Submitted by Dr T on November 28, 2012 – 9:37am
A QTc>490 is called Long QT Syndrome (LQTS). Patients with LQTS should avoid taking drugs that prolong the QT interval or reduce their serum potassium or magnesium levels. LQTS may be brought on by certain medicines or other medical conditions that include Trazodone.
Besides holding Trazodone your potassium, calcium and magnesium blood levels should be checked and for the time being you should avoid strenuous exercising till you get your next test results. Since you have remained asymptomatic (no lightheadedness or fainting), it is unlikely you are at risk for a dangerous arrhythmia, particularly if Trazodone is withdrawn.
You can calculate this risk here.
Hope this helps,