Discussion
This is probably the first described case of diminishing cardiac
systolic function after implantation of a direct left bundle branch
pacing lead reversed by the introduction of a left ventricular pacing
lead. Worsening of a cardiomyopathy substrate and subsequently heart
failure with His bundle pacing has not been described. This particular
case highlights an incomplete understanding of the relationship between
simultaneous electrical activation and cardiac synchrony. Thus, a
narrower QRS complex may not always correspond to better myocardial
performance. In our case a QRS of 103 ms was achieved with direct left
bundle branch pacing. This however, by exclusion, resulted in
dyssynchronous left ventricular contraction, progressive cardiomyopathy
and heart failure. The timeline of heart failure events in this patient
strongly suggests a poor response to direct left bundle branch pacing
confirmed by resolution after an upgrade to a biventricular system.
Improvement of EF after the upgrade raises the possibility of an added
benefit from the lateral left ventricular wall pre-excitation in
restoring cardiac synchrony in some patients. It is unclear what
characteristics may define poor responders to direct left bundle branch
stimulation.