DISCUSSION
The main findings of this study were: 1) LBBAP may improve FTR in
patients with persistent AF and bradycardia; 2) A high ventricular
pacing percentage of LBBAP maybe needed to improve FTR.
Long-term hemodynamic disturbance resulting from an irregular and slow
heart rate may be the main mechanism of FTR in patients with persistent
AF and bradycardia. Compared to regular rhythm, irregular rhythm leads
to hemodynamic effects including cardiac output decreases, capillary
wedge pressure increases and right atrial pressure increases in AF
patients[10, 22, 23]. And the slow heart rate
causes a prolonged diastole phase, resulting in ventricular filling
pressure increasing, which is correlated with a higher PASP and right
atrial pressure. Those hemodynamic disturbances may contribute to RAV
enlargement, PASP increase, and FTR development subsequently.
Preclinical and exploratory clinical studies suggested that pacing at
moderately accelerated heart rates was able to decrease ventricular
filling pressures and improve hemodynamic
effects[24-26]. Besides, the clinical trial also
demonstrated the benefits of moderately accelerated heart rate compared
to usual care[27]. In our study, LBBAP elevated
and regularized the heart rate, and the RAV and PASP reduction were
observed, which may contribute to the FTR improvement.
The physiological pacing effect of LBBAP was essential for FTR
improvement. Lead interference and pacing-induced ventricular
dyssynchrony were considered to be the main mechanisms of TR
deterioration following right ventricular
pacing[11]. With a thinner pacing lead and
physiological pacing mode, LBBAP has the potential to preserve tricuspid
valve function during long-term follow-up[28-30].
Lead interference was avoidable, as relevant
studies[29, 30] showed that farther
distance from the electrode
fixation site to the tricuspid annulus (Lead-TA-dist) was correlated
with a lower incidence of TR worsening after LBBAP. With the
Lead-TA-dist of 19.7 ± 5.0 mm in our study, the interference of 3830
lead on tricuspid valve (TV) was relatively small. And pacing effect of
LBBAP could preserve tricuspid valve function in the acute phase also
had been proved[31]. Taken together, the effect of
a high percentage of LBBAP on FTR in persistent AF patients with
bradycardia challenged the old belief that pacemaker implantation was
correlated with TR deterioration only. PVC burden can decrease VP
percentage and impact the improvement of FTR. Drugs such as beta blocker
or catheter ablation could be considered to eliminate PVC burden.