This study is the first, to our knowledge, to provide a comprehensive evaluation of the feasibility of AIT in CR settings. In this retrospective mixed-method analysis, we found that most patients attended ≥ 70% of the scheduled AIT classes and were able to exercise at the prescribed HI and LO target HR ranges. Interestingly, most patients found the AIT program difficult and classes challenging. Yet, all participants reported that they were satisfied with AIT. Adverse events were rare (0.0012% occurrence) and the majority of patients perceived the classes to be safe. Our sex-based comparisons revealed that more women dropped-out of the AIT program than men. For all other outcomes, there were no significant sex differences. Our findings show that AIT appears to be a feasible and well-tolerated exercise paradigm for patients undergoing CR.
While there have been some investigations demonstrating low attendance with AIT (8,20), most studies have reported high attendance (≥ 70% of the scheduled sessions) with AIT in cardiac patients (7,18,19,21,26). Specifically, Moholdt and colleagues revealed that individuals in an AIT program (4 × 4 minutes at 85–95% HRmax with 3-minute active recoveries at 70% HRmax, two supervised sessions and one home session per week) attended 57% of the CR classes offered across a 12-week intervention (8). Aamot et al. found significantly lower attendance with home exercise AIT (4 × 4 minutes at 85–95% HRmax with 3-minute active recoveries at 70% HRmax, twice a week for 12 weeks) when compared to supervised treadmill or group AIT sessions (p < 0.05) (20). Given our program implemented supervised exercise sessions, this may explain our high attendance rates. Interestingly, most studies have not reported on the compliance to AIT protocols (7,8,19,26). One study by Kim and colleagues reported that cardiac patients spent 86% of their exercise sessions within the target HR ranges with AIT (21). We similarly observed that most patients were able to meet or exceed the prescribed target HR for the HI (80%) and LO (84%) intervals, indicating that cardiac patients were able to comply with AIT. Our qualitative data revealed that some patients found the location (i.e. an inconvenient/long distance) of the classes reduced their attendance. This is consistent with previous findings showing that when CR offerings are not easily accessible or convenient, it may be a barrier to cardiac patient participation (27). Given our high attendance, other community exercise programs may consider implementing AIT for those with CVD.
Practitioners may be hesitant to prescribe AIT in CR as high-intensity exercise acutely increases the risk of myocardial infarctions and sudden cardiac death, particularly in sedentary individuals (28). Interestingly, we found that 27% of individuals exceeded the HI target HR range and very few adverse events occurred (3 out of 2,349 training sessions) with AIT. Our results are consistent with previous work indicating that adverse events are rare with AIT in cardiac patients. A recent systematic review (n = 23 studies) showed that major cardiovascular events were rare when implementing AIT in adults with coronary artery disease and heart failure with only one major cardiovascular event for 17,083 training sessions (14). Vasovagal syncope is more common within a CR setting due to the cardiovascular complications in this patient group (29). In response to the vasovagal episodes, we implemented a step-by-step reduction in the exercise intensity following the HI intervals. This was to ensure patients had a more gradual reduction in HR to avoid future events (29). No further vasovagal syncope episodes were reported. Our study supports previous work showing that AIT is safe in a CR setting (14,15) and the importance of a progressive reduction in HR following an AIT session. Practitioners involved in CR should be reassured that the risk of an adverse event is small in cardiac patients. Our qualitative data showed that supervision during the AIT classes helped patients feel safe and understand their physical abilities with exercise. Cardiac patients may not be aware of the low risk associated with AIT and major cardiovascular events.
There is limited evidence investigating the patient experience with AIT programs. Keteyian and colleagues implemented a similar AIT program in a CR setting and found that patients reported a mean RPE of 15 and 12 for the HI and LO intervals, respectively (26). We observed similar mean reported RPE during the HI (14 ± 1 points, “somewhat hard”) and LO (10 ± 2 points “very light”) intervals. A survey of 1,273 cardiac patients found that a barrier for patients attending CR was perceiving exercise to be tiring or painful (30). The integration of recovery periods in AIT serves to reduce the fatigue and discomfort experienced by patients during exercise. This may explain why patients in our study have a high attendance and satisfaction. To our knowledge, this is the first study to examine cardiac patient perception regarding AIT intensity difficulty; whether the program was challenging and satisfying for patients; and, the perceived patient safety of the program. Despite most patients finding the intensity of AIT difficult and completing the classes challenging, all patients reported that they were satisfied with AIT. Importantly, most patients thought AIT was safe to perform, challenging and increased their confidence in their ability to exercise. A common barrier to participating in CR is low self-efficacy (27). Given the individualized care and feedback that is often received in a supervised exercise program, patients can learn what their physical abilities are when exercising at higher intensities and improve their self-efficacy. Further, the patient’s experience with an exercise program is vital for predicting attendance (31). Our study highlights that AIT is well-received and an appealing exercise offering for cardiac patients which appears to lead to a positive patient experience.
The secondary aim of our study was to determine if there were sex differences in feasibility outcomes. While we did not observe any sex differences for most parameters, we found that significantly more women dropped-out of the AIT program than men. This finding is consistent with a large study in 1,088 women and 4,833 men with coronary artery disease who were enrolled in CR which found women to withdraw from CR more often than men (32). Further, we observed that more men were taking prescribed medications and had undergone an invasive procedure (percutaneous coronary intervention or coronary artery bypass) than women. These findings are unsurprising as men tend to receive more aggressive treatment for CVD than women (33–36). For instance, men receive more cardiac catherizations (15.4% women, 27.3 men, p < 0.001) or coronary artery bypass graft surgeries (5.9% women, 12.7% men, p < 0.001) than women, despite women having greater functional disability with angina than men (35). Given that men are more likely to receive medications and surgical interventions for CVD, they may be more informed about their medical condition and understand the importance of attending CR. This may leave women with a lack of knowledge regarding the severity and management of CVD (37), which may influence their participation in CR programs. Our study reinforces the findings of previous work showing that there is a need to understand how to attract and improve the retention of women in CR.
There are limitations that warrant mention. While this is the first study examining the feasibility of AIT in cardiac patients, a retrospective mixed-methods analysis limits the ability to inform study design. For instance, we do not have the data to examine if patients complied to the duration of the HI and LO intervals. This was also a single centre trial, which may limit the generalizability of our results across other CR settings. Other aspects of the patient’s experience should be explored such as patient confidence and self-efficacy to more thoroughly examine if AIT is feasible for this patient group. Similar to previous work (8,18–20,22,26), significantly more men participated in this study than women; the results from our sex analysis should, therefore, be interpreted with caution. Knowing the feasibility of an exercise provides valuable insight for practitioners who may wish to offer AIT for their cardiac patients but are unsure of the possible challenges with instructing AIT in this population.