Prolonged QT interval? Need some advice!

I'm a 26-year old woman and I'd need some advice regarding my QT values. If I understand correctly, QTc intervals of less than 440 ms are considered to be normal, whereas QTc intervals of 440 ms to 460 ms in men and 440 ms to 470 ms in women are considered borderline. A couple of days ago I had an ECG. My QT/QTc was 412/447 ms at a heart rate of 71 bpm. Is this something to worry about (long QT syndrome)? I've been suffering from PVCs every day for over a year, but my heart should be structurally fine according to an echocardiogram. During the past few months I've had short bursts of an accelerated heartbeat with fluttering sensation and sometimes irregular heartbeat. I've decided to have 24-hour Holter monitoring again, just in case.