Q Waves and Myocardial Infarction

Pathologic Q Waves

A pathologic Q wave is defined by specific duration and amplitude criteria (≥0.03 sec and ≥0.1 mV deep) and indicates myocardial necrosis from prior myocardial infarction, according to the American Heart Association 1, 2
Pathologic Q waves are characterized by duration ≥0.03 seconds and depth ≥0.1 mV in any two contiguous leads of a lead group, as recommended by the American College of Cardiology 3, 1
QS complex (absence of R wave) in leads V2-V3 with duration ≥0.02 seconds is indicative of pathologic Q waves, as stated by the American College of Cardiology 3
Pathologic Q waves are pathognomonic of prior myocardial infarction in patients with ischemic heart disease, regardless of symptoms, according to the American Heart Association 1, 2
The presence of pathologic Q waves in several leads or lead groupings has the highest specificity for MI diagnosis, as recommended by the American Heart Association 1

Significant Q waves may include Q waves with duration <0.03 seconds and depth <25% of R wave amplitude, as stated by the American Heart Association 2, 4
Minor Q waves (0.02-0.03 sec that are 0.1 mV deep) are suggestive of prior MI if accompanied by inverted T waves in the same lead group, according to the American College of Cardiology 1, 5

Transmural myocardial infarction with necrosis is indicated by pathologic Q waves, as stated by the American College of Cardiology 3
Larger infarct size (typically >6.2% of left ventricular mass) is associated with pathologic Q waves, according to the American Heart Association 1, 4
Increased mortality risk, even in "silent" Q-wave MIs, is associated with pathologic Q waves, as recommended by the American College of Cardiology 1, 4
Pathologic Q waves may occur due to myocardial fibrosis in the absence of coronary artery disease (e.g., in cardiomyopathy), as stated by the American College of Cardiology 3

QS complex in lead V1 is normal, as stated by the American Heart Association 2, 4
Q wave <0.03 sec and <25% of R wave amplitude in lead III is normal if frontal QRS axis is between 30° and 0°, according to the American College of Cardiology 3, 2
Q wave may be normal in aVL if frontal QRS axis is between 60° and 90°, as recommended by the American College of Cardiology 3, 4
Septal Q waves are small, non-pathological Q waves <0.03 sec and <25% of R-wave amplitude in leads I, aVL, aVF, and V4-V6, as stated by the American College of Cardiology 3, 2
Pre-excitation syndromes, cardiomyopathies, cardiac amyloidosis, bundle branch blocks, and left ventricular hypertrophy can mimic pathologic Q waves, according to the American College of Cardiology 3, 2, 5

Combining Q waves with other ECG findings (ST-T changes) increases diagnostic accuracy, as recommended by the American Heart Association 1, 5

Pathologic Q waves in the inferior leads (II, III, aVF) are defined as a duration ≥0.03 seconds and depth ≥0.1 mV in two or more contiguous inferior leads, according to the American Heart Association, as published in Circulation 6
Alternatively, a Q/R ratio ≥0.25 in two or more contiguous leads is also considered pathologic, as recommended by the American College of Cardiology, published in the Journal of the American College of Cardiology 7
QS complexes (complete absence of R wave) also qualify as pathologic, as stated in Circulation 6

The American Heart Association recommends verifying technical factors, such as proper lead placement, and applying strict criteria to confirm Q waves meet pathologic definitions in at least two contiguous inferior leads, as published in Circulation 6
The American College of Cardiology suggests obtaining echocardiography to assess for regional wall motion abnormalities consistent with prior inferior MI, and to evaluate for alternative diagnoses, such as cardiomyopathy or infiltrative disease, as published in the Journal of the American College of Cardiology 7
Cardiac MRI may be considered based on echocardiographic findings or when diagnosis remains uncertain, as recommended by the American College of Cardiology, published in the Journal of the American College of Cardiology 7

Non-ischemic causes of inferior Q waves include hypertrophic cardiomyopathy (HCM), arrhythmogenic right ventricular cardiomyopathy (ARVC), cardiac amyloidosis, and infiltrative diseases, as stated in the Journal of the American College of Cardiology 7