, ▁ 3 4 0 ▁ms ▁or ▁even ▁ 3 6 0 ▁ms ▁when ▁other ▁clin ical , ▁famil ial , ▁or ▁gen etic ▁factors ▁are ▁present . ▁The ▁Q T ▁interval ▁normally ▁var ies ▁with ▁heart ▁rate , ▁but ▁this ▁variation ▁occurs ▁to ▁a ▁less er ▁extent ▁in ▁those ▁with ▁short ▁Q T ▁synd rome . ▁It ▁is ▁therefore ▁recommended ▁that ▁the ▁Q T ▁interval ▁is ▁ass essed ▁at ▁heart ▁rates ▁close ▁to ▁ 6 0 ▁be ats ▁per ▁minute . ▁Other ▁features ▁that ▁may ▁be ▁seen ▁on ▁the ▁E CG ▁in ▁short ▁Q T ▁synd rome ▁include ▁tall , ▁pe aked ▁T - w aves ▁and ▁PR ▁segment ▁de pression . ▁ ▁Other ▁features ▁supporting ▁diagn osis ▁ ▁Other ▁features ▁that ▁support ▁a ▁diagn osis ▁of ▁short ▁Q T ▁synd rome ▁include : ▁a ▁history ▁of ▁vent ric ular ▁f ibr ill ation ] or ▁vent ric ular ▁t ach y card ia ▁despite ▁an ▁apparently ▁struct ur ally ▁normal ▁heart ; ▁a ▁family ▁history ▁of ▁confirmed ▁short ▁Q T ▁synd rome ; ▁a ▁family ▁history ▁of ▁sudden ▁card iac ▁death ▁aged ▁< 4 0 ▁years ; ▁and ▁identification ▁of ▁a ▁gen etic ▁mut ation ▁consistent ▁with ▁short ▁Q T ▁synd rome . ▁ ▁In vas ive ▁electro phys i ological ▁studies , ▁in ▁which ▁w ires ▁are ▁passed ▁into ▁the ▁heart ▁to ▁stim ulate ▁and ▁record ▁the ▁heart ' s ▁elect rical ▁imp uls es , ▁are ▁not ▁currently ▁recommended ▁for ▁diagn osing ▁short ▁Q T ▁synd rome ▁or ▁predict