1. What is amyloidosis? What are the main precursor proteins in cardiac amyloidosis?

• Amyloidoses are protein-folding disorders in which proteinaceous deposits known as amyloid can infiltrate multiple organs. Cardiac amyloidosis is typically secondary to two main subtypes: 1) immunoglobulin light chain produced by clonal plasma cells (AL cardiac amyloidosis), and 2) transthyretin produced by the liver (ATTR cardiac amyloidosis). AL and ATTR account for >95% of cardiac amyloidosis. Rare precursors include serum amyloid A (AA) and apolipoprotein A-1 (ApoA-1).
  • AL cardiac amyloidosis
    • Overall incidence of AL amyloidosis is estimated to be 8.0-14.4 million persons per year in the USA with cardiac involvement in ~50% of patients. Median survival of patients with cardiac AL amyloidosis is 6 months from the onset of heart failure. Survival has improved with earlier detection and advancements in oncologic treatments.
    • AL may deposit in any tissue outside the CNS and so patients often have multiorgan involvement (kidneys, liver, etc).
  • ATTR cardiac amyloidosis
    • ATTR typically results in cardiac amyloidosis, peripheral neuropathy, and MSK sequelae (i.e., bilateral carpal tunnel, lumbar spinal stenosis, biceps tendon rupture) with relative proportions dependent on the mutant variant.
    • Transthyretin amyloidosis can occur secondary to the deposition ofnormal TTR (known as “ATTR wild type” or “ATTRwt”) or a mutant form (hereditary form known as “ATTR mutant” or “ATTRm”).
      • ATTRwt
        • Has a 15:1 male to female prevalence ratio and usually occurs in older patients  (>65 y.o.)
        • Almost always involves the heart
          • May be responsible for as many as 30% of heart failure with preserved ejection fraction (HFpEF) cases in patients >75 years old!
      • ATTRm
        • Has only a slight male predominance and occurs in younger patients (>40 y.o.)
        • Inherited in an autosomal dominant fashion with multiple genotypes with variable degrees of penetrance and cardiac involvement
        • There are more than 100 genetic variants of ATTR that are associated with amyloidosis. However, only a few of these variants, including Val30Met, Thr60Ala, Ser77Tyr, and Val122Ile, are responsible for the majority of cases of hereditary ATTR
          • As stated in Podcast Episode #7, the specific mutation is closely linked with the age of onset, natural history, and phenotype of the affected individual!
          • The Val122Ile mutation is the most common variant in the USA and a has prevalence of 3-4% in the US African American population. It is associated with cardiac amyloidosis with minimal neuropathy.
          • Thr60Ala is the 2^nd most common variant in the USA and is seen most commonly in those of Irish descent. It is associated with a mixed cardiomyopathy and neuropathy phenotype.
          • Val30Met causes a prototypical hATTR polyneuropathy (heriditary ATTR with polyneuropathy also known as “Familial Amyloid Polyneuropathy”
          • The specific genetic variant affects treatment decision and screening is indicated for individuals with known or suspected familial amyloidosis presenting w/ new symptomatic heart failure.

2. What are some classic cardiac and extracardiac manifestations of amyloidosis?

• For fantastic case presentations of cardiac amyloidosis including suggestive history and physical exam findings, diagnostic considerations, and recommended management, tune in to CardioNerds Podcast Episodes #7-10 and #54! As  described in Podcast Episode #7, amyloidosis is associated with many classic extracardiac findings based on which organ it deposits in, and can also deposit in every layer of the heart—coronary, ventricular, valvular, electrical, and pericardial tissues! Below is a brief outline of some of the classic extracardiac and cardiac manifestations of amyloidosis.
  • Extracardiac:
    • ATTR: peripheral nerves (sensorimotor and autonomic defects) and musculoskeletal sequelae (bilateral carpal tunnel syndrome, lumbar spinal stenosis, biceps tendon rupture). Degree of cardiac vs nerve involvement differs by mutant variant as above. A prior Cleveland Clinic study showed Congo red staining of tenosynovial tissue detected amyloid deposits in 10.2% of patients undergoing carpal tunnel release surgery
    • AL: any tissue outside the CNS. For instance, typical organs involved include the kidneys (nephrotic syndrome), liver, intestines, and nervous system. On exam one may find macroglossia and periorbital bruising.
  • Cardiovascular:
    • Decreased antihypertensive medication requirements with increasing age or presenting with lower than expected blood pressure
    • Postural hypotension
    • Coronary microvascular disease
      • Chronically elevated but flat troponin (infiltration into the coronary microvasculature)
      • Almost all patients with cardiac amyloidosis have significantly reduced peak stress myocardial blood flow (<1.3 ml/g/min) which may explain symptoms of angina in these patients with absence of epicardial coronary artery disease
    • Myocardial
      • Signs and symptoms of both left and right heart failure
      • Restrictive physiology
      • LVH tends to be greater in ATTR than in AL by time of symptom onset. This is because AL is also directly toxic, thereby causing a toxic-infiltrative cardiomyopathy. ATTR is more likely to deposit asymmetrically and thus may more closely mimic hypertrophic cardiomyopathy
    • Valvular
      • Thickened AV valves and interatrial septum
      • Paradoxical low-flow, low-gradient severe aortic stenosis (~15% of patients who undergo transcatheter aortic valve replacement have ATTRwt). The low flow and low gradient are because of restrictive filling and significant diastolic dysfunction
    • Electrical
      • AV Block, Bundle Branch Block
      • Atrial fibrillation from infiltration of the atria (especially ATTR), chronically high left atrial pressure, and/or aging.
      • Low voltage EKG[NJ1] [GU2]  (in most cases, however in up to ~10% of cases you may see voltage criteria for LVH on the EKG. However, the magnitude of electrocardiographic LVH  would still pale in comparison to the degree of hypertrophy you would see on echocardiography)
      • Pseudoinfarct pattern with septal Q-waves mimicking an anteroseptal MI
    • Pericardium
      • Pericardial Effusion

3. How can multimodality imaging help in the evaluation and management of cardiac amyloidosis? What are features suggestive of cardiac amyloidosis on echocardiography, Technetium-99m pyrophosphate (99mTc-PYP) scan, and cardiac MRI (CMR)?

• Multimodality imaging has several roles in the evaluation of possible cardiac amyloidosis: establishing the clinical suspicion, diagnosing ATTR CA, surveillance of ATTR mutation carriers, monitoring disease progression, and assessing response to therapy.
  • Echocardiography
    • RV and LV wall hypertrophy (>12 mm) with normal chamber size
    • Biatrial enlargement
    • Thickened AV valves and interatrial septum
    • Possible concurrent LFLG aortic stenosis
    • Reduced Global Longitudinal Strain (GLS) with relatively preserved longitudinal function in the apex compared to the base. This “apical sparing” or “cherry on top” pattern has a 93% sensitivity and 82% specificity in identifying patients with cardiac amyloidosis in differentiating from “mimics” such as hypertrophic cardiomyopathy, aortic stenosis, or hypertensive heart disease.
    • Speckled pattern of the myocardium (less apparent with contemporary imaging)
    • Restrictive filling pattern on mitral inflow with ≥ Grade 2 Diastolic Dysfunction
    • Small pericardial effusion
  • Technetium-99m pyrophosphate (99mTc-PYP) Scan
    • 99mTc-PYP is a bone-avid radiotracer. In the 1980s there was excitement in the possibility of using 99mTc-PYP scan for diagnosis of cardiac amyloidosis however, enthusiasm waned when there started to be reports of low sensitivity. There was a resurgence of interest after the 2005 paper by Perugini et al. that showed that PYP scan can differentiate ATTR cardiac amyloidosis from AL cardiac amyloidosis with high sensitivity and specificity. It is likely that the previously reported low sensitivities were due to cases of AL amyloidosis.
    • How does 99mTc-PYP bind to amyloid protein and how does this differentiate ATTR from AL cardiac amyloidosis? 
      • Mechanisms of 99mTc-PYP binding to amyloid include the possible binding to “amyloid P component” (which binds the amyloid fibrils together via a calcium-dependent mechanism) via a calcium mediated mechanism or 99mTc-PYP binding to small microcalcifications which are much more prevalent in ATTR cardiac amyloidosis than with AL cardiac amyloidosis.
      • Usually there is no reason to have large myocardial uptake of 99mTc-PYP unless an individual has ATTR cardiac amyloidosis! Patients with AL cardiac amyloidosis can have myocardial uptake of 99mTc-PYP but usually at a much lower quantity. One rare caveat of this is in patients who are treated with hydroxychloroquine as hydroxychloroquine toxicity can present with restrictive cardiomyopathy in which you can have myocardial uptake of 99mTc-PYP. Remember that PYP was used to grade the size of myocardial infarction in the past, and following an acute MI we may see uptake as well (see below).
    • How and why is a 99mTc-PYP Scan combined with Single-photon emission computerized tomography (SPECT) to evaluate for ATTR amyloidosis?
      1. The 99mTc-PYP radiotracer is injected into the patient
      2. Planar imaging (a 2-D Nuclear image similar to CXR A/P) AND Cardiac SPECT images are obtained either 1 or 3 hours after injection of the radiotracer
      3. The planar images are examined both quantitatively and semiquantitatively.
         • Quantitative: Two circular regions of interest of the same size are drawn over the heart  and the contralateral chest (to account for background and ribs). The total and absolute mean counts are measured from both regions of interest. The heart to contralateral (H/CL) ratio is calculated. A ratio of ≥1.5 is considered positive for ATTR amyloid on a 1 hour protocol and a ratio of ≥1.3 is considered positive for ATTR amyloid on a 3 hour protocol
           • 99mTc-PYP radiotracer has peak myocardial counts 60 minutes after injection with gradual decline at 2 and 3 hours. Bone counts, however, increase gradually and peak 2-3 hours after injection. Because of this, the sensitivity of a 1 hour protocol is increased and specificity decreased (myocardial counts + blood pool counts which are at close to peak / Bone counts which are not at peak will give a higher H/CL). The sensitivity of the 3 hour protocol is decreased and the specificity is increased (myocardial counts + blood pool counts which are now reduced from peak / Bone counts which are now at peak will give a lower H/CL ratio). Because of this, the H/CL uptake ratio threshold of ≥ 1.5 has been established for 1 hour imaging and a lower cutoff of ≥ 1.3 established for 3-hour imaging. These cutoffs have been suggested to identify ATTR amyloid and distinguish it from AL amyloid with high sensitivity and specificity.
         • Semiquantitative: The myocardial uptake of 99mTc-PYP is visually compared to bone uptake
           • Grade 0: no myocardial uptake
           • Grade 1: myocardial uptake < bone uptake
           • Grade 2: myocardial uptake equal to bone uptake
           • Grade 3: myocardial uptake > bone uptake
      4. The Cardiac SPECT images are examined to:
         • Distinguish overlying rib uptake adding to counts over the region of interest over the heart on planar imaging
         • Distinguish blood pool activity from myocardial activity
         • This co-registration with CT is important to make sure you’re not counting tracer in the blood pool of the ventricle chamber (perhaps due to low cardiac output) or in the ribs (perhaps from rib fracture(s)) as myocardial uptake!
      5. Information from the planar Images (in point 3 above) and the Cardiac SPECT images (point 4 above) are synthesized to obtain a final interpretation regarding diagnosis of ATTR Cardiac Amyloidosis
         • Positive scan: Semiquantitative Grade ≥ 2 w/ confirmation of myocardial uptake on SPECT (rather than bone or blood-pool uptake). When there is Semiquantitative Grade ≥ 2 combined with negative free light chain and immunofixation assays this can diagnose ATTR cardiac amyloidosis and exclude AL cardiac amyloidosis w/ 100% PPV!
         • Equivocal scan: Semiquantitative Grade 1 with H/CL ratio 1-1.5 (on a 1 hour protocol) or 1-1.3 (on a 3 hour protocol). May represent AL cardiac amyloidosis or early ATTR cardiac amyloidosis. These patients need further specialized assessment for diagnosing cardiac amyloid; histological confirmation and typing of cardiac amyloidosis is recommended.
         • Negative scan: Semiquantitative Grade 0 with H/CL ratio <1
    • What are some limitations of 99mTc-PYP Scan and examples of why concomitant Cardiac SPECT is useful?
      • Most early experience highlighting the high accuracy of 99mTc-PYP scans for diagnosis of ATTR cardiac amyloidosis was with patients who were presenting with advanced disease and clinical heart failure where all the manifestations of amyloidosis including the imaging manifestations were more readily apparent
        • Sensitivity: More and more we are starting to send genetic testing for ATTRm and we may identify family members who are asymptomatic but have high risk genes. These are NYHA Functional Class 1, Stage A patients  at risk for disease but without clinical manifestations. We don’t have large scale population studies on these groups of patients and thus we don’t have sensitivity data.
        • Specificity: In the setting of rib fracture on the left, you can have active bone regeneration overlying the heart on planar images and your H/CL ratio will be increased resulting in false positive. Alternatively, rib fractures on the right can lead to a false negative. Persistent blood pool presence of the radiotracer even up to 3 hours despite no uptake in the myocardium will give ratios in the 1.3 to 1.4 range and can be misdiagnosed as ATTR cardiac amyloidosis
        • Originally, several decades ago, 99mTc-PYP Scan was done to identify the infarct area in the setting of acute MI. However, after around 1-2 weeks, you should no longer have 99mTc-PYP Scan uptake in that area. So early after MI, you may have a false positive result for ATTR and late following MI (when muscle is replaced by scar) you may have a false negative (lack of amyloid deposition and PYP tracer uptake in the scarred segments).
        • Patients who are high risk based on genetics and family history but do not yet have clinical disease can have negative blood work, ECG, imaging, and then a few years later—while they are still asymptomatic—can have a positive 99mTc-PYP Scan. These tests are not static—they can change over time! We don’t know what the appropriate intervals for follow-up testing for these patients with preclinical disease
        • Phe64Leu and Val30Met mutations are associated with false negative 99mTc-PYP scans!
  • Cardiac MRI (CMR)
    • Same anatomical evaluation as with echocardiography: diffuse increase in wall thickness, longitudinal apical function better than basal, etc.
    • Additionally, we get tissue characterization looking for scar
    • As the amyloid fibrils deposit into the myocardium, there is edema and infiltration, with increased space between cells (extracellular space) leading to elevated T1 times. As T1 relaxation time prolongs compared to normal myocardium, that is reflective of edema or diffuse fibrosis.
    • The space between the cells, the extracellular volume, is significantly increased by amyloid fiber deposition. Global extracellular volume (ECV) > 40% increase is suggestive of cardiac amyloidosis. This is not a specific sign for cardiac amyloidosis—anything that can give inflammation or fibrosis in the myocardium can increase the extracellular volume; however, the degree of elevation is far beyond what we see with other pathologies.
    • GLS on echocardiography and CMR w/ECV may be useful in monitoring response to therapy!
    • Gadolinium deposits into the extracellular space in areas that have been expanded by fibrosis. The classic area of deposition of amyloid fibrils is in the subendocardium. Diffuse subendocardial late gadolinium enhancement (LGE) in a non-coronary artery distribution with a dark blood pool is classic for cardiac amyloidosis; as the disease becomes more advanced, this can evolve into transmural LGE
    • Cardiac MRI does not have the power to discriminate between AL or ATTR cardiac amyloidosis. You can get some suggestion of the difference. Because AL cardiac amyloidosis is a relatively acute process, you may have more subendocardial LGE, a little less increased wall thickness, and some evidence of edema along with fibrosis when we look at T2 imaging compared to ATTR cardiac amyloidosis which is a more indolent process that takes years to develop.
  • What is in the works regarding the multimodality imaging evaluation of Cardiac Amyloidosis?
    • Novel Cardiac SPECT radiotracers and Cardiac PET radiotracers have shown promise in being able to follow response to treatment and assess prognosis respectively
    • PET radiotracers originally developed for imaging B-amyloid and Alzheimer’s disease (e.g. 18-F-florbetapir) can bind to the beta-pleated motif of amyloid fibrils regardless of the precursor protein (e.g., can bind to both ATTR and AL cardiac amyloid).
      • Researchers are also attempting to repurpose clinically available radiotracers to adequately image AL amyloid burden in the heart
      • PET tracers are quantitative and allow the possibility of quantifying amyloid burden and detecting changes in burden of disease (potential use for monitoring response to therapy). The 18-F-tracers have a long half-life of 109.7 minutes and allows delivery to sites without a cyclotron on site.

4. What are the ASNC/AHA/ASE/EANM/HFSA/ISA/SCMR/SNMMI expert consensus recommendations for multimodality imaging in cardiac amyloidosis? A summary of the consensus recommendations is provided below. A link to the recommendations is provided in the “References” section below.

• In the absence of a clonal plasma cell process, 99mTc-PYP/DPD/HMDP scintigraphy consistent with ATTR cardiac amyloidosis combined with consistent echo or CMR findings obviates the need for invasive endomyocardial or extracardiac biopsy!
• For asymptomatic gene carriers, echocardiography and 99mTc-PYP Scan were rated as “Appropriate” while CMR was rated as “May Be Appropriate”
  • ECV has the potential to identify disease earlier in asymptomatic gene carriers compared with echocardiography
  • In patients with suspicion for cardiac AL amyloidosis (biopsy-proven systemic AL amyloidosis or MGUS w/abnormal FLC levels) 99mTc-PYP was rated as “Rarely Appropriate”
• For patients with new symptomatic heart failure or those who are ATTR gene carriers/patients with AL or ATTR amyloidosis with new or worsening cardiac symptoms (chest pain, fatigue, effort intolerance, dyspnea, palpitations, dizziness/lightheadedness, syncope, orthopnea, PND, bloating, leg swelling, leg or jaw claudication) in which we are screening for cardiac amyloidosis, echocardiography, CMR, and 99mTc-PYP were rated as “Appropriate”
  • Again, for patients suspicion for cardiac AL amyloidosis (biopsy-proven systemic AL amyloidosis or MGUS w/abnormal FLC levels) 99mTc-PYP was rated as “Rarely Appropriate” apart from the rare instance in long-term survivors of AL amyloidosis where concurrent ATTR cardiac amyloidosis is suspected
• For patients with biopsy-proven AL and ATTR cardiac amyloidosis, CMR and echocardiography were rated as “Appropriate” for assessing amyloid burden, response to therapy, or eligibility for stem cell transplant.
  • 99mTc-PYP was rated as “Rarely Appropriate”
  • 24 month assessment of response to therapy for echocardiography or CMR was rated as “Appropriate” with more frequent evaluation varying across expert amyloidosis centers
• For patients with conditions with high risk for potential cardiac amyloidosis (bilateral carpal tunnel syndrome; biceps tendon rupture; unexplained neuropathy; arrhythmias in the absence of usual risk factors and no signs/symptoms of heart failure) echocardiography was rated as “Appropriate” and CMR and 99mTc-PYP were rated as “May Be Appropriate”
• For patients with prior suggestive echocardiogram of cardiac amyloidosis, CMR was rated as “Appropriate”. For patients with prior suggestive CMR of cardiac amyloidosis, echocardiography was rated as “Appropriate”
  • 99mTc-PYP was rated as “May Be Appropriate” as it should only be used in cases of suspected ATTR cardiac amyloidosis.