Amyloidosis is a condition where abnormal proteins, known as amyloid, accumulate in organs and tissues, interfering with their normal function. This buildup can affect various organs, including the kidneys, liver, nerves, and heart. When amyloid proteins specifically deposit in the heart, the condition is called cardiac amyloidosis.
The Nature of Cardiac Amyloidosis
Amyloid refers to misfolded proteins that become insoluble and aggregate into fibrils, which then deposit in various tissues. In cardiac amyloidosis, these amyloid fibrils infiltrate the interstitial spaces between heart muscle cells, or myocytes. This deposition causes the heart walls to thicken and stiffen, leading to restrictive cardiomyopathy.
The increased stiffness impairs the heart’s ability to relax and fill with blood between beats, a problem known as diastolic dysfunction. While pumping strength may initially be preserved, reduced filling capacity means less blood is effectively pumped to the body. This can lead to progressive heart failure, as the heart struggles to meet the body’s demand.
Different Types of Cardiac Amyloidosis
Cardiac amyloidosis primarily involves two main types of amyloid proteins. AL amyloidosis originates from abnormal plasma cells in the bone marrow. These cells produce misfolded light chain proteins that form amyloid fibrils.
ATTR amyloidosis involves the transthyretin (TTR) protein. Transthyretin normally transports thyroid hormone and vitamin A in the bloodstream. This type can manifest in two forms: hereditary ATTR, caused by genetic mutations in the TTR gene, or wild-type ATTR, where the normal TTR protein becomes unstable and misfolds with age. Wild-type ATTR amyloidosis is a cause of heart failure, particularly in men over 80.
Recognizing the Symptoms
The symptoms of cardiac amyloidosis often arise from the heart’s impaired function due to amyloid deposition. Individuals may experience shortness of breath, which can worsen with exertion or when lying flat due to fluid accumulation in the lungs. Fatigue and weakness are common, reflecting the heart’s reduced ability to pump enough blood.
Fluid retention can lead to swelling, particularly in the legs, ankles, and abdomen. Amyloid infiltration into the heart’s electrical system can disrupt its rhythm, causing irregular heartbeats or palpitations. Some individuals may experience dizziness or lightheadedness due to blood pressure fluctuations. Chest pain can also occur.
Diagnosing Cardiac Amyloidosis
Diagnosis involves evaluations to identify amyloid deposits and determine their type. It often begins with a clinical evaluation, where a doctor assesses symptoms and medical history. Blood and urine tests are used to check for abnormal proteins, such as free light chains for AL amyloidosis. Genetic testing may be performed for hereditary ATTR.
An electrocardiogram (ECG) may show characteristic low voltage readings despite a thickened heart wall. An echocardiogram provides images of the heart, revealing thickened walls and assessing its pumping function. Cardiac magnetic resonance imaging (MRI) provides detailed views of the heart muscle and can help detect amyloid deposits.
A definitive diagnosis often requires a tissue biopsy from areas like the fat pad, bone marrow, or the heart itself, to confirm amyloid presence and type. Nuclear scintigraphy, or a bone scan, is a valuable non-invasive tool for diagnosing ATTR amyloidosis without a heart biopsy in many cases.
Treatment and Management
Treatment focuses on managing symptoms and targeting the underlying cause of amyloid production. Symptom management often includes medications like diuretics to reduce fluid retention and alleviate swelling and shortness of breath. Other medications may control irregular heart rhythms.
For AL amyloidosis, treatment involves chemotherapy to suppress abnormal plasma cells that produce misfolded light chains. For ATTR amyloidosis, newer medications stabilize the transthyretin protein or reduce its production, slowing or halting further amyloid deposition.
Supportive care, including lifestyle adjustments and monitoring, helps manage disease progression. In severe cases where other treatments are insufficient, a heart transplant may be considered, particularly for certain types of amyloidosis.