Cardiovascular evaluation in thoracopagus twins.

Thoracopagus is the most common form of conjoined twins. Cardiovascular evaluation is necessary to establish the existence of 2 separate hearts before planning surgical separation of the twins. This is usually done by cardiac ultrasound, cardiac catheterization, documenting 2 separate pulse rates on physical examination, and the presence of 2 independent QRS complexes on simultaneously recorded ECGs. A set of thoracopagus twins underwent cardiac catheterization to confirm the presence of severe congenital heart defect in 1 of the twins before surgical separation. The other twin had no congenital heart defect. ECG electrodes were placed in the chest of the twins, and the recording is shown in the Figure. Two independent QRS complexes were recorded in ECG lead III. One QRS complex (small arrow) appears to be marching through the other complex (larger arrow). Heart rates are similar.