hypokelly

Hello,
I have been here before asking about my 11yr olds heart problem and got great response, so I need help again.
My daughter has been sick with a cold for some time, she developed a fever,so I thought I should get her checked by the doc.
She has bronchitis and doc prescribed Biaxin (clarithromycin) 250mg.
Anyway.....gave 1st dose and decided to read the "fact sheet" the drug store always sends home with the prescription.I was a little alarmed as the precautions stated "this medication should be used with caution if you have certain medical conditions.Consult doctor if you have certain heart disease( eg. QTC prolongation, bradycardia)or family history of certain heart rhythm disorders (QTc prolongations)"
My daughter was hospitalized last year with a heart rate of 35bpm, she also has heart block and may be getting a pacemaker in the future.
Well....I phoned the pharmacist....He put me on hold and came back a little alarmed also, he then said he would phone the doc and get back to me...... He phoned back and said " doc said the precautions are just a "minut" possibility".I don't feel comfortable giving this medicine to her,am I over reacting are these precautions "minut"
My daughter has an appointment with her peditrician Thursday, should I just wait and get a different presciption from her or what?
Also what is QTc prolongation? looked it up on the net but most info just said "sudden death"
TIA , kelly