From the Guidelines
Pathological Q waves are abnormal deflections on an electrocardiogram (ECG) that can indicate various pathological disorders, including hypertrophic cardiomyopathy (HCM), arrhythmogenic right ventricular cardiomyopathy (ARVC), infiltrative myocardial diseases, accessory pathways, and transmural myocardial infarction, as well as lead misplacement 1. These Q waves can be exaggerated, deep, or wide, and may appear in atypical leads. According to the international recommendations for electrocardiographic interpretation in athletes, pathological Q waves have been reported in approximately 1% to 2% of all athletes, with a higher prevalence in males and black athletes 1. Some key characteristics of pathological Q waves include:
- Depth: >3 mm in depth or >40 ms in duration in two or more leads (except III and aVR) 1
- Q/R ratio: normalizing Q wave depth to the degree of proceeding R-wave voltage can help decrease the false positive rate without compromising sensitivity for the detection of cardiomyopathy 1
- Lead placement: pseudo-septal infarct pattern with pathological Q waves in leads V1 to V2 can be due to high-lead placement relative to cardiac position 1 It is essential to note that pathological Q waves can be a result of various conditions, and clinical correlation is necessary for accurate diagnosis. The use of a Q/R ratio is recommended to overcome issues with false positive ECG results, particularly in trained athletes with physiological left ventricular hypertrophy (LVH) and thin adolescent athletes 1.
From the Research
Definition and Prognostic Implications of Pathological Q Waves
Pathological Q waves on an electrocardiogram (ECG) are a significant indicator of myocardial necrosis, particularly in the context of myocardial infarction (MI) 2, 3, 4. The presence of Q waves, especially when accompanied by ST elevation, can signify irreversible myocardial damage and is associated with a worse prognosis in patients with ST-segment elevation myocardial infarction (STEMI) 2, 3, 5.
Clinical Significance of Q Waves
The clinical significance of Q waves lies in their ability to predict cardiac mortality and non-viable myocardium. Studies have shown that new Q waves on the presenting ECG are independently associated with increased cardiac mortality following a first STEMI 3. Additionally, Q-wave area, a novel ECG parameter, can predict non-viable myocardial territories and the presence of a significant myocardial scar extension 4.
Transient Q Waves and Ischemia
Transient Q waves, which may appear acutely or chronically, can be associated with intense but reversible ischemia, rather than irreversible myocardial damage 6. The presence of transient Q waves can indicate potentially salvageable, severely ischemic myocardium, and their disappearance may suggest return of myocardial viability.
Prognostic Value of Q Waves
The prognostic value of Q waves is influenced by baseline characteristics, such as male sex and time from symptom onset to balloon inflation 5. However, the presence of Q waves on the presenting ECG remains an independent predictor of mortality, regardless of sex or rapidity of revascularization 5.
Key Findings
- Pathological Q waves are associated with myocardial necrosis and a worse prognosis in STEMI patients 2, 3, 5.
- New Q waves on the presenting ECG are independently associated with increased cardiac mortality 3.
- Q-wave area can predict non-viable myocardial territories and significant myocardial scar extension 4.
- Transient Q waves can indicate reversible ischemia, rather than irreversible myocardial damage 6.