Phenotyping patients with borderline elevated esophageal acid exposure

Acid exposure time (AET) <4% on ambulatory reflux monitoring definitively rules out pathologic gastroesophageal acid reflux, while AET >6% indicates pathologic reflux per the Lyon Consensus, leaving AET of 4-6% as borderline. We aimed to elucidate the borderline AET population and identify metrics that could help differentiate this group. A total of 50 subjects in each group, AET <4, 4-6, and >6% on pH-impedance monitoring between 2015 and 2019, were retrospectively reviewed. In addition to demographic and clinical information, the extracted data included mean nocturnal baseline impedance (MNBI) on reflux study and high-resolution manometry (HRM) parameters and diagnosis. After excluding patients with prior foregut surgery, major esophageal motility disorder, or unreliable impedance testing, a total of 89 subjects were included in the analysis (25 with normal AET < 4%, 38 with borderline 4-6%, 26 with abnormal >6%). MNBI in borderline AET patients was significantly lower compared to normal AET (1607.7 vs. 2524.0 ohms, P < 0.01), and higher than abnormal AET (951.5 ohms, P < 0.01). Borderline subjects had a greater frequency of ineffective esophageal motility (IEM) diagnosis per Chicago classification v3.0 (42.1 vs. 8.0%, P = 0.01), but did not demonstrate any differences compared to abnormal subjects (34.6%, P = 0.56). Patients with borderline AET had an average MNBI that was in between normal AET and abnormal AET. Borderline AET patients also commonly demonstrate IEM on HRM, similar to those with abnormal AET. Our findings can be potentially useful in assigning higher clinical significance for patients found to have borderline AET with concomitant low MNBI and IEM on manometry.