Hi H.,
I am not familiar with the particular condition mentioned above, but as a nurse I would suspect that your daughter's "spell" would more likely be related to her cardiac condition as opposed to a neurological condition.
A vasovagal reaction, as I'm sure your sister has told you is a relatively common occurence. It occurs when the vagus nerve is stimulated (that can occur with coughing or "bearing down" to move your bowels etc.) When the vagus nerve is stimulated the heart rate slows down causing a transient drop in blood pressure which subsequently diminishes blood flow to the brain resulting in "fainting" or syncope. This reaction is usually self limited and the patient has returned to normal within a few minutes.
An EKG gives a picture of the electrical activity of the heart. This electrical activity usually corresponds with the mechanical act of the heart pumping so certain things can be predicted by it. There are three major components of each "heart beat" which are represented on the EKG. The first waveform on the normal EKG is called the "P" wave. The P wave indicates the electrical activity which begins each heart beat. The P wave is intitiated in the right atria. (The heart has four chambers two on top (the atria) and two on bottom (the ventricals). The atria are the collecting chambers and the ventricals are the beating chambers.)
The next waveform on the EKG is the QRS. This is the largest most obvious waveform on the EKG and it represents the actual "heartbeat" and usually corresponds with the pulse. The final waveform is the T wave. The T wave indicates that the heart has recovered from the previous heart beat and is ready to begin another heart beat.
The QT is measured from the end of the QRS to the beginning of the T wave. This called the refractory period as the heart is not ready for another heart beat yet. If an electrical impulse hits during the refractory period it could potentially cause a serious heart dysrrythmia because the heart has not fully recovered.
Naturally, if this period is prolonged there is more opportunity for an electrical impulse to fall at the wrong time.
A borderline QT is often simply the result of a slower heart beat (bradycardia) This can occur in athletes. Therefore it is important that doctors check (as I am sure they have) the QTc. The c stands for corrected, so it is the corrected QT. The QT is corrected via a mathematical calculation (the QT divided by the square root of the r-r)
(more information then you need!)
Anyway, many things can cause a prolonged QT. Most commonly it is the side effect of certain drugs. So a diagosis of borderline QT really doesn't give you much information in and of itself.
It is possibly that your daughter fainted seconary to another condition called orthostatic hypotentsion. This occurs when a person changes positon too quickly and their blood vessels don't contract fast enough so blood pressure drops, temporarily decreasing blood flow to the heart. This can simply be a side effect of a normally low blood pressure combined with a little dehydration.
I hope I have been able to educate you a little and prepared you a little for your conversation with your daughter's cardiologist. Best Wishes and God Bless.
J. L.