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Rate control remains the mainstay for the majority of patients (pts) with chronic atrial fibrillation (AF) including those after AF ablations fail to maintain sinus rhythm (SR). Medications used for rate control and other medical conditions can cause acquired long QT syndrome. Other than f wave artifacts, irregular RR is a challenge for QT assessment. After developing a new method for ECG lead selections in AF, this study aimed to manage the effect of RR variability on QT interval.
ECG tracings of 107 AF pts who underwent rate control therapy (HR 79±6 bpm) were analyzed. ECGs in sinus rhythm (HR 76±6 bpm) of the same pts were used as controls. RR and QT intervals were measured in 10 beats in the lead showing the best T wave morphology and with least visible f waves. QT-RR relationship and QTc (Bazett’s) were compared between AF and SR. The frequency of QT shortening (QT_S) or lengthening (QT-L) following the sudden change of RR was elucidated.
The QT-RR relationship is similar between AF and SR. Although QT_S and QT_L occurred in 64% and 66% of cases, respectively, the QTc averaged from 10 beats was comparable between 2 groups (AF vs SR 439±27 ms vs 437±22 ms, p = ns).
With rate control, the QT-RR relationship is similar between AF and SR. In the presence of RR irregularity, QT measurement can be achieved using a 10-beat average.