Scintigraphic and Echocardiographic Study of Patients with Pathogenic or Probably Pathogenic Variants of the TTR Gene without Overt Cardiac Involvement

Abstract

Background: Transthyretin amyloidosis (ATTR) is an infiltrative disease caused by abnormal protein deposition mainly in the heart and peripheral nervous system. When it affects the heart, the disease presents as restrictive cardiomyopathy; when it affects the peripheral and autonomic nervous system, it manifests as polyneuropathy, and is called familial amyloid polyneuropathy (FAP). There are two ATTR subtypes: wild-type ATTR, where there is no mutation, and mutant ATTR (ATTRm), which is characterized by a mutation in the gene encoding the transthyretin protein (TTR). In both subtypes, cardiac involvement is the major marker of poor prognosis. Objectives: To assess the prevalence of subclinical cardiac involvement in a sample of patients with TTR gene mutation by using pyrophosphate scintigraphy and strain echocardiography; to compare scintigraphy and strain findings; to evaluate the association between neurological manifestations (FAP) and subclinical cardiac involvement; and to analyze whether there is an association between any specific mutation and cardiac involvement. Methods: This is a cross-sectional study with carriers of the TTR gene mutation, without cardiovascular symptoms or changes in electrocardiographic or conventional echocardiographic parameters. All patients underwent pyrophosphate scintigraphy and strain echocardiography. Subclinical cardiac involvement was defined as a Perugini score ≥ 2, heart-to-contralateral lung (H/CL) ratio ≥ 1.5 at 1 h, H/CL ≥1.3 at 3 h, or global longitudinal strain (GLS) ≤ −17%. Descriptive and analytical analyses were performed and Fisher's exact test and Mann–Whitney test were applied. A value of p < 0.05 was considered significant. Results: The 23 patients evaluated had a median age of 51 years (IQR 37–57 years), 15 (65.2%) were female, 12 (52.2%) were Pardo, nine (39.1%) had systemic arterial hypertension, and nine (39.1%) had a previous diagnosis of FAP. Of the nine patients with FAP, 8 (34.8%) were on tafamidis. The associated mutations were Val142IIe, Val50Met, and IIe127Val. The median GLS in the sample was −19% (−16% to −20%). Of the 23 patients, nine (39.1%; 95% CI = 29–49%) met criteria for cardiac involvement, six (26%) by the GLS-based criteria only. There was no association between having FAP and being an asymptomatic carrier, as assessed by strain echocardiography and pyrophosphate scintigraphy (p = 0.19). The prevalence of systemic arterial hypertension, diabetes mellitus, dyslipidemia, smoking, and reduced GLS did not differ between groups. Septal e’ wave velocity was the only variable that significantly differed between individuals with and without reduced GLS, with an area under the ROC curve of 0.80 (95% CI = 0.61–0.98, p = 0.027). The best diagnostic accuracy was achieved with a septal e’ velocity ≤ 8.5 cm/s. There was no association between mutation type and preclinical cardiac involvement, nor between tafamidis use and lower degree of cardiac involvement (37.5% versus 40.0%, p = 0.90). Conclusion: Subclinical cardiac involvement was common in a sample of TTR mutation carriers without cardiac involvement. Reduced left ventricular GLS was the most frequent finding. There was no association between the presence of amyloid polyneuropathy and subclinical cardiac involvement. Type of mutation was not associated with early cardiac involvement. In this sample, the use of tafamidis 20 mg/day was not associated with a lower prevalence of subclinical cardiac involvement.