The present observational retrospective study suggest that RH represents a predictive risk factor for composite outcome in patients with CRM. It is well known that RH is significantly associated with increased major cardiovascular events [12], end stage renal disease and all-cause mortality and represents a recognized burden for economical/health system [13, 14].

Of note, in the cohort studied, the prevalence of RH was 52.5%, thus higher than described in the overall hypertensive population [1]. The higher prevalence observed in the present study could be partially explained by the underlying disease burden that can be caused or complicated by hypertension in hospitalized patients, such as CKD and HF.

The prevalence of RH in patients affected by CKD ranges from 15.8 to 33.4%, according to the CKD stage [15], with an average value of 22.9% [3] and up to 48.3% when patients with RH were classified according to the albumin-creatinine ratio [16]. In patients with HF and CAD the prevalence ranges from 13.7 to 21.8%, respectively [17, 18].

Literature data suggest that, in general population, individuals with RH are at greater risk for renal failure in addition to cardiovascular events [14]. The relationship between heart and kidney is critical for maintaining physiological hemodynamic and perfusion homeostasis, but the crosstalk becomes a double-edged sword in pathological conditions in which dysfunction of one organ promotes functional and/or structural alteration of the other [19]. According to this synergistic interaction, both CKD and HF share same pathophysiological mechanisms, such as sodium and water retention with consequent volume overload, vascular dysfunction, increased activity of the renin-angiotensin-aldosterone and sympathetic nervous systems [20]. Considering these shared pathophysiological mechanisms and the use of the same pharmacological strategies, among which antihypertensive drugs and diuretics, a higher RH prevalence in our study with respect to literature is not surprising [2, 3, 5,6,7].

Although the analysis of our data did not show an association between in-hospital mortality or LOS and RH, we observed a statistically significant association between RH and the composite outcome of morbidity and mortality. Also, we described a significantly higher free survival in patients without RH, than patients with RH.

The worst prognosis of RH patients with respect to non-RH patients is documented in previous studies and explained by structural and functional cardiac and renal changes, such as left ventricular hypertrophy, increased aortic stiffness, atherosclerotic plaques and microvascular disease. These changes, moreover, promote and further worsen hypertension creating a self-sustaining mechanism [21]. Of interest, in the present study we highlighted for the first time an association between f RH and worse prognosis, specifically in a cohort of in-patients affected by CRM. These data suggest that RH patients deserve more clinical attention and early therapeutic optimization in specialized centers, to improve clinical outcomes and quoad vitam prognosis.

In the last decade, the importance of adequately recognizing and early treating of RH patients conferred more interest on the research of innovative device-based therapies such as renal denervation (RDN) [1, 22]. The RDN represents an alternative treatment, in patients with an eGFR >40 ml/min/1.73 m2, able to modulate the overactive pathway between the kidneys and the central nervous system, mainly responsible for the trigger in RH [23, 24].

However, there is still no clear position on RDN recommendation and it is obviously not free from procedural risks. Furthermore, a significant reduction in cardiovascular events over long-term follow-up after RDN is not studied yet [21, 23,24,25].

Finally, it should be remembered that the modification of lifestyle always represents the first line intervention for the hypertension management. Data suggest that a physical exercise program, besides the medical therapy alone, is effective at lowering the ambulatory BP (till a reduction of at least 5 mmHg) [26].