CONTENTS
- When are Q-waves pathological?
- Causes of Q-waves
- Effect of Q-waves on ST/T morphology
- QRS fragmentation
is the Q-wave pathological?
- Different sources disagree. The table above is based on the fourth universal definition of myocardial infarction, so it's a reasonable reference. The relative size of the Q-wave in comparison to the QRS complex might be more meaningful than the absolute size of the Q-wave, especially among patients with small QRS complexes (e.g., Q-wave >25% of the R-wave is more likely to be pathological).
- Pathological Q-waves present in multiple anatomically contiguous leads support a prior MI.
- For patients with conduction system disease, the approach to Q-waves may be different. This is discussed within the corresponding algorithms (see LBBB, RBBB, LAHB, LPFB).
- LVH:
- May have a QS pattern in V1-V2, but rarely beyond V3.
- May have Qs in inferior leads.
- RVH:
- SI-QIII-TIII pattern (McGinn & White pattern) – may reflect RV overload of any etiology or chronicity.
- QS in I and aVL may be seen.
- qR in V1 may be seen.
- HCM:
- Prominent septal Q-waves (I, aVL, V4-V6, occasionally inferior leads).
- Basically, Q-waves are present in leads with tall, upright QRS complexes.
- Vertical heart (e.g., emphysema or tall/thin person):
- Q-waves may be present in the right or mid-precordial leads when tachycardic.
- Hyperkalemia: Misleading Q-waves may appear & disappear.
- Q-wave MI:
- Q-waves may develop within 6-14 hours of symptoms (often more rapidly in anterior MI than inferior MI).
- Traditionally, Q-waves are associated with myocardial necrosis. However, the presence of Q-waves doesn't preclude benefit from reperfusion (sometimes they disappear over time, especially with reperfusion).
Q-waves may cause abnormal depolarization, leading to abnormal repolarization (e.g., abnormalities in the ST/T wave segments; see example below).
definition of fragmentation
- QRS with normal length (<120 ms) with any of the following in two contiguous leads.
- Additional R wave(s) (i.e., RSR').
- Notching of the nadir of the S wave.
- (Note, however, that RSR' in the right precordial leads has a broader differential diagnosis, which is discussed here. RSR' in V1 isn't generally representative of fragmentation.)
pathophysiology of fragmentation
- Fragmentation may be caused by anything interfering with the normal homogeneous depolarization of the myocardium (E.g., ischemia, scar, fibrosis, inflammation, or microvascular abnormality). (30950722)
causes of fragmentation
- Coronary artery disease & prior MI:
- Fragmentation may serve as a Q-wave equivalent that reveals prior infarction.
- Among patients with coronary disease, fragmentation may have superior performance for the detection of myocardial scar compared to Q-waves (with a sensitivity and specificity in the ~85-90% range). (30950722)
- Fragmentation may correlate with reperfusion failure and greater mortality.
- Nonischemic cardiomyopathies
- Dilated nonischemic cardiomyopathy.
- Pulmonary hypertension.
- Cardiac sarcoidosis.
- HCM (hypertrophic cardiomyopathy).
- Arrhythmogenic right ventricular dysplasia.
- Takotsubo cardiomyopathy.
- Arrhythmogenic right ventricular dysplasia.
- Primary arrhythmias:
- Brugada syndrome.
- Acquired long QT syndrome.
- Other disorders:
- Congenital heart disease.
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References
- 28130029 Illescas-González E, Araiza-Garaygordobil D, Sierra Lara JD, Ramirez-Salazar A, Sierra-Fernández C, Alexanderson-Rosas E. QRS-fragmentation: Case report and review of the literature. Arch Cardiol Mex. 2018 Apr-Jun;88(2):124-128. doi: 10.1016/j.acmx.2016.12.008 [PubMed]
- 30950722 Brohet C. Fragmentation of the QRS complex: the latest electrocardiographic craze? Acta Cardiol. 2019 Jun;74(3):185-187. doi: 10.1080/00015385.2019.1600827 [PubMed]
- 31843558 Supreeth RN, Francis J. Fragmented QRS – Its significance. Indian Pacing Electrophysiol J. 2020 Jan-Feb;20(1):27-32. doi: 10.1016/j.ipej.2019.12.005 [PubMed]