The cardiothoracic ratio in newborn infants

Area of Science:

• Pediatric Radiology
• Cardiology
• Neonatology

Background:

• Accurate assessment of cardiac size in infants is vital for diagnosing various conditions.
• Existing methods for measuring cardiothoracic ratio (C/T) in neonates lack standardized, reliable techniques.
• Establishing precise radiographic standards is essential for improved infant cardiac evaluation.

Purpose of the Study:

• To develop improved techniques and standards for measuring radiographic heart size in infants.
• To determine the most reliable thoracic measurements for calculating cardiothoracic ratios (C/T) in neonates.
• To establish normal C/T ranges and identify criteria for cardiomegaly in infants.

Main Methods:

• Calculation of cardiothoracic ratios (C/T) from anteroposterior supine chest radiographs of 175 normal infants (≤ 1 week old).
• Utilized four different thoracic measurements to assess C/T variation.
• Evaluated the impact of respiratory distress, parenchymal abnormalities, and assisted ventilation on C/T.
• Assessed inspiratory phase using posterior and anterior rib counts.

Main Results:

• Lowest C/T variation observed using chest width at inner margins of eighth ribs (normal range: 43.2%-56.5%) or maximum internal chest width (normal range: 42.7%-56.4%).
• A C/T of 57% or greater, by these methods, suggests an enlarged heart.
• Elevated average C/T was noted in infants with respiratory distress syndrome (131) and other parenchymal abnormalities (105).
• Assisted ventilation did not significantly affect C/T.
• Posterior rib count (normal inspiratory range: 6.6-9.4) was more predictive of heart size than anterior rib count.

Conclusions:

• Chest width at the inner margins of the eighth ribs or maximum internal chest width provide the most reliable C/T measurements in infants.
• A C/T threshold of 57% or higher indicates potential cardiomegaly.
• These standardized methods improve radiographic assessment of heart size in neonates, aiding in the diagnosis of conditions like respiratory distress syndrome.