# ATTR Cardiac Amyloidosis

Andrew Bland, MD, FACP, FAAP

[← Amyloid Series Index](https://urinenephrology.org/mastery/amyloid-series/index.html)

## Executive Summary

#### Key Points

- Transthyretin amyloid cardiomyopathy (ATTR-CM) is an underdiagnosed infiltrative cardiomyopathy resulting from extracellular deposition of misfolded transthyretin protein in the myocardium, producing restrictive physiology with preserved ejection fraction
- Wild-type ATTR-CM (ATTRwt) may affect 10–15% of older adults with HFpEF, with strong male predominance and typical onset after age 65
- The median diagnostic delay is 13 months from first heart failure manifestation, with a 44% initial misdiagnosis rate and 3- to 5-fold mortality increase from delayed diagnosis
- Ejection fraction is fundamentally unreliable in restrictive cardiomyopathy — critically low cardiac output (CI \<2.0 L/min/m²) can coexist with preserved EF, necessitating invasive hemodynamic assessment
- Tc-99m PYP scintigraphy with the Gillmore algorithm enables noninvasive diagnosis when grade 2–3 uptake is present and monoclonal protein is absent
- FDA-approved therapies include tafamidis and acoramidis (TTR stabilizers); gene silencers and anti-amyloid antibodies represent the next frontier

## 1. Epidemiology and the ATTRwt Prevalence Problem

Transthyretin amyloid cardiomyopathy exists in two forms: wild-type (ATTRwt, previously "senile cardiac amyloidosis") and hereditary/variant (ATTRv). ATTRwt is by far the more common form, accounting for the majority of ATTR-CM cases diagnosed in contemporary practice. Autopsy studies have detected TTR amyloid deposits in the myocardium of 25% of individuals over age 80, though most of these deposits are subclinical.

The clinically significant figure is this: **10–15% of patients hospitalized with HFpEF may have undiagnosed ATTR-CM** as the underlying etiology. In specific HFpEF subpopulations — elderly males with unexplained left ventricular hypertrophy, patients with aortic stenosis undergoing TAVR, and patients with bilateral carpal tunnel syndrome — the prevalence is even higher.

| Feature | ATTRwt | ATTRv |
|----|----|----|
| Etiology | Age-related TTR instability | Pathogenic TTR gene mutation |
| Typical Age at Dx | \>65 years (median ~75) | Variable (40–80 years) |
| Sex Predominance | Male \>\> Female | Variable by mutation |
| Common Variant | N/A | V122I (3.4% African Americans), T60A, V30M |
| Extracardiac Features | Carpal tunnel, spinal stenosis | Polyneuropathy, carpal tunnel, vitreous opacities |
| Untreated Median Survival | 2.5–3.5 years from diagnosis | Variable by mutation |

#### Clinical Pearl

Bilateral carpal tunnel syndrome frequently precedes cardiac amyloidosis diagnosis by 5–10 years. In any elderly male presenting with HFpEF who has a history of bilateral carpal tunnel release, ATTR-CM should be specifically evaluated. Lumbar spinal stenosis and spontaneous biceps tendon rupture are additional extracardiac "red flags."

## 2. The Preserved EF Trap

Preserved ejection fraction is the single most dangerous cognitive trap in cardiac amyloidosis diagnosis. The mechanism is straightforward: in infiltrative cardiomyopathy, the stiff ventricle fills with a markedly reduced end-diastolic volume but ejects a normal percentage of that small volume.

#### The EF-Cardiac Output Dissociation

A ventricle filling 50 mL and ejecting 28 mL produces an EF of 55% — appearing reassuringly normal — while delivering a stroke volume less than half of normal. **EF is a ratio, not a measure of output.** When EDV is small (stiff ventricle cannot fill), SV is small, but the ratio can look acceptable while the patient is in cardiogenic shock.

### 2.1 Evidence of Diagnostic Failure

| Study | Finding | Implication |
|----|----|----|
| Ladefoged et al. 2020 | Median diagnostic delay of 13 months (IQR 2–47) from first HF manifestation to ATTRwt diagnosis | Prolonged delay associated with worse NYHA class and diastolic dysfunction at diagnosis |
| Cardiac amyloidosis can be underrecognized. The 2023 ACC consensus supports a structured evaluation using monoclonal-protein testing, cardiac imaging, and tissue diagnosis when indicated. Diagnostic delay is clinically important, but no universal misdiagnosis percentage or mortality multiplier is established here. [ACC consensus](https://pubmed.ncbi.nlm.nih.gov/36697326/) |  |  |
| Cardiac amyloidosis can be underrecognized. The 2023 ACC consensus supports a structured evaluation using monoclonal-protein testing, cardiac imaging, and tissue diagnosis when indicated. Diagnostic delay is clinically important, but no universal misdiagnosis percentage or mortality multiplier is established here. [ACC consensus](https://pubmed.ncbi.nlm.nih.gov/36697326/) |  |  |

### 2.2 EF-CO Dissociation: A Worked Example

| Parameter | Dilated Cardiomyopathy (EF 30%) | Amyloid Heart (EF 55%) |
|----|----|----|
| End-diastolic Volume | 250 mL | 50 mL |
| Stroke Volume | 75 mL | 28 mL |
| Ejection Fraction | 30% | 55% |
| Heart Rate | 80 bpm | 85 bpm |
| Cardiac Output | 6.0 L/min | 2.4 L/min |
| Cardiac Index (BSA 2.0) | 3.0 L/min/m² | **1.2 L/min/m²** |
| Clinical Status | Compensated HF | **Cardiogenic shock** |

#### Clinical Pearl

In any patient where clinical severity (diuretic resistance, hypotension, AKI, severe fatigue) seems disproportionate to echocardiographic findings, the EF is lying. Pursue stroke volume index (SVI) calculation or right heart catheterization. An SVI \<33 mL/m² with preserved EF is the hemodynamic signature of infiltrative cardiomyopathy.

## 3. Echocardiographic Red Flags

Standard echocardiography provides multiple clues to cardiac amyloidosis beyond wall thickness and EF:

| Finding | Significance | Sensitivity |
|----|----|----|
| Biventricular wall thickness \>12 mm | Infiltrative pseudohypertrophy (amyloid deposits, not myocyte hypertrophy) | Moderate |
| Biatrial enlargement | Chronic elevation of filling pressures | High |
| Thickened interatrial septum and valve leaflets | Amyloid infiltration of non-ventricular structures | Moderate |
| Small LV cavity | Stiff, non-compliant ventricle with reduced filling | Moderate |
| Granular sparkling myocardial texture | Classic but neither sensitive nor specific | Low |
| e’ velocity \<5 cm/s | Severe diastolic impairment — myocardium "functionally a brick" | High |
| E/e’ \>14 | Elevated filling pressures; correlates with PCWP | High |
| **Apical sparing on GLS (bull’s-eye pattern)** | **Highly specific for cardiac amyloidosis (\>80% sensitivity and specificity)** | **High** |
| Low-voltage ECG with thick walls | Voltage-mass discordance — present in 25–40% | Low-Moderate |

#### Warning

"LVH" in amyloidosis is infiltrative pseudohypertrophy — amyloid fibrils depositing in the myocardial interstitium, not true myocyte hypertrophy from pressure overload. These walls appear thick but are physiologically hostile: stiff, non-compliant, and dependent on elevated filling pressures. Do not accept "hypertensive heart disease" as the explanation for LVH in a patient whose BP history does not support that degree of remodeling.

## 4. Diagnostic Algorithm: The Gillmore Pathway

The 2023 ACC Expert Consensus Decision Pathway and the landmark Gillmore et al. (2016) multicenter study establish a systematic noninvasive diagnostic pathway:

### Step 1: Clinical Suspicion

Raise the index of suspicion in HFpEF with increased wall thickness, especially males \>65, with concordant extracardiac features (carpal tunnel, spinal stenosis) or discordance between wall thickness and ECG voltage.

### Step 2: Monoclonal Protein Screening

Serum free light chains (kappa and lambda with ratio), serum protein immunofixation, and urine protein immunofixation **must** be performed in all patients with suspected cardiac amyloidosis. This serves the dual purpose of screening for AL amyloidosis (which requires urgent hematologic treatment) and enabling interpretation of the scintigraphy result.

### Step 3: Tc-99m Bone Scintigraphy (PYP Scan)

Technetium-99m pyrophosphate (PYP), DPD, or HMDP scintigraphy with planar and SPECT imaging at 1 and 3 hours post-injection. Myocardial uptake is graded on the Perugini scale:

| Perugini Grade | Visual Description              | H/CL Ratio (1 hour) |
|----------------|---------------------------------|---------------------|
| 0              | No myocardial uptake            | \<1.0               |
| 1              | Mild uptake, less than rib      | 1.0–1.5             |
| 2              | Moderate uptake, equal to rib   | ≥1.5                |
| 3              | Strong uptake, greater than rib | \>\>1.5             |

In Gillmore et al. (2016, n=1,217), grade 2 or 3 myocardial uptake demonstrated **\>99% sensitivity and 86% specificity** for cardiac ATTR amyloidosis. Specificity increased to **nearly 100%** when patients with a detectable monoclonal protein were excluded.

#### Noninvasive Diagnostic Criteria for ATTR-CM

**Grade 2 or 3 myocardial uptake on Tc-99m PYP/DPD/HMDP scintigraphy** PLUS **absence of monoclonal protein** on serum and urine studies = diagnostic of ATTR-CM without the need for endomyocardial biopsy.

### Step 4: TTR Gene Sequencing

Performed after ATTR-CM diagnosis is confirmed to distinguish ATTRwt from ATTRv. This informs genetic counseling, family cascade screening, and treatment selection.

#### Clinical Pearl

TTR gene testing answers "what type?" while PYP scintigraphy answers "is it there?" A positive gene test without scintigraphic confirmation could lead to misattribution of heart failure to amyloidosis when another etiology is responsible. The noninvasive pathway requires appropriate scintigraphy and exclusion of AL; typed biopsy provides a separate diagnostic route. A positive gene test does not obviate the need for PYP.

#### Critical Caveat

A positive PYP scan in a patient WITH a detectable monoclonal protein **cannot be used to diagnose ATTR noninvasively**. AL amyloidosis can produce low-grade PYP uptake, and both ATTR and AL can coexist. In this scenario, tissue biopsy with amyloid typing by mass spectrometry is mandatory. This is why monoclonal protein screening (Step 2) must precede PYP interpretation.

## 5. Disease-Modifying Therapy

### 5.1 TTR Stabilizers

| Agent | Mechanism | Pivotal Trial | Key Result | Status |
|----|----|----|----|----|
| **Tafamidis** (Vyndaqel/Vyndamax) | Binds TTR tetramer thyroxine-binding sites, prevents dissociation | ATTR-ACT (Maurer, NEJM 2018; n=441) | 30-month mortality 29.5% vs 42.9% placebo (NNT ~8); reduced CV hospitalization | FDA-approved |
| ATTRibute-CM randomized 632 patients to acoramidis or placebo. Its four-component hierarchical primary analysis favored acoramidis (win ratio 1.8, 95% CI 1.4–2.2). The outcome incorporated death, cardiovascular hospitalization, NT-proBNP change, and six-minute walk distance; the win ratio is not a mortality hazard ratio. [ATTRibute-CM](https://pubmed.ncbi.nlm.nih.gov/38197816/) |  |  |  |  |

### 5.2 Gene Silencing Therapies

RNA interference (RNAi) and antisense oligonucleotide (ASO) therapies reduce hepatic TTR production by 80–90%, eliminating new amyloid precursor supply:

- **Patisiran** (RNAi) and **inotersen** (ASO): Approved for ATTRv polyneuropathy
- **Vutrisiran** (RNAi, SC every 3 months): HELIOS-B trial showed 28% reduction in composite of all-cause mortality and recurrent CV events in ATTR-CM
- **NTLA-2001 / nexiguran ziclumeran** (CRISPR-Cas9 in vivo gene editing): \>90% sustained TTR knockdown after a single IV dose; phase 2/3 trials ongoing

### 5.3 Anti-Amyloid Antibodies: Toward Disease Reversal

The phase 1 NI006 trial enrolled 40 patients. At higher doses, imaging-based surrogate markers of amyloid load appeared to decrease during follow-up. These early findings do not establish improved survival or a proven clinical amyloid-removal treatment. [Phase 1 trial](https://pubmed.ncbi.nlm.nih.gov/37212440/)

### 5.4 Therapeutic Pipeline Summary

| Class | Mechanism | Status | "Cure" Potential |
|----|----|----|----|
| TTR stabilizers | Prevent tetramer dissociation | FDA-approved | Slows progression; does not remove deposits |
| Gene silencers | Reduce hepatic TTR 80–90% | Approved (neuropathy); positive CM data | Stops production; native clearance may reduce burden |
| CRISPR gene editing | Permanent TTR gene knockdown (\>90%) | Phase 2/3 | Single dose, permanent production halt |
| Anti-amyloid antibodies | Phagocytic removal of deposited fibrils | Phase 3 | Highest — direct amyloid removal demonstrated |
| Combination (silencer + depleter) | Halt production + remove deposits | Theoretical | Greatest — addresses supply and burden |

## 6. Heart Failure Management in ATTR-CM

#### Medications to Avoid or Use With Extreme Caution

- **Beta-blockers:** The stiff ventricle is rate-dependent for output — stroke volume is fixed, so CO = HR x SV. Rate reduction further compromises output.
- **Non-dihydropyridine calcium channel blockers** (verapamil, diltiazem): Same mechanism as beta-blockers — rate-dependent output.
- **Digoxin:** Binds preferentially to amyloid fibrils, causing toxicity at standard "therapeutic" levels.
- **ACE inhibitors/ARBs:** May cause profound hypotension due to autonomic involvement and low output state; use only with extreme caution.

**Diuretics** remain the cornerstone of volume management but frequently prove inadequate in advanced ATTR-CM. Diuretic resistance reflects the overwhelming hemodynamic driver: elevated RA pressure (often \>20 mmHg) acting on intact, permeable hepatic sinusoids generates ascites faster than the kidney can excrete salt and water. When oral diuretics fail, strategies include IV loop diuretics, metolazone for sequential nephron blockade, and serial large-volume paracentesis.

**SGLT2 inhibitors** (dapagliflozin, empagliflozin) are increasingly used based on HFpEF evidence, though dedicated ATTR-CM trial data are limited.

## 7. Nephrology Considerations

### 7.1 Cardiorenal Syndrome

ATTR-CM with severely reduced cardiac output and elevated right-sided pressures produces cardiorenal syndrome through: reduced renal arterial perfusion pressure (forward failure), elevated renal venous pressure (congestive nephropathy), neurohormonal activation (RAAS, sympathetic), and impaired diuretic delivery to the nephron.

### 7.2 Drug Dosing

Both tafamidis and acoramidis are hepatically metabolized and do not require dose adjustment for renal impairment. However, ATTRibute-CM excluded patients with eGFR \<30 mL/min/1.73 m², and limited data exist in advanced CKD or dialysis populations.

### 7.3 The Nephrologist’s Role

Interpreting diuretic resistance as a hemodynamic signal (not a renal failure), optimizing volume management, recognizing when RHC is needed to guide therapy, and monitoring for renal amyloid involvement (proteinuria, progressive GFR decline) are core nephrology contributions.

## References

1.  Kittleson MM, Maurer MS, Ambardekar AV, et al. Cardiac amyloidosis: evolving diagnosis and management: a scientific statement from the AHA. *Circulation*. 2020;142(1):e7-e22. [PubMed](https://pubmed.ncbi.nlm.nih.gov/32476490/)
2.  Ruberg FL, Grogan M, Hanna M, et al. Transthyretin amyloid cardiomyopathy: JACC state-of-the-art review. *J Am Coll Cardiol*. 2019;73(22):2872-2891. [PubMed](https://pubmed.ncbi.nlm.nih.gov/31171094/)
3.  Lane T, Fontana M, Martinez-Naharro A, et al. Natural history, quality of life, and outcome in cardiac transthyretin amyloidosis. *Circulation*. 2019;140(1):16-26. [PubMed](https://pubmed.ncbi.nlm.nih.gov/31109193/)
4.  Kittleson MM, Ruberg FL, Ambardekar AV, et al. 2023 ACC expert consensus decision pathway on comprehensive multidisciplinary care for the patient with cardiac amyloidosis. *J Am Coll Cardiol*. 2023;81(11):1076-1126. [PubMed](https://pubmed.ncbi.nlm.nih.gov/36697326/)
5.  Gillmore JD, Maurer MS, Falk RH, et al. Nonbiopsy diagnosis of cardiac transthyretin amyloidosis. *Circulation*. 2016;133(24):2404-2412. [PubMed](https://pubmed.ncbi.nlm.nih.gov/27143678/)
6.  Maurer MS, Schwartz JH, Gundapaneni B, et al. Tafamidis treatment for patients with transthyretin amyloid cardiomyopathy. *N Engl J Med*. 2018;379(11):1007-1016. [PubMed](https://pubmed.ncbi.nlm.nih.gov/30145929/)
7.  Gillmore JD, Judge DP, Cappelli F, et al. Efficacy and safety of acoramidis in transthyretin amyloid cardiomyopathy. *N Engl J Med*. 2024;390(2):132-142. [PubMed](https://pubmed.ncbi.nlm.nih.gov/38197816/)
8.  Fontana M, Berk JL, Gillmore JD, et al. Vutrisiran in patients with transthyretin amyloidosis with cardiomyopathy. *N Engl J Med*. 2024;391(17):1582-1593. [PubMed](https://pubmed.ncbi.nlm.nih.gov/39213194/)
9.  Garcia-Pavia P, aus dem Siepen F, Donal E, et al. Phase 1 trial of antibody NI006 for depletion of cardiac transthyretin amyloid. *N Engl J Med*. 2023;389(3):239-250. [PubMed](https://pubmed.ncbi.nlm.nih.gov/37212440/)
10. Ladefoged B, Dybro A, Povlsen JA, et al. Diagnostic delay in wild type transthyretin cardiac amyloidosis. *Int J Cardiol*. 2020;304:138-143. [PubMed](https://pubmed.ncbi.nlm.nih.gov/32033783/)
11. Wechalekar AD, Fontana M, Quarta CC, et al. AL amyloidosis for cardiologists: awareness, diagnosis, and future prospects. *JACC CardioOncol*. 2022;4(4):427-441. [PubMed](https://pubmed.ncbi.nlm.nih.gov/36444232/)
12. Rangaswami J, Bhalla V, Blair JEA, et al. Cardiorenal Syndrome: Classification, Pathophysiology, Diagnosis, and Treatment Strategies: A Scientific Statement From the AHA. *Circulation*. 2019;139(16):e840-e878. [PubMed](https://pubmed.ncbi.nlm.nih.gov/30852913/)

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