Abstract
Ventricular pacing is most commonly performed at the right ventricular (RV) apex. This is not without risk as placement requires crossing the tricuspid valve (TV) and may cause valvular dysfunction and dyssynchronous activation of the ventricles. The fact that the tricuspid valve lies more apically than the mitral valve allows for the possibility of pacing the ventricles from the right atrium (RA) via the “atrio-ventricular septum” without crossing the TV or entering the coronary sinus (CS). In order to mitigate far field activation inherent to current pacing technology, we constructed a novel lead in which the cathode and anode are both intra-myocardial. We demonstrate safety and efficacy of this novel lead for ventricular pacing at the atrio-ventricular septum in canines, including improved synchronous activation of both ventricles, improved differentiation in ventricular versus atrial sensing, while providing reliable ventricular capture, opening novel and a potentially safer alternative to human cardiac resynchronization therapy.
1
Introduction
The most common site for ventricular pacing is the right ventricular (RV) apex . Accessing the RV apex, however, involves crossing the tricuspid valve (TV) , with the inherent potential for repetitive mechanical trauma between the TV leaflets and the lead which may cause tricuspid regurgitation . Additionally, RV apical pacing causes dyssynchrony . Even though bi-ventricular pacing using left sided leads placed in the coronary sinus (CS) and is used to improve ventricular synchrony, the CS lead carries its own inherent problems, including difficulty with placement, long term durability, and unwanted stimulation of neighboring organs . Because of the positioning of the tricuspid valve annulus being more apically oriented than the mitral valve annulus, the right atrium lies adjacent to the left ventricular basal septum; this landmark we define as the “atrio-ventricular septum” (AVS) .
AVS provides an innovative opportunity to pace the ventricle which would be beneficial because placing the pacing lead on the AVS would require neither crossing the tricuspid valve nor entering the CS, as AVS could be accessed directly from the RA . The proximity of AVS to the intrinsic conduction system of the human heart may also result in improved more physiological activation sequence of the ventricles with potentially increased ventricular synchrony .
The traditionally used intra-cardiac active fixation leads consist of an extendable active fixation helix (cathode) and a ring electrode approximately 10 mm proximal (anode) . The size and separation of both electrodes create an un-intentional “antenna” effect, which can lead to stimulation of neighboring structures and causes far-field signals that can interfere with sensing . In order to safely and effectively capture the ventricular myocardium via pacing of the AVS, the need for a novel lead design arose.
2
Methods and results
We have built a novel intra-myocardial lead that consists of an electrically active external helix (0.005 inch platinum/iridium wire) and central pin (0.009 inch MP35N wire) as shown in Fig. 1 (International Patent # WO 2007/073435 A1) . This innovation differs from conventional pacing leads because both the cathode and anode are intra-myocardial, thus minimizing the unwanted “antenna” effect with subsequent decrease in the undesirable stimulation of neighboring structures, while reliably capturing the AVS and translating to effective stimulation of the ventricular myocardium. Polyimide insulation with micropores was used to coat the inner pin in order to prevent potential short-circuiting in the event of electrode contact. The placement of this novel electrode requires precise deployment on the AVS as shown in Fig. 2 .
