What is the difference between pathologic and nonpathologic Q waves?

From the Guidelines

Pathologic Q waves on an electrocardiogram (ECG) indicate myocardial infarction or scarring, while non-pathologic Q waves are normal variants, with the key difference being the duration and depth of the Q wave, as well as the leads in which they appear, as outlined in the third universal definition of myocardial infarction 1. The distinction between pathologic and non-pathologic Q waves is crucial for accurate diagnosis and treatment of myocardial infarction.

• Pathologic Q waves are typically wider (≥0.03 seconds) and deeper (≥0.1 mV or ≥25% of the following R wave amplitude) and appear in contiguous leads representing a specific coronary artery territory, as seen in leads I, II, aVL, aVF, or V1–V6 in any two leads of a contiguous lead grouping 1.
• Non-pathologic Q waves, on the other hand, are narrower (<0.03 seconds), shallower (<0.1 mV or <25% of R wave), and often appear in isolated leads, such as lead III or aVL, depending on the frontal QRS axis 1. Some conditions, such as pre-excitation, obstructive, dilated or stress cardiomyopathy, cardiac amyloidosis, LBBB, left anterior hemiblock, LVH, right ventricular hypertrophy, myocarditis, acute cor pulmonale, or hyperkalemia, may be associated with Q waves or QS complexes in the absence of MI, making clinical context essential for interpretation 1. The presence of pathologic Q waves generally indicates a transmural infarction that has damaged the full thickness of the myocardial wall, and should be correlated with symptoms, cardiac biomarkers, and imaging studies to confirm myocardial damage 1. In clinical practice, it is essential to consider the clinical context, including symptoms, cardiac biomarkers, and imaging studies, to accurately interpret Q waves and diagnose myocardial infarction, as outlined in the 2014 AHA/ACC guideline for the management of patients with non-ST-elevation acute coronary syndromes 1.

From the Research

Difference between Pathologic and Nonpathologic Q Waves

• Pathologic Q waves are associated with myocardial infarction (MI) and are a sign of permanent damage to the heart muscle 2, 3, 4, 5.
• Nonpathologic Q waves, on the other hand, can be seen in healthy individuals or in conditions other than MI, such as bundle branch block or ventricular hypertrophy.
• The presence of Q waves on an electrocardiogram (ECG) can indicate the size and location of the MI, with larger infarcts more likely to produce Q waves 2, 4, 5.
• The distinction between Q-wave and non-Q-wave MI is important, as it can affect treatment and prognosis 3, 6, 5.

Clinical Significance of Q Waves

• Q-wave regression is associated with improvement in left ventricular ejection fraction (LVEF) and reduction in infarct size 4, 5.
• Persistent Q waves are associated with a higher risk of heart failure and death compared to non-Q-wave MI or Q-wave regression 5.
• The presence of Q waves can also affect the choice of treatment, with some studies suggesting that patients with Q-wave MI may benefit from different therapies than those with non-Q-wave MI 3, 6.

Diagnostic Criteria for Q Waves

• The classic ECG criteria for Q waves are the most commonly used and are associated with the strongest correlation with infarct size 4.
• Other criteria, such as the Thrombolysis In Myocardial Infarction criteria and the 2000 and 2007 consensus criteria, may also be used to diagnose Q waves 4.
• The number and location of Q waves can affect the diagnosis and prognosis of MI 2, 3, 4, 5.