Method: The study included 306 dual-chamber device recipients who were in sinus rhythm and had preserved atrioventricular conduction. Patients were grouped according to their normal or impaired EF (35 ± 9%) as well as to their baseline narrow or wide QRS. Intrinsic f-QRS in the presence of narrow or wide QRS (f-nQRS, f-wQRS) as well as ventricular-paced f-QRS (f-pQRS) were analyzed following different heart rates (baseline, 100 bpm) and pacing modes.
Results: Patients with impaired-EF VT, compared to those with normal EF, had more f-nQRS or f-wQRS (56% versus 27%, P < 0.001) and f-pQRS (62% versus 16%, P < 0.0001), irrespective of their baseline QRS. The increased heart rate led to similar detections of intrinsic f-QRS. Ventricular pacing conferred both at baseline, compared with the nonpaced QRS, and at higher rate significantly more f-pQRS in patients with impaired-EF VT (P < 0.001). Detection of f-pQRS improved overall specificity (84%) and positive predictive value (91%) in identifying patients with impaired-EF VT, whereby, along with f-wQRS, it appeared particularly useful in patients with baseline wide QRS. (Table I.)
Conclusion: Increased heart rate or/and pacing reveal more fragmented QRS. The presence of f-pQRS as well as f-wQRS offer promise towards noninvasive identification of patients with impaired-EF VT.