81 years old man implanted with a triple chamber pacemaker Consulta CRT-P with bipolar RV and LV leads for severe ischemic cardiomyopathy with right bundle branch block; Routine follow-up ; The ECG shows two slightly different aspect of the paced QRS; LV pacing amplitude is set at 3.5 V/0.4 ms in a (distal) tip LV – ring (anode) RV;
LV pacing Threshold test realized in LV bipolar configuration (LV tip – LV ring / anode);
In this patient the loss of LV capture occurs at an amplitude below 1 Volt / 0.4 ms (not shown on this tracing) which corresponds to the threshold value of the LV;
This patient presents an anodal RV capture when the pacing configuration is set to LV tip – RV ring configuration. The modification of the electrocardiogram is clear during the LV threshold test where the QRS appearance varies from a biventricular appearance (in LV tip – RV ring configuration) to a pure LV paced appearance (LV bipolar) for amplitudes below 3.5 Volts. It is more difficult to differentiate anodal capture during biventricular pacing (actually pseudo-triventricular: anode and cathode RV + distal LV) compared to a traditional biventricular pacing (cathode RV + distal LV). In this patient, the ECG appearance was slightly different on the distal portion of the QRS in leads V2, V3 and V4. The real threshold of LV stimulation was less than 1 Volt / 0.4 ms. In the absence of demonstration of any hemodynamic superiority of a configuration with anodal capture, given the very small change in the electrocardiographic appearance, and to save the battery energy, an output amplitude of 2.5 volts / 0.4 ms (without anodal capture) was selected. Therefore, at the selected output, this patient will present a RV anodal capture if the chosen pacing configuration is LV tip – RV ring (anode).
