What are the EKG findings for an old myocardial infarct (MI)?

From the Guidelines

The EKG findings for an old myocardial infarction (MI) typically include pathological Q waves, which are deep and wide (>0.04 seconds or >1 small box in width and >25% of the height of the R wave in depth), as stated in the most recent guidelines 1. These Q waves represent scarred myocardium and are permanent markers of previous infarction. Other findings may include:

• Persistent T wave inversions
• Poor R wave progression in precordial leads
• Sometimes persistent ST segment elevation (known as a ventricular aneurysm pattern) The location of these changes corresponds to the anatomical area of the previous infarct -
• Anterior (V1-V4)
• Inferior (II, III, aVF)
• Lateral (I, aVL, V5-V6) Unlike acute MI, old infarcts lack dynamic ST segment elevation or depression. These EKG changes occur because the infarcted heart tissue has been replaced by non-conductive scar tissue, altering the normal electrical conduction pathways. It's essential to compare the ECG at presentation to prior ECG tracings, when available, to identify any changes or abnormalities 1. Additionally, it's crucial to consider other conditions that may mimic myocardial ischemia or MI, such as acute pericarditis, left ventricular hypertrophy (LVH), left bundle branch block (LBBB), Brugada syndrome, stress cardiomyopathy, and early repolarization patterns 1. It's also important to note that not all old MIs produce Q waves, and some patients may have "electrically silent" infarcts with minimal EKG changes despite significant previous damage. The ECG is an integral part of the diagnostic work-up of patients with suspected MI and should be acquired and interpreted promptly, with serial recordings in symptomatic patients with an initial non-diagnostic ECG performed at 15–30 min intervals 1.

From the Research

EKG Findings for Old Myocardial Infarct (MI)

To identify an old myocardial infarct on an EKG, several findings can be considered:

• The presence of Q waves in specific leads can indicate the location and size of the infarct. For example, Q waves in leads V1-V4 may indicate an anterior infarct, while Q waves in leads II, III, and aVF may indicate an inferior infarct 2.
• The number of Q waves can be related to the size of the infarct, particularly in anterior infarctions. A study found that the number of anterior Q waves was related to anterior MI size (r=0.70) 2.
• A tall and broad R wave in leads V1-V2 can be a predictor of lateral MI size, and may be more powerful than Q waves in this regard 2.
• The presence of S waves can also be correlated with R waves and/or Q waves, although this correlation may be weak or fair 3.
• Q-wave "remodeling" can occur over time after a reperfused ST-segment elevation myocardial infarction, with some patients developing non-diagnostic ECGs for previous MI 4.
• Abnormal Q waves on the admission ECG can have prognostic implications, particularly in patients with anterior MI. A study found that patients with abnormal Q waves on admission had higher peak creatine kinase, higher prevalence of heart failure, and increased mortality compared to those without abnormal Q waves 5.
• The significance of abnormal Q waves can vary depending on the age of the patient. In adults under 40 years old, abnormal Q waves are less likely to indicate MI, but may still be a strong indicator of organic heart disease 6.

Key Considerations

When interpreting EKG findings for old MI, it's essential to consider the following:

• The location and size of the infarct, as indicated by Q waves and other EKG findings.
• The presence of other EKG abnormalities, such as S waves or R waves.
• The patient's age and medical history, as these can impact the interpretation of EKG findings.
• The use of additional diagnostic tests, such as cardiac magnetic resonance imaging, to confirm the presence and extent of MI.