Effect of heart rate and pacing mode on QRS fragmentation.

Background: The study was designed to investigate the effect of heart rate and pacing mode on QRS fragmentation (f-QRS). Moreover, the usefulness of f-QRS in distinguishing patients with impaired left ventricular ejection function (EF) and ventricular tachycardia (VT) from patients with normal EF was assessed.

Methods: Three hundred and six recipients, with dual-chamber device, with intrinsic narrow or wide QRS complex and preserved atrioventricular conduction were grouped into normal-EF or impaired-EF VT. We analyzed intrinsic narrow f-QRS and wide f-QRS as well as ventricular-paced f-QRS following different heart rates (baseline, 100 bpm) and pacing modes.

Results: In the baseline state, overall, patients with impaired-EF VT (35 ± 9%), compared to those with normal-EF, had more f-QRS (56% vs 27%, P  <   .001) and ventricular-paced f-QRS (62% vs 16%, P  <   .0001). Ventricular pacing conferred both at baseline and at higher heart rate more ventricular-paced f-QRS in patients with impaired-EF VT than in normal-EF ( P  <   .001). Detection of ventricular-paced f-QRS markedly improved overall specificity (84%) and positive predictive value (91%) in identifying patients with impaired-EF VT.

Conclusions: Increased heart rate or/and ventricular pacing uncover QRS fragmentations. Detection of ventricular-paced f-QRS adds value toward noninvasive identification of patients with impaired-EF VT.