[Post-extrasystolic long QT: evaluation and significance].

The dynamic behaviour of the QT interval was studied in 13 patients with a prolongation of greater than 80 ms of the QT interval of the QRS complex following a post-extrasystolic pause. Normal repolarisation under basal conditions (QTc 410 +/- 30 ms) was significantly (p less than 0.001) prolonged after pauses (QTc 512 +/- 90 ms). The study protocol included the measurement of QT during a Holter recording, an exercise test, Valsalva's manoeuvre and the isoprenalin test. Hydroquidine 600-900 mg/d was given to evaluate its action on ventricular repolarisation. The longest sinus cycles seen on the night Holter tracing (mean: 1,395 +/- 666 ms) were accompanied by normal repolarisation (QTc 380 +/- 30 ms). In contrast, exercise or Valsalva's manoeuvre caused a prolongation of QTc (QTc greater than 460 ms) in 11 patients out of 13: exercise QTc 471 +/- 54 ms; Valsalva QTc 480 +/- 50 ms. No arrhythmia occurred during these dynamic manoeuvres nor during the isoprenalin test. Hydroquinidine (mean: 729 mg) induced a QTc of greater than 500 ms in 6 patients out of 13 (46%). A triplet suggestive of a "torsade de pointes" was seen in one patient only. In conclusion, patients with a post-extrasystolic T wave abnormality under basal conditions were shown to fail to appropriately adapt their QT interval during autonomic stimulation manoeuvres and the prescription of hydroquinidine at the usual dose induced a mean QTc of greater than 500 ms in 46% of them.