PVC induced QT prolongation for unmasking the LQTS

Abstract Background Long QT Syndrome (LQTS) is a congenital or acquired disorder of cardiac ion channels resulting in disturbances of myocardial repolarization, usually manifested by QT prolongation. Diagnostic criteria include the presence of the corrected QT interval (QTc) of at least 480ms (milliseconds) in repeated 12-lead ECGs or confirmed LQTS gene mutations. Patients with LQTS have an increased likelihood of developing life-threatening ventricular arrhythmias and sudden cardiac death. Hence, establishing an accurate diagnosis is crucial. Purpose About 50% of patients with LQTS presents with normal or borderline QTc interval. Such cases warrant additional work-up to confirm the diagnosis and can often get overlooked. Based on two separate patient cases we hypothesized that significant QTc interval prolongation occurring after premature ventricular contractions (PVCs) may be a valuable diagnostic clue for suspected LQTS or potentially life-threatening arrhythmia in cases with unclear diagnosis. Above mentioned patients displayed normal baseline QTc interval values that prolonged only after PVC. Later, one of them was diagnosed with congenital and another with drug-induced LQTS (see ECG 1). Methods We observed QT interval behavior after PVC in three prespecified groups:(I) Electrocardiographically affected LQTS subjects (QTc ≥480ms) – 10 patients, (II) Control group of unaffected, asymptomatic, otherwise healthy subjects (QTc<460ms) – 72 patients, (III) Index Group of 2 patients with baseline QTc interval of 360-460ms, prolonged only after PVC. 24-hour-ECG records were analyzed. We calculated means of QTc interval before and after PVC in abovementioned three groups and compared them to each other using ANCOVA analysis. Results The QT interval after PVC increased 488+23ms in the first and 390+10ms in the second group. In contrast to the index group, the QT interval was prolonged by 380+160ms after PVC. Post-PVC QTc interval mean difference adjusted to covariate, baseline QTc interval values, were statistically insignificant between I and II groups (P=0.o66), but significant between both I -III(P=0.000055) and II-III groups (P<.0001). Conclusion There are several studies indicating that PVCs affect QT interval, but the phenomena need more investigation. From the perspective of our study, we have also observed that QTc interval indeed increased after PVCs in both ECG-phenotype positive LQTS individuals and healthy subjects, but not in the extent of the index patients. Our study is limited by the small number of concealed LQTS cases. However, it gives us some basis to think, that this finding could be particularly useful to suspect and unmask concealed LQTS in the patients with non-diagnostic baseline ECG.ECG1