Is a long qtc interval still serious if it is only slightly too long?

Long QT: Long QT syndrome (LQTS) is a heart rhythm condition that can potentially cause fast, chaotic heartbeats. These rapid heartbeats might trigger a sudden fainting spell or seizure. http://www.mayoclinic.org/diseases-conditions/long-qt-syndrome/basics/definition/con-20025388

ECG: Details matter.Why was ECG done?What are the actual timing intervals?what medicines are taking? Etc ; have a cardiologist review the ECG.

It can be: You need to see a cardiologist to determine if this is serious or not.