QT Prolongation after PVCs – New Diagnostic Criteria for Long QT Syndrome or for Lifethreatening Arrhythmia

Abstract

Background: Long QT Syndrome (LQTS) is a congenital or acquired disorder of cardiac ion channels resulted in disturbances of myocardial repolarization. The diagnosis is usually based on QT prolongation >460msec in respect of 12-lead ECGs, or in the presence of a confirmed LQTS mutation. QT interval prolongation >480msec is highly diagnostic, but there are several limitations and difficulties to make diagnosis: QT measurement accuracy, QT behavior during different HR, age and gender, or genotype.

Aim: On the basis of two consequent patients, we found that prominent QT prolongation after Premature Ventricular Contraction (PVC) might be one of the powerful criteria to suspect LQTS or life-threatening arrhythmia. The interesting finding of their ECGs was the QT prolongation only after the ventricular ectopic beats. While reported QTc was 430msec, QT interval followed the first sinus beat after PVC ranging from 520 to 600msec. Both of them were admitted in clinic with life-threatening arrhythmias. Later, one of them was diagnosed with congenital and another with acquired LQTS.

Methods: we studied QT interval behavior after PVC in three prespecified subgroups that included (1) electrocardiographically affected LQTS subjects (QTc ≥480 ms) – 7patients, (2) unaffected,otherwise healthy subjects (QTc<460 ms) – 23 patients and compared with third group including 2 of index patients. 24-hour-ECG records were analyzed. QT corrected was calculated by Bazet’s Formula.

Results: Mean QT interval after PVCs was 490msec in the first and 500msec in the second group, consequently, differently from the third (index) group, where QT interval after PVCs prolonged up to 600msec.

Conclusion:QT prolongation following premature ventricular beat (PVB) is a known finding but not fully investigated. The knowledge related to this phenomenon is based on the small studies or observations and particular cases. Our study shows that QT prolongation just after PVCs might be one of the strong markers to reveal QT abnormality leading to malignant arrhythmias due to congenital or acquired disorder of cardiac ion-channels.