(274) Real World Use of the Incremental A-STEP at Two International Adult Cystic Fibrosis Units: Feasibility, Safety and Factors Involved in the Achievement of a Maximal Effort Exercise Capacity Test

Background: The recently developed incremental maximal effort A-STEP was introduced at a second independent international adult CF Unit during the past two years for further evaluation, development and fine tuning.

Aims: Evaluate the experiences of feasibility, safety and usefulness of the A-STEP at two adult CF centers and identify factors that limited the ability to achieve a maximal effort exercise capacity test.

Methods: The A-STEP was developed on a 20cm non-slip step. It consists of 16 levels starting at 18 steps per minute (pm) and increases by 2 steps pm up to 48 steps pm at level 16. A maximal effort test is achieved when at least one of the following is achieved: BORG score of ≥9 or 10/10 for shortness of breath (lungs) and /or leg fatigue (legs); Heart rate ≥90% for age predicted maximum (220-age) or volitional fatigue. A modulator naïve group (MNG) of adults at the CF Unit in Melbourne (MAG) and a group treated with elexacaftor/ tezacaftor/ivacaftor (Trikafta) in Glasgow, Scotland (GSG) participated in the study.

Results: Seventy-seven (51 male) adults completed the A-STEP: the GSG 35 (male 21) and the MAG 39 (male 30). The subject demographics and results of the A-STEP studies are seen in Table 1. Results are presented for GSG versus (vs) MAG consecutively. The number of A-STEP Levels completed: 9.8 [3.9] vs 10.9 [2.6] with six of 35 (17%) completing all 16 levels in the GSG vs zero in the MAG (highest level completed 15). The number of subjects who achieved ≥90% of HR for age: 9/35 (26.0%) vs 24/39 (61.5%) and ≥85% HR for age: 14/35 (40%) vs 32/39 (82.0%) The number of participants who achieved a maximal effort test using the list of 4 criteria: 14/35 (40%) vs 37/39 (94.8%). Factors identified for not achieving a maximal test included: inability to regularly change leading leg resulting in early leg fatigue; unable to keep up with the beat; and some stopping the test early possibly because of lack of motivation. Lessons learned to optimize the A-STEP to be a maximal effort test include: participant education prior to the test requiring the operator to instruct the subject to practice changing legs regularly during the test; providing enthusiastic encouragement to keep up with the beat and to keep pushing to a maximal level throughout the test; provide coaching on the achievement of a maximal test by aiming for 9 or 10/10 on BORG for lungs and/or legs and the achievement of ≥90% of HR for age. It appears that treatment with Trikafta provided the ability for the GSG to exercise to a higher level than the MNG. In the future we may need to consider using a 25cm step with adults with good lung function who exercise regularly and are on Trikafta. There were no safety issues in either groups. The test can be done efficiently in an outpatient clinic space allowing optimal infection control.

Conclusions: The A-STEP is a feasible and safe incremental maximal effort exercise capacity test; and people with CF need prior training in all the elements of the test. Operators need to enthusiastically coach participants to keep up with the beat and cheer subjects on to actively keep pushing during the test to enable achievement of a maximal effort test as is done during cardiopulmonary exercise testing (CPET).

Acknowledgements:

References: Wilson LM, Ellis MJ, Lane RL, Wilson JW, Keating DT, Jaberzadeh S, Button BM. Development of the A-STEP: A new incremental maximal exercise capacity step test in cystic fibrosis. Pediatr Pulmonol. 2021 Sep 9. doi: 10.1002/ppul.25667. Epub ahead of print. PMID: 34499432.