None of this is new mind you. I blogged this very concern over two years ago and said this:
Although the traditional assessment for prolongation of repolarization is the measurement of the QT interval, that assessment is simplistic and fraught with error due to controversy about normal limits and rate corrections, poor T wave demarcation, poor distinction between the T wave and the U wave and cycle length dependency. More subjective features including pause dependency, particularly in short-long cycle sequences, splayed T waves (or TU fusion) and macroscopic T wave alternans may be more important.
Among drugs that prolong the QT interval amiodarone has a uniquely low risk of producing TdP because the prolongation of repolarization it induces is homogeneous. Heterogeneous repolarization abnormality is the more likely substrate for TdP.