Cardiomyopathy refers to diseases of the heart muscle that lead to structural and functional abnormalities, often resulting in heart failure. Infiltrative cardiomyopathy is characterized by the deposition of abnormal substances within the heart muscle tissue. This accumulation causes the ventricular walls to thicken and become rigid, impairing the heart’s ability to relax and fill with blood between beats. This restriction significantly compromises overall cardiac output. Infiltrative cardiomyopathy is a secondary form of heart muscle disease, arising from a systemic issue affecting the entire body.
Understanding the Infiltration Process
The core problem in this cardiomyopathy is the mechanical obstruction and stiffening of the heart wall, known as restrictive physiology. Abnormal proteins or other materials deposit into the myocardium and surrounding interstitial spaces. This material makes the ventricular walls firm, noncompliant, and less elastic.
This stiffness primarily affects diastolic function, the relaxation phase when the ventricles should expand to accept blood. Rigid ventricles cannot stretch adequately, causing pressure inside the chambers to rise rapidly. This prevents efficient filling, backing pressure up into the atria and causing them to enlarge.
Infiltrative disease often presents with increased wall thickness and a stiff muscle, leading to diastolic dysfunction as the main problem. Systolic function is typically preserved until advanced stages. The progressive deposition of material can eventually lead to scarring and disruption of the heart’s conduction system, contributing to arrhythmias.
Identifying the Primary Underlying Causes
Infiltrative cardiomyopathy results from several underlying systemic conditions, with the specific deposited material determining the cause. Cardiac amyloidosis is the most frequently encountered type, involving the accumulation of misfolded proteins called amyloid fibrils. This is divided into light chain (AL) amyloidosis, a plasma cell disorder, and transthyretin (ATTR) amyloidosis, which can be hereditary or age-related (wild-type).
Cardiac sarcoidosis is another cause, where the heart muscle is infiltrated by inflammatory cells forming granulomas. This patchy infiltration can lead to focal inflammation and scarring that disrupts electrical pathways, often causing conduction abnormalities.
Hemochromatosis, a disorder of iron metabolism, results from excessive iron deposition within heart muscle cells. Early stages of iron overload cardiomyopathy present with restrictive physiology because the iron interferes with muscle relaxation. Identifying the precise cause is paramount because treatment is entirely different and tailored to the deposited substance.
Common Symptoms and Clinical Presentation
Symptoms of infiltrative cardiomyopathy are often non-specific and mirror those associated with advanced heart failure, frequently appearing late. Patients commonly experience shortness of breath (dyspnea), which worsens with exertion or when lying flat. Swelling (edema) is a prominent feature, particularly in the legs and abdomen, reflecting pressure back-up from the stiff heart chambers.
Fatigue is a common complaint due to the heart’s difficulty increasing output to meet the body’s demands. Palpitations or lightheadedness may occur as infiltration disrupts the heart’s electrical system, leading to arrhythmias. Non-cardiac signs, such as bilateral carpal tunnel syndrome or peripheral neuropathy, can suggest underlying systemic amyloidosis.
Diagnostic Tools and Techniques
Diagnosis relies on initial screening and advanced imaging to confirm the condition and determine the specific cause. Echocardiography is typically the first test, revealing increased left ventricular wall thickness, non-dilated ventricles, and severely impaired diastolic function. Thickened walls alongside a low voltage reading on an electrocardiogram is a classic clue for cardiac amyloidosis.
Cardiac Magnetic Resonance Imaging (CMR) characterizes the myocardial tissue itself, which is not possible with echocardiography. Specific patterns of late gadolinium enhancement (LGE) on a CMR scan, such as diffuse enhancement in the subendocardium, strongly suggest amyloid deposition. CMR is also effective in quantifying myocardial iron content in hemochromatosis, often eliminating the need for invasive procedures.
Nuclear scintigraphy, using a bone-seeking tracer like Technetium-99m pyrophosphate, is a non-invasive method to differentiate amyloidosis types. A positive scan is highly specific for wild-type or hereditary ATTR amyloidosis, often allowing diagnosis without a biopsy. Despite advances in non-invasive imaging, endomyocardial biopsy remains the definitive gold standard for confirming the presence and type of abnormal material.
Treatment Strategies and Management
Management involves addressing heart failure symptoms and the underlying disease process. Standard heart failure medications, such as beta-blockers and ACE inhibitors, must be used cautiously or avoided. Since restrictive physiology patients rely on a higher heart rate to maintain output, drugs that slow the heart rate or drop blood pressure can be detrimental.
Diuretics manage fluid overload and congestion, but their use requires careful monitoring to prevent excessive fluid removal and hypotension. Therapeutic advancements focus on cause-specific treatments that target the source of the infiltration. For AL amyloidosis, the goal is to eliminate the abnormal protein source using chemotherapy or immunomodulatory agents targeting the plasma cell clone.
Treatments for ATTR amyloidosis focus on stabilizing the transthyretin protein or “silencing” the gene that produces it, using stabilizers or siRNA therapies. For hemochromatosis, the mainstay of treatment is removing excess iron through phlebotomy, which can reverse cardiac damage if started early. Cardiac sarcoidosis is typically treated with immunosuppressive therapy, often corticosteroids, to reduce inflammatory granulomas and prevent scarring.