Introduction
The heart and kidneys are vital organs that are essential for the well-being of an individual. If one of the organs fails, the other organ will subsequently fail. Cardiorenal syndrome is a condition in which an acute or chronic dysfunction in the heart or kidneys results in an acute or chronic dysfunction of the other organ. It describes that cardiac and renal dysfunctions coexist, in which a disorder in one organ causes dysfunction in the other organ.
What Is Cardiorenal Syndrome?
The heart and the kidneys are vital in maintaining hemodynamic stability and organ perfusion. Both organs communicate with each other through a variety of pathways. Hence, an acute or chronic dysfunction in the heart causes acute or chronic dysfunction in the kidneys and vice versa.
How Are the Heart and Kidneys Connected?
The heart transports a continuous supply of oxygenated blood throughout the body, including the kidneys. The kidneys are responsible for filtering the blood, removing waste, and also helps in regulating water and salt levels to control blood pressure. Cardiac dysfunction reduces the heart's pumping efficiency, and the heart is congested with blood. This causes pressure build-up in the veins that are connected to the kidneys. This leads to congestion of blood in the kidneys, and it also suffers from a reduced supply of oxygenated blood. As the renal function is impaired, the hormone system that regulates the blood pressure attempts to increase the blood supply to the kidneys. This further increases the heart's workload because it has to pump against higher pressure. Hence, heart and kidney diseases are interconnected.
What Are the Types of Cardiorenal Syndrome?
Various factors can cause the cardiorenal syndrome. The cardiorenal syndrome is classified into multiple subtypes based on pathology and chronicity. It includes the following:
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Type 1 - It indicates a sharp decline in cardiac function, resulting in an acute decline in renal function.
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Type 2 - It describes a chronic dysfunction in the heart, which causes a sustained reduction in renal function.
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Type 3 - It indicates a sharp decline in renal function, which causes an acute reduction in cardiac function.
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Type 4 - It describes a chronic cardiac dysfunction due to chronic decline in renal function.
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Type 5 - It is due to systemic diseases that cause cardiac and renal dysfunction.
Type 1 cardiorenal syndrome is the most common type. Each type of cardiorenal syndrome has a unique pathophysiology that requires unique management strategies. Each type has varying prognoses.
How Does Cardiorenal Syndrome Occur?
Type 1 - Type 1 cardiorenal syndrome, also called acute cardiorenal syndrome, is characterized by a rapid decline in cardiac function, which results in acute kidney injury. Acute cardiac failure may be due to cardiogenic shock, right ventricular failure, hypertensive pulmonary edema with preserved left ventricular function, or acute decompensated chronic heart failure. This type of cardiorenal syndrome is usually due to acute decompensation of cardiac dysfunction, which causes a decrease in glomerular filtration. Increased venous pressures due to worsening cardiac functions cause a decrease in the glomerular filtration pressure and result in renal injury.
Type 2 - Type 2 cardiorenal syndrome is also referred to as a chronic cardiorenal syndrome, characterized by the presence of chronic cardiac abnormalities like chronic congestive heart failure, resulting in progressive chronic kidney disease. Worsening renal functions due to heart failure are associated with longer hospitalizations and adverse outcomes. Type 2 condition is caused by chronic heart failure, which results in decreased renal perfusion. Other factors that are responsible for type 1 and type 2 are elevated intraabdominal pressures, activation of the renin-angiotensin-aldosterone system, and activation of the sympathetic nervous system.
Type 3 - Type 3 cardiorenal syndrome is also referred to as acute renocardiac syndrome. In this type, acute cardiac dysfunction is seen due to worsening kidney function. Acute kidney injury, ischemia, or glomerulonephritis results in heart failure, arrhythmia, and ischemia. Renal dysfunction causes volume overload and results in cardiac dysfunction in the presence of metabolic disturbances like acidemia and neurohormonal changes that are associated with renal diseases. Acute kidney injury can cause cardiac dysfunction through several pathways. Fluid overload leads to pulmonary edema. Hyperkalemia causes arrhythmias and may result in cardiac arrest. Renal ischemia may cause inflammation and apoptosis in the heart. A bilateral or unilateral renal artery stenosis causes type 3 cardiorenal syndrome.
Type 4 - Type 4 cardiorenal syndrome is referred to as chronic renocardiac syndrome. Chronic kidney diseases like chronic glomerular disease cause cardiac dysfunction. It leads to diastolic dysfunction and ventricular hypertrophy. The underlying pathological mechanism is similar to type 3 cardiorenal syndrome. Cardiac dysfunction is due to volume overload caused by chronic renal dysfunction in the setting of acidemia and neurohormonal changes that are associated with renal diseases.
Type 5 - Type 5 cardiorenal syndrome, also called secondary cardiorenal syndrome, is caused by acute or chronic systemic disorders. Acute or chronic systemic disorders cause cardiac and renal dysfunction. Type 5 syndrome develops in the presence of sepsis, diabetes mellitus, systemic lupus erythematosus, decompensated cirrhosis, sarcoidosis, or amyloidosis. Chronic diabetes and hypertension may cause type 2 and type 4 cardiorenal syndrome. The pathological mechanism explaining the relationship between systemic diseases and combined cardiac and renal dysfunction remains unknown.
What Are the Signs and Symptoms of Cardiorenal Syndrome?
The cardiorenal syndrome presents volume overload symptoms, including;
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Increased jugular venous pressure.
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Generalized edema with pleural effusions, ascites, or peripheral edema.
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Crackles or rales in the lungs.
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Hypotension, fatigue, diminished peripheral pulses, and abnormal heart rates due to decreased cardiac output.
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Pallor from anemia, oliguria, or anuria are signs of renal cause.
What Are the Complications of Cardiorenal Syndrome?
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Liver failure.
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Respiratory failure.
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Worsening renal failure.
How Is Cardiorenal Syndrome Diagnosed?
The diagnosis depends on the history, examination, and the following tests:
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Complete blood count, complete metabolic panel, urinalysis, brain natriuretic peptide, troponin, and estimated glomerular filtration rate values are determined to assess cardiac and renal functions.
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An electrocardiogram (ECG) is performed to evaluate arrhythmias.
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A transthoracic echocardiogram detects motion abnormalities and pericardial effusion.
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Renal ultrasound helps determine the kidneys' size and function.
How Is Cardiorenal Syndrome Treated?
The treatment is aimed at improving the complications of the syndrome. Drugs like loop diuretics are given for fluid removal. Inotropes are given to improve the heart's function and decrease venous congestion. Type 3 and type 4 are managed by treating the underlying conditions and avoiding nephrotoxic medications. Type 5 is managed by treating the underlying systemic conditions.
Conclusion
The heart and kidneys are related through various pathways, and dysfunction in one organ disrupts the function of the other organ. Lifestyle modifications like avoiding smoking, regular exercise, and diet preserve cardiac and kidney health. Early diagnosis and treatment of heart or kidney disease help preserve the other organ's function.
