The results of our study indicate that in rate control refractory AF patients with moderately reduced EF (EF ≥ 35% and < 50%) and narrow QRS (≤ 120 ms), HBP after AVNA provides superior ventricular activation and improvement of cardiac function compared to BiV pacing. However, both pacing modalities yielded similar symptomatic benefit.
Electrocardiographic and Echocardiographic outcomes
Biventricular pacing could be detrimental in HF patients without significant electrical dyssynchrony as non-physiological ventricular resynchronization does not return LV activation times to those seen in individuals with intrinsically narrow QRS (16, 17). Patients in our study who received BiV pacing and AVNA for symptomatic AF exhibited significant prolongation of QRS duration and no improvement in echocardiographic parameters. Although post-BiV QRS measurements in AVNA studies (8–10) were not specifically addressed, similar increase in QRS duration (40.2 ms) after BiV pacing could be observed in The Evaluation of Resynchronization Therapy for Heart Failure (LESSER-EARTH) trial which enrolled HF patients with narrow QRS (18). Furthermore, Post AV-Nodal Ablation (PAVE) study showed that BiV pacing superiority was the consequence of functional deterioration in the RV pacing group rather than improvement in the BiV group where LVEF remained unchanged (7). In the study by Khan et al. (19), which compared pulmonary-vein isolation and “ablate and pace” strategy, slight deterioration of LVEF (mean absolute change of -1 ± 4%) was noticed in BiV group after AVNA. In contrast, the Ablate and Pace in Atrial Fibrillation (APAF) trial reported significant improvement of echocardiographic parameters in the BiV group alone and compared to RV pacing (8). Heterogenous study population could explain the discrepancy, as it is conceivable that treatment effect of BiV pacing was more pronounced in patients with EF ≤ 35% (47% of patients) and QRS ≥ 120 ms (50% of patients) which were not included in our study (8). The same observation could be made in Ablate and Pace in Atrial Fibrillation plus Cardiac Resynchronization Therapy (APAF-CRT) trial where, although echocardiographic parameters were not presented, no clear benefit of BiV pacing and AVNA compared to pharmacological treatment was observed in AF patients with narrow QRS and LVEF 36–50% (10). Focusing on these patients, the results of our study showed that HBP plus AVNA is associated with significant improvement of cardiac function compared to BiV pacing. Structural improvements observed in our HBP group resemble those in previous studies (11, 12). Therefore, it is reasonable to assume that HBP in conjunction with AVNA could be a better alternative to BiV pacing in rate control refractory AF patients with moderately reduced EF and narrow QRS.
Alleviation of symptoms in HF patients with permanent AF is an interplay of adequate rate control and improvement of LV function (15). Symptomatic benefit after AVNA in our study was equal in both pacing modalities, but natriuretic peptides reduction was more pronounced in the HBP group. Similar conclusions were made in the APAF-CRT trial, where patients with LVEF > 35% exhibited significant symptomatic benefit after AVNA and BiV pacing, yet no clear benefit regarding mortality or HF progression (10). Thus, with our findings of greater LV volumes and natriuretic peptide levels reduction in HBP compared to BiV patients, we might speculate that regularization of ventricular rate after AVNA is the primary driver of symptom improvement in patients with moderately reduced EF, but physiological ventricular activation with HBP could enable additional LV reverse remodelling.
Procedural outcomes and clinical implications
Recent development of dedicated tools and encouraging data from the literature made HBP a logical physiologic pacing option for patients undergoing “ablate and pace” strategy (11–14). The results of the present study further support wider adoption of this technique in routine clinical practice. Our study showed similar success and adverse event rates of HBP compared to BiV pacing with significantly lower device implantation fluoroscopy times. Lower HBP fluoroscopy times in our study compared to previous reports (20) may be attributed to the implantation technique which primarily relies on intracardiac signals. Compared to BiV device, AVNA procedure could prove more challenging in HBP due to the vicinity of HBP lead. However, with implanting the HBP lead more distally (no visible atrial electrograms) and by maintaining the ablation catheter tip at or below the level of the ring electrode we were able to avoid ablation-related complications. Of note, only one acute increase in His capture threshold was registered after AVNA. In line with previous reports, no significant increase in short-term HBP lead threshold was observed (11, 12).
Patients with tachycardiomyopathy are often very symptomatic and have greater mortality (15). The “ablate and pace” strategy is a feasible therapeutic option when rhythm control interventions are no longer pursued (14). With long-term consequences of irreversible AVNA in mind, appropriate patient and therapy selection should be thoroughly considered. The results of our study indicate that compared to BiV pacing, HBP could provide additional hemodynamic advantage in symptomatic AF patients with moderate HF and narrow QRS undergoing AVNA. Thus, larger prospective studies are warranted to address clinical and structural outcomes between both “ablate and pace” strategies in different subgroups of rate control refractory AF patients.
Retrospective design of the study and low number of patients limits the strength of our findings. As only short-term procedural, clinical, and echocardiographic outcomes at 6-months were assessed, longer follow-up might have produced different results. Comparison of two pacing modalities implanted at different time periods may have led to treatment bias. However, all device implantations and AVNA procedures were performed in the same electrophysiological laboratory and by the same operators. Relatively high post-implant QRS duration (172 ± 13 ms) in the BiV paced group might have impacted on the lack of echocardiographic improvement. Addition intra-operative measures (activation times, identification of scars) and device optimization could have yielded shorter BiV paced QRS intervals. However, ECG-based VV delay optimization to ensure left ventricular capture was performed in all patients. Finally, as only rate control refractory AF patients with moderately reduced EF (EF ≥ 35% and < 50%) and narrow QRS (≤ 120 ms) were specifically assessed, the results cannot be extrapolated to other subgroup of patients undergoing AVNA. While we can assume similar effect in patients with reduced EF (12), superiority of HBP in patients with wide QRS may be controversial since only proximal conduction abnormalities are amenable by recruitment of latent Purkinje fibres distal to the site of block (21).