When are pathological Q waves labeled on an electrocardiogram (ECG)?

From the Guidelines

Pathological Q waves are labeled on an electrocardiogram (ECG) when they meet specific criteria, including a Q/R ratio ≥ 0.25 or ≥ 40 ms in duration in two or more leads (excluding III and aVR) 1.

Definition of Pathological Q Waves

• A Q wave is considered pathological if it has a duration of ≥ 0.03 seconds and a depth of ≥ 0.1 mV in leads I, II, aVL, aVF, or V1-V6 in any two leads of a contiguous lead grouping 1.
• The Q/R ratio is used to normalize Q wave depth to the degree of proceeding R-wave voltage, with a ratio of ≥ 0.25 indicating a pathological Q wave 1.

Clinical Context

• Pathological Q waves may be a result of various conditions, including myocardial infarction, hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, and infiltrative myocardial diseases 1.
• In athletes, pathological Q waves may be seen in approximately 1% to 2% of cases, and may be higher in males and black athletes 1.

ECG Interpretation

• When interpreting an ECG, it is essential to consider the clinical context and to use the Q/R ratio and other criteria to distinguish between physiological and pathological Q waves 1.
• The use of high-sensitivity troponins and other biomarkers may also be helpful in diagnosing myocardial infarction and other conditions that may cause pathological Q waves 1.

Key Points

• Pathological Q waves are labeled on an ECG when they meet specific criteria, including a Q/R ratio ≥ 0.25 or ≥ 40 ms in duration in two or more leads (excluding III and aVR) 1.
• The Q/R ratio is used to normalize Q wave depth to the degree of proceeding R-wave voltage 1.
• Pathological Q waves may be a result of various conditions, including myocardial infarction and hypertrophic cardiomyopathy 1.

From the Research

Pathological Q Waves on Electrocardiogram (ECG)

Pathological Q waves on an ECG are labeled when they meet certain criteria, including:

• A Q wave is considered pathological if it has a duration of more than 0.04 seconds and an amplitude of more than 0.2 millivolts [ 2 ]
• The presence of a Q wave on a 12-lead ECG has been considered a marker of a large myocardial infarction (MI) [ 2 ]
• Q waves can be labeled as pathological if they are associated with a significant myocardial scar extension [ 2 ]

Prediction of Non-Viable Myocardium

The presence of Q waves on an ECG can be used to predict non-viable myocardium, with:

• A Q-wave area greater than 6 ms mV demonstrating high performance in predicting the presence of myocardium scar larger than 10% [ 2 ]
• The positive predictive value and the negative predictive value of 'Q' waves on ECG to predict non-viable myocardium being 43% and 85% respectively [ 3 ]
• New Q waves on the presenting electrocardiogram being independently associated with a worse outcome after a first myocardial infarction [ 4 ]

Prognostic Implications

The presence of abnormal Q waves on the admission electrocardiogram has prognostic implications, including:

• Higher peak creatine kinase, higher prevalence of heart failure, and increased mortality in patients with anterior MI [ 5 ]
• No difference in peak creatine kinase, prevalence of heart failure, in-hospital mortality, and cardiac mortality between patients with and without abnormal Q waves in inferior MI [ 5 ]
• Abnormal Q waves on the admission ECG being associated with higher mortality in patients with anterior MI [ 5 ]