Optimization of cardiac resynchronization therapy using fusion pacing algorithm - spectacular electrical imporvement does not trnslate into immediate hemodynamic result

Although Cardiac Resynchronization Therapy (CRT) has an established role in a treatment of heart failure, there is still a significant proportion of non-responders even in properly selected CRT recipients. Optimization of CRT pacing is one of possibilities to improve the effect. Fusion pacing algorithm allow for self-excitation of RV combined with left ventricular (LV) pacing, thus leading to further improvement of LV contraction synchrony compared to simultaneous biventricular pacing

The aim of the study was to assess the acute, beat to beat effect of standard BiV vs fusion-pacing on myocardial function as assessed by standard and speckle tracking echocardiography in HF patients with LBBB.

28 heart failure patients (22 men and 6 women) with EF<35% and LBBB (QRS>150ms) and CRT-D (Abbott) had an echocardiographic assessment directly after device implantation and echo parameters (including left atrial strain, left ventricular strain, TAPSE, mitral and tricuspid valve function and cardiac output) were measured in 5 minutes interval at 3 different settings: pacing off, simultaneous BIV pacing and fusion-pacing (Abbott’s sync-AV algorithm).

In our study CRT resulted in shortening od QRS complex from 169±19ms to 131±17ms for standard BiV pacing and further reduction to 118±16ms for fusion pacing (p<0.05). The acute effect of QRS shortening did not affect GLS (-9.15±3.05 vs -9.39±3.02 vs -9.13±3.65, p=NS), but affected segmental strain changes causing more homogenous contractility of LV.

Also it did not affect stroke volume (67,5±17.5ml vs 68,4±14.82ml vs 68,5±16.70ml p=NS) and did not translate to changes in LA strain, LA area or LA ejection fraction.

Spectacular changes in QRS duration visible in CRT patients just after implant, even more pronounced in fusion pacing-optimized patients are responsible for more homogenous pattern of LV contractility, but do not immediately improve stroke volume, global LV strain and LA function immediately. Longer observation is required for improved electrical parameters to translate into hemodynamic effect in CRT patients.