Prescribing safe, and effective, exercise programs is critical to improving functional capacity in cardiovascular disease (CVD) patients. "Functional capacity" refers to maximal oxygen consumption (VO2max), or aerobic fitness, and is a measure of the hearts ability to deliver oxygen to tissue, and proficiency of the tissue to extract oxygen. It is commonly reported in metabolic equivalents (METs) where 1 MET is considered "at rest". Research suggests that a 1 MET improvement in functional capacity, after participation in a prescribed exercise program, confers a 17–30% decrease in all-cause mortality.
It is recommended that CVD patients perform a symptom limited graded exercise test (GXT) prior to beginning their cardiac rehabilitation program. The GXT provides accurate hemodynamic information that clinical exercise physiologists use to build patient specific exercise prescriptions.
Despite this approach being the gold standard for exercise programming, in a recent survey study among clinics in the United States, it was reported that only 33% of clinics conduct baseline GXTs (1). Possible reasons for not performing baseline GXT include, lack of reimbursement, patient safety concerns, inadequate equipment, and overall feasibility concerns.
The absence of maximal baseline exercise testing raises an important discussion regarding exercise prescription techniques for CVD patients. In particular, how do clinicians appropriately prescribe exercise to maximize improvements in functional capacity, but also maintain patient safety? Unfortunately, limited guidance is available for clinicians in this situation.
ONE EXAMPLE: Hypertrophic Cardiomyopathy
For individuals diagnosed with CVD, such as hypertrophic cardiomyopathy (HCM), whether (and how much) exercise is a question that may have significant impact on quality of life. How exercise may impact progression of disease in HCM is currently debated. Isometric exercise induces physiological hypertrophy, which intuitively may seem deleterious in HCM. However, isotonic exercise induces cavity dilation which could be favorable in the HCM population.
Understanding how to increase activity in the sedentary HCM population may be a more important question. A recent survey compared HCM patients with NHANES participants (National Health and Nutrition Examination Survey), finding that the patients with HCM reported less time engaged in physical activity at work and for leisure, as well as higher body mass index. An Australian study similarly found that a majority of HCM patients did not meet physical activity recommendations. In that study, many participants reported that they had been advised not to exercise at all.
In a small pilot study, Klempfner et al. investigated the benefits and feasibility of increasing exercise in 20 symptomatic patients with HCM who were significantly limited in their everyday activity. Patients exercised in a cardiac rehabilitation center twice a week, using treadmill, arm ergometer, and upright cycle exercise, with exercise prescription based on heart rate reserve determined from a symptom limited graded exercise stress test. The result found that functional capacity, assessed by a graded exercise test, improved significantly. During the study period and the following 12 months, none of the patients experienced clinical deterioration or significant adverse events.
This study suggests that moderate exercise may be beneficial in decreasing symptom burden. These benefits could be related to the fact that exercise improves diastolic and endothelial function. It is also noteworthy that the study included high-risk patients; more than 30% had ICDs, and 4% had a history of sustained VT or cardiac arrest. No patient with HCM experienced a major adverse cardiovascular event during the study period.
exercise is medicine
The chronic effects of exercise training have been shown to be cardioprotective in humans with a variety of cardiac diseases. Increased parasympathetic tone, reduced sympathetic tone, and improved myocardial function (compared to sedentary state) result in a substantially lower risk of life-threatening arrhythmias, when compared to sedentary individuals.
Although high-intensity exercise is believed to induce fatal arrhythmias in predisposed individuals, studies show that exercise-related sudden cardiac death (SCD), and sustained ventricular arrhythmias, are rare in HCM; and most ventricular arrhythmias occur at rest (or during sedentary or light activities). In a study of 1,380 patients with HCM who underwent an exercise test, ventricular arrhythmias during the test were uncommon occurring only in 2% of patients. Of note, no implanted cardiodefibrillator (ICD) discharges were recorded in association with exercise.
A recent study found that more than 50% of patients with HCM did not meet minimum exercise recommendations aimed at the general public (4). This reluctance to exercise may stem from anxiety around the proposed effects of exercise on disease progression and SCD.
Vigorous Exercise Not Associated With Increased Risk of Cardiac Events in Patients With HCM
For most patients with HCM, mild-to-moderate-intensity recreational exercise is beneficial to improve cardiorespiratory fitness, physical functioning, quality of life, and for overall improved health in keeping with physical activity guidelines for the general population. Recreational exercise, of mild-to-moderate intensity, has not been associated with increased risk of ventricular arrhythmias in recent studies. This has led to a new recommendation for mild-to-moderate exercise in most HCM patients, highlighting the beneficial effects of exercise. Every 6% increase in peak Vo2 was associated with an 8% lower risk for cardiovascular mortality. As the only nonsurgical intervention proven to improve exercise capacity in patients with HCM to date, these results support the implementation of moderate-intensity exercise as part of routine clinical care.
Current guidelines
HCM patients are most likely to benefit from regular aerobic exercise, by which most body muscles move in a cyclic manner to allow human locomotion (walking, brisk walking, running, or cycling). Aerobic cardiovascular exercise targeting approximately 60% of heart rate reserve, and sub-maximal weight training with low-weight and high reps (>10), may be reasonably suggested to patients with HCM, while the evidence is awaited to tailor more specific exercise prescriptions.
Exercise initiated at a minimum of 3 sessions per week, 20 minutes per session, at a heart rate corresponding to 60% of heart rate reserve (resting heart rate +0.6 [maximal heart rate minus resting heart rate]) is indicated.
A rating of perceived exertion should be correlated with a moderate level of intensity. The exercise prescription should increase in duration by 5 to 10 minutes every week, up to 60 minutes per session, 4 to 7 sessions per week, and then incrementally increase training intensity to a goal of 70% of heart rate reserve.
Please note: HCM patients can exhibit certain disease-specific features that constitute contraindications to physical activity, including a history of syncope/hypotension during effort, clinically relevant arrhythmias (particularly during effort), LV outflow tract obstruction ≥50 mm Hg at rest or during effort, and recent history of acute heart failure.
When properly administered, exercise is the ideal drug for prevention of comorbidities and promotion of personal well-being. In adults with a recent diagnosis of genetic cardiomyopathies, an event which often undermines confidence and precipitates psychological frailty, exercise is the ultimate resource to counter these effects. The specific level of activity for patients with HCM remains an active question. It is certain, however, that sitting on the couch is the wrong exercise prescription.
*You should consult with your healthcare provider before engaging in any exercise program
References
1. O’Neil S., Thomas A., Pettit-Mee R., Pelletier K., Moore M., Thompson J., Barton C., Nelson R., Zuhl M. Exercise Prescription Techniques in Cardiac Rehabilitation Centers in Midwest States. J. Clin. Physiol. 2018;7:8–14. doi: 10.31189/2165-6193-7.1.8
2. Reineck E, Rolston B, Bragg-Gresham JL, et al. Physical activity and other health behaviors in adults with hypertrophic cardiomyopathy. Am J Cardiol 2013;111:1034-9.
3. Klempfner R, Kamerman T, Schwammenthal E, et al. Efficacy of exercise training in symptomatic patients with hypertrophic cardiomyopathy: results of a structured exercise training program in a cardiac rehabilitation center. Eur J Prev Cardiol 2015;22:13-9.
4. Sweeting J, Ingles J, Timperio A, Patterson J, Ball K, Semsarian C . Physical activity in hypertrophic cardiomyopathy: prevalence of inactivity and perceived barriers. Open Heart 3: e000484, 2016. doi:10.1136/openhrt-2016-000484.
5. Luna Cavigli, Iacopo Olivotto, Francesco Fattirolli, Nicola Mochi, Silvia Favilli, Sergio Mondillo, Marco Bonifazi, Flavio D’Ascenzi, Prescribing, dosing and titrating exercise in patients with hypertrophic cardiomyopathy for prevention of comorbidities: Ready for prime time, European Journal of Preventive Cardiology, Volume 28, Issue 10, October 2021, Pages 1093–1099, https://doi.org/10.1177/2047487320928654