Also known as: Siamese twins
Twin sisters conjoined at the head undergo separation surgery. Post-operatively, Katie falls into a coma while Jenny recovers but develops severe heart failure, driving the episode's central conflict about reconnecting them.
Also known as: Blocked brain artery
Katie's middle cerebral artery is severely narrowed post-separation surgery, causing inadequate blood flow to her brain and resulting in a coma. Attempted stenting fails due to arterial dissection.
Also known as: Brain blood vessel abnormality
A congenital abnormality in Katie's Circle of Willis contributes to her inadequate brain blood flow following the separation surgery.
Also known as: CHF
Jenny's heart is discovered to be severely compromised post-separation, with poor ventricular function. Katie's heart had been compensating for Jenny's failing heart when they were conjoined. Jenny ultimately dies from cardiac arrest.
Also known as: Persistent vegetative state
Katie remains in a coma following separation surgery due to inadequate cerebral blood flow. She later awakens when reconnected to her sister, suggesting the shared circulation improved her brain perfusion.
Also known as: V-fib
Jenny develops ventricular fibrillation as her failing heart cannot sustain both her and Katie's circulation after they are reconnected. This leads to her death despite resuscitation attempts.