Lose your heart to NephMadness 2022! Dr. Joel Topf (@kidney_boy) and Dr. Sadiya Khan (@HeartDocSadiya) tackle the NephMadness 2022 Cardiorenal Syndrome region, leading us through the pathophysiology of cardiorenal syndrome, how to approach the creatinine “bump” with diuresis, managing patients with diuretic resistance, and more. This episode is part of our first ever NephMadness Pod Crawl, so check out the other podcasts, and fill out your NephMadness 2022 brackets!
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Definition of cardiorenal syndrome: Cardiorenal syndrome describes the bi-directional interactions between the heart and the kidneys. It encompasses both the effects that impaired heart function can have on renal function, as well as the impact of renal injury or chronic kidney disease on cardiac function (Rangaswami 2019).
Cardiorenal syndrome classification schemes: The five categories of cardiorenal syndrome first introduced by Ronco 2010 are:
These classification schemes can be a helpful framework for thinking about what is happening. However, according to Dr. Topf, the vast majority of cases seen in the hospital will fall into the bucket of type 1 cardiorenal syndrome.
Pathophysiology of cardiorenal syndrome: Classically, the pathophysiology of cardiorenal syndrome was thought of as decreasing cardiac index leading to poor forward flow and subsequent reduced kidney perfusion/kidney dysfunction. However, in recent years, it has become apparent that reduced cardiac index/forward flow is not the primary driver of kidney dysfunction (Hanberg 2016). In fact, most patients coming in with decompensated heart failure, even those with reduced ejection fraction, have preserved cardiac indices.
Instead, it has become increasingly recognized that elevated venous pressure/ venous congestion plays a critical role in the pathophysiology of cardiorenal syndrome (Rangaswami 2019; Mullens 2020). Perfusion of any organ depends on the difference in pressure between the arterial and venous sides. While for many years it was thought that decreased arterial pressure was the culprit in causing kidney dysfunction in acute decompensated heart failure, it turns out that increased back pressure on the venous side leading to impaired kidney perfusion appears to be much more important (Mullens 2009; Damman, 2009). According to Dr. Topf, this pathophysiology directly points to the therapeutic solution: If venous congestion is the problem, then drugs to reverse this congestion are the answer. Thus, we should not shy away from using diuretics in patients with acute decompensated heart failure presenting with an elevated creatinine – in fact, decongestion will likely directly address the underlying pathophysiology of their renal dysfunction.
Of course, if a patient is frankly hypotensive, the story is different, and poor forward flow may also contribute to renal dysfunction (Mullens 2020). In this case, use of inotropes and other measures will come into play, according to our guests.
Use of home ACE-is/ARBs and SGLT-2 inhibitors in patients presenting with acute heart failure and elevated Cr: In a patient presenting with acute decompensated heart failure and an elevated creatinine, there is a knee-jerk reaction to stop their home ACE-is/ARBs and SGLT-2 inhibitors. However, Dr. Topf argues that if they are not hypotensive or hyperkalemic, then there may not be any need to stop their ACE-is/ARBs and SGLT-2 inhibitors. If these medications are stopped during the hospitalization, our guests stressed that it is critically important to make sure that they are re-started prior to discharge, so that these important medications don’t fall off following a hospital stay as too often happens in practice.
Very commonly, a bump in creatinine will be observed with diuresis for acute decompensated heart failure, which can prompt fear of continuing to diurese, even if a patient still appears volume up. However, Dr. Topf and Dr. Khan both stress that a creatinine increase with diuresis does not necessarily signify kidney injury (Ahmad 2018; NephMadness blog post). In fact, our guests note that increased blood volume in the setting of volume overload can often dilute the creatinine to a certain degree, and thus decreasing the blood volume with diuresis will concentrate the creatinine and result in an increased creatinine lab value (akin to hemoconcentration, i.e. concentration of red blood cells, that is also seen with volume contraction). Thus, hemodynamic changes in creatinine with diuresis most often don’t actually represent intrinsic, permanent damage to the kidney.
Indeed, in a post-hoc analysis of the DOSE trial, a rise in creatinine during admission for decongestion for acute decompensated heart failure was actually associated with improved outcomes (primary endpoint of death or rehospitalization / ER visit within 60 days) (Brisco 2016). According to Dr. Khan, this is likely because these patients were better diuresed. Dr. Khan notes that one of the most important markers of how well a patient admitted for decompensated heart failure will do when they leave the hospital is how dry they were when they left (Rubio-Gracia 2018). Thus, our guests emphasized that if a patient is still volume overloaded, it is important to continue to diurese even if their creatinine starts to rise – a concept known as “permissive hypercreatininemia” (NephMadness blog post).
Of course, the frequent ambiguity of the volume exam is one of the major challenges in deciding whether to push forward with diuresis and one of the reasons for the temptation to use a creatinine bump as an indication to stop diuresing. Dr. Khan notes that the volume exam can be especially tricky given that many patients don’t have significant right-sided heart failure, so they won’t present with marked lower extremity edema or a significantly elevated JVP. She says that it may be beneficial to turn more often to invasive hemodynamics (i.e. a right heart cath) to directly measure pulmonary artery pressure. The growing use of implantable pulmonary artery pressure monitoring devices will be very useful in this regard. Additionally, the use of POCUS to non-invasively evaluate the JVP or lungs can also help with clarifying volume status in combination with the history and exam (Beaubien-Souligny 2020).
Cardiac biomarkers such as troponin and BNP are difficult to interpret in patients with chronic kidney disease, as they are often chronically elevated in this population (NephMadness blog post; Bansal 2022). Yet these biomarkers are not completely uninformative in the setting of CKD. First of all, Dr. Khan stresses that while the absolute BNP may be difficult to interpret, the relative change in BNP from baseline in an individual with CKD is still valuable, as it can help point towards development of volume overload. Additionally, chronic elevation of cardiac biomarkers in many patients with CKD is not simply due to reduced clearance of these markers by the kidney. It turns out that prognostically, patients with CKD and elevated cardiac biomarkers have worse outcomes than those with normal cardiac biomarker levels (Michos 2014; Bansal 2019; Lamprea-Montealegre 2019; Wang 2020). Our guests emphasized that while a chronically elevated troponin in patients with CKD is usually not indicative of epicardial coronary disease (i.e. atherosclerotic coronary blockage), it does indicate that the patient has cardiac disease resulting in loss of cardiac muscle, most likely due to microvascular disease/endothelial dysfunction, which can lead poor cardiac outcomes down the road.
Definition of diuretic resistance: Inability to achieve euvolemia despite being on a maximally tolerated dose of a diuretic (NephMadness blog post).
Maximizing Loop Diuretic Efficacy: Dr. Topf and Dr. Khan shared several tricks to optimizing use of loop diuretics in the setting of diuretic resistance:
Sequential nephron blockade – layering on other diuretics: One of the major drivers of diuretic resistance is compensatory sodium reabsorption at sites distal to where loop diuretics act (NephMadness blog post; Rao 2017). A key strategy in managing patients with diuretic resistance is sequential nephron blockade, or blocking other “ports of re-entry” through which the kidney can try to reabsorb sodium. This can be done by layering on agents from different diuretic classes (NephMadness blog post.)
Hyperdiuresis: Hyperdiuresis refers to the seemingly paradoxical strategy that has emerged in recent years of giving patients a small bolus of hypertonic saline with a loop diuretic (NephMadness blog post; Paterna 2011; Griffin 2020). According to Dr. Topf, this strategy may work by several possible mechanisms, including suppressing RAAS signaling to prevent sodium retention and drawing in interstitial fluid to the vascular compartment by osmosis (NephMadness blog post). This strategy should be used with caution and typically as a last resort. (Call to MedTwitter – has anyone used this strategy?)
Listeners will develop an approach to evaluating and managing patients with cardiorenal syndrome, treating patients with diuretic resistance, and interpreting cardiac biomarkers in CKD.
After listening to this episode listeners will…
Dr. Topf has commercial interests with Bayer and AstraZeneca. Dr. Khan reports no relevant disclosures. The Curbsiders report no relevant financial disclosures.
Gandhi MM, Khan S, Topf J, Williams PN, Watto MF. #326 NephMadness 2022: Cardiorenal Syndrome.” The Curbsiders Internal Medicine Podcast. http://thecurbsiders.com/episode-list March 14, 2022.
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