Acid reflux event detection using the Bravo wireless versus the Slimline catheter pH systems: why are the numbers so different?

OBJECTIVE This study analysed the relative accuracy of the Bravo wireless and the Slimline catheter-Mark III Digitrapper pH systems in the detection of acid reflux events. METHODS Twenty five asymptomatic subjects were studied. A Bravo capsule was placed 6 cm above the squamocolumnar junction (SCJ), marked by an endoclip, and a Slimline pH catheter was placed 5 cm above the manometrically localised lower oesophageal sphincter. The distance between the SCJ and each pH electrode was measured fluoroscopically. An in vivo pH reference was established using swallows of orange juice (pH 3.88). Concurrent pH data from the two systems were analysed in Excel spreadsheets. RESULTS Significantly more acid reflux events were reported by the Digitrapper system than the Bravo system (117.0 v 41.8). This was not explained by electrode position as there was no difference in median distance between the SCJ and either pH electrode (7.25 cm v 7.08 cm). The dominant source of discrepancy between systems was inaccuracy in electrode calibration and, after adjustment using the in vivo orange juice pH measurement, the discrepancy improved by 40%. However, discrepancy still existed and was most pronounced with short reflux events (1-15 s for the catheter, 1-17 s for the Bravo) associated with minimal intraoesophageal acidity and poor concordance between systems. CONCLUSION Substantially more reflux events were reported by the Digitrapper system compared with the Bravo system; 40% of excess events were attributable to a flawed software scheme for electrode thermal calibration while most of the remainder were brief events with poor reproducibility between systems.