Executive Summary
Key Points
- Cardiac amyloidosis produces restrictive physiology: elevated biventricular filling pressures, reduced cardiac output, and preserved or mildly elevated pulmonary vascular resistance
- Classic diastolic pressure equalization (RA ≈ RVEDP ≈ PCWP within 5 mmHg) is a late finding — its absence does not exclude restriction
- Elevated RA pressure is the primary hemodynamic driver of diuretic resistance and ascites formation in cardiac amyloidosis
- The Forrester classification places most advanced amyloid patients in Profile C (cold and wet): low CI with elevated PCWP
- Differentiating restriction from constriction requires assessment of respirophasic ventricular interdependence, not simply checking for pressure equalization
- RHC changes management by defining safe diuretic targets, identifying when vasopressors are needed, and assessing transplant candidacy
1. Normal Hemodynamic Values
| Parameter | Normal Range | Unit |
|---|---|---|
| Right atrial pressure (mean RA) | 0–8 | mmHg |
| RV systolic / diastolic | 15–30 / 0–8 | mmHg |
| PA systolic / diastolic | 15–30 / 4–12 | mmHg |
| Mean PA pressure (mPAP) | 10–20 | mmHg |
| Pulmonary capillary wedge pressure (PCWP) | 4–12 | mmHg |
| Cardiac output (CO) | 4.0–8.0 | L/min |
| Cardiac index (CI) | 2.5–4.0 | L/min/m² |
| Pulmonary vascular resistance (PVR) | 0.25–1.6 | Wood units |
| Mixed venous O2 saturation (SvO2) | 65–75 | % |
2. The Restrictive Hemodynamic Profile
Cardiac amyloidosis produces a characteristic hemodynamic signature defined by elevated biventricular filling pressures with reduced cardiac output:
2.1 Typical Amyloid Hemodynamic Profile
| Parameter | Typical Amyloid Value | Normal | Significance |
|---|---|---|---|
| RA | 15–25 mmHg | 0–8 | Drives hepatic congestion, ascites, renal venous HTN |
| RVEDP | 15–25 mmHg | 0–8 | Reflects RV stiffness |
| PA systolic | 40–60 mmHg | 15–30 | Elevated from transmitted left-sided pressures |
| PCWP | 20–35 mmHg | 4–12 | Reflects LV stiffness; drives pulmonary congestion |
| CI | 1.2–2.0 L/min/m² | 2.5–4.0 | Critically reduced forward flow |
| SvO2 | 45–60% | 65–75 | Increased O2 extraction from low flow |
2.2 Derived Parameters
| Parameter | In Pure Restriction | Threshold | Meaning |
|---|---|---|---|
| TPG | <12 mmHg | >12 = pre-capillary component | Low TPG = purely post-capillary PH |
| DPG | <7 mmHg (may be negative) | >7 = pulmonary vascular remodeling | Negative DPG = no intrinsic pulmonary disease |
| PVR | <2 WU | >2 WU abnormal | Normal PVR = passive PH from left heart failure |
Clinical Pearl
A negative DPG and PVR near zero confirms isolated post-capillary pulmonary hypertension (IpcPH, WHO Group 2). The pulmonary vasculature is a passive conduit transmitting elevated left-sided pressures. The pulmonary hypertension will improve if left heart failure is treated. This has direct implications for transplant evaluation — PVR <3 WU is generally required for cardiac transplant candidacy.
3. Forrester Classification in Amyloidosis
| Profile | CI | PCWP | Description | Amyloid Relevance |
|---|---|---|---|---|
| A (Warm & Dry) | ≥2.2 | ≤18 | Compensated | Early disease; uncommon at diagnosis |
| B (Warm & Wet) | ≥2.2 | >18 | Congested, adequate perfusion | Moderate disease; diuretics effective |
| L (Cold & Dry) | <2.2 | ≤18 | Low output, no congestion | Over-diuresed amyloid patient — danger zone |
| C (Cold & Wet) | <2.2 | >18 | Low output with congestion | Most advanced amyloid patients; vasopressor + careful diuresis |
The Profile L Danger
Aggressive diuresis in a Profile C amyloid patient can push them into Profile L — cold and dry. The stiff ventricle needs elevated filling pressures to maintain even its meager output. Removing preload drops SV further and causes hypotension, AKI, and hemodynamic collapse. The treatment for Profile L is NOT more diuretics — it is fluid repletion or inotropic support. RHC defines where the patient sits on this map and how much volume can safely be removed.
4. RA Pressure, Diuretic Resistance, and Ascites
Elevated right atrial pressure is the hemodynamic engine of diuretic resistance in cardiac amyloidosis. The mechanisms are multiplicative:
- Reduced renal perfusion gradient: Renal perfusion pressure = MAP − renal venous pressure. With RA 23 mmHg transmitted to renal veins, the transrenal pressure gradient narrows even at normal MAP.
- Splanchnic congestion: High RA pressure drives transudation through hepatic sinusoidal fenestrations (unlike cirrhotic capillarized sinusoids), generating cardiac ascites. Liters reaccumulate rapidly.
- Impaired oral diuretic absorption: Gut edema from splanchnic congestion reduces bioavailability of oral loop diuretics.
- Neurohormonal activation: Low CO triggers RAAS, sympathetic activation, and AVP release — all promoting sodium and water retention.
Clinical Pearl
The pattern of massive ascites with minimal or absent peripheral edema in a patient with cardiac disease is not a contradiction. With RA pressure >20 mmHg, the hepatic venous bed — with its uniquely permeable sinusoidal endothelium — offers the path of least resistance for fluid extravasation. The peritoneal cavity fills while the critically low cardiac output is insufficient to generate capillary hydrostatic pressures in lower extremity beds for peripheral edema.
5. The Big Comparison: Restrictive vs. Constrictive vs. HFpEF vs. Tamponade
| Feature | Restrictive (Amyloid) | Constrictive Pericarditis | HFpEF (Non-Infiltrative) | Tamponade |
|---|---|---|---|---|
| RA waveform | Prominent Y descent | Prominent Y descent | Normal or blunted | Blunted Y descent |
| Kussmaul sign | Variable | Present | Absent | Absent |
| Dip-and-plateau (square root) | Present | Present | Absent | Absent |
| Ventricular interdependence | Absent | Present (key differentiator) | Absent | Present |
| Respirophasic PCWP variation | Concordant (both ventricles rise together) | Discordant (LV and RV move oppositely) | Minimal | Concordant |
| PCWP level | Markedly elevated | Elevated | Mildly-moderately elevated | Elevated |
| Diastolic equalization | Often present (late) | Present | Usually absent | Present |
| CI | Markedly reduced | Reduced | Normal or mildly reduced | Reduced |
| Pericardium | Normal | Thickened/calcified | Normal | Effusion |
| Wall thickness | Increased | Normal | Normal or mildly increased | Normal |
| Treatment | Disease-modifying Rx + diuretics | Pericardiectomy | GDMT, SGLT2i, diuretics | Pericardiocentesis |
Warning: The Equalization Misconception
The most common teaching error is that restrictive cardiomyopathy always shows diastolic pressure equalization (RA ≈ RVEDP ≈ PCWP within 5 mmHg). In reality, left-dominant or asymmetric infiltration — where the LV is more heavily infiltrated than the RV — commonly produces a large gradient (PCWP >> RA). A PCWP of 30 mmHg with RA of 11 mmHg (gradient 19 mmHg) does NOT exclude restriction. Classic equalization is a late finding when both ventricles are equally stiff.
6. PCWP Interpretation in Amyloidosis
PCWP reflects left atrial pressure, which in turn reflects LV filling pressure. In cardiac amyloidosis, PCWP is elevated because the stiff LV requires supranormal filling pressures to generate even a small stroke volume.
| PCWP Range | Interpretation | Clinical Action |
|---|---|---|
| ≤12 mmHg | Normal | Adequate preload; output depends on ventricular function |
| 13–18 mmHg | Mildly elevated | Mild congestion; cautious diuresis may be safe |
| 18–25 mmHg | Moderately elevated | Significant congestion; diurese with CI monitoring |
| >25 mmHg | Severely elevated | Pulmonary edema risk; aggressive decongestion — but in amyloid, CI may drop if preload reduced |
Clinical Pearl
In amyloidosis, there is a narrow "safe operating range" for PCWP. Too high causes pulmonary edema; too low causes output failure. RHC allows identification of this window. A reasonable target is often PCWP 15–20 mmHg — above normal but enough to maintain the stiff ventricle's output. This is fundamentally different from dilated cardiomyopathy where aggressive PCWP reduction improves output.
7. Why RHC Changes Management
| Clinical Question | RHC Answer | Management Change |
|---|---|---|
| Why is the patient not responding to diuretics? | CI 1.2, RA 23 — cardiogenic shock, not diuretic failure | Add vasopressor before continuing diuresis; consider ultrafiltration |
| Is diuresis safe? | PCWP 30 but CI 1.5 — preload-dependent | Very slow net negative with CI monitoring; avoid bolus diuretics |
| Is this restrictive or constrictive? | No ventricular interdependence — restrictive | Medical therapy, not pericardiectomy |
| Is the patient a transplant candidate? | PVR 1.5 WU — acceptable | Proceed with transplant evaluation |
| What is the target filling pressure? | CI peaks at PCWP 18 — drops below | Set diuretic target at PCWP 18, not "dry weight" |
References
- Kittleson MM, Maurer MS, Ambardekar AV, et al. Cardiac amyloidosis: AHA scientific statement. Circulation. 2020;142(1):e7-e22. PubMed
- Hoit BD. Right heart catheterization: hemodynamic interpretation. In: Braunwald's Heart Disease. 12th ed. Elsevier; 2022.
- Humbert M, Kovacs G, Hoeper MM, et al. 2022 ESC/ERS guidelines for diagnosis and treatment of pulmonary hypertension. Eur Heart J. 2022;43(38):3618-3731. PubMed
- Nishimura RA. Constrictive pericarditis in the modern era: a diagnostic dilemma. Heart. 2001;86(6):619-623. PubMed
- Rangaswami J, Bhalla V, Blair JEA, et al. Cardiorenal syndrome: AHA scientific statement. Circulation. 2019;139(4):e52-e154. PubMed
- Kittleson MM, Ruberg FL, Ambardekar AV, et al. 2023 ACC expert consensus on cardiac amyloidosis. J Am Coll Cardiol. 2023;81(11):1076-1126. PubMed
- Fortea JI, Puente A, Cuadrado A, et al. Congestive hepatopathy. Int J Mol Sci. 2020;21(24):9420. PubMed
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© Urine Nephrology Now | Amyloid Series
Andrew Bland, MD, MBA, MS