*Limitationss*

This paper shares all the limitations characterizing all prospective observational studies. In addition, this study's population was relatively small, and the low sample size made subgroup analyses unfeasible. Nonetheless, current available literature relies on case series and, to our knowledge, this is the largest dataset on pure TCM taken into account so far.

The cut-off used to define pure TCM (improvement of at least one NYHA class and > 5% EF) could seem rather small, but unfortunately, there is no consensus on any cut-off for TCM. Although surely arbitrary, the authors chose this cut-off because it was thought that, after ruling out all causes of structural heart disease, a patient undergoing a clinical and echographic improvement could be considered as having TCM, being the arrhythmia the only remaining and plausible cause of his/her condition. A higher cut-off, as the one proposed by Jeong and colleagues [13], could have ruled out many TCM that just had not time to recover completely because of arrhythmic recurrence, without offering alternative explanations behind the first decompensation. Moreover, according to Table 3, all the patients reached a LVEF of 50% or more after one year, making the authors quite confident that the population was correctly selected.

Furthermore, HF treatment could be considered as a potential confounder in the association between the heart rate and EF improvement/worsening. However, the heart rate was a predictor of the recurrence independently of any kind of pharmacological treatment at discharge (Table 3). As the criteria for TCM recurrence are the same as for the first event, it can be hypothesized that, in the patients, the heart rate is what matters and the association with LVEF worsening could be considered as independent of HF treatment. Of course, subsequent modification or intensification of the HF therapy over time could have modified the strength of such an association, but there is no means to assess that as it would be a daunting task to properly include all treatment changes in the statistical models.

#### **5. Conclusions**

In conclusion, TCM is an under-diagnosed entity, affecting nearly one out of ten patients admitted for HF. Pure TCM (i.e., without underlying structural heart disease) is associated with a good long-term survival. Nonetheless, recurrences are frequent and can occur after many years. The treatment aimed at reversing OSAS and lowering the heart rate after the acute event could prevent these recurrences and their related hospitalizations.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2077-0383/8/9/1411/s1, Figure S1a: splines curve detailing the association between heart rate at discharge and the risk or TCM, Figure S1b: splines curve detailing the association between BNP on admission and the risk or TCM, Figure S1c: splines curve detailing the association between heart rate at discharge and the risk of cardiovascular hospitalization, Figure S1d: splines curve detailing the association between LVEF at discharge and the risk of cardiovascular hospitalization, Table S1: STROBE Statement—checklist of items that should be included in reports of observational studies, Table S2: univariable and multivariable Cox-proportional hazard model for tachycardiomyopathy recurrence, Table S3: univariable and multivariable Cox-proportional hazard model for cardiovascular hospitalization.

**Author Contributions:** Conceptualization, G.S. and F.G.; methodology, G.S. and F.G.; formal analysis, G.S. and F.G.; investigation, G.S., F.G., G.C., and A.U.; data curation, G.S., F.G. and L.C.; writing—original draft preparation, G.S. and F.G.; writing—review & editing, all; supervision, A.C.; funding acquisition, F.G.

**Funding:** This research was funded by Marche Polytechnic University (FFARB 2017).

**Acknowledgments:** The authors would like to thank Mary Elizabeth Orme for the linguistic support and editing assistance.

**Conflicts of Interest:** The authors declare no conflict of interest.
