A newborn exhibits left axis deviation and decreased pulmonary markings on a chest x-ray. What is the likely diagnosis?

The findings of left axis deviation and decreased pulmonary markings on a chest x-ray in a newborn suggest that the diagnosis is likely Tricuspid Valve Atresia. In this condition, the absence or abnormal development of the tricuspid valve leads to a range of hemodynamic changes.

In Tricuspid Valve Atresia, the right ventricle is underdeveloped (hypoplastic) because blood does not flow well into it from the right atrium. This results in limited pulmonary blood flow, which explains the decreased pulmonary markings observed on the chest x-ray. The left axis deviation can be attributed to the increased workload on the left side of the heart due to compensation for the inadequate blood flow from the right heart.

This combination of findings is characteristic of Tricuspid Valve Atresia and helps differentiate it from other conditions. Other diagnoses listed, such as Congenital Diaphragmatic Hernia or Pulmonary Hypoplasia, may also present with respiratory distress and diminished lung markings but would not typically demonstrate left axis deviation. Coarctation of the Aorta primarily affects blood flow distribution and might show different radiographic signs without the specific combination of findings present in this scenario.