Intrarenal venous flow (IRVF) patterns were more dependent on right atrial pressure (RAP), rather than arterial resistance index (RI), which suggests a possible correlation with renal congestion, according to data published in JACC: Heart Failure.
IRVF patterns also strongly correlated with clinical outcomes independent of RAP, and may help stratify vulnerable patients with heart failure (HF).
According to the study authors, cardiorenal syndrome has been widely recognized as an important component in the pathophysiology of HF, with focus on renal impairment and congestion caused by central venous pressure (CVP). “However, CVP is a surrogate of renal congestion in HF, and intrarenal hemodynamics have not been well studied in the assessment of renal congestion,” researchers wrote.
Therefore, they decided to evaluate intrarenal hemodynamics using intrarenal Doppler ultrasound (IRD), hypothesizing that the intrarenal arterial and venous flow profiles might be altered by accompanying changes in parenchymal conditions related to renal congestion.
A total of 224 patients with HF (n=151 inpatients during HF hospitalization; n=73 outpatients) were enrolled at the authors’ institution of University of Tsukuba in Japan. Seven patients had to be excluded because of inadequate IRD images. The remaining 217 patients were studied against 38 normal control patients.
The primary end points were either death from cardiovascular disease or unplanned HF hospitalization. Transthoracic echocardiography and cardiac catheterizations, as well as peripheral blood samples, were performed.
IRVF was associated with mean RAP. Three IRVF patterns were stratified by RAP—continuous pattern: 5.4 ± 2.5 mmHg; biphasic pattern: 9.5 ± 3.5 mmHg; and monophasic pattern: 14.9 ± 4.3 mmHg (P<.001). Prognosis for the monophasic IRVF pattern was poorer than the other patterns (log rank P<.001) and the biphasic pattern had a worse prognosis than the continuous flow pattern (log rank P=.01).
During a mean observation period of 304 ± 114 days (range 7 to 365 days), 59 patients met the clinical end points—14 of whom died from cardiovascular disease and 45 of whom experienced unplanned hospitalizations for HF.
Control patients had RI ranges between 0.48 and 0.68 (99% confidence interval [CI]) and only the continuous IRVF pattern was observed. In addition, their venous impedance indices (VII) ranged from 0.14 to 0.52 (99% CI). “Thus, RI ≥0.70 and VII ≥0.53 were each considered to indicate abnormal values of RI and VII, and biphasic and monophasic discontinuous flows were considered as abnormal IRVF patterns,” researchers explained.
However, in 105 patients who had VII ≥0.53, more than 96% (n=101) demonstrated VII=1.0 which indicates a “discontinuous IRVF pattern.” Researchers then classified patients based on IRVF pattern and not VII.
Patients with RI ≥0.70 were older, had significantly lower hemoglobin and estimated glomerular filtration rates (eGFR) as well as blood urea nitogren (BUN) brain natriuretic peptide (BNP), and E/E’ compared to patients with RI <0.70. They also had higher incidences of significant tricuspid regurgitation compared to those patients with RI <0.70, as well as an estimated RAP >10 mmHg, pulmonary capillary wedge pressure, and a significantly higher mean RAP. The cardiac index, however, was not different between the 2 groups.
Patients with a monophasic IRVF pattern were older than those with a biphasic pattern. In addition, BUN, BNP, E/E’, PCWP, and mean RAP were significantly higher in monophasic pattern patients whereas eGFR, sodium, and hepatic systolic and diastolic flow velocities were significantly lower than in the other 2 IRVF patterns. As in the case with RI, the cardiac index also did not different among the 3 IRVF patterns.
“This study showed that IRVF could be noninvasively assessed with high clinical feasibility and acceptable reproducibility by a conventional echocardiographic system,” researchers concluded. “A few studies reported changes in IRVF in obstructive uropathy and renal diseases, preeclampsia, and diabetic nephropathy, but CVP and TR [tricuspid regurgitation] were never considered determinants of IRVF. The IRVF profile was altered by increases in RAP, whereas the cardiac index was not associated with the IRVF profile.”
They added that future studies should investigate the pathophysiological determinants of IRD profiles so that they may be implemented as guides for HF therapy.
Iida N, Seo Y, Sai S, Machino-Ohtsuka T, Yamamoto M, Ishizu T. Clinical implications of intrarenal hemodynamic evaluation by Doppler ultrasound in heart failure. JACC Heart Fail. 2016. doi:10.1016/j.jchf.2016.03.016.