Limitations
heart disease
RECRUITMENT, HEART DISEASE
This study had some limitations:Group 1 had, in the pre-intervention phase, higher age, worse quality of life, and higher rMSSD than Group 2, which may impair the analysis after the intervention. We attributed this finding to the small sample size, but the results showed that such discrepancies did not influence the final findings.The COVID-19 pandemic was an obstacle to carrying out this study. The concern of patients for having heart disease and the risk of contagion is highlighted. Such obstacles were overcome by changing the environment and informing that protective measures would be provided, although this did not affect the data analysis.Another limitation brought about by the pandemic was the economic crisis, making it difficult to mobilize to carry out treatment and serial examinations. We provide tickets, food allowance, and fundamental clarification on the importance of treatment.We did not measure biomarkers in this study as, until the time of recruitment, we did not have a laboratory with such resources available in our region. However, the original idea was to generate a hypothesis for outpatient treatment, which was done.An important limitation stems from the short term of the study. Most studies of vagal stimulation have shown a more noticeable result after a longer stimulation period, whereas the treatment period in this study was only 1 month. As the results were still promising, new studies are expected to clarify the minimum and ideal time soon to obtain a reasonable effect of vagal modulation in HF.Another limiting factor was the NYHA functional class of the patients, most were class I (27.9%) or II (39.5%), and therefore the objective of evaluating the improvement in functional class in these patients lost its meaning. New studies involving the use of taVNS in the treatment of HF should exclude NYHA class I since the desired clinical benefit has already been achieved in these patients.