Table 1 Modified classification of cor triatriatum according to Lucas [3]

I.

Accessory atrial chamber receives all pulmonary veins and communicates with left atrium

 A. No other connections (classic cor triatriatum)

 B. Other anomalous connections

  1. To right atrium directly

  2. With totally anomalous pulmonary venous connection

II.

Accessory atrial chamber receives all pulmonary veins and does not communicate with the left atrium

 A. Anomalous connection to right atrium directly (cardiac TAPVC with all pulmonary veins first draining to a venous confluence)

 B. With totally anomalous pulmonary venous connection (supracardiac or infracardiac TAPVC)

III.

Subtotal cor triatriatum

 A. Accessory atrial chamber receives part of the pulmonary veins and connects to the left atrium

  1. Remaining pulmonary veins connect normally

  2. Remaining pulmonary veins connect anomalously (partial cor triatriatum with PAPVC)

 B. Accessory atrial chamber receives part of the pulmonary veins and connects to the right atrium

  1. Remaining pulmonary veins connect normally (PAPVC with anomalously connected pulmonary veins first draining to a venous confluence)

  2. Remaining pulmonary veins connect anomalously (mixed TAPVC)