Can an Inferior Wall Myocardial Infarction (MI) manifest as a new onset Left Anterior Hemiblock on an Electrocardiogram (ECG)?

Left Anterior Hemiblock Can Manifest as a Complication of Inferior Wall MI

Yes, inferior wall myocardial infarction (MI) can manifest as new onset left anterior hemiblock (LAH) on ECG, occurring in approximately 12.5% of cases, typically between the first and third day after infarction. 1

Pathophysiological Mechanism

The development of LAH in inferior wall MI has important clinical implications:

• LAH typically develops as a complication of inferior wall MI rather than being the primary ECG manifestation 1
• When LAH appears in inferior wall MI, it suggests more extensive coronary artery disease 2
• Specifically, it may indicate involvement of the left anterior descending coronary artery in addition to the right coronary artery or left circumflex artery that typically causes inferior MI 2

Diagnostic Challenges

The combination of inferior MI and LAH creates specific diagnostic challenges:

• LAH causes initial r waves in the inferior leads (II, III, aVF)
• Inferior MI typically causes Q waves in these same leads
• These opposing electrical forces can mask each other, potentially obscuring the diagnosis of inferior MI 3

ECG Criteria for Identifying Inferior MI with LAH

When suspecting the combination of inferior MI and LAH, look for these specific ECG findings:

1. Leads aVR and aVL both ending in R waves, with the peak of the terminal R wave in lead aVR occurring later than in lead aVL 4
2. A Q wave of any magnitude in lead II 4
3. A "q wave or q equivalent" in lead II is particularly important as it strongly suggests inferior infarction even when LAH is present 5

Clinical Significance

The development of LAH in inferior MI has several important implications:

• It suggests more extensive coronary artery disease 2
• It indicates potential involvement of the left anterior descending coronary artery 2
• It requires careful ECG interpretation to avoid missing the diagnosis of inferior MI 3

Myocardial Perfusion Imaging Findings

Thallium-201 scintigraphy studies in patients with ECG evidence of both inferior MI and LAH show:

• Defects in the inferior left ventricular wall consistent with inferior infarction in most patients
• Sparing of part of the inferior wall (either the posterior or anterior part) 5

Pitfalls to Avoid

1. Failing to recognize that LAH can mask the typical Q waves of inferior MI
2. Missing the diagnosis of inferior MI in the presence of LAH
3. Not considering more extensive coronary artery disease when LAH develops in the setting of inferior MI

While LAH complicating inferior MI doesn't appear to significantly affect hospital mortality, heart failure rates, or arrhythmia incidence 1, its presence should alert clinicians to potentially more extensive coronary disease requiring comprehensive evaluation.