Background: The ligament of Marshall (LOM) may play a role in the pathophysiology of several tachyarrhythmias and accurate electrophysiological localization of this structure is crucial for effective ablation therapy. This study therefore quantifies electrophysiological properties of the LOM, and identifies which electrogram (EGM) recording (uni- or bipolar) and processing technologies [local activation time (LAT) and/or voltage mapping] are most suitable for accurate localization of the LOM. Methods: The LOM was electrophysiologically identified in 19 patients (mean age 66 ± 14 years; 12 male) undergoing elective cardiac surgery using intra-operative high-density epicardial mapping, to quantify and visualize EGM features during sinus rhythm. Results: Only a third of LOM potentials that were visualized using unipolar EGMs, were still visible in bipolar activation maps. Unipolar LOM potentials had lower voltages (P50: LOM: 1.51 (0.42–4.29) mV vs. left atrium (LA): 8.34 (1.50–17.91) mV, p < 0.001), less steep slopes (P50: LOM: –0.48 (–1.96 to –0.17) V/s vs. LA: –1.24 (–2.59 to –0.21) V/s, p < 0.001), and prolonged activation duration (LOM: 20 (7.5–30.5) ms vs. LA: 16.5 (6–28) ms, p = 0.008) compared to LA potentials. Likewise, bipolar LOM voltages were also smaller (P50: LOM: 1.54 (0.48–3.28) mV vs. LA: 3.12 (0.50–7.19) mV, p < 0.001). Conclusion: The LOM was most accurately localized in activation and voltage maps by using unipolar EGMs with annotation of primary deflections in case of single potentials and secondary deflections in case of double or fractionated potentials.
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