Hemodynamic Insights to Cardio-Renal Syndrome: A View Looking Back to See Forward

Heart failure has long been pictured as intersecting disorders of forward flow and backward pressure. This early simplification gradually unfolded to reveal the more complex physiology of dynamic mitral and tricuspid regurgitation as both detracting from forward flow and increasing congestion. Compromise of kidney function was initially assumed to be the result of impaired forward flow, with elevations in serum creatinine triggering termination of diuresis and sometimes even administration of fluids. However, growing recognition of right ventricular dysfunction such as from HF with preserved ejection fraction and right ventricular failure with left ventricular assist devices illuminated the deleterious effect of elevated right-sided filling pressures on renal dysfunction. It has now clearly been shown that right ventricular, right atrial, and triscupid valve disorders correlate more closely with progressive renal dysfunction than systolic abnormalities of systemic perfusion, except in the extreme case of cardiogenic shock in which many organs suffer. As for the cardinal symptoms of heart failure, the backward components dominate the disease for the kidney as well. The sequential addition of new medical and pacing device therapies and the strategy to monitor and manage filling pressures in ambulatory patients have dramatically reduced the episodes of congestion and hopefully the progressive deterioration of renal function during the heart failure journey. Still remaining, however, are the fundamental questions about the optimal way to treat heart failure while preserving renal function, and the primary pathophysiologic trigger for the first retention of fluid in cardiac disease.