And the answer is B, the exercise stress test is useful for the diagnosis of both long QT syndrome type one and long QT syndrome type two. So in CV, his baseline QT interval or corrected QT interval, QTC is 450 milliseconds, which is at the low end of the borderline range, but it prolongs to greater than 600 milliseconds during exercise and remains long in early recovery, consistent with long QT syndrome. Now CV has long QT syndrome type one or LQT1. This is caused by mutations in the KCNQ1 gene that encodes the alpha subunit of the KVLQT1 potassium channel and produces the polarizing current IKS. The current IKS shortens the action potential and QT interval, especially at fast heart rates. This leads to QTC prolongation at fast heart rates, even if the QTC interval is normal at slow heart rates and also then leads to arrhythmias and sudden death at fast heart rates. Long QT type two is caused by mutations in KCNH2 or HERG and the EKG usually shows T-wave abnormalities, especially in the precordial leads. Long QT syndrome type three or LQT3 is caused by mutations in SCN5A, the cardiac sodium channel, and the EKG usually shows a prolonged QT interval or a QT segment on the EKG. The exercise stress test is useful for the diagnosis of long QT syndrome, both long QT1 and long QT2 and is most sensitive during early recovery. NADALOL is highly effective in preventing arrhythmias and sudden death and is better than other beta blockers for primary prevention of arrhythmias and sudden death in patients with long QT1, including patients who carry asymptomatic mutations of the KVL-QT1 or KCNQ1 gene.

Long QT syndrome

QT interval prolongation

KCNQ1 gene mutations

NADALOL effectiveness

arrhythmia prevention