Effect of Reference Electrode on Intracardiac Electrograms: Close Indifferent Electrode vs. Wilson Central Terminal

Background Unipolar electrograms (Uni-EGM) are an essential part of intracardiac mapping. Although Wilson Central Terminal (WCT) is conventionally used as a reference for signals, avoiding contamination by far-field and non-physiological signals is challenging. Objective To explore the impact of an intracardiac indifferent reference electrode close to the recording electrodes, in lieu of WCT, on electrograms. Methods Sinus node activation was mapped in patients undergoing catheter ablation, using a multielectrode array with a close indifferent electrode (CIE) embedded in the distal end of the catheter shaft. An equal number of points was sequentially acquired at each site using CIE as a reference first, and subsequently using WCT. Uni-EGMs, bipolar EGMs (Bi-EGMs) and the earliest activation area (EAA, defined as the area activated in the first 10ms of the beat) were compared between CIE- and WCT-based activation maps. Results Seventeen patients (61±18 years, 76% male) were studied. Uni-EGM voltages acquired with CIE were significantly larger (N=11) or comparable (N=4) than those acquired with WCT. When points from the entire cohort were analyzed altogether, unipolar voltages and their maximum negative dV/dT, and bipolar voltages recorded using CIE were significantly larger than those recorded with WCT (2.36[1.42-3.79]mV vs 1.96[1.25-3.03]mV, p<0.0001; 0.40[0.18-0.77]mV/s vs 0.35[0.15-0.71]mV/s, p<0.0001; 1.46[0.66-2.81]mV vs 1.33[0.54-2.64]mV, p<0.0001, respectively). EAA was significantly smaller in CIE-based activation maps than in WCT-based ones (0.3[0.7-1.4]cm2 vs 0.6[1.0-1.8]cm2, p=0.01). Conclusions CIE-based maps were associated with an approximately 20% increase in unipolar voltage and may highlight the origin of a focal activation more clearly than WCT-based ones.