- Q wave: 1st negative deflection of QRS complex after P wave or before 1st R wave
- Q waves normally seen in inferior (II, III, aVF) & left-lateral precordial leads (V5-V6)
- Duration: <20-30 ms
- Amplitude: up to 14 mm  (esp. large in infants )
- Q waves often absent in I & aVL in infants; if present, often suggests cardiac pathology
Abnormal Q waves:
- Anomalous left coronary artery arising from pulmonary artery (ALCAPA):
- Consider if Q waves ≥3 mm deep & ≥30 ms wide in I & aVL (esp. if no Q waves in inferior leads) [3,4]
- Q waves >4 mm deep & >30 ms wide: consider (1) MI (esp. in Kawasaki syndrome) or (2) ALCAPA
- Q waves in right precordial leads (V1-V2): always pathologic & associated with RVH
- Q waves ≥3 mm deep & normal duration in inferior leads (II, III, aVF) & left-lateral precordial leads (V5-V6): associated with LVH
- Familial hypertrophic cardiomyopathy:
- Q waves ≥3 mm deep or ≥40 ms wide in ≥2 leads (except V1, V2, or III)
- Low sensitivity, but high specificity in genetically-tested positive children & adolescents 
1. Rivenes SM, Colan SD, Easley KA, et al. Usefulness of the pediatric electrocardiogram in detecting left ventricular hypertrophy: results from the Prospective Pediatric Pulmonary and Cardiovascular Complications of Vertically Transmitted HIV Infection (P2C2 HIV) multicenter study. Am Heart J 145:716, 2003.
2. Davignon A, Rautaharju P, Boisselle E, et al. Normal ECG standards for infants and children. Ped Cardiol 1:123, 1979.
3. Johnstrude CL, Perry JC, Cecchin F, et al. Differentiating anomalous left main coronary artery originating from the pulmonary artery in infants from myocarditis and dilated cardiomyopathy by electrocardiogram. Am J Cardiol 75:71, 1995.
4. Chang RR, Allada V. Electrocardiographic and echocardiographic features that distinguish anomalous origin of the left coronary artery from pulmonary artery from idiopathic dilated cardiomyopathy. PediatrCardiol 22:3, 2001.
5. Charron P, Dubourg O, Desnos M, et al. Diagnostic value of electrocardiography and echocardiography for familial hypertrophic cardiomyopathy in genotypes children. Eur Heart J 19:1377, 1998.