Cardiorenal Syndrome: Classification, Pathophysiology, Diagnosis, and Treatment Strategies — AHA Scientific Statement 2019

Authors, Journal, Affiliations, Type, DOI

• Authors: Janani Rangaswami (Chair); Vivek Bhalla; John E.A. Blair; Tara I. Chang; Salvatore Costa; Krista L. Lentine; Edgar V. Lerma; Kenechukwu Mezue; Mark Molitch; Wilfried Mullens; Claudio Ronco; W.H. Wilson Tang; Peter A. McCullough (Chair)
• Journal: Circulation, Vol. 139, pp. e840–e878, April 16, 2019
• Affiliations: Einstein Medical Center/Jefferson University; Stanford University; University of Chicago; Dartmouth Hitchcock; Cleveland Clinic; Università degli Studi di Padova; among others
• Type: AHA Scientific Statement (expert-based consensus summary)
• DOI: https://doi.org/10.1161/CIR.0000000000000664

Overview

This AHA Scientific Statement provides a comprehensive reference for cardiorenal syndrome (CRS), a spectrum of disorders in which acute or chronic dysfunction of the heart may induce dysfunction of the kidney and vice versa. It formally classifies CRS into 5 phenotypes based on the Acute Dialysis Quality Initiative consensus, explains both hemodynamic and non-hemodynamic pathophysiological pathways, and summarises clinical diagnostic tools (biomarkers, imaging, volume assessment). The document provides detailed evidence tables for pharmacological therapies (RAAS inhibitors, beta-blockers, MRAs, ARNI, SGLT-2 inhibitors, GLP-1 agonists) and device therapy (ICD, CRT) across GFR strata in CKD, and covers special populations including diabetes, kidney transplant recipients, and advanced CRS patients requiring palliative care.

Keywords

AHA Scientific Statements; acute kidney injury; biomarkers; cardio-renal syndrome; chronic kidney disease; dialysis; diuretics; heart failure; hospitalization; kidney transplantation; mortality; ultrafiltration

Key Takeaways

Definition and Classification

• CRS defined as a spectrum of disorders in which acute or chronic dysfunction in 1 organ (heart or kidney) may induce acute or chronic dysfunction in the other
• Acute Dialysis Quality Initiative 5-type classification:
  • Type 1 (Acute CRS): Acute HF (e.g., ACS with cardiogenic shock) → AKI
  • Type 2 (Chronic CRS): Chronic HF → CKD
  • Type 3 (Acute Renocardiac): AKI (volume overload, uremia) → AHF
  • Type 4 (Chronic Renocardiac/Uremic Cardiomyopathy): CKD → chronic HF; LVH driven by CKD-associated cardiomyopathy; FGF-23 causally linked to LV hypertrophy
  • Type 5 (Secondary CRS): Systemic process (amyloidosis, sepsis, cirrhosis) → simultaneous HF and kidney failure
• Up to 40% of patients hospitalised for AHF present with Type 1 CRS
• Subtypes overlap clinically; 16% Type 2 CRS and 20% Type 4 CRS patients develop acute CRS

Pathophysiology

Hemodynamic Mechanisms

• Elevated CVP and renal venous hypertension is the primary hemodynamic driver of AKI in CRS — not low cardiac output alone
  • ADHERE registry: rising serum creatinine was similar in AHF patients with reduced vs preserved systolic function
  • Many acute CRS patients have preserved or elevated blood pressure
  • Elevated CVP → renal venous hypertension → increased renal resistance → impaired intrarenal blood flow → decreased GFR
  • ESCAPE trial post hoc: RA pressure was the only hemodynamic parameter associated with baseline renal dysfunction
  • Increased CVP associated with reduced GFR and all-cause mortality in a broad cardiovascular spectrum
• Filtration fraction is initially preserved via efferent arteriolar constriction (RAAS activation); lost in severe decompensation
• Elevated IAP in AHF contributes to renal dysfunction via direct renal compression; elevated in 60% of AHF admissions
• RV dysfunction and RV pressure overload contribute to CRS through interventricular asynchrony, ventricular interdependence, and reduced LV filling

Non-Hemodynamic Mechanisms

• Sympathetic nervous system activation, chronic inflammation, reactive oxygen species/nitric oxide imbalance, persistent RAAS activation
• TNFα, IL-1, IL-6 elevated in AKI → direct cardiodepressant effects including reduced LVEF
• FGF-23 has an independent causal effect on LV hypertrophy in uremic cardiomyopathy (Type 4)
• Endothelial stretch from venous congestion activates a proinflammatory endothelial phenotype
• Cardiac and kidney dendritic cells cross-talk via innate/adaptive immune responses

Distinguishing Pseudo-AKI from True AKI in AHF Diuresis

• Small creatinine rises during aggressive diuresis in AHF may not reflect tubular injury
• Ahmad et al.: tubular injury (by validated biomarkers) was NOT associated with worsening renal function (by cystatin C) with aggressive diuresis
• Increases in NGAL, NAG, and KIM-1 were paradoxically associated with improved survival in ROSE-AHF (HR 0.80 per 10-percentile increase)
• Key distinction relies on: perfusion status assessment, hemodynamic parameters, urine microscopy (tubular cells, granular casts), exclusion of intrinsic causes
• Do NOT reduce diuresis solely based on creatinine rise in AHF — this leads to suboptimal decongestion

Biomarkers

Renal Biomarkers

• Cystatin C (CysC): Highest quartile (>1.55 mg/L) associated with 2× CV mortality; strong predictor of rehospitalization and mortality in AHF
• Albuminuria: Strong prognostic value across CHARM, GISSI-HF, Val-HeFT substudies
• NGAL: Most upregulated protein in AKI; meta-analysis (n=2000): AUC 0.78/0.75 for dialysis/death; serial measurements improve predictive value (AUC 0.91)
• TIMP-2 × IGFBP7: G1 cell cycle arrest markers; superior to other AKI biomarkers in SAPPHIRE validation cohort (n=728); available for clinical use in the US
• KIM-1, NAG, IL-18, L-FABP, urine angiotensinogen: Additional tubular injury markers

Cardiac Biomarkers

• BNP/NT-proBNP: Class 1A for HF diagnosis/prognosis; elevated higher in CKD (impaired renal clearance); significantly higher in CRS vs AHF without renal impairment
• ST2: Not affected by renal function; incremental prognostic value over natriuretic peptides
• Galectin-3: Synthesised by cardiac macrophages; independently predicts CV mortality; worse with lower eGFR; 15% rise over 3–6 months → higher all-cause mortality and HF hospitalization risk
• High-sensitivity troponin: Higher prevalence of elevation with declining GFR; sustained elevation → higher mortality

Imaging

• Echocardiography: CVP estimation, systolic PA pressure, PCWP (E/E′ >15 correlates with PCWP ≥18 mmHg); acute CRS (Types 1+3) has 3× higher mortality vs CKD without CRS; declining LVEF, rising PA pressure, larger RV diameter independently predict CRS
• Renal Doppler (intrarenal venous flow): Iida et al. (n=217 AHF): continuous intrarenal venous flow pattern (54%) → low RA pressures + >95% 1-year survival; monophasic/discontinuous pattern → <40% 1-year survival
• Speckle tracking echo (GLS): Detects subclinical LV dysfunction in CKD; LV longitudinal systolic strain significantly reduced in CKD despite preserved EF; GLS HR 1.08 per unit for all-cause mortality in CKD
• CMR: Prolonged native T1 relaxation time and abnormal GLS in hemodialysis patients with HFpEF; non-gadolinium CMR validated in advanced CKD

Volume Assessment Strategies

• BIVA (Bioimpedance Vector Analysis): Distinguishes dyspnoea causes in ED; short vectors = volume overload, long vectors = depletion; guides discharge timing when combined with BNP
• IAP measurement: Bladder catheter transducer; reversing elevated IAP with decongestive therapy ameliorates creatinine
• CardioMEMS PA sensor (CHAMPION trial): PA-guided HF management → HR 0.72 for hospitalization; trend toward lower mortality; data lacking in advanced CKD

Treatment Strategies

Diuretics in CRS

• Loop diuretics prescribed in ≈90% of AHF patients; Class I recommendation based on expert opinion only — no mortality benefit demonstrated
• DOSE-AHF: High-dose (2.5×) vs standard furosemide — trend toward better symptoms (P=0.06), no difference in renal function (P=0.21); continuous vs intermittent dosing showed no difference
• Stepwise diuretic algorithm (pooled analysis of DOSE-AHF/CARRESS-HF/ROSE-AHF, n=198 Type 1 CRS): greater weight loss, more fluid removal, and improved renal function vs standard therapy
• ROSE-AHF: Low-dose nesiritide and dopamine both showed no difference in primary endpoints (urine volume + CysC change at 72h)
• High-dose intermittent furosemide appears safe and effective in AHF
• Oral bioavailability: furosemide ≈50%; torsemide and bumetanide higher and more predictable
• Diuretic efficiency ratio (urine Na/urine furosemide <2 mmol/mg) independently predicts worse outcomes (HR 2.2, ESCAPE trial: HR 2.86)

Diuretic Resistance

• Defined as attenuation of maximal diuretic effect limiting Na/Cl excretion
• Associated with renal impairment, higher rehospitalisation rate, and mortality
• Mechanisms: reduced oral bioavailability (hypoalbuminemia, uremic toxin competition), braking phenomenon (within hours), distal tubular hypertrophy (long-term)
• Enhanced distal sodium transport > proximal transport as driver of resistance → rationale for thiazide augmentation
• Hypochloremia plays a critical role in neurohormonal activation driving resistance
• See concepts/Diuretic-Resistance for full mechanisms and strategies

Ultrafiltration in CRS

• UNLOAD (n=200): UF > diuretics for weight loss at 48h (5.0 vs 3.1 kg, P=0.001); no difference in dyspnoea; reduced 90-day rehospitalisation
• CARRESS-HF (n=188, Type 1 CRS): No difference in weight loss; fixed-rate UF significantly worsened creatinine vs stepwise diuretic algorithm (Δ+0.23 vs −0.04 mg/dL, P=0.003); higher adverse events (72% vs 53%)
• AVOID-HF: Terminated early (slow enrolment); nonsignificant trend toward fewer HF readmissions; higher adverse events in UF arm
• CARRESS-HF provides strong argument against primary UF in Type 1 CRS; UNLOAD results likely reflect inadequate dose escalation in the diuretic arm

Neurohormonal Modulation

• Tolvaptan (V2 antagonist): EVEREST: no long-term mortality/hospitalization benefit; TACTICS-HF/SECRET: no improvement in dyspnoea
• Nesiritide: ASCEND-HF (n=7141): no difference in primary endpoint; more hypotension; ROSE-AHF: no effect on urine volume or CysC
• Dopamine (low-dose): ROSE-AHF: no benefit; post hoc: improved urine volume in LVEF ≤40% but no effect on CysC

RAAS Inhibition in Chronic CRS

ACEi/ARB

• CONSENSUS: 11% had creatinine doubling with enalapril, but trends predominantly early and reversible
• SOLVD Treatment: enalapril group — 33% higher likelihood of Cr rise >0.5 mg/dL but mortality benefit preserved across CKD subgroups
• DIG Database (propensity-matched): ACEi vs no ACEi in CKD HF → HR 0.58 for all-cause mortality
• Ahmed et al. (HFpEF + CKD3): ACEi/ARB → HR 0.82 for all-cause mortality
• Edner et al. (CKD4 HFrEF, n=2410): ACEi/ARB → HR 0.83 for all-cause mortality
• Evidence limited in advanced CKD (stages 4–5) — most trials excluded Cr >2.5 mg/dL

Sacubitril/Valsartan (ARNI)

• Meta-analysis (IMPRESS, OVERTURE, PARADIGM-HF): combined neprilysin/RAAS inhibition → HR 0.86 for death or HHF; less renal dysfunction and hyperkalemia vs ACEi alone
• PARADIGM-HF subset: sacubitril/valsartan → slower GFR decline including in CKD patients despite modest albuminuria increase
• PARAMOUNT: LCZ696 → preserved eGFR to greater extent (−1.6 vs −5.2 mL/min/1.73m² decline at 36 weeks, P=0.007)

MRA

• RALES: HR 0.68 for all-cause mortality; 17% vs 7% worsening renal function with spironolactone
• EMPHASIS-HF (33% with eGFR <60): consistent eplerenone benefit across CKD subgroups
• Hyperkalemia doubled with MRA vs control; novel antihyperkalemic agents (patiromer, sodium zirconium cyclosilicate) may enable continued use in CRS

Beta-Blockers in CKD

• MERIT-HF: significant benefit across all eGFR ranges; most pronounced in eGFR <45 (60% reduction in HHF and mortality)
• CIBIS-II: bisoprolol → mortality reduction across GFR quartiles; higher discontinuation rates in lowest eGFR
• SENIORS: nebivolol benefit less robust in lowest eGFR tertile (<55 mL/min/1.73m²)
• Meta-analysis (6 RCTs): beta-blockers in CKD+HF → RRR 28% all-cause mortality, RRR 34% CV mortality

SGLT-2 Inhibitors in Diabetic CRS

• EMPA-REG OUTCOME (n=7020, T2DM, high CV risk): Empagliflozin → 14% RRR primary MACE (P=0.001); 38% RRR CV death; 35% RRR HF hospitalisation; 39% RRR incident or worsening nephropathy; GFR decline delayed by ≈1 year
• CANVAS program (n=10,142): Canagliflozin → HR 0.86 for primary MACE; HR 0.73 for albuminuria progression; HR 0.60 for renal composite; increased amputation risk (HR 1.97) — especially at toe/metatarsal level; avoid in peripheral artery disease
• CVD-REAL (n=309,056): Class-effect — SGLT-2 inhibitors vs other glucose-lowering drugs → HF hospitalisation HR 0.61; death HR 0.49

Incretin-Based Therapies in Diabetic CRS

• LEADER (liraglutide, n=9340): HR 0.87 for primary MACE; significant reduction in composite renal outcome (HR 0.78), driven by reduction in macroalbuminuria
• SUSTAIN-6 (semaglutide, n=3297): HR 0.74 for MACE; driven by 39% reduction in nonfatal stroke; increased retinopathy complications (HR 1.76)
• DPP-4 inhibitors: SAVOR-TIMI 53 — saxagliptin increased HF hospitalisation (HR 1.27), especially in elevated natriuretic peptides/HF/CKD; EXAMINE and TECOS — neutral

Cardiac Device Therapy in CKD

ICD

• Meta-analysis (MADIT I, MADIT-II, SCD-HeFT): ICD survival benefit in GFR >60 (HR 0.49) but NOT in GFR <60 (HR 0.80)
• Cleveland Clinic CKD Registry: ICD benefit preserved in eGFR 30–59 range (HR 0.58–0.65) but not in eGFR <30 (HR 0.98)
• DANISH trial: no ICD benefit in non-ischaemic HFrEF including CKD subgroup
• Higher complication rates in CKD: infections, bleeding, central venous stenosis, tricuspid regurgitation

S-ICD in CKD

• EFFORTLESS registry: 8.6% of S-ICD patients had CKD; CKD was an independent predictor of appropriate therapy (HR 2.10 for polymorphic VT/VF)
• Safety and efficacy at midterm comparable to transvenous ICDs; no device-related infections in CKD series

CRT in CKD

• MIRACLE post hoc: improvements in NYHA class, EF, and MR across eGFR >90, 60–89, 30–59; eGFR improvement in the CKD3 subgroup
• Meta-analysis (Bazoukis): 13/16 studies showed higher all-cause mortality with baseline CKD post-CRT; HR 1.66 for eGFR <60 vs ≥60

HF and Kidney Transplantation

• HF prevalence in ESKD dialysis patients 12–36× the general population; 3-year mortality after HHF is 83%
• 70% of HFrEF patients had LVEF >50% by 1 year post-KT; longer pre-KT dialysis duration predicted failure to improve LVEF
• De novo HF after KT: 10.2% at 12 months, 18.3% at 36 months; predicts death (HR 2.6) and graft failure (HR 2.7)
• ACEi in KT: conflicting evidence; Paoletti et al. showed benefit; Knoll et al. showed no benefit; meta-analysis showed higher hyperkalemia (RR 2.44)
• PH in KT candidates: sPAP >50 mmHg → nearly 4× post-KT mortality; associated with lower graft survival

Palliative Care in CRS

• Symptom burden in advanced CRS comparable to advanced lung and pancreatic cancer
• NSAIDs contraindicated in both HF and CKD (AKI, salt/water retention)
• Morphine contraindicated in moderate-severe CKD (metabolite accumulation → delirium, myoclonus, respiratory depression); safer alternatives: hydromorphone, oxycodone, fentanyl
• Methadone safe in HF and CKD with QTc monitoring
• Appropriate palliative care reduces ED visits and hospitalisations in advanced CKD

Future Directions

• Need for dedicated multidisciplinary cardiorenal teams for early identification and joint inpatient/outpatient management
• MARCE (Major Adverse Renal and Cardiovascular Events): composite of MI, renal replacement therapy, stroke, HF, hospitalization, death — proposed as novel cardiorenal trial endpoint
• MAKE (Major Adverse Kidney Events): composite of persistently impaired renal function, new hemodialysis, death
• Cross-specialty educational programs and national quality benchmarks for cardiorenal outcomes

Limitations of the Document

• Expert-based consensus summary, not a systematic review with formal GRADE evidence evaluation
• Most HF outcome trials excluded moderate-to-severe CKD — evidence for CRS management in CKD stages 4–5 is largely post hoc analysis and observational data
• ICD/CRT data in CKD relies on post hoc subgroup analyses; no RCTs designed for this population
• RAAS inhibition data in kidney transplant recipients is conflicting and based on small studies
• SGLT-2 inhibitor data at time of writing was in T2DM only (pre-DAPA-HF, pre-EMPA-KIDNEY)
• Ultrafiltration algorithms not standardised; fixed-rate protocols (CARRESS-HF) may overestimate harm vs flexible protocols

Key Concepts Mentioned

• concepts/Cardiorenal-Syndrome — primary topic; CRS 5-type classification, pathophysiology, management
• concepts/Diuretic-Resistance — comprehensive mechanisms and management strategies
• concepts/HFpEF — CRS in preserved EF; tolvaptan, ARNI in HFpEF
• concepts/Late-Gadolinium-Enhancement — uremic cardiomyopathy, non-gadolinium CMR in CKD

Key Entities Mentioned

• entities/Heart-Failure — CRS types 1–5 classification, beta-blockers/RAAS in CKD, device therapy
• entities/ATTR-Amyloidosis — Type 5 CRS aetiology
• entities/Pulmonary-Hypertension — RV dysfunction, PH in KT candidates

Wiki Pages Updated

• wiki/sources/cardiorenal-aha-2019.md — created
• wiki/concepts/Cardiorenal-Syndrome.md — updated with CRS classification, hemodynamic pathophysiology, biomarkers, UF trial evidence
• wiki/concepts/Diuretic-Resistance.md — created
• wiki/entities/Heart-Failure.md — updated with beta-blocker CKD evidence, device therapy in CKD, SGLT-2i in diabetic CRS, KT outcomes
• wiki/sourceindex.md — updated
• wiki/wikiindex.md — updated