Taboo in cardiology: renin–angiotensin–aldosterone system antagonists worsening renal failure

The renin–angiotensin–aldosterone system (RAAS) allows normal kidneys to maintain a stable function in every situation of daily life but also intervenes to help when critical situations occur that reduce the filtrate. A typical example is heart failure with reduced ejection function (HFrEF) which inexorably becomes complicated over time with renal failure in what is now commonly defined as cardiorenal syndrome. Renin–angiotensin–aldosterone system antagonists have long been irreplaceable in the treatment of HFrEF due to their beneficial haemodynamic and prognostic effects. However, their use often leads to an acute reduction in the filtrate which often scares the clinician and sometimes leads them to suspend their use. In reality, no guideline has ever clearly indicated when a decline in renal function in a patient taking RAAS antagonists should be acceptable and not lead us to fear the associated acute kidney injury. Usually the nephrologist, called for advice, recommends reducing or suspending the RAAS antagonists, knowing that this will improve the filtration and reassure everyone. But is this the right solution? Are we certain that this choice leads to a better prognosis? This article will try to give a reasonable answer to one of the most frequent doubts that arise in our daily practice.