into a high-risk category based on multiple factors: 1

• ST depression in multiple contiguous precordial leads suggests extensive myocardium at risk. 1
• Symmetrical T-wave morphology increases specificity for acute ischemia. 1
• High-grade AV block indicates either extensive ischemia affecting the conduction system or concurrent severe conduction disease. 6
• The combination of these findings predicts poor prognosis and calls for rapid diagnosis and management. 1

Immediate cardiology consultation and consideration for urgent coronary angiography is warranted, as this ECG pattern—regardless of whether it represents posterior STEMI, critical LAD disease, or ischemia complicated by conduction disease—indicates life-threatening pathology requiring definitive intervention. 1