Device Measured Rapid Shallow Breathing Index and not Minute Ventilation Reflects Changes in Dyspnea Status in Ambulatory Heart Failure Patients

Abstract

Background Dyspnea is common in heart failure (HF) patients and a primary driver for HF hospitalizations. Minute Ventilation (MV), a product of respiratory rate (RR) and tidal volume (TV), is known to be elevated in HF patients due to ventilation/perfusion mismatch. However, it is not known if changes in MV accurately reflect changes in dyspnea status in ambulatory HF patients over time. Methods The MultiSENSE trial enrolled 900 patients implanted with a COGNIS CRT-D and followed them for up to 1 year. Device software was modified to permit collection of chronic diagnostic sensor data including impedance based RR and TV, which was used to compute MV (RR*TV) and Rapid Shallow Breathing Index (RSBI=RR/TV). Dyspnea status was assessed on a 3-point scale (0=No dyspnea, 1=dyspnea on exertion, 2=dyspnea at rest) at routine follow-up visits scheduled every three months or sooner. Changes in dyspnea scores between follow-ups were calculated: Improve+ (2->0), Improve (2->1 or 1->0), No change, Worsen (0->1 or 1->2), and Worsen+ (0->2). Relative changes in the respiration parameters between the start (ST) and end (ED) of each epoch were calculated as (ED-ST)/STx100%, reported as mean +/- SEM for each category and compared across categories using Kruskal-Wallis test. Results Of 4717 total follow-up intervals with dyspnea assessments, 3388 had no change, 561 had 1-point worsening, 41 had 2-point worsening, 689 had 1-point improvement, while 37 had 2-point improvement. 24-hour average MV was not significantly different between dyspnea change categories (p=0.42) and changed inconsistent with expectation (i.e. increased MV with improved dyspnea assessment). In contrast changes in 24-hour average RSBI (p=0.03) as well as day-time minimum RSBI (p Conclusion Changes in RSBI correlated with changes in patient's dyspneic status whereas MV did not. Automatic longitudinal measurements of day-time minimum RSBI may better quantify the dyspneic status in ambulatory HF patients, enabling continuous monitoring of dyspnea in HF patients.