Assessing efficacy of cardiac rehabilitation exercise therapy in heart failure patients

Background: Exercise-based cardiac rehabilitation (CR) is considered routine practice for patients following an acute cardiac event or surgical intervention. Although there is a seemingly strong evidence base supporting it for patients with chronic heart failure (CHF), provision in the UK remains poor for this patient group. In addition, data for CHF patients reported in key CR reviews and meta-analyses are not a true representation of the UKs CHF population. The transferability of current evidence into actual practice settings in the UK therefore remains incongruous. Rationale and aims: Study outcomes have typically included an increase in VO2 peak/ VO2 max, a decrease in natriuretic peptides, improved left ventricular function and improved health related quality of life (QoL). Access to facilities and equipment, such as cardiopulmonary exercise testing equipment is limited in the UK for the majority of CR services thus an alternative means of assessment and exercise prescription is required. The recommended alternative for testing CHF patients is the six-minute walk test (6MWT); this requires a given space and a full practice test, the latter which adds to valuable clinical and staff time available. Methods: The first set of studies of this thesis therefore investigated two adapted assessment procedures for use with CHF patients: i. the use of a shorter practice walk test of two minutes vs six minutes prior to a 6MWT and ii. the use of the space saving Chester step test with an adapted lower step height protocol to accommodate the anticipated lower fitness in CHF (4-inch vs 6-inch). Having determined a more practical and efficient means of assessing exercise capacity in CHF patients, this thesis then used the 6MWT to evaluate the efficacy of a typically recommended 12-week programme (for the UK) of exercise-based rehabilitation. It was the aim of this PhD to also combine the use of the Chester step test with cardiopulmonary measures as a corresponding physiological outcome in a sub-sample of participants; however due to resource problems, only validation of the low-step protocol was possible. In the main intervention study, the efficacy of a 12-week course of supervised moderate intensity exercise in CHF patients (ejection fraction <44%, NYHA class II to III) was then evaluated. For purposes of evaluating safety and recovery of any acute myocardial stress induced by exercise in CHF, a sub-group study was performed to evaluate the influence of an acute exercise session on two-day post-exercise levels of circulating NT-proBNP. Results: In this current suite of studies, participants were more representative of the UK CHF population than typically reported in the current evidence. Their profile involved a median age of 76 ± 16 years (mean: 67 years and range: 30 to 84 years). 98% of whom were prescribed beta-blockers, 66% were diagnosed with atrial fibrillation and 98% had two or more co-morbidities. Study 1 (Chapter 3a) verified the efficacy of a two-minute practice walk in comparison to the recommended six-minute practice walk prior to performing a baseline 6MWT in patients with CHF. Study 2 (Chapter 3b) demonstrated that a 4-inch Chester step test is a reliable assessment when space is an issue, but the criterion validity of the actual oxygen costs at each stage compared with those estimated in healthy populations were significantly lower than recommended estimations from healthy populations. Study 3 (Chapter 4) revealed individual variability in the acute response of NT-proBNP release to exercise that is worthy of further study. However the NT-proBNP data overall did not suggest a need for ‘rest days’ between exercise training sessions. The main intervention study (Study 4, Chapter 5) demonstrated a significant improvement in 6MWT performance responses, compared with control, where an increased walking distance of 25 m (p < .0001) was coupled with a reduction in heart-rate-walking speed index (T1 16.3 ± 7.3 vs T2 15.3 ± 8.7 beats per 10 walked; p < .0001). Perceptually, patients were walking faster for the same rating of perceived exertion (RPE 12 to 13). This improved aerobic functioning coincided with an improved NYHA class (T1 2.3 ± .5 vs T2 1.8 ± .6; p < .0001); however there was no change in resting NT-proBNP levels after 12 weeks. Patients in the “control group” who then went on to be offered the same 12-week intervention achieved similar outcomes, but delaying their commencement of an exercise programme by 12 weeks negatively impacted on participation uptake. Key findings and conclusions: These results have demonstrated that exercise training in CHF can lead to an improvement in both physical and perceived functioning (NYHA class). In light of some previous studies showing decreases in BNP following an exercise programme and others like this one showing no change, further questions are raised about the effect of different types and doses of activity being offered to CHF patients and the responsiveness to training of different types of patients (disease severity and demographics). The nature of the cross-over design of this study revealed that delayed commencement of exercise negatively affects participation uptake by patients, which supports current UK standards in aiming for early referral to CR.Buckley, Joh