Electrical Characteristics of a Split Cathodal Pacing Configuration

Several electrical configurations can be used for biventricular pacing to achieve cardiac resynchronization. Commercially approved biventricular pacing systems stimulate the RV with an endocardial lead and the LV with a unipolar lead positioned in the cardiac venous circulation using the tip electrodes of both leads linked as a common cathode. The distribution of current with this parallel circuit, split cathodal configuration is dependent on the separate impedances of the two leads. A total of 19 patients with left bundle branch block and congestive heart failure underwent implantation of a cardiac venous lead and standard bipolar right atrial and RV pacing leads. Stimulation thresholds and impedances were measured for the RV and LV in five electrical configurations: (1) unipolar LV from the cardiac venous lead; (2) bipolar LV using the tip electrode in the cardiac vein as the cathode and the ring electrode of the RV lead as the anode; (3) bipolar RV from the RV lead; (4) unipolar split cathodal stimulation of the cardiac venous and RV leads; and (5) bipolar split cathodal stimulation of the cardiac venous and RV leads. Repeat measurements of RV and LV thresholds were made from the pulse generator at 1-year follow-up. The LV stimulation threshold increased from 0.7 ± 0.5 V in the unipolar configuration to 1.0 ± 0.8 V in the unipolar split cathodal configuration (P = 0.01) and from 1.0 ± 0.7 V in the bipolar configuration to 1.3 ± 0.9 V in the bipolar split cathodal configuration (P < 0.001). The RV stimulation threshold increased from 0.3 ± 0.2 V in the bipolar configuration to 0.5 ± 0.2 V in the bipolar split cathodal configuration (P = 0.005). The bipolar impedance measured 874 ± 299 Ω for the coronary venous lead, 705 ± 152 for the RV lead, 442 ± 87 in the split unipolar cathodal configuration, and 516 ± 64 in the bipolar split cathodal configuration. At 1-year follow-up, the LV stimulation threshold was 1.8 ± 1.6 in the unipolar split cathodal configuration and 2.4 ± 1.6 in the bipolar split cathodal configuration (P = 0.003). The RV stimulation threshold at 1 year was 0.7 ± 0.3 in the unipolar split cathodal configuration and 0.8 ± 0.3 in the bipolar split cathodal configuration (P = 0.02). The split cathodal configuration significantly increases the apparent stimulation threshold for both the LV and the RV as compared with individual stimulation of either chamber alone. Programming to the bipolar split cathodal configuration further increases the apparent stimulation threshold. These observations support the development of pacing systems with separate LV and RV output circuits for resynchronization therapy. (PACE 2003; 26:2264–2271)