We wish to thank Dr. Dominguez-Rodriguez and Dr. Abreu-Gonzalez for their interest and comments regarding our publication.

Cardiopulmonary exercise testing is a functional test of indisputable value in patients with cardiac resynchronization therapy (CRT) devices since, in addition to enabling objective evaluation of the functional response to treatment, it also provides prognostic information, an input that eventually could have therapeutic implications. Treadmill exercise testing is far more limited in the functional and prognostic assessment of patients with CRT devices and, in this respect, we are in complete agreement.

However, the objective of our study was not to carry out a strictly functional assessment, much less a prognostic evaluation, of patients receiving CRT. This study was prospectively designed to determine the number of patients who experienced a loss of pacing capture during exercise, analyze the causes, and attempt to correct them, because nearly constant pacing is considered to be essential for achieving a response to therapy.1–3

The results obtained indicate that pacing capture was lost during exercise in 24% of the patients, which led to a process of clinical decision making to correct it. Thus, we concluded that treadmill exercise testing is a simple, accessible, and useful tool for follow-up of patients with CRT, and helps to guide clinical decisions related to drug therapy, device programing, and indications for atrioventricular node ablation.4

Given the small sample size, it is not possible to conclude from our report that exercise testing should be systematically employed in all the patients receiving CRT. However, we firmly believe that it can be highly useful in the assessment of certain patients, such as nonresponders or those who have atrial arrhythmias as the baseline rhythm.