Cardiac Medications Can Influence the Exercise Prescription in Chagas Heart Disease

2. Sousa L, Rocha MO, Britto RR, Lombardi F, Ribeiro AL. Chagas disease alters the relationship between heart rate variability and daily physical activity. Int J Cardiol. 2009;135(2):257-9. 3. Lima MM, Rocha MO, Nunes MC, Sousa L, Costa HS, Alencar MC, et al. A randomized trial of the effects of exercise training in Chagas cardiomyopathy. Eur J Heart Fail. 2010;12(8):866-73. References DOI: 10.5935/abc.20150054 Dear Editor, The study by Nascimento et al.1 provides information on the effects of physical training and the Heart Rate Variability (HRV) in patients with Chagasic heart disease. Changes in HRV were not observed after exercise intervention, but the intervention group showed improved functional capacity after 12 weeks of the study. Changes in the autonomic nervous system are observed in Chagasic heart disease and although physical training can improve HRV in other forms of heart failure, evidence suggests it does not happen in Chagasic heart disease2, corroborating findings by Nascimento et al1. However, in addition to the relatively few studies on the subject, which limits further conclusions, questions related to exercise prescription in the present study need to be better clarified. Although the protocol was established through a previous publication of a randomized clinical trial on the subject3, the lack of description on drug use by the study subjects such as beta blockers, which can have an effect on chronotropism, reducing the heart rate, might have altered the study outcome. Therefore, formulas that estimate the intensity of training, such as the one used in the aforementioned study, become limited in the presence of drugs with chronotropic interaction.