Background: The genes for the long QT syndrome (LQTS) linked to chromosomes 3 (LQT3) and 7 (LQT2) were identified as SCN5A, the cardiac Na+ channel gene, and as HERG, a K+ channel gene. These findings opened the possibility of attempting gene-specific control of ventricular repolarization. We tested the hypothesis that the QT interval would shorten more in LQT3 than in LQT2 patients in response to mexiletine and also in response to increases in heart rate. Methods and Results: Fifteen LQTS patients were studied. Six LQT3 and 7 LQT2 patients were treated with mexiletine, and its effects on QT and QTc were measured. Mexiletine significantly shortened the QT interval among LQT3 patients (QTc from 535±32 to 445±31 ms, Pc from 530±79 to 503±60 ms, P=NS). LQT3 patients (n=7) shortened their QT interval in response to increases in heart rate much more than LQT2 patients (n=4) and also more than 18 healthy control subjects (9.45±3.3 versus 3.95±1.97 and 2.83±1.33, P+ channel blockers and from cardiac pacing because they would be at higher risk of arrhythmia at slow heart rates. Conversely, LQT2 patients may be at higher risk to develop syncope under stressful conditions because of the combined arrhythmogenic effect of catecholamines with the insufficient adaptation of their QT interval when heart rate increases.
|Number of pages||6|
|Publication status||Published - Dec 15 1995|
- Death, sudden
- Long QT syndrome
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine