TABLE 1

Distinguishing Features of LQTS For the 3 Most Common Genetic Mutations

GenotypeLQT1LQT2LQT3
GeneticsKCNQ1KCNH2SCNA5
Frequency, %35–4530–358–10
FunctionLossLossGain
Ion current affected↓ IKs↓ IKr↑ INa
Incidence of cardiac events22, %634618
Likelihood of dying during a cardiac event22, %4420
Triggers21Swimming, exercise, adrenergic stimuliLoud noises, emotion, peripartum periodSleep
ECGBroad-based T waveLow-amplitude bifid T waveLong isoelectric ST segment
Response to β-blockade21,33++++++
Response to mexilitine21++++
Exercise restriction+++++Uncertain
Exercise-triggered events22, %68294
  • +, low likelihood; ++, moderate likelihood; +++, high likelihood.