Cardiorenal syndrome: a complex series of combined heart/kidney disorders

Over the last decade, it has become increasingly clear that the cardiovascular and renal systems are interdependent. Primary disorders of either system have been shown to disturb the other system. As a result, a class of cardiorenal syndrome (CRS) has been identified where in a vicious cycle is established in which acute/chronic dysfunction of either the kidney or the heart exacerbates the loss of function in the other organ. The ADQI organization has proposed a classification derived from a consensus conference held in 2008. CRS is classified as a disorder of the heart and kidneys whereby acute or chronic dysfunction in one organ may induce acute or chronic dysfunction in the other. The general definition has been expanded into five subtypes: CRS type 1 = acute worsening of heart function (acute heart failure-acute coronary syndrome) leading to kidney injury and/or dysfunction; CRS type 2 = chronic abnormalities in heart function (chronic heart failure-chronic heart disease) leading to kidney injury or dysfunction; CRS type 3 = acute worsening of kidney function (acute kidney injury) leading to heart injury and/or dysfunction; CRS type 4 = chronic kidney disease (chronic kidney disease) leading to heart injury, disease and/or dysfunction; and CRS type 5 = systemic conditions leading to simultaneous injury and/or dysfunction of heart and kidney. A major problem with previous terminology was that it did not allow for identification of pathophysiological interactions occurring in the different types of combined heart/kidney disorders. The subdivision into different subtypes seems to provide a better approach to this syndrome.