Reference:   Simantirakis EN, Vardakis KE, Kochiadakis GE, Manios EF, Igoumenidis NE, Brignole M, Vardas PE, Left ventricular mechanics during right ventricular apical or left ventricular-based pacing in patients with chronic atrial fibrillation after atrioventricular junction ablation, J Amer Coll Cardiol 2004; 43: 1013-1018     

At the Annual Scientific Sessions of the American College of Cardiology in early March 2004, St. Jude Medical presented the results of the PAVE trial at a Late Breaking Clinical Trials session.  The study was strongly positive in favor of biventricular pacing in this population of patients, even those with normal ventricular function.  The PAVE study effectively started six weeks after device implantation and AV node ablation so as to not be impacted by the expected improvement associated with the initial regularization and control of the ventricular rate. 

This present study published in the April 9th issue of the Journal of the American College of Cardiology reported on acute hemodynamic studies performed in a series of twelve patients with chronic atrial fibrillation who underwent AV nodal ablation (for standard clinical indications) and implantation of a biventricular pacing system.  Six patients had impaired LV function with a mean ejection fraction of < 40% while six had basically normal LV function.  All patients were studied with an invasive hemodynamic study; including pressure volume loops approximately 24 hours post-AV nodal ablation and implantation of the permanent biventricular pacemaker.  The hemodynamic assessment was performed at a stable rate of 75 bpm, during suspended respiration after 5 minutes of pacing in the particular pacing state (RV pacing only, biventricular pacing with a LV-RV delay of 10 ms or pure LV pacing.  The implanted devices were capable of independent output control for the LV and RV enabling the three separate pacing states.  For RV pacing, the lead was placed in the RV apex, which is the clinically standard location.  Alternative sites such as RV outflow track were not studied as these patients all had permanent leads in place rather than temporary leads. 

The relative changes were similar for the patients with compromised ventricular function as well as normal baseline ventricular function based on ejection fraction.  LV-based pacing (both pure LV and BiVentricular) indices of contractile function were improved compared to RV-based pacing.  There was no significant impact on diastolic relaxation from any of the pacing modalities.  Angiography confirmed that all patients had some mitral regurgitation, but the semi-quantitative mitral valve regurgitation score decreased from 2.8 (scale 1 to 4 with 4 being the worse) associated with RV-based pacing to 1.2 with LV-based pacing.

Comment:
This study demonstrated an acute benefit of LV-based pacing in these patients who have chronic atrial fibrillation and have undergone AV nodal ablation for standard indications.  While most of these patients have done very well with RV apical pacing in the past, there are a small number who deteriorate.  While this study cannot address the long-term results and progressive hemodynamic improvement that might accompany chronic rate stabilization, it did demonstrate an acute benefit of LV-based pacing.  There was no significant difference between LV only and BiVentricular pacing and for this reason, the results from these two pacing modalities were combined. 

The pacemaker manufacturer/model that was implanted in these patients was not identified in this paper.  It should be noted that St. Jude Medical’s Epic HF and Atlas + HF both have independent control of the RV and LV output and the nominal simultaneous pacing is actually a separation of 10 ms (LV before RV).   This paper made no attempt to determine if there was a further benefit of other V-V timing intervals. 

Indexing Terms:
Cardiac Resynchronization Therapy
Atrial Fibrillation
AV nodal ablation
Ablate and pace
Ventricular function
Hemodynamic studies