*3.1. Tachycardiomyopathy Recurrences*

Out of the 17 patients experiencing recurrences, seven had multiple recurrences, with six patients experiencing two recurrences and one experiencing four. The arrhythmic disorder underlying TCM recurrences was AF in 15 cases (88%) and atrial flutter in two cases (12%).

The majority of recurrences occurred between the fifth and the sixth year after the first diagnosis as seen in Figure 2.

**Figure 2.** Time free from tachycardiomyopathy recurrence according to the Kaplan-Meier curves.s.

The multivariate Cox regression analysis showed that presence of obstructive sleep apnoea syndrome (OSAS), BNP on admission and the heart rate at discharge were all independent predictors of TCM recurrence (Table 3).

**Table 3.** Multivariable Cox-proportional hazard model for tachycardiomyopathy recurrence.


The univariate model included: The male gender, age, body mass index, hypertension, diabetes, dyslipidaemia, chronic kidney disease, chronic obstructive pulmonary disease, OSAS, hyperthyroidism, hypothyroidism, type of arrhythmia, NYHA class on admission and at discharge, heart rate on admission and at discharge, BNP on admission and at discharge, Troponin I on admission and at discharge, LVEF on admission and at discharge, iLAV, rate or rhythm control (dummy variable) and pharmacological treatment at discharge (with each drug class from Table 2 considered as a separate variable). The complete model is detailed in Table S2.

BNP: brain natriuretic peptide; CI: confidence interval; iLAV: indexed left atrial volume; LVEF: left ventricular ejection fraction; NYHA: New York Heart Association; OSAS: obstructive sleep apnoea.

According to the spline curves, the heart rate at discharge and the risk or TCM recurrence had a linear association (Figure S1a,b, s*p* for linearity < 0.001). The mean values for both the heart rate and LVEF throughout the index event, the follow-up and at the time of recurrence are shown in Figure 3a,b. Consistently with other statistical models, the heart rate at discharge and during follow-up is significantly higher in patients experiencing a recurrence when compared with the patients with no recurrence. Furthermore, all patients showed a LVEF ≥50% at a 1-year follow-up.

**Figure 3.** The mean values of the heart rate (**a**) and let ventricular ejection fraction (**b**) during follow-up, according to the presence or absence of future recurrences.

Comparing TIS for each drug class considered in Table 2 showed no differences between patients with and without recurrences (all *p* > 0.05).

From the 17 patients experiencing recurrences, 13 were under a rhythm-control strategy and four were under a rate-control strategy. Twelve patients underwent catheter ablation of AF and two underwent ablation of atrial flutter. The patients undergoing catheter ablation of atrial flutter experienced no further TCM recurrences, while five patients presented a second TCM recurrence after the procedure. Three patients with AF refused consent to catheter ablation and were therefore shifted to a rate-control strategy, with one patient experiencing no further recurrences, one experiencing a second recurrence and another patient experiencing three more recurrences over the follow-up.
