From the Guidelines
Pathological Q waves are defined as being at least 0.03 seconds in width and 0.1 mV deep or QS complex in leads I, II, aVL, aVF, or V1–V6 in any two leads of a contiguous lead grouping, indicating myocardial necrosis or scarring, typically from a previous myocardial infarction 1.
Definition and Diagnosis
The presence of pathological Q waves on an electrocardiogram (ECG) is a significant indicator of myocardial damage, usually resulting from a previous myocardial infarction. These Q waves are characterized by specific criteria, including a duration of at least 0.03 seconds and a depth of 0.1 mV, or the presence of a QS complex in certain lead groupings 1.
Clinical Implications
When identified, pathological Q waves should prompt further cardiac evaluation, including assessment of cardiac function with echocardiography and consideration of coronary angiography if not previously performed 1. Optimization of secondary prevention measures, such as antiplatelet therapy, statins, ACE inhibitors or ARBs, and beta-blockers, is also crucial 1.
Key Considerations
It is essential to distinguish pathological Q waves from normal physiological Q waves, which are not indicative of myocardial damage. The location and characteristics of the Q waves can help in identifying the area of infarction, with anterior leads (V1-V4) indicating anterior infarcts, lateral leads (I, aVL, V5-V6) indicating lateral infarcts, and inferior leads (II, III, aVF) indicating inferior infarcts 1.
Recent Guidelines
According to the most recent guidelines, the diagnosis of myocardial infarction is more accurately defined by the presence of Q waves or QS complexes in the absence of QRS confounders, with the specificity of the ECG diagnosis being greatest when Q waves occur in several leads or lead groupings 1.
Conclusion Not Applicable - Direct Answer Only
The presence of pathological Q waves indicates transmural infarction, where necrosis has occurred through the full thickness of the myocardial wall, resulting in loss of viable myocardium that can no longer generate electrical forces toward the recording electrode 1.
From the Research
Pathological Q Wave Characteristics
- Pathological Q waves are associated with infarct size, as measured by cardiac magnetic resonance (CMR) 2
- The presence of Q waves on the presenting electrocardiogram (ECG) is independently associated with increased cardiac mortality following a first ST-elevation myocardial infarction (STEMI) 3
- Q waves can be present in patients without a history of myocardial infarction, and their presence does not always indicate prior myocardial infarction 4
Prognostic Implications
- Abnormal Q waves on the admission ECG are associated with higher peak creatine kinase, higher prevalence of heart failure, and increased mortality in patients with anterior myocardial infarction (MI) 5
- Admission Q waves are associated with microvascular injury, including microvascular obstruction (MVO) and intramyocardial hemorrhage (IMH), in patients with STEMI treated with primary percutaneous coronary intervention (pPCI) 6
- Q-wave regression is associated with improvement of left ventricular ejection fraction (LVEF), infarct size, and left ventricular dimensions in STEMI patients with early Q-wave formation 2
Diagnostic Accuracy
- The sensitivity and specificity of ECG-defined scar to detect infarct are 66% and 85%, respectively 4
- The presence of Q waves on the ECG does not always indicate prior myocardial infarction, and can be associated with false positivity 4
- CMR-defined scar is more accurate than ECG-defined scar in detecting myocardial infarction 4