Cardiorenal Syndrome

Etiology

There are five subtypes of cardiorenal syndrome:

• Type 1: a sharp decline in cardiac function that results in an acute decrease in renal function
• Type 2: chronic cardiac dysfunction that results in a sustained reduction in renal function
• Type 3: a sharp decline in renal function that results in an acute reduction in cardiac function
• Type 4: a chronic decline in kidney function that results in chronic cardiac dysfunction
• Type 5: systemic diseases that result in both cardiac and renal dysfunction

Each type has its unique pathophysiology with unique management strategies and varying prognoses.[2][3] Cardiorenal syndrome type 1 is the most common and most analyzed type. 

Epidemiology

The 2007 report on the 118465 patients admitted with acutely decompensated heart failure in the ADHERE database showed that 9.0% of patients had normal renal function on admission whereas 27.4% had mild renal dysfunction (defined as GFR 60 to 89 mL-min-1.73 m), 43.5% had moderate renal dysfunction (GFR 30 to 59 mL-min-1.73 m), 13.1% had severe renal dysfunction (GFR 15 to 29 mL-min-1.73 m), and 7.0% had a GFR less than 15 mL-min-1.73 or were on chronic dialysis.[4][5] Other large databases have shown that the prevalence of cardiac or renal dysfunction increases the incidence of the other.

Pathophysiology

Type 1 cardiorenal syndrome occurs when there is acute decompensation of cardiac function leading to a decrease in glomerular filtration. Researchers have previously proposed a decline in cardiac output with decreased renal perfusion as the leading underlying cause for worsening kidney function in cardiorenal syndrome types 1 and 2.  However, recent studies have postulated that increased central venous pressures are a more critical factor.[1] When patients develop fluid overload due to worsening cardiac function, venous pressures increase and are transmitted back to the efferent arterioles; this results in a net decrease in the glomerular filtration pressure and renal injury. Other factors involved in the pathogenesis of types 1 and 2 cardiorenal syndromes include elevated intraabdominal pressures, activation of the renin-angiotensin-aldosterone system (RAAS), activation of the sympathetic nervous syndrome, and increased inflammatory damage to the kidney related to heart failure.[6][7] Targeting this cycle is the mainstay of therapy for type 1 cardiorenal syndrome. Types 3 and 4 cardiorenal syndromes more likely result from volume overload from renal dysfunction, abnormal cardiac function in the setting of metabolic disturbances (such as acidemia), and neurohormonal changes that accompany renal disease.[8] Patients can develop type 5 cardiorenal syndrome in the setting of sepsis, systemic lupus erythematosus (SLE), diabetes mellitus, decompensated cirrhosis, or amyloidosis; all of these disorders can lead to disease in both the heart and kidney.[9]

History and Physical

The patient’s history and physical exam can help clinicians to differentiate between acute and chronic decompensation as well as primarily cardiac or renal causes. Examples of helpful historical information would include if the patient presents with an acute myocardial ischemic event that can be triggering for severe cardiac dysfunction, which subsequently results in renal injury or recent-onset diarrhea and vomiting, causing acute renal injury, which might lead to a sharp decline in heart function. Other historical clues, such as medication use and prior laboratory values (such as creatinine), may be helpful.[1] Although the clinical examination may not help differentiate the different types of cardiorenal syndrome, many patients will have evidence of volume overload with signs, including[1]:

• Elevated jugular venous pressure
• Generalized swelling and edema with “third spacing” presenting as pleural effusion(s), ascites, or peripheral edema
• Crackles or rales on lung auscultation
• Patients may also demonstrate manifestations of decreased cardiac output with hypotension, fatigue, diminished peripheral pulses, and abnormal heart rates (either tachycardia or bradycardia)

Other possible signs indicating a primary renal cause of cardiorenal syndrome may include:

• Pallor from anemia
• Monitoring oliguria or anuria preceding cardiac dysfunction

Evaluation

Initial history and physical examination tailor the provider's approach towards the appropriate investigation for determining the underlying etiology. The initial laboratory workup should include a complete blood count (CBC), complete metabolic panel (CMP), urine studies (urinalysis with microscopy, urine protein to creatinine ratio, urine sodium), brain natriuretic peptide (BNP), and troponin. The estimated glomerular filtration rate (eGFR) is calculable from the creatinine level to help determine the degree of renal impairment. In patients with possible cardiorenal syndrome type 5, further investigations including blood & urine cultures, lupus serologies (antinuclear antibody [ANA], anti-double-stranded DNA, serum complement levels [C3, C4]), and a procalcitonin may be useful. An electrocardiogram and cardiac monitoring should be included in the initial evaluation to evaluate for any underlying arrhythmias that may be contributing to or resulting from the cardiorenal syndrome. A transthoracic echocardiogram is invaluable in evaluating for wall motion abnormalities, obtaining measurements such as the left ventricular ejection fraction (LVEF), and determining whether or not there is a pericardial effusion. A renal ultrasound can help evaluate kidney size and function. Smaller kidney disease and increased renal echogenicity are consistent with chronic kidney disease.[7]

Treatment / Management

Although no therapies have been demonstrated to improve outcomes in patients with cardiorenal syndrome, treatment generally is directed at the underlying etiology and to improve the complications of the syndrome as most patients with cardiorenal syndrome have volume overload, the primary treatment targets typically fluid removal either with diuretics or ultrafiltration.[1] Loop diuretics, including furosemide, torsemide, and bumetanide, are the most potent diuretic class. They can be used alone or in conjunction with other types of diuretics. There are two strategies in terms of diuresis: either a continuous infusion dose or using intravenous boluses. Creatinine clearance can be used to help determine the dosage. For example, treatment can start with a loading dose of 40 mg intravenous furosemide loading dose followed by 10 mg/hr if the creatinine clearance is between 25 and 75 mL/min. In contrast, one can start with 80 mg to 160 mg of intravenous furosemide as a maximum dose that can be repeated several times a day to achieve a desirable response for the same creatinine clearance.[1][5] Definitive clinical evidence is still lacking to support either strategy over the other. However, using the continuous infusion strategy would give clinicians more opportunities to evaluate the response to therapy. Also, adding a thiazide diuretic can help overcome diuretic resistance in some cardiorenal patients. Metolazone is typically used and is considered one of the most common combinations with loop diuretics. On the other hand, ultrafiltration can be useful in resistive cases. Still, recent studies showed that diuretic therapy was better than ultrafiltration for symptom control and creatinine level decline in the initial approach towards obtaining euvolemia. Inotropes can be used for refractory cases and can help to improve cardiac function and decrease venous congestion. Unfortunately, no conclusive data have supported their use in cardiorenal syndrome.[2][7] On the other hand, the treatment of cardiorenal syndrome type 3 and 4 would target treating underlying kidney disease and avoiding nephrotoxic medications and contrast. Finally, treatment of the underlying systemic conditions would be the treatment of type 5 cardiorenal syndrome.  (B3)

Differential Diagnosis

It is difficult to determine the etiology of the cardiorenal syndrome on initial presentation in many patients as they might present without all the classic features, making the diagnosis challenging. History of a recent increase in diuretic doses, diarrhea, vomiting, skin or throat infection, heatstroke, fever, recent extensive workout, or non-steroid anti-inflammatory drug (NSAID) use can help towards a hypovolemic etiology.

Prognosis

The overall prognosis is poor. There are multiple mortality and readmission predictor calculators available to predict the individual patient’s prognosis further. They use multiple variables to predict in-hospital mortality and readmission rate, including the blood urea nitrogen (BUN), systolic blood pressure, serum creatinine, brain natriuretic peptide, and response to diuretics.[10][11][12]

Complications

• Liver failure
• Respiratory failure requiring invasive and non-invasive ventilation
• Worsening renal failure requiring dialysis (either temporarily or permanently)