Prognosticating in Cardiac Amyloidosis: Let Me Count the Ways

Impact of vutrisiran on exploratory cardiac parameters in hereditary transthyretin-mediated amyloidosis with polyneuropathy

AIMS

HELIOS-A was a Phase 3, open-label study of vutrisiran, an RNA interference therapeutic, in patients with hereditary transthyretin (ATTRv) amyloidosis with polyneuropathy. This analysis evaluated vutrisiran's impact on exploratory cardiac endpoints in HELIOS-A patients.

METHODS AND RESULTS

Patients were randomized 3:1 to subcutaneous vutrisiran 25 mg every 3 months or intravenous patisiran 0.3 mg/kg every 3 weeks (reference group) for 18 months. Exploratory cardiac endpoints included change from baseline in N-terminal prohormone of brain-type natriuretic peptide (NT-proBNP) and echocardiographic parameters versus external placebo (APOLLO study). The modified intent-to-treat (mITT) population comprised randomized patients receiving any study drug (n = 122). A cardiac subpopulation with evidence of cardiac amyloid involvement (n = 40) was prespecified. 99mTc scintigraphy exploratory assessments in a planned vutrisiran-treated cohort at select sites were compared with baseline. At Month 18, vutrisiran demonstrated beneficial effects on NT-proBNP versus external placebo in the mITT and cardiac subpopulations (adjusted geometric mean fold change ratio [95% confidence interval] 0.480 [0.383-0.600], p = 9.606 × 10-10 and 0.491 [0.337-0.716], p = 0.0004, respectively). Benefits or trends towards benefit in echocardiographic parameters versus external placebo were observed for both populations. In 99mTc scintigraphy assessments, 32/47 (68.1%) and 31/48 (64.6%) patients exhibited reduced normalized left ventricular total uptake and heart-to-contralateral lung ratio, respectively. Perugini grade was reduced or unchanged versus baseline in 55/57 (96.5%) evaluable patients. No increase in cardiac adverse events was observed with vutrisiran versus external placebo.

CONCLUSIONS

Vutrisiran demonstrated evidence of potential benefit on cardiac manifestations in patients with ATTRv amyloidosis with polyneuropathy, with an acceptable safety profile.

Association of Right Ventricular Myocardial Blood Flow With Pulmonary Pressures and Outcome in Cardiac Amyloidosis

BACKGROUND

Cardiac amyloidosis (CA) is a restrictive and infiltrative cardiomyopathy, characterized by increased biventricular filling pressures and low output. Symptoms are predominantly of right heart origin. The role of right ventricular (RV) myocardial blood flow (MBF) in CA has not been studied.

OBJECTIVES

This study aimed to first associate RV MBF measured by using positron emission tomography (PET) with reference standards of RV pressures and then to explore its prognostic value in CA.

METHODS

Cardiac PET was performed at rest in 52 patients with CA and 9 healthy control subjects. MBF was quantified from the right and left ventricles by using 11C-acetate, 15O-water, or both (n = 25). RV pressure was measured invasively or by echocardiography. Associations between biventricular MBF toward symptoms, RV function, and outcome (death or acute heart failure) were studied in patients with CA.

RESULTS

MBF of the right ventricle (MBFRV) and the ratio of MBFRV and MBF of the left ventricle (MBFRV/LV) for the 2 tracers were significantly correlated (r > 0.92). MBFRV was directly correlated with RV systolic pressures with both tracers (P ≤ 0.005). MBFLV was inversely correlated with wall thickness (P < 0.0001). MBFRV/LV was significantly associated with N-terminal pro-B-type natriuretic peptide levels, NYHA functional class, RV pressures, and RV systolic function (all; P < 0.001). Twenty-six cardiac events (25 deaths) occurred during follow-up (median 44 months). MBFRV/LV higher than 56% was associated with a diagnosis of pulmonary hypertension (AUC: 0.96 [95% CI: 0.91-1.00]; P < 0.0001); and predicted outcome with HR: 9.0 (95% CI: 4.2-14.5), P < 0.0001).

CONCLUSIONS

Measurements of MBFRV using PET are feasible, as confirmed with 2 different tracers. Imbalance between RV and LV myocardial perfusion is associated with increased RV load and adverse events in cardiac amyloidosis.

Cardiac Amyloidosis Imaging, Part 3: Interpretation, Diagnosis, and Treatment

Cardiac amyloidosis was thought to be rare, undiagnosable, and incurable. However, recently it has been discovered to be common, diagnosable, and treatable. This knowledge has led to a resurgence in nuclear imaging with ^99mTc-pyrophosphate-a scan once believed to be extinct-to identify cardiac amyloidosis, particularly in patients with heart failure but preserved ejection fraction. The renewed interest in ^99mTc-pyrophosphate imaging has compelled technologists and physicians to reacquaint themselves with the procedure. Although ^99mTc-pyrophosphate imaging is relatively simple, interpretation and diagnostic accuracy require an in-depth knowledge of amyloidosis etiology, clinical manifestations, disease progression, and treatment. Diagnosing cardiac amyloidosis is complicated because typical signs and symptoms are nonspecific and usually attributed to other cardiac disorders. In addition, physicians must be able to differentiate between monoclonal immunoglobulin light-chain amyloidosis (AL) and transthyretin amyloidosis (ATTR). Several clinical and noninvasive diagnostic imaging (echocardiography and cardiac MRI) red flags have been identified that suggest a patient may have cardiac amyloidosis. The intent of these red flags is to raise physician suspicion of cardiac amyloidosis and guide a series of steps (a diagnostic algorithm) for narrowing down and diagnosing the specific amyloid type. One element in the diagnostic algorithm is to identify monoclonal proteins indicative of AL. Monoclonal proteins are detected by serum or urine immunofixation electrophoresis and serum free light-chain assay. Another element is identifying and grading cardiac amyloid deposition using ^99mTc-pyrophosphate imaging. When monoclonal proteins are present and the ^99mTc-pyrophosphate scan is positive, the patient should be further evaluated for cardiac AL. The absence of monoclonal proteins and a positive ^99mTc-pyrophosphate scan is diagnostic for cardiac ATTR. Patients with cardiac ATTR need to undergo genetic testing to differentiate between wild-type ATTR and variant ATTR. This article is the third in a 3-part series in this issue of the Journal of Nuclear Medicine Technology Part 1 reviewed amyloidosis etiology and outlined ^99mTc-pyrophosphate study acquisition. Part 2 described ^99mTc-pyrophosphate image quantification and protocol technical considerations. This article discusses scan interpretation along with cardiac amyloidosis diagnosis and treatment.

Cardiac Amyloidosis: Current Diagnostic Strategies Using Multimodality Imaging

Amyloidosis is a systemic disorder in which abnormal amyloid proteins deposit in body organs, leading to organ dysfunction and death. Cardiac amyloid deposition, causing a sort of restrictive cardiomyopathy and associated with increased risk of mortality. Most cases of cardiac amyloidosis are of either light chain or transthyretin type. Early and accurate diagnosis of cardiac amyloidosis may improve outcomes. However, diagnosis requires systematic approach including electrocardiography and biomarkers when encountered suspicious candidate. Diagnosis by multimodality noninvasive imaging have been substantially studied and established for differentiation from subtypes. Recent advance in the treatment of amyloidosis offers therapeutic monitoring and prognosis.