There were significant differences in the patient population between the quality categories for delivery of CR services. Previous research that examined the quality of delivery of CR programmes in the UK identified three distinct categories and proportions—low (30.6%), middle (45.9%), and high (18.2%) of CR quality . We investigated whether the three quality categories differed with regard to the populations being treated within them. A CR programme was more likely to be categorised as high quality if it included patients with a higher mean total of comorbidities, including diabetes, stroke, and asthma in addition to high BMI.
According to our findings, high-quality programmes recruit more patients with multiple comorbidities, who are more representative of the broader CVD population than those with few comorbidities. The presence of multiple comorbidities including stroke, diabetes, chronic obstructive pulmonary disease is an important factor associated with a lower likelihood of a patient being referred to and participating in CR [23,24,25,26], and the authors of a systematic review warned that CR programmes need to pay greater attention to recruitment of patients with multiple morbidities . However, patients with multiple morbidities represent populations at significantly increased cardiovascular risk who may benefit from the services provided in CR [23,24,25,26].
For one additional comorbidity, the odds of being in the high-quality service increases by a factor of 2.13 as opposed to low quality and by a factor of 1.85 as opposed to middle quality, which indicates that high-quality CR programmes take on more complicated cases and potentially higher risk patients than low or middle-quality programmes. The presence of multiple comorbidities is an important factor associated with lower odds of referral to, participation in, and uptake of CR [23,24,25,26]. The high-quality CR programmes included more patients with the most dominant morbidities associated with CVD according to the NACR — hypertension, hypercholesterolaemia or dislipidaemia, diabetes, angina, combination of respiratory conditions (chronic bronchitis, emphysema, and asthma), arthritis, chronic back problems, cancer, stroke,—at entry to CR than the low-quality programmes.
For each unit increase in the BMI, the odds of being in the high-quality category increases by a factor of 1.49 as opposed to low quality. Obesity is an independent risk factor for the development of CVD  and higher BMI was associated with shorter longevity and significantly increased risk of cardiovascular morbidity and mortality compared with normal BMI . At entry into CR, more than 80% of patients are overweight and 30% have BMI > 30 kg/m2 [10, 29]. Cardiac rehabilitation programmes do not generally include weight-loss components , but CR programmes with high-quality delivery recruit more patients with CVD and higher BMI than those with low-quality delivery.
For each percent increase in the proportion of patients with diabetes comorbidity, the odds of being in the high-quality category increases by a factor of 1.10 as opposed to low quality. Despite the fact that CVD is the most prevalent cause of mortality and morbidity in diabetic populations  and in addition to the fact that patients with diabetes had more CVD risk factors and lower physical capacity than patients without diabetes at the beginning of CR [30, 31], the findings show that high-quality programmes recruit more patients with CVD and diabetes than low-quality programmes. Previous studies have examined the benefit of CR in diabetes [32, 33]. Cardiac rehabilitation patients with diabetes comorbidity emphasizes the need to target diabetic patients in CR programs for an aggressive program of risk factor management . The prevalence of diabetic patients in CR programs appears to be increasing, and is likely to continue to rise as the current trends indicating increase of prevalence of diabetes . Diabetic patients are more depressed following CVD and have lower scores for functional status, well-being, and total quality of life than non-diabetic patients . Cardiac rehabilitation in diabetic patients results in marked reduction in depression to a prevalence rate identical to non- diabetic patients in addition to improvements in exercise capacity and total quality of life following CR .
For each percent increase in the proportion of patients with asthma comorbidity, the odds of being in the high-quality category increases by a factor of 1.19 as opposed to middle quality. The findings show that high-quality programmes recruit more patients with CVD and asthma than low- and middle- quality programmes. Asthma is one of the global morbidity and is the most common chronic respiratory diseases worldwide and it was prospectively associated with increased risk of major CVD [35, 36]. Recent meta-analysis results indicate that asthma was associated with an increased risk of CVD and all-cause mortality in cohort studies . Large cohort studies provide more evidence that asthmatics have a higher CVD event rates and an increased risk of death than non-asthmatics [38, 39]. Comorbidity asthma was associated with a decreased likelihood of CR attendance among cardiac patients .
The results of the analysis of social deprivation showed no statistically significant difference in social deprivation among quality categories, high-quality programmes tended to recruit more socially deprived patients than low- and middle-quality programmes. Previous studies suggested that socioeconomic deprivation is associated with lower participation in CR, as non-participants tend to be more socially deprived [41,42,43]. A systematic review showed that patients with greater deprivation are less likely to attend CR programmes but may have the most to gain from CR because of a linear relation between socioeconomic status and cardiac outcomes .
Patients who participated in high-quality CR programmes tended to be those with high-risk status, high BMI score, high waist circumference, and high blood pressure, high HADS anxiety and depression score, smokers; to have more comorbidities; and to be in more socially deprived groups than patients in the low-quality programmes. In addition, high-quality CR programmes also take on patients with lower fitness levels than low-quality programmes. Such patients often have more severe functional impairment and are most in need of CR, as well as being most likely to benefit .
Ensuring equity of access to CR and improving the consistency of delivery should increase long-term behaviour changes and contribute to a reduction in CVD-related health inequality . The data analysis shows that there are significant differences between low-, middle and high quality of CR programme in staffing or number of qualified multidisciplinary team (MDT) as a surrogate for well-resourced programmes. 63% of CR programmes in the low-quality programmes comprise of at least three different professions in the CR team while 73.7 and 85.4% of middle and high quality programmes delivered by MDT (3+) respectively.
Although the BACPR recommends staffing to be multi-disciplinary , some CR programmes have varying staffing and less physical resource (equipment and location space) which can impact on patient recruitment. In addition, around 20% of CR programmes don’t carry out formal assessment at baseline which again may influence the type of patients they receive . Patient choice is a reality in the UK where patients can ask to be referred to a CR programme not associated with their local hospital.
This is the only UK-specific study to ascertain whether the variation in quality of CR delivery is, in-part, determined by the patient characteristics, while also addressing whether these differences are associated with better quality delivery. This study accounted for the range of patients within programmes in terms of demographic characteristics, cardiovascular risk factors, comorbidities, and physical and psychosocial health measures collected by the NACR. Evaluation and dissemination of information about the populations served by CR programmes may help low-quality programmes to be more inclusive.
Strengths and limitations of this study
The use of an observational approach based on voluntary and routinely collected patient data is a strength in respect of real-world representation. According to the 2017 NACR report , only 224 of the 303 CR programmes in the UK entered data electronically to the NACR. It can be argued that this provided enough data to be representative and to carry out a reliable analysis, but future studies should aim to achieve greater capture of available patient records across the UK.