In Torsades de Pointes, which wave form can typically not be measured?

In the context of Torsades de Pointes, the measurement of the PR interval is typically not possible due to the nature of the arrhythmia itself. Torsades de Pointes is characterized by a series of alternating QRS complexes that appear to twist around the baseline, making it challenging to identify discrete P waves preceding each QRS complex. This chaotic rhythm often results in obscured or absent P waves, leading to a situation where the PR interval, which is determined by the time from the P wave onset to the QRS complex onset, cannot be accurately measured.

In contrast, T waves can usually be observed, although they may also appear altered due to the tachyarrhythmia. Similarly, while QRS duration can still be measured during Torsades de Pointes, it reflects the width of the QRS complexes, which can vary significantly depending on the morphology and duration typical of this arrhythmia.