Cardiac amyloidosis is a condition in which misfolded proteins build up in the heart muscle, making the walls thick and stiff. Sometimes called “stiff heart syndrome,” it interferes with the heart’s ability to fill with blood and pump effectively. The condition is more common than once thought: studies estimate that 5% to 17% of patients diagnosed with a common type of heart failure actually have undiagnosed cardiac amyloidosis.
How Protein Deposits Damage the Heart
Normally, proteins fold into precise shapes to do their jobs. In amyloidosis, certain proteins misfold and clump together into tough fibers called amyloid. These fibers deposit in the spaces between heart muscle cells, combining with other structural molecules to form dense, insoluble sheets. As amyloid accumulates, it physically wedges between the cells that contract your heart, thickening the walls and making them rigid.
This stiffness is the central problem. The heart can’t relax properly between beats, so less blood fills the chambers each time. Stroke volume drops, and the heart compensates poorly. Amyloid can also infiltrate the heart’s electrical system, disrupting the natural pacemaker and the wiring that coordinates each heartbeat. That leads to rhythm problems, including atrial fibrillation and various types of heart block. In some forms of the disease, amyloid deposits even damage tiny blood vessels within the heart, occasionally causing chest pain or, rarely, a heart attack.
The Two Main Types
Not all cardiac amyloidosis is the same. The two types that account for nearly all cases differ in which protein misfolds, who gets the disease, and how fast it progresses.
Light Chain (AL) Amyloidosis
In AL amyloidosis, the problem starts in the bone marrow. A small, abnormal population of plasma cells produces excess fragments of antibodies called light chains. These light chains misfold into amyloid and deposit throughout the body, including the heart. Beyond the physical buildup, the circulating light chains themselves are directly toxic to heart cells, generating oxidative stress that accelerates damage. AL amyloidosis tends to progress quickly and can affect multiple organs at once, including the kidneys, liver, and nerves.
Transthyretin (ATTR) Amyloidosis
ATTR amyloidosis involves a liver protein called transthyretin, which normally carries thyroid hormone and vitamin A in the bloodstream. This type comes in two forms. The hereditary form results from a genetic mutation in the transthyretin gene (more than 120 different mutations have been identified). The wild-type form has no genetic mutation at all; the protein simply becomes unstable with age and begins misfolding. Wild-type ATTR is overwhelmingly a disease of older adults. Autopsy studies have found amyloid deposits in the hearts of up to 25% of people over age 85, suggesting many cases go unrecognized during life.
ATTR amyloidosis generally progresses more slowly than AL, but because it’s often diagnosed late, patients can already have significant heart damage by the time it’s caught.
Symptoms and Early Warning Signs
The hallmark symptoms are those of heart failure: shortness of breath with activity, swelling in the legs and abdomen, and fatigue that worsens over time. But cardiac amyloidosis often announces itself years earlier through clues outside the heart.
Carpal tunnel syndrome is one of the most common early red flags, particularly in ATTR amyloidosis. Amyloid deposits compress the nerve running through the wrist, causing numbness and tingling in the hands. Many patients undergo carpal tunnel surgery years before anyone suspects a heart problem. Spinal stenosis (narrowing of the spinal canal) is another musculoskeletal clue. Other non-cardiac signs include easy bruising, especially around the eyes in AL amyloidosis, and numbness or tingling in the feet from nerve involvement.
When the heart is involved, the thickened walls create a distinctive pattern. Blood pressure may drop or become unusually low, even in someone who previously had high blood pressure. Dizziness on standing, irregular heartbeats, and exercise intolerance are common. The combination of a thickened heart wall on imaging with low voltage on an electrocardiogram is a classic mismatch that should raise suspicion.
How It’s Diagnosed
Diagnosing cardiac amyloidosis has become significantly easier in recent years, and for one type, a biopsy is often no longer needed.
The first and most critical step is ruling out AL amyloidosis with a monoclonal protein screen, which is a set of blood and urine tests looking for abnormal antibody fragments. This distinction matters because AL amyloidosis requires a completely different treatment approach and progresses faster.
If the monoclonal protein screen comes back negative, a nuclear bone scan (using a radioactive tracer called technetium pyrophosphate) can diagnose ATTR cardiac amyloidosis without a biopsy. Doctors grade the scan on a 0 to 3 scale based on how much tracer the heart absorbs compared to bone. A grade of 2 (uptake equal to bone) or 3 (uptake greater than bone), combined with a negative screen for AL, is considered diagnostic. This non-invasive approach has transformed the speed and ease of diagnosis at many centers.
If the monoclonal protein screen is abnormal, a tissue biopsy with specialized protein typing is required to confirm which type of amyloid is present. This is essential because some patients have both a monoclonal protein abnormality and ATTR amyloidosis, and treatment depends entirely on getting the type right.
Prognosis Varies Significantly by Type
The outlook for cardiac amyloidosis depends heavily on which type you have and how early it’s caught. Historically, AL amyloidosis with heart involvement carried a grim prognosis, with median survival as short as four months in advanced cases. In modern treatment cohorts, that number has improved to nearly five years, largely thanks to newer therapies that target the abnormal bone marrow cells producing the toxic light chains.
Doctors stage AL amyloidosis using blood markers of heart stress and damage. A widely used system assigns points based on levels of a heart stress hormone (NT-proBNP), a marker of heart cell injury (troponin), and the amount of abnormal light chains circulating in the blood. Higher stages, meaning more points, correspond to more advanced heart involvement and a shorter expected survival. This staging helps guide how aggressively treatment should begin.
ATTR amyloidosis generally has a longer timeline, particularly the wild-type form, but outcomes depend on how much heart function has already been lost at diagnosis.
Treatment Options
Treatment strategies differ completely between the two types, which is why accurate diagnosis is so important.
Treating AL Amyloidosis
Because AL amyloidosis is driven by abnormal bone marrow cells, treatment borrows from the playbook used for blood cancers. The goal is to eliminate the clone of cells making the toxic light chains, allowing the body to gradually clear amyloid deposits and the heart to recover some function. A landmark trial (called ANDROMEDA) showed that adding a targeted antibody therapy to a standard three-drug chemotherapy regimen tripled the rate of complete elimination of the abnormal protein, from 19% to 59%. This combination has become a standard first-line approach for newly diagnosed patients.
Treating ATTR Amyloidosis
For ATTR amyloidosis, the approach focuses on stabilizing the transthyretin protein so it doesn’t misfold. A medication called tafamidis works by binding to the transthyretin protein and holding it in its normal shape. In studies of patients over age 80, tafamidis was associated with a 56% reduction in mortality over two years and a 35% reduction in hospital readmissions for heart failure within the first year. Newer therapies that reduce the liver’s production of transthyretin altogether are also now available or in late-stage development.
Regardless of type, standard heart failure management plays a supporting role: carefully adjusted diuretics to manage fluid retention, monitoring for dangerous heart rhythms, and sometimes a pacemaker if the electrical system is severely affected. Traditional heart failure medications like beta-blockers and ACE inhibitors are often poorly tolerated in cardiac amyloidosis because patients already have low blood pressure, so management requires careful tailoring.
Why It’s Often Missed
Cardiac amyloidosis has historically been considered rare, but better diagnostic tools have revealed it’s far more common than previously recognized. A 2021 community screening study found that 6.3% of patients with heart failure and preserved pumping function who also had thickened heart walls turned out to have ATTR cardiac amyloidosis. Many of these patients had been living with a generic heart failure diagnosis for years.
The years-long gap between early signs like carpal tunnel syndrome and eventual cardiac diagnosis represents a window where earlier detection could change outcomes. Awareness of the non-cardiac clues, the distinctive echocardiographic pattern, and the availability of a simple nuclear scan have all contributed to faster diagnosis in recent years, but many cases still slip through. If you have unexplained heart wall thickening, heart failure that doesn’t respond typically to standard medications, or a history of bilateral carpal tunnel surgery, these are patterns worth discussing with a cardiologist familiar with amyloidosis.