Old Myocardial Infarction Of The Inferior Wall: ECG Features And Interpretation

When evaluating an old myocardial infarction involving the inferior wall, the electrocardiogram (ECG) typically reveals several key characteristics. These findings help clinicians determine the presence and extent of previous heart damage, particularly in the inferior region of the heart.

Pathological Q Waves In Inferior Leads

One of the most definitive signs of a prior inferior wall myocardial infarction is the presence of pathological Q waves. These abnormal waves are most commonly observed in the inferior leads — specifically lead II, lead III, and aVF. A Q wave is considered pathological when it is wider than 0.04 seconds or deeper than 25% of the amplitude of the subsequent R wave. This pattern strongly suggests the presence of scar tissue resulting from a previous heart attack.

ST Segment Abnormalities

Another notable ECG feature is abnormal ST segment activity. In some cases, patients may show persistent ST segment elevation, especially if a complication like an inferior wall ventricular aneurysm has developed. This persistent elevation indicates that the ST segment does not return to the baseline level following the acute phase of infarction. Conversely, other patients may display ST segment depression or flattening, which can be a sign of ongoing ischemia or prior injury.

T Wave Changes In Inferior Leads

Changes in the T wave are also commonly observed in the inferior leads. These changes may include T wave inversion or flattening in leads II, III, and aVF. Additionally, some individuals may demonstrate T wave abnormalities in other leads such as lead I and aVR. These alterations are often indicative of myocardial damage or ischemia and may persist long after the initial infarction event.

Diagnostic Significance Of Pathological Q Waves

While all of the above ECG findings are important in the assessment of old inferior wall myocardial infarction, the presence of pathological Q waves in the inferior leads remains the most specific diagnostic criterion. These waves serve as a reliable marker of prior myocardial necrosis and are crucial in confirming a history of heart attack in asymptomatic or atypical presentations.