Right ventricular septal pacing- clinical and electrical predictors for LV contraction asynchrony

Prolonged pacing from the right ventricular apex (RV) is associated with the LV dyssynchrony leading to progressive left ventricular dysfunction and increased morbidity and mortality. Alternate RV pacing sites-in particular the mid- RV septum and the RV outflow tract (RVOT) septum were considered, but no clear benefit was proven till now for this pacing sites. This may be due to the heterogeneity of the RV septal positions and to the significant number of leads placed on the RV free wall. The aim of this study is to find a reliable method of septal lead placement and to identify those pacing sites which provide better LV electrical activation Methods: 50 consecutive patients referred for pacemaker implants due to AV block were included. Patients with history of heart failure or LVEF < 50% at the implant were excluded. All patients had RV leads placed in septal position. This was achieved with a double curved stilet with the distal curve aimed posteriorly. RV septum and RVOT were mapped during implant aiming for a narrow paced QRS with an axis as close to normal as possible. Pacing lead position was evaluated during the implant using fluoroscopy (AP and LAO 40 °) and than by 12 lead ECG and echo. IntraLV dyssynchrony was evaluated during pacing using SPWMD in short axis parasternal view and the TDI septal to lateral ∆ t. Paced QRS duration and axis were also recorded. The correlation was sought between lead position evaluated by Rx and by echo and between paced QRS duration and axis and LV dyssynchrony.

92%(46) of the patients had the lead in septal position RV (32 in the mid-septal RV and 14 in RVOT), while 8% (4 pts) had the lead on the RVOT RV free wall as shown by echo. An anterior-oriented lead in the left anterior oblique fluoroscopic projection was specific for free wall position while positive QRS in DI in RVOT position was suggestive for free wall position on the ECG. No correlation was made between paced QRS axis and LV dyssynchrony while the QRS duration of > 160 ms was associated with significant LV dyssynchrony (SPWMD > 130 ms and to lateral septal ∆ t > 70 ms).

RV lead placement on the RV septum can be reliably achieved using a specially curved stilet and the LAO projection for confirmation. The wide paced QRS is correlated with significant intra LV dyssynchrony and therefore the RV pacing site with the narrowest QRS should be sought.